Method for ultrasonic inspection of structures with radiused surfaces using multicentric radial focusing

Abstract

To provide methods and apparatus for ultrasonic inspection of composite structures having radiused surfaces.SOLUTION: Multi-centric radius focusing is used to inspect a radiused surface of a radiused part having a varying radius without mechanically adjusting an array sensor. Multiple focal laws are designed to electronically steer and focus ultrasound at respective focal points corresponding to centers of curvature of a simulated radiused surface having a varying radius. As a mechanical probe that carries the array sensor is moved along the radiused part, the probe maintains the array sensor at a constant location relative to the radiused part. As the array sensor scans the radiused part, the array sensor is electronically adjusted to focus at the respective focal points in sequence.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates generally to methods and apparatus for ultrasonic inspection, and more particularly to methods and apparatus for ultrasonic inspection of composite structures having radiused surfaces. [Background technology]

[0002] The desire to maximize performance and minimize weight in commercial aircraft has led to the widespread use of composite materials, such as fiber-reinforced plastic materials. Various elongated composite structures may have relatively narrow internal cavities that require inspection to ensure the structure meets manufacturing and / or performance specifications. In many cases, these internal cavities are partially bounded by multiple stiffeners. Each stiffener comprises a web and a flange that meet at an intersection with one or more fillets. More generally, components made from fiber-reinforced plastic materials may have internal or external fillets.

[0003] In mechanical engineering, a fillet is a rounding of an interior or exterior corner of a part design. The fillet geometry is a concave line when on an interior corner and a convex line when on an exterior corner. In composite part manufacturing, fillets are often referred to as "radii" because they typically have an arc-like profile. To avoid confusion that may arise from the use of terms such as "radius of a radius," this disclosure adopts the convention of referring to a fillet with a circular profile as a "radiused surface" and the radial dimension of the radiused surface as a "radius." As used herein, the term "arc" is a portion of the circumference of a circle. The arcs referred to herein are theoretical (e.g., simulated) constructs that can be mathematically defined within the frame of reference of the radiused part. For example, a circular arc is defined such that first and second non-parallel planes of the radiused part (defined mathematically within the frame of reference of the radiused part) are theoretically tangent at opposite ends of the arc.

[0004] For elongated composite structures, manufacturing using soft tooling produces radiused surfaces whose radii vary along the length of the composite part. Many individual composite parts also exist with radiused surfaces with unique radii. Whether inspecting multiple parts with different radii or a single part with multiple radii, operators spend a lot of time adjusting their probes to the various radii. Furthermore, nondestructive inspection (NDI) system designers must design and manufacture unique probes containing arrays of transducer elements (hereinafter "array sensors") for the various contours of the radiused surface.

[0005] Existing methods for ultrasonic inspection of fillet corners in composite structures include: (1) physically adjusting the ultrasonic array sensor by an operator as the probe moves along the radiused surface; (2) having highly complex mechanical designs for moving the array sensor during inspection, which may include motorized mechanical adjustments, robotic joints, dimensional feedback sensors, etc. (disadvantages include expensive inspection probes, expensive maintenance, and expensive retraining of the robot due to system variability); (3) taking multiple scans of the radiused surface, each scan acquiring data with different adjustments to the configuration file and / or different adjustments to the array sensor (which increases cycle time); and (4) taking a single scan with different array sensors placed at different locations (which increases the cost of the system and the complexity of the inspection probe). (5) using beam steering to direct the ultrasonic beam at the radiused surface (this helps to some extent, but is not ideal as the physical angle of the ultrasound into the part is not perpendicular to the part's surface at all points, so the data may not be good); (6) using ultrasonic beam steering to send sounds at various angles into the part's radiused surface, adjust the electronic beam steering based on the response, and then resound into the part's surface with the new, adjusted electron beam, the iterative process repeated several times until an adequate signal response is obtained (the process can tend to mask surface irregularities that the operator would like to see; another drawback is that the software algorithm is confused by unwanted reflections from irregularities located near the fillets).

[0006] The challenge is to provide a method for inspecting radiused surfaces of composite parts without having to mechanically adjust the array sensor as the radius changes. Examples could be the radius of a wing skin stiffener, fuselage stiffener, or spar, where mechanically adjusting the array sensor during inspection would be very expensive, time consuming, or would create a complex mechanical system. Summary of the Invention

[0007] The subject matter disclosed in some detail below is directed to a method and apparatus for ultrasonic inspection of composite parts having radiused surfaces using a phased ultrasonic transducer array (hereinafter "array sensor"). The method is designed using multiple focal points corresponding to the centers of curvature of simulated curved contours (e.g., arcs) of varying radii of the simulated radiused surface. Unlike conventional methods for inspecting structures or parts having radiused surfaces of varying radii (hereinafter "radiated parts"), the method proposed herein does not require mechanical probe adjustment. Instead, the method employs electronic adjustment of the focusing of ultrasonic waves (hereinafter "ultrasound") based on the dimensional design (simulation) of the radiused part. Because scanning is developed to focus ultrasound waves at different focal points (referring to the different radii of the simulated radiused surface), the scanning is referred to herein as "multi-centric radius focusing."

[0008] According to the embodiments disclosed below, multicentric radius focusing can be used to inspect radiused parts with varying radii without mechanically adjusting the probe. Multiple focal laws are designed to electronically steer and focus ultrasound waves at respective focal points corresponding to the centers of curvature of simulated radiused surfaces with varying radii. A mechanical probe carrying an array sensor is positioned at two physical locations that are outside the radiused area and have a spatial relationship that varies less than the radius variation of the radiused surface. As the probe moves along the radiused part, it maintains the array sensor in a constant position relative to the radiused part. As the array sensor scans the radiused part, the array sensor is electronically adjusted to focus at each focal point in turn.

[0009] The location of the center of the arc that describes the contour of the radiused surface changes as its radius dimension varies along the length of the radiused surface, but the position of the array sensor relative to the web and flange does not need to change. Because radiused surfaces with various radii also have various centers of curvature, a respective focus method is generated for each of a plurality of specified radii. Each focus method is generated to electronically steer and focus the ultrasonic beam at a respective focus. The multiple focuses are selected to encompass the expected range of radii in the as-manufactured variable radius radiused part. The multicentric radius focusing inspection technique disclosed herein can also accommodate the overlap of various focus methods, so that detections seen in the sensor data when one focus method is applied can also be seen in the sensor data when the next focus method is applied.

[0010] Multicentric radial focusing can be applied to both internally and externally radiused surfaces. While this disclosure focuses on curved array sensors for best performance, the method can be applied using linear (flat) array sensors as well.

[0011] Various embodiments of methods and apparatus for ultrasonic inspection of composite parts using multicentric radial focusing are described in some detail later in this specification, one or more of which may be characterized by one or more of the following aspects:

[0012] One aspect of the subject matter disclosed in detail herein is a method for inspecting a radiused part having first and second non-parallel planes connected by the radiused surface, the method comprising: (a) positioning a probe body relative to the radiused part such that a scan plane of an array sensor of transducer elements supported by the probe body intersects and is perpendicular to a length axis of the radiused surface; (b) pulsing each aperture of the transducer elements of the array sensor to transmit a first plurality of beams focused at a first focal point and steered at a respective steering angle within the scan plane, the first plurality of beams impinging on respective regions of the radiused surface; and (c) pulsing the transducer elements of each aperture to derive a respective parameter value characterizing the intensity of a respective echo returning from the radiused part after each beam of the first plurality of beams is emitted onto the radiused surface. (d) applying pulses to respective apertures of the transducer elements of the array sensor to transmit a second plurality of beams focused at a second focal point and steered at respective steering angles within the scan plane, the second plurality of beams impinging on respective regions of the curved surface; and (e) characterizing the intensity of respective echoes returning from the curved surface after each beam of the second plurality of beams is emitted and after each beam of the second plurality of beams impinges on the curved surface. a first focal point located at the same location as a first center of curvature of a first circular arc having a first radius, a second focal point located at the same location as a second center of curvature of a second circular arc having a second radius different from the first radius, and the first and second arcs calculated within a frame of reference of the radiused part such that first and second planes of the radiused part are tangent to the first and second arcs, respectively.

[0013] Another aspect of the subject matter disclosed in detail hereinafter is an apparatus for inspecting a radiused part, the apparatus comprising an array sensor of transducer elements, a probe body holding the array sensor of transducer elements, and a pulser / receiver device programmed to perform operations including: (a) pulsing the transducer elements of the array sensor according to a first transmit focusing method calculated to cause the array sensor to emit a first beam focused at a first focal point located along a centerline of the array sensor, and (b) processing transducer output signals from the transducer elements after the first beam is emitted according to a first receive focusing method calculated to cause the array sensor to derive a first parameter value characterizing the intensity of echoes received after impingement of the first beam on a radiused surface of the radiused part. (c) pulsing the transducer elements of the array sensor according to a second transmit focusing method calculated to cause the array sensor to emit a second beam focused at a second focal point located along a centerline of the array sensor, and (d) processing the transducer output signals from the transducer elements after the second beam is emitted according to a second receive focusing method calculated to cause the array sensor to derive a second parameter value characterizing the intensity of echoes received after impingement of the second beam on the radiused surface, wherein the first focal point is at a first distance from the center of the array sensor and the second focal point is at a second distance from the center of the array sensor different from the first distance.

[0014] A further aspect is a method for inspecting a radiused part, the method comprising: (a) generating a cross-sectional model of a probe in contact with the radiused part having first and second surfaces connected by the radiused surface, the probe comprising an array sensor of transducer elements, the cross-sectional model comprising first and second lines representing the contours of the first and second surfaces, respectively, and a plurality of arcs spanning an expected range of variation in radius of the radiused surface of the radiused part, each of the arcs terminating in the first and second lines; (b) a set of transmit focusing techniques that, when performed, cause the array sensor to emit a plurality of beams that converge at a plurality of foci positioned at various distances from a center of the array sensor, the foci corresponding to the centers of each of the plurality of arcs positioned at various distances from a center of the simulated array sensor of transducer elements; (c) calculating a set of transmit focusing laws designed to cause the array sensor to derive a plurality of parameter values ​​characterizing the intensity of echoes received after the multiple beams impinge on the curved surface of the curved component; (d) positioning the probe with respect to the curved component in a position corresponding to the relative position represented by the cross-sectional model; (e) applying pulses to each aperture of the transducer elements of the array sensor to transmit a plurality of beams that are respectively focused at a plurality of foci according to the set of transmit focusing laws; and (f) processing transducer output signals from the transducer elements according to the set of receive focusing laws after each beam of the multiple beams is emitted to derive a set of parameter values ​​characterizing the intensity of echoes received after the multiple beams impinge on the curved surface of the curved component.

[0015] Other aspects of methods and apparatus for ultrasonic inspection of composite parts using multicentric radial focusing are disclosed below.

[0016] The aforementioned features, functions, and advantages may be implemented individually in various embodiments or may be combined in yet other embodiments. To illustrate the foregoing and other aspects, various embodiments are described below with reference to the drawings. None of the drawings briefly described in this section are drawn to scale. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 depicts an exploded end view of a typical composite skin and I-stringer assembly. [Figure 2] 10 depicts a perspective view of a portion of an L-shaped stringer with a circular radius. The arrow indicates the direction of scanner movement during inspection of the radius, which will be referred to herein as the X-direction. [Figure 3] FIG. 1 is a diagram illustrating a CAD model of an inspection probe and a part having a radius to be inspected. [Figure 4] FIG. 1 illustrates the position of a curved array sensor of ultrasonic transducer elements concentric with the radiused surface of the composite part being inspected. [Figure 5] FIG. 1 illustrates the position of a curved array sensor of ultrasonic transducer elements concentric with the radiused surface of a composite part being inspected according to the multicentric radial focusing technique proposed herein. [Figure 6] FIG. 10 illustrates trigonometric relationships for deriving transducer element offsets used to calculate the time delays incorporated into the focusing method associated with a curved array sensor. [Figure 7] FIG. 10 illustrates relationships for deriving transducer element offsets used to calculate the time delays incorporated into the focus method associated with a linear array sensor. [Figure 8] 1 is a flowchart identifying steps in a process for designing and implementing a system for multicentric radial focusing of radiused parts, according to one embodiment. [Figure 9]FIG. 10 depicts a side view of a mechanical probe designed to support a curved array sensor in a fixed position during longitudinal scanning of a radiused part. [Figure 10] Figures 10-15 show examples of constraints for inspection covering various array sensor / radiused surface configurations. In Figures 10-14, the array sensor is curved. In Figure 15, the array sensor is linear. In Figures 10-12, the radiused surface is concave. In Figures 13-15, the radiused surface is convex. [Figure 11] Figures 10-15 show examples of constraints for inspection covering various array sensor / radiused surface configurations. In Figures 10-14, the array sensor is curved. In Figure 15, the array sensor is linear. In Figures 10-12, the radiused surface is concave. In Figures 13-15, the radiused surface is convex. [Figure 12] Figures 10-15 show examples of constraints for inspection covering various array sensor / radiused surface configurations. In Figures 10-14, the array sensor is curved. In Figure 15, the array sensor is linear. In Figures 10-12, the radiused surface is concave. In Figures 13-15, the radiused surface is convex. [Figure 13] Figures 10-15 show examples of constraints for inspection covering various array sensor / radiused surface configurations. In Figures 10-14, the array sensor is curved. In Figure 15, the array sensor is linear. In Figures 10-12, the radiused surface is concave. In Figures 13-15, the radiused surface is convex. [Figure 14]Figures 10-15 show examples of constraints for inspection covering various array sensor / radiused surface configurations. In Figures 10-14, the array sensor is curved. In Figure 15, the array sensor is linear. In Figures 10-12, the radiused surface is concave. In Figures 13-15, the radiused surface is convex. [Figure 15] Figures 10-15 show examples of constraints for inspection covering various array sensor / radiused surface configurations. In Figures 10-14, the array sensor is curved. In Figure 15, the array sensor is linear. In Figures 10-12, the radiused surface is concave. In Figures 13-15, the radiused surface is convex. [Figure 16] FIG. 1 is a block diagram illustrating a control system, according to one embodiment. [Figure 17] FIG. 1 is a diagram of the display of scan data in place on a display according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] Reference will now be made to the figures, in which like elements in different figures are given the same reference numerals.

[0019] For illustrative purposes, an exemplary method and apparatus for ultrasonic inspection of composite parts using multicentric radial focusing is disclosed in more detail below. However, not all features of an actual implementation are described herein. Those skilled in the art will understand that the development of such an implementation will require the exercise of numerous implementation-specific judgments to achieve the developer's particular objectives, including compliance with system-related constraints, business-related constraints, and the like, which may vary with each implementation. Furthermore, it will be appreciated that such a development effort will be complex and time-consuming, but will be a routine undertaking for those skilled in the art having the benefit of this disclosure.

[0020] In ultrasonic inspection of composite structures, the ultrasonic beam should ideally enter at 90 degrees to the local surface of the composite part being inspected. If the beam does not enter at 90 degrees, it will refract away from normal and the echoes returning from any possible internal structures or anomalies will be suboptimal. Traditionally, the 90 degree angle of incidence is maintained by holding the array sensor at a precisely fixed position in space relative to the surface.

[0021] A process for nondestructive inspection of radiused parts having varying radii will now be described. The process may be used, for example, to inspect elongated composite parts such as wing panel stringers made from fiber-reinforced plastic. The radius of the radiused surfaces of fillet joint regions (intersections) of such elongated composite parts may be constant or may vary along the length of the part.

[0022] Instead of mechanically adjusting the probe to accommodate the various radii and shapes of radiused parts, multiple wavefronts are generated by a computer-controlled array sensor. These multiple wavefronts are adjusted using ultrasonic beam generation application software. The transmission of multiple sets of ultrasonic beams to inspect fillets of different radii and shapes is accomplished electronically by phasing elements in the array sensor(s) to cover the expected (i.e., predicted) surface of the part as well as the full range of radius variability. The phasing is performed according to a predetermined focusing method. (As used herein, the term "focusing method" refers to a predetermined pattern of time delays applied to the pulses and outputs of individual transducer elements during the generation of the transmit and receive beams.)

[0023] FIG. 1 is an exploded, partial cross-sectional view of a typical composite panel and stringer assembly. The composite panel and stringer assembly includes an elongated stringer 10 having a web 14 disposed between a first flange 16 and an opposing second flange 18. The web 14 may have a height designed to provide a desired resistance to an applied load. The first flange 16 and the second flange 18 may be generally planar members. The web 14, the first flange 16, and the second flange 18 may be constant along the span of the stringer (i.e., within a page), or they may vary continuously or discontinuously along the span of the stringer 10. The web 14, the first flange 16, and the second flange 18 are formed from a fiber-reinforced plastic material having multiple plies. The assembly also includes a skin 20 to which the second flange 18 is attached, for example, using a suitable adhesive material. The skin 20 is also made from a fiber-reinforced plastic material.

[0024] It is common practice to inspect stringer 10 for defects before attaching it to skin 20. In particular, each fillet region 12a / 12b may be subjected to non-destructive inspection using a scanner platform that moves along the length of stringer 10. According to embodiments disclosed herein, the scanner platform supports an ultrasonic probe that transmits a focused ultrasonic beam and generates a return signal corresponding to each echo returned to the probe.

[0025] In the embodiment depicted in FIG. 1 , stringer 10 has an I-shaped cross-sectional profile. The NDI system disclosed herein also has application in inspecting fillets of composite parts having alternative geometries. For example, FIG. 2 shows a portion of an L-shaped composite part 22 being inspected. Composite part 22 includes a web 24, a flange 28 (forming an obtuse angle with web 24), and a fillet 25. Using the inspection techniques disclosed herein, fillet 25 can be scanned in a series of parallel planes perpendicular to X and separated by equal distances. This is accomplished by moving an array sensor (not shown in FIG. 2 ) a predetermined incremental distance after each plane is scanned. The scanner is moved along the length of fillet 25 in the X direction (indicated by the arrow in FIG. 2 ).

[0026] According to embodiments described herein below, multicentric radial focusing inspection is used to inspect radiused parts with variable radii without mechanically adjusting the array sensor. The focusing method is designed to electronically steer and focus ultrasound waves at a focal point calculated to be the center of an arc representing the contour of a radiused surface with a specified radius dimension. To inspect radiused surfaces with varying radius dimensions, more focusing methods corresponding to other specified radius dimensions are generated. A file containing digital data representing the focusing method is written and stored in a non-transitory, tangible, computer-readable storage medium incorporated in the phased array instrument. Within the focusing method file, time delays exist for transmitting and receiving ultrasound waves. These time delays control the electronic firing of the array sensor's ultrasonic transducers during transmission and the multiplexing of the ultrasonic transducer outputs during reception. The multicentric radial focusing inspection technique can also accommodate overlapping of various focusing methods. Thus, for example, detections seen in sensor data obtained when a focus method for one radius is applied may also be seen in sensor data obtained when a focus method for another radius is applied.

[0027] According to the inspection methodology disclosed herein, a scanning system is programmed to transmit respective overlapping ultrasonic beams in each scan plane, with each overlapping ultrasonic beam converging at a respective focal point located between the array sensor and the radiused surface. The scanning program is specified by first generating a cross-sectional CAD model (depicted in FIG. 3) of the probe body 40 in position relative to a part designed to include a web 24 and a flange 28 (each represented by a line in FIG. 3) connected by a fillet joint region (hereinafter "fillet"). The fillet is designed to have a radiused surface whose cross-sectional shape is a circular arc. The CAD model further includes a curve representing the curved array sensor 30 (hereinafter "array sensor 30") and lines representing a plurality of bearings with respective shafts 44 and rotatably mounted rollers 42a and 42b. As seen in FIG. 3 , the array sensor 30 is positioned within the probe body 40, which is positioned relative to the radiused part, allowing for each set of rollers 42 to contact the web 24 and flange 28. Based on the known geometry and dimensions of the probe and part, the position of the array sensor 30 relative to the web 24 and flange 28 is known from the CAD model. The relative positions of the individual transducers are included within these values ​​determined from the CAD model. In other embodiments, the array sensor is linear and / or the probe has sliding contacts instead of bearings, and that configuration would be incorporated into the CAD model.

[0028] In the cross-sectional CAD model depicted in FIG. 3 , the radiused surface of the inspected part is represented by a set of arcs 34 spanning the expected range of radius variation for the radiused surface. For illustrative purposes, one embodiment will be described in which the arcs 34 are non-concentric line segments having various radii. The arcs 34 intersect the web 24 and flange 28. Ideally, the web 24 and flange 28 have planes represented by straight lines in the cross-sectional CAD model. The arcs 34 are drawn in the CAD model such that straight lines representing the surfaces of the web 24 and flange 28 are tangent to each of the arcs 34 at their respective endpoints. If the part's fillet radii are non-circular, the actual surface shape is input into the CAD model. In one embodiment of the method, a set of non-circular shapes is input from a photomicrograph of a physical cross-section of the inspected part.

[0029] The method for inspecting a radiused part proposed herein uses multicentric radial focusing. The inspection method is characterized by the following steps: First, a cross-sectional CAD model of a probe in contact with a radiused part having first and second planes connected by a radiused surface is generated. The probe includes an array sensor of transducer elements. The cross-sectional CAD model includes first and second lines representing the contours of the first and second planes, respectively, and a plurality of arcs spanning the expected range of radius variation of the radiused surface of the radiused part. Each of the arcs terminates in the first and second lines. A set of transmit focusing methods is calculated, which, when executed, causes the array sensor to emit multiple beams that converge at multiple focal points positioned at various distances from the center of the array sensor. The multiple focal points correspond to the centers of the multiple arcs positioned at various distances from the center of the simulated array sensor of transducer elements. Additionally, a set of receive focusing laws is calculated that is designed to cause the array sensor to derive a plurality of parameter values ​​that characterize the intensity of received echoes after the impingement of the plurality of beams on the radiused surface of the radiused component. The transmit and receive focusing laws are stored in a non-transitory, tangible, computer-readable storage medium incorporated within the phased array instrument and then retrieved as needed during the inspection procedure.

[0030] During the inspection procedure, the probe body 40 is placed in a position relative to the radiused part so that its position in the cross-sectional plane corresponds to the relative position represented by the cross-sectional model shown in Figure 3. As the probe body 40 moves longitudinally along the radiused part, the array sensor 30 is electronically adjusted to account for variations in the radial dimension.

[0031] In conventional radius inspection, a curved array sensor is aligned concentrically with the radiused surface. FIG. 4 illustrates the position of a curved array sensor 30 concentric with the fillet radiused surface 26 of a composite part being inspected. The array sensor 30 comprises a plurality of transducer elements 32 arranged side by side along a circular arc. In the illustrated embodiment, the array sensor 30 includes 64 transducer elements, numbered E1 through E64. In this situation, all individual travel times of the ultrasonic beam to the concentric point 8 are the same because the transducer elements E1 through E64 are all equidistant from the face of the array sensor 30.

[0032] In contrast, with the multicentric radial focusing technique proposed herein, the curved array sensor does not need to be aligned concentrically with the radiused surface. Pulses are applied to each aperture of the transducer elements of the array sensor 30 according to a set of transmit focusing methods to transmit multiple beams that are focused at multiple focal points, respectively. After each beam of the multiple beams is emitted, the transducer output signals from the transducer elements are processed according to a set of receive focusing methods to derive a set of parameter values ​​that characterize the intensity of the received echoes following impingement of the multiple beams on the radiused surface of the radiused part.

[0033] FIG. 5 is a diagram illustrating the position of a curved array sensor 30 that may not be concentric with the radiused surface being inspected. In the embodiment depicted in FIG. 5, the array sensor 30 includes 64 transducer elements, numbered E1 through E64, respectively. However, it should be understood that the nondestructive testing techniques disclosed herein do not require the array sensor to have 64 transducer elements. The array sensor 30 may have more or fewer transducer elements. To generate a focused ultrasound beam 36, pulses are applied to only a subset of the transducer elements E1 through E64. For example, a group of adjacent transducer elements E31 through E42 may be sequentially activated according to a transmit focusing method designed to generate a focused ultrasound beam 36 having a specified focal length FL and steering angle A. Such a grouping of sequentially activated transducer elements will be referred to herein as an "aperture." As is well known to those skilled in the art, for each transmitted beam, the same aperture (e.g., aperture 31 of array sensor 30) is employed to detect the echo response and convert the echo response into a respective one of a plurality of transducer output signals.

[0034] As is well understood in the art, one set of focusing techniques (hereinafter "transmit focusing techniques") is applied when an element of an aperture is transmitting a beam, while another set of focusing techniques (hereinafter "receive focusing techniques") is applied when the same element is converting echo responses to generate a receive beam. The transmit and receive focusing techniques are different but still related by the following fact: for each transmitted ultrasound beam 36 centered at a particular focal point, the receive focusing technique is designed so that the array sensor detects each expanding ultrasound beam returning from the radiused element through the same focal point. For example, the time delay applied to elements E31-E42 to detect the receive beam returning from the focal point will be the same as for the beam transmitted by E31-E42 to the same focal point, but the order in which electrical echo data is acquired from elements E31-E42 will be the reverse of the order in which pulses were applied to those elements.

[0035] FIG. 5 illustrates the position of the curved array sensor 30 not concentric with either the radiused surface 26a (shown by the solid line) having a radius of 0.250 inches or the radiused surface 26b (shown by the dashed line) having a radius of 0.125 inches. During a first transmit beamforming sequence (depicted in FIG. 5), the transducer elements are pulsed according to a first set of transmit focusing techniques to transmit (at various times) multiple ultrasound beams 36 centered at a focal point FP1. The focal point FP1 is located a first distance from the array center along the center line CL of the array sensor 30. During a second transmit beamforming sequence (not shown in FIG. 5), the transducer elements are pulsed according to a second set of transmit focusing techniques to transmit (at various times) multiple ultrasound beams centered at a focal point FP2. The focal point FP2 is located a second distance along the center line CL of the array sensor 30 that is greater than the first distance from the array center.

[0036] Each echo returns from the curved component to the same transducer element that applied the pulse. The detecting transducer element converts the received ultrasonic energy into electrical transducer output signals. These transducer output signals are time-delayed by an ultrasonic pulser / receiver device (not shown in FIG. 5 ) according to a set of receive-focusing methods using known gating techniques. The gated signals are then gain-corrected to compensate for different amounts of energy loss caused by transmission inefficiencies at higher angles, and the gain-corrected signals are then summed by the ultrasonic pulser / receiver device to generate a return signal representing a parameter value that characterizes the intensity of the echoes received from the curved component.

[0037] According to one proposed embodiment of the multicentric radius focusing technique depicted in FIG. 5, the previously described CAD model (depicted in FIG. 3) employs five non-concentric circular arcs 34. The radii of each of the adjacent arcs 34 differ by a delta radius equal to 0.025 inches (ΔR=0.025 inches), resulting in a group of arcs 34 having the following radii: 0.125, 0.150, 0.180, 0.220, and 0.250 inches. Thus, the set of transmit focusing methods includes five transmit focusing methods designed to concentrate each ultrasonic beam 36 at a respective focal point co-located with the center of the arc 34. According to this proposed embodiment, the five focusing methods are used to inspect a composite radiused part having radiused surfaces varying from 0.125 inches to 0.250 inches, with each focusing method addressing a radius variation of approximately 0.03 inches. For example, a center position for a radiused surface having a radius equal to 0.150 inches is 0.025 inches closer to the array sensor face than a center position for a radiused surface having a radius equal to 0.125 inches. Furthermore, the multicentric radius focusing inspection technique proposed herein can accommodate the overlap of various focusing methods, such that, for example, an anomaly seen in sensor data acquired when a focusing method for a 0.125 inch radius is applied during interrogation may also be seen in sensor data acquired when a focusing method for a 0.150 inch radius is applied.

[0038] To focus the beam at a focal point co-located with the center of the curved array sensor 30 without moving the array sensor 30, the individual ultrasonic waves emitted by each transducer element must travel various distances from the array sensor face to the focal point. This is done by applying a time delay to the individual elements of the array sensor 30 so that the ultrasonic waves intersect at the focal point simultaneously. FIG. 5 illustrates this by showing one outer element of the array sensor 30 farther from the focal point FP1 (0.376 inches) than the distance separating the center of the array sensor 30 from the focal point FP1 (0.338 inches). Therefore, the time delay between the outer element and the center element of the array sensor 30 can be (0.376 - 0.338) = 0.038 inches divided by the speed of the ultrasonic waves in inches per second.

[0039] A time delay is calculated for each aperture for each focal point included in a multicentric radial focusing scheme applied to a particular radiused component. The time delay in the activation of the first and second transducer elements can be calculated by first determining the difference between the respective distances separating the first and second transducer elements from the focal point and then dividing that difference by the velocity of ultrasound. The distance of each element to the focal point can be determined by its respective offset relative to the center of the array sensor face, as shown in FIG. 6. FIG. 6 illustrates a curved array sensor 30 having a center of curvature 60 and an array center 38 with an equal number of transducer elements 32 on each side. The coordinates of the array center 38 are (xpos, ypos). Each transducer element 32 has a transducer element center 62. The transducer element centers of adjacent transducer elements 32 are separated by a distance referred to herein as the "pitch." The distance from the center of curvature 60 to each transducer element center 62 is the radius of the array sensor 30.

[0040] Referring to Figure 6, the calculation of the time delay follows the trigonometric identity of the angle theta, which can be expressed by the following mathematical formula: arclen = ((i - 0.5) * pitch) - ArrayARC / 2 theta = arclen / radius elx(i) = xpos + radius * sin(theta) ely(i) = ypos + radius * (1 - cos(theta)) where "i" is the number of transducer elements, elx(i) and ely(i) are the coordinates of the transducer element center 62 of the i-th transducer element, "theta" is the central angle between a radial line from the center of curvature 60 to the transducer element center 62 of the i-th transducer element and a radial line from the center of curvature 60 to the array center 38, "arclen" is the arc length of the arc subtended by the central angle "theta" (measured in radians), which is the arc length of the arc extending from the transducer element center 62 of the i-th transducer element to the array center 38, and "ArrayARC / 2" is equal to half the arc length of the array sensor 30. In the particular embodiment depicted in FIG. 6, the angle theta is the angle between the radial line from the center of curvature 60 to the array center 38 and the radial line from the center of curvature 60 to the transducer element center 62 of the third transducer element number E3 (i=3). Therefore, the x and y offsets for the i-th transducer element are functions of theta, i.e., xoffset = radius * sin(theta) yoffset = radius * (1 - cos(theta))

[0041] The offset for calculating the time delay for the linear array sensor 46 (shown in FIG. 7) may be calculated using the following formula: elx(i) = xpos - ArrayARC / 2 + ((i - 0.5) * pitch) ely(i) = ypos where "i" is the transducer element number, (xpos, ypos) are the coordinates of the array center 38, elx(i) and ely(i) are the offset coordinates of the transducer element center 62 of the i-th transducer element, "pitch" is the distance between the transducer element centers 62 of adjacent transducer elements 32, and "ArrayARC / 2" is equal to half the length of the linear array sensor 46. For planar array applications, yoffset will be zero.

[0042] FIG. 8 is a flowchart showing steps in a process 100 for designing and implementing a system for multicentric radial focusing inspection of radiused parts. The first step in the process is to position a curved array sensor within the probe body (step 102). A cross-sectional CAD model of the probe in contact with the part to be inspected is then generated. The part may have non-parallel first and second surfaces (e.g., planes) connected by a radiused surface. The cross-sectional model includes first and second lines representing the contours of the first and second surfaces, respectively. Because the true radius of the radiused surface of the inspected part is unknown, the expected radius is represented in the CAD model by a set of circular arcs with various radii spanning the expected range of radius variation (step 104). Each of the arcs terminates in a first and second line.

[0043] Using the CAD model, an ultrasound beam centered at the center of the arc is graphically generated (step 106). Using the defined beam, multiple sets of transmit and receive focusing methods are calculated (step 108). More precisely, a set of transmit focusing methods is calculated for controlling the transducer elements to emit multiple beams each centered at multiple foci located at the same positions as the centers of the multiple arcs. Additionally, a set of receive focusing methods is calculated, designed to receive respective return signals representing respective echoes returning to the transducer elements via the multiple foci. These focusing methods are then programmed into a pulser / receiver device to which the probe is connected.

[0044] The probe is then positioned adjacent to the inspection area (step 110). More specifically, the probe is positioned relative to the radiused part to match the relative position represented by the cross-sectional CAD model. The scan plane of the array sensor is preferably perpendicular to the longitudinal axis of the part being inspected. The probe may be moved lengthwise in increments, starting from an initial position and stopping at a final position.

[0045] Still referring to FIG. 8 , nondestructive testing is performed by pulsing one or more groups of transducer elements of the array sensor to transmit a respective plurality of beams focused at a respective plurality of focal points (step 112) according to a transmit focusing method. As previously described, various (possibly overlapping) apertures can be used to interrogate a respective portion of the radiused part for each focal point. After each beam is emitted, the resulting echoes contain ultrasonic waves that impinge on the same transducer elements contained within the transmit aperture for each beam. Those transducer elements transmit the impinging ultrasonic waves into electrical transducer output signals. Those transducer output signals are time-delayed according to a receive focusing method to generate receive beams (step 114). Optionally, the time-delayed transducer output signals are gain-corrected. The transducer output signals are then processed to derive a respective set of parameter values ​​for each focal point (step 116). For example, the derived parameter value may be the amplitude of the received beam. The best parameter values ​​are then selected (step 118) and then converted to respective pixel values ​​for display (step 120).

[0046] In general, steps 112, 114, and 116 of process 100 may be performed alternately during inspection of a convexly or concavely radiused part having non-parallel first and second planes connected by the radiused surface. The basic pattern of such alternating pulsing and processing may be characterized by the following steps, which are performed after the probe body is positioned so that the scan plane of the array sensor intersects and is perpendicular to the length axis of the radiused surface: (a) applying pulses to respective apertures of transducer elements of the array sensor to transmit a first plurality of beams focused at a first focal point and steered at respective steering angles within the scan plane, the first plurality of beams impinging on respective regions of the curved surface; (b) processing transducer output signals from the transducer elements of each aperture after each beam of the first plurality of beams is emitted to derive a respective parameter value characterizing the intensity of a respective echo returning from the curved surface after impingement of each beam of the first plurality of beams on the curved surface; (c) applying pulses to respective apertures of the transducer elements of the array sensor to transmit a second plurality of beams centered at a second focal point and steered at respective steering angles in the scan plane, the second plurality of beams impinging on respective regions of the radiused surface, and (d) processing the transducer output signal from the transducer element of each aperture after each beam of the second plurality of beams is emitted to derive a respective parameter value characterizing the intensity of a respective echo returning from the radiused part after each beam of the second plurality of beams impinges on the radiused surface. In this embodiment, the first focal point is located at the same location as a first center of curvature of a first circular arc having a first radius, the second focal point is located at the same location as a second center of curvature of a second circular arc having a second radius different from the first radius, and the first and second circular arcs are calculated within a reference frame of the radiused part such that the first and second planes of the radiused part are tangent to the first and second circular arcs, respectively.

[0047] According to one embodiment, multiple sets of ultrasound beams corresponding to multiple focal points are successively initiated after a set of probe movement distances along the length of the radiused part (e.g., the X direction as seen in FIG. 2 ). The set of probe movement distances serves as the scan resolution, which is obtained from an encoder attached to the movable platform carrying the probe. According to one implementation, each scan plane is perpendicular to the X axis and separated from adjacent scan planes by the aforementioned set of distances. This spacing determines the horizontal resolution of the displayed pixel image. Preferably, the resolution is the same in the vertical direction.

[0048] 9 is a side view of a mechanical probe 50 (hereinafter "probe 50") designed to support a curved array sensor 30 in a fixed position during longitudinal scanning of a radiused part. The probe 50 includes a probe body 40 configured to house the array sensor 30. The array sensor 30 is electrically coupled to a pulser / receiver device (not shown in FIG. 9) by an electrical cable 52. The probe body 40 includes a water fitting 54 that provides a flowing column of water between the array sensor 30 and the radiused part to acoustically couple the radiused surface being inspected.

[0049] The probe body 40 is further configured to mount to (contact) two portions of a radiused part (e.g., web 24 and flange 28) that have a fixed spatial relationship (unlike the radiused surfaces of the fillet joint area, which have a varying radius). The radius of the probe body 40 is designed for the largest radius application (0.25 inch radius in the illustration). There are two arcs in the radiused part fillet joint area that represent radiused surfaces 26a and 26b with radii of 0.250 and 0.125 inches, respectively. In reality, these two radius dimensions may not occur at the same location within the structure, but the presence of the two curves is intended to illustrate the concept of a smaller radius dimension below the probe housing. Because the probe body 40 (array sensor housing) is designed for the largest radius application, the radius of the structure may vary below the corner of the moving probe 50 without mechanically adjusting the probe 50. The use of multicentric radial focusing can compensate for the varying radius by adjusting the electronic focus of the ultrasound beam.

[0050] The array sensor (or series of array sensors) must be positioned so that the outermost transducer elements used in the multicentric radius focusing method adequately cover the fillet joint area (specifically, the "corner radius") being inspected. This is done by tracing two straight lines from the two tangent points (TP) of the radiused surface (e.g., where the radiused surface meets the web and flange) through the corresponding focal points (FP) and back to the face of the array sensor 30. Ensuring there are enough outer transducer elements to capture the straight lines is the objective for obtaining array sensor coverage. In practice, given a range of corner radii with their own respective centers of curvature (co-located foci), the center of curvature (foci) farthest from the face of the array sensor 30 is the consideration that limits array sensor coverage. Increasing the beam steering angle required to steer the ultrasound through the centers of curvature (foci) impacts data quality.

[0051] Examples demonstrating the principles summarized in the immediately preceding paragraph are shown in FIGS. 10 through 15 for various array sensor / radiused surface configurations. Each of FIGS. 10 through 15 shows an array sensor (or multiple array sensors) in spatial relationship with a pair of radiused surfaces. One radiused surface (26a or 56a) has a radius larger than the radius of the other radiused surface (26b or 56b). The tangent point TP1 is the point where the plane of the radiused component (not shown in FIGS. 10 through 15) meets the radiused surface 26a (in FIGS. 10 through 12) or 56a (in FIGS. 13 through 15). The focal point FP1 is located at the same location as the center of curvature of the radiused surface 26a or 56a. The point of tangency TP2 is the point where the plane of the radiused part (not shown in FIGS. 10-15) meets the radiused surface 26b (in FIGS. 10-12) or 56b (in FIGS. 13-15). The focal point FP2 is located at the same position as the center of curvature of radiused surface 26b.

[0052] 10, array sensor 30 is curved, with radiused surfaces 26a and 26b being concave. The outermost portions 2a and 2b (shown by the thick arcs) of array sensor 30 provide sufficient coverage for inspection of radiused surface 26b.

[0053] 11, array sensor 30 is curved and radiused surfaces 26a and 26b are concave. The outermost portions 4a and 4b (indicated by the thick arcs) of radiused surface 26b have no covering for this array sensor / radiused surface configuration.

[0054] 12, array sensor 30 is curved, with concave radiused surfaces 26a and 26b, and outermost portions 2a and 2b (shown by the thick arcs) of array sensor 30 provide sufficient coverage for inspection of outermost portions 6a and 6b (shown by the thick arcs) of obtuse radiused surface 26a.

[0055] 13, the array sensor 30 is curved and the radiused surfaces 56a and 56b are convex. The outermost portions 2a and 2b (shown by the thick arcs) of the array sensor 30 provide sufficient coverage for inspection of the radiused surface 56a.

[0056] 14, array sensor 30 is curved and radiused surfaces 56a and 56b are convex. The outermost portions 4a and 4b (indicated by the thick arcs) of radiused surface 56a have no covering for this array sensor / radiused surface configuration.

[0057] In Figure 15, array sensors 60a-60c are curved and radiused surfaces 56a and 56b are convex. In the arrangement shown in Figure 15, a set of linear array sensors 60a-60c provides sufficient coverage for both radiused surfaces 56a and 56b.

[0058] An apparatus for inspecting fillet joint areas of elongated composite parts will now be described with reference to Figure 16. The apparatus includes a movable radial scanner platform 70 that supports at least one array sensor 30. According to one embodiment, the control system includes a ground-based computer 84 programmed with motion control application software 86 and NDI scan application software 88. The control computer 84 is connected to an electronics box (not shown), which in turn is connected to the radial scanner platform 70 via a flexible electrical cable (not shown). The electronics box houses the system power supply, integrates all scanner control connections, and provides the interface between the computer and the radial scanner platform 70.

[0059] According to one embodiment, computer 84 may comprise a general-purpose computer programmed with motion control application software 86, which includes software modules for controlling drive motors 72 that move radial scanner platform 70 in the X direction. Motion control application software 86 also controls motors (not shown) in cable management systems 92. Cable management systems 92 consist of two sets of motorized wheels (not shown), each gripping a cable connecting a motion control center to radial scanner platform 70. The motors in cable management systems 92 are under computer control. The computer control synchronizes the cables with the movement of radial scanner platform 70, which extends and retracts the cables as needed. Alternatively, the methodology disclosed and claimed herein may be employed using a manual probe that does not have a motor.

[0060] 16, an ultrasonic pulser / receiver device 82 is connected to the array sensor 30 for pulsing the transducer elements of an aperture according to a pre-calculated focusing method and for processing the transducer output signals from the transducer elements of the same aperture. The ultrasonic pulser / receiver device 82 includes a processor for executing a software application that incorporates a pre-calculated focusing method for each focal point.

[0061] For example, the ultrasonic pulser / receiver device 82 is programmed to perform the following operations: first, pulse the transducer elements of the array sensor 30 according to a first transmit focusing method calculated to cause the array sensor 30 to emit a first beam centered at a first focal point located along the centerline of the array sensor 30; after the first beam is emitted, process the transducer output signals from the transducer elements according to a first receive focusing method calculated to cause the array sensor 30 to derive a first parameter value characterizing the intensity of echoes received after the first beam impinges on the radiused surface of the radiused component; and later, pulse the transducer elements of the array sensor 30 according to a second transmit focusing method calculated to cause the array sensor 30 to emit a second beam centered at a second focal point located along the centerline of the array sensor. After the second beam is emitted, the transducer output signals from the transducer elements are processed according to a second receive focus method calculated to cause the array sensor 30 to derive a second parameter value characterizing the intensity of the echoes received after the second beam impinges on the radiused surface of the radiused component, the first focus being at a first distance from the center of the array sensor 30 and the second focus being at a second distance from the center of the array sensor 30 that is different from the first distance.

[0062] According to one embodiment depicted in Figure 16, an X-axis displacement encoder 74 is attached to the radial scanner platform 70 (e.g., a rotary encoder attached to an idler wheel). Encoded X-axis position data (in the form of encoder pulses) from the X-axis displacement encoder 74 is received by an ultrasonic pulser / receiver device 82, which in turn sends those encoder pulses to an NDI scanning application software 88. The NDI scanning application software 88 uses those pulses to position the scan data in the proper location on a display monitor 90, as shown in Figures 17A-17E.

[0063] The X-motion drive motor 72 may be a programmable stepper motor that can communicate with a computer 84 via a serial communications interface (not shown). An operator or automated path planning system specifies the desired incremental movement (at several radial positions as shown in Figures 17A-17E) and an optional final target position of the radial scanner platform 70 via motion control application software 86. X-axis positioning is controlled using proportional feedback of encoder count data.

[0064] The NDI scan application software 88 includes ultrasound data acquisition and display software that controls the ultrasound pulser / receiver device 82, which in turn sends pulses to and receives output signals from the array sensor 30. The NDI scan application software 88 controls all details of the scan data and the display of the data, as shown in Figures 17A-17E. The pulser / receiver device 82 correlates the acquired ultrasound scan data with X-position information.

[0065] Ultrasonic inspection at the frequencies used by the systems disclosed herein requires the presence of an acoustic matching agent between the array sensor and the part being inspected. The scanning system shown in FIG. 16 uses water as the acoustic matching agent. According to one embodiment, the probe body has a water cavity (not shown) that is supplied with water via a water supply tube (not shown). The water supply tube is also managed by the cable management system 92. A fluid acoustic matching agent is supplied into the space between the curved array sensor 30 and the radiused surface of the part. Return signal processing can include applying respective gains to each return signal. The gains are selected to compensate for different amounts of energy loss caused by transmission inefficiencies at higher angles. These respective gains can be a function of the distance each echo travels through the fluid acoustic matching agent. Another variable is the response variation between different elements of the array sensor. Another variable is the number of elements used for each beam. Due to physical limitations, the method may use six transducer elements per beam at the outer edges of the array sensor 30, as opposed to twelve elements per beam at the center of the array sensor.

[0066] The X position of the array sensor 30 is measured by an X-axis displacement encoder 74, which encodes the rotation of an encoder wheel (not shown) attached to the underframe of the radial scanner platform 70. The encoder wheel rides on the surface of the part as the radial scanner platform 70 moves along the radius. The X-axis displacement encoder 74 sends an encoder pulse to a control computer 84 after each incremental movement of the radial scanner platform 70 in the X direction. The encoder pulse is used by the control computer 84 and by the ultrasonic pulser / receiver device 82 to identify the X coordinate of each scan plane in well-known fashion.

[0067] In one particular application involving the inspection of the soft-tooled radii of an integrally stiffened wing box, the ultrasonic data acquisition / analysis system described above may be integrated into a non-destructive testing system comprising: an active trailer transporter carrying one or more array sensors for inspecting the soft-tooled radii, an external electric tractor used to move the active trailer transporter through the wing box tunnel, one or more ultrasonic pulser / receivers connected to the array sensor, a computer hosting ultrasonic analysis, data acquisition, and motion control software, and a monitor for displaying C-scan images of the part being inspected.

[0068] The teachings disclosed above can ultimately replace many unique NDI probe designs with a single probe design, allowing an operator to scan the radius of a wing panel or fuselage stiffener without having to mechanically adjust the probe. As an example of cost reduction, an inspection technique requiring three scan passes to inspect the radius of a wing panel stringer could conceivably be replaced by a single-pass radius inspection method. Due to the large number of composite stiffeners incorporated into some modern airplanes, the methodology disclosed herein can significantly reduce inspection costs.

[0069] While a method and apparatus for ultrasonic inspection of composite parts using multicentric radial focusing has been described with reference to various embodiments, those skilled in the art will recognize that various changes can be made and equivalents substituted for elements thereof without departing from the scope of the teachings herein. Additionally, numerous modifications can be made to adapt the teachings herein to a particular situation without departing from their scope. Accordingly, it is intended that the claims not be limited to the specific embodiments disclosed herein.

[0070] The embodiments disclosed above use one or more computer systems. As used in the claims, a "computer system" comprises a single processing or computing device or multiple processing or computing devices that communicate via electrical conductors or wireless transmissions. Such processing or computing devices typically include one or more of the following: a processor, controller, central processing unit, microcontroller, reduced instruction set computer (RISC) processor, application specific integrated circuit, programmable logic circuit, field programmable gate array, digital signal processor, and / or any other circuit or processing device capable of performing the functions described herein.

[0071] The methods described herein may be encoded as executable instructions embodied in a non-transitory, tangible computer-readable storage medium, including, but not limited to, a storage device and / or a memory device, such instructions, when executed on a processing system or computer system, cause the system device to perform at least a portion of the methods described herein.

[0072]

[0002] Furthermore, the present disclosure includes embodiments according to the following clauses: Clause 1 1. A method for inspecting a radiused part (10, 22) having non-parallel first and second planar surfaces (24, 28) connected by a radiused surface (26), comprising: (a) positioning a probe body (40) relative to the radiused part such that a scan plane of an array sensor (30, 46) carrying a plurality of transducer elements (32) and supported by the probe body intersects and is perpendicular to a length axis of the radiused surface; (b) pulsing the apertures of each of the transducer elements of the array sensor to transmit a first plurality of beams (36) centered at a first focal point (FP1) and steered at respective steering angles within the scan plane, the first plurality of beams impinging on respective regions of the radiused surface; (c) processing transducer output signals from the transducer elements of each aperture after each beam of the first plurality of beams is emitted to derive a respective parameter value characterizing the intensity of a respective reflection returning from the radiused component after impingement of each beam of the first plurality of beams on the radiused surface; (d) pulsing the apertures of each of the transducer elements of the array sensor to transmit a second plurality of beams (36) centered at a second focal point (FP2) and steered at respective steering angles within the scan plane, the second plurality of beams impinging on respective regions of the radiused surface; and (e) processing a transducer output signal from the transducer element of each aperture after each beam of the second plurality of beams is emitted to derive a respective parameter value characterizing the intensity of a respective reflection returning from the radiused component after impingement of each beam of the second plurality of beams on the radiused surface; the first focal point is located at the same position as a first center of curvature of a first arc having a first radius, the second focal point is located at the same position as a second center of curvature of a second arc having a second radius different from the first radius, and the first arc and the second arc are calculated within a reference frame of the radiused part such that the first plane and the second plane of the radiused part are tangent to the first arc and the second arc, respectively. Article 2. (e) pulsing the apertures of each of the transducer elements of the array sensor to transmit a third plurality of beams focused at a third focal point and steered at respective steering angles within the scan plane, the third plurality of beams impinging on respective regions of the radiused surface; and (f) processing a transducer output signal from the transducer element of each aperture after each beam of the third plurality of beams is emitted to derive a respective parameter value characterizing the intensity of a respective reflection returning from the radiused component after impingement of each beam of the third plurality of beams on the radiused surface; 2. The method of claim 1, wherein the third focal point is located at the same position as a third center of curvature of a third arc having a third radius different from the first radius and the second radius, and the third arc is calculated within the reference frame of the curved part so that the first plane and the second plane of the curved part are tangent to the third arc. Article 3. 3. The method of claim 2, wherein the first radius and the second radius differ by a first delta radius, the first radius and the third radius differ by a second delta radius, and the first delta radius is equal to the second delta radius. Article 4. 2. The method of claim 1, wherein the parameter is amplitude. Article 5. identifying a range of variation of the radius of the radiused surface, the range including the first radius and the second radius differing by a delta radius; positioning the first focal point where a center of a first arc representing a contour of the radiused surface would be located if the radius of the radiused surface were the first radius; and 10. The method of claim 1, further comprising positioning the second focal point where a center of a second arc representing a contour of the radiused surface would be located if the radius of the radiused surface were the second radius. Article 6. 10. The method of claim 1, wherein the array sensor of transducer elements is curved. Article 7. 10. The method of claim 1, wherein the array sensor of transducer elements is linear. Article 8. 10. The method of claim 1, wherein the radiused surface is concave. Article 9. 2. The method of claim 1, wherein the radiused surface is convex. Article 10. 1. An apparatus for inspecting radiused parts, comprising: an array sensor (30) having a plurality of transducer elements (32); a probe body (40) that holds the array sensor; and a pulser / receiver device (82) programmed to perform operations, said operations including: (a) pulsing transducer elements of the array sensor according to a first transmit focusing method calculated to cause the array sensor to emit a first beam centered at a first focal point (FP1) positioned along a centerline of the array sensor; (b) after the first beam is emitted, processing transducer output signals from the transducer elements according to a first receive focus method calculated to cause the array sensor to derive a first parameter value characterizing the intensity of echoes received after impingement of the first beam on the radiused surface of the radiused component; (c) pulsing transducer elements of the array sensor according to a second transmit focusing method calculated to cause the array sensor to emit a second beam centered at a second focal point (FP2) positioned along the centerline of the array sensor; and (d) after the second beam is emitted, processing transducer output signals from the transducer elements according to a second receive focus method calculated to cause the array sensor to derive a second parameter value characterizing the intensity of echoes received after impingement of the second beam on the radiused surface; The apparatus, wherein the first focal point is at a first distance from a center of the array sensor and the second focal point is at a second distance from the center of the array sensor that is different from the first distance. Article 11. The pulser / receiver device is further programmed to perform operations, including: (e) pulsing transducer elements of the array sensor according to a third transmit focusing method calculated to cause the array sensor to emit a third beam that is concentrated at a third focal point located along the centerline of the array sensor; and (f) after the third beam is emitted, processing transducer output signals from the transducer elements according to a third receive focus method calculated to cause the array sensor to derive a third parameter value characterizing an intensity of echoes received after impingement of the third beam on the radiused surface; 11. The apparatus of claim 10, wherein the third focal point is at a third distance from the center of the array sensor that is different from the first distance and the second distance. Article 12. 11. The apparatus of clause 10, wherein the transducer element array sensor is curved. Article 13. 11. The apparatus of clause 10, wherein the array sensor of transducer elements is linear. Article 14. 11. The apparatus of clause 10, wherein the probe body is designed for the largest radius of the radiused surface to enable inspection of smaller radii of the radiused surface without any mechanical adjustment. Article 15. The apparatus described in clause 10, further comprising a non-transitory, tangible, computer-readable storage medium (88) having stored thereon a file containing digital data representing the first transmit focus method and the second transmit focus method and the first receive focus method and the second receive focus method. Article 16. 1. A method for inspecting a radiused part, comprising: (a) generating a cross-sectional model of a probe (30, 40, 46) in contact with a radiused part (10, 22) having a first surface (24) and a second surface (28) connected by a radiused surface (26), the probe comprising an array sensor (30, 46) of transducer elements (32), the cross-sectional model comprising first and second lines representing the contours of the first and second surfaces, respectively, and a plurality of circular arcs spanning an expected range of variation in radius of the radiused surface of the radiused part, each of the circular arcs terminating at the first and second lines; (b) calculating a set of transmit focusing methods that, when executed, cause the array sensor to emit a plurality of beams (36) converging at a plurality of foci positioned at various distances from a center of the array sensor, the foci corresponding to respective centers of the plurality of arcs positioned at various distances from a center of the simulated array sensor of transducer elements; (c) calculating a set of receive focusing laws designed to cause the array sensor to derive a plurality of parameter values ​​characterizing the intensity of received echoes after impingement of the plurality of beams on the radiused surface of the radiused component; (d) positioning the probe relative to the radiused part in a position consistent with the relative position represented by the cross-sectional model; (e) pulsing the apertures of each of the transducer elements of the array sensor to transmit a plurality of beams that are respectively focused at the plurality of focal points according to the set of transmit focusing methods; and (f) after each beam of the plurality of beams is emitted, processing transducer output signals from the transducer elements according to the set of receive focus techniques to derive a set of parameter values ​​characterizing the intensity of received reflections after impingement of the plurality of beams on the curved surface of the curved component. Article 17. 17. The method of claim 16, wherein the arcs of the plurality of arcs have different radii. Article 18. 18. The method of clause 17, wherein the various radii include a first radius, a second radius that is a delta radius greater than the first radius, and a third radius that is the delta radius greater than the second radius. Article 19. 17. The method of claim 16, wherein the parameter is amplitude. Article 20. 17. The method of clause 16, wherein the transmit focusing time delay is derived from a trigonometric identity relative to the center of the simulated array sensor.

[0073] Unless the claim language expressly specifies or declares a condition dictating a particular order in which some or all of the steps recited in the claim are to be performed, the process claims set forth below should not be construed as requiring that those steps be performed in alphabetical order (any alphabetical order herein is used solely to refer to previously recited steps) or in the order in which the steps are recited. Nor should the process claims be construed as excluding any portion of two or more steps being performed simultaneously or alternately, unless the claim language expressly declares a condition excluding such an interpretation.

Claims

1. 1. A method for inspecting a radiused part (10, 22) having non-parallel first and second planar surfaces (24, 28) connected by a radiused surface (26), comprising: (a) positioning a probe body (40) relative to the radiused part such that a scan plane of an array sensor (30, 46) comprising a plurality of transducer elements (32) and supported by the probe body intersects and is perpendicular to a length axis of the radiused surface; (b) pulsing the apertures of each of the transducer elements of the array sensor to transmit a first plurality of beams (36) centered at a first focal point (FP1) and steered at respective steering angles within the scan plane, the first plurality of beams impinging on respective regions of the radiused surface; (c) processing transducer output signals from the transducer elements of each aperture after each beam of the first plurality of beams is emitted to derive a respective parameter value characterizing the intensity of a respective reflection returning from the radiused component after impingement of each beam of the first plurality of beams on the radiused surface; (d) pulsing the apertures of each of the transducer elements of the array sensor to transmit a second plurality of beams (36) centered at a second focal point (FP2) and steered at respective steering angles within the scan plane, the second plurality of beams impinging on respective regions of the radiused surface; and (e) processing transducer output signals from the transducer elements of each aperture after each beam of the second plurality of beams is emitted to derive a respective parameter value characterizing the intensity of a respective reflection returning from the radiused component after impingement of each beam of the second plurality of beams on the radiused surface; the first focal point is located at the same position as a first center of curvature of a first arc having a first radius, the second focal point is located at the same position as a second center of curvature of a second arc having a second radius different from the first radius, and the first arc and the second arc are calculated within a reference frame of the radiused part such that the first plane and the second plane of the radiused part are tangent to the first arc and the second arc, respectively.

2. (e) pulsing the apertures of each of the transducer elements of the array sensor to transmit a third plurality of beams focused at a third focal point and steered at respective steering angles within the scan plane, the third plurality of beams impinging on respective regions of the radiused surface; and (f) after each beam of the third plurality of beams is emitted, processing a transducer output signal from the transducer element of each aperture to derive a respective parameter value characterizing the intensity of a respective reflection returning from the radiused part after impingement of each beam of the third plurality of beams on the radiused surface; 2. The method of claim 1, wherein the third focal point is located at the same position as a third center of curvature of a third arc having a third radius different from the first radius and the second radius, and the third arc is calculated in the frame of reference of the radiused part such that the first plane and the second plane of the radiused part are tangent to the third arc.

3. 3. The method of claim 2, wherein the first radius and the second radius differ by a first delta radius, the first radius and the third radius differ by a second delta radius, and the first delta radius is equal to the second delta radius.

4. The method of claim 1 or 2, wherein the parameter is amplitude.

5. identifying a range of variation of the radius of the radiused surface, the range including the first radius and the second radius differing by a delta radius; positioning the first focal point where a center of a first arc representing a contour of the radiused surface would be located if the radius of the radiused surface were the first radius; and 5. The method of claim 1, further comprising: positioning the second focal point at a location where a center of a second arc representing a contour of the radiused surface would be located if the radius of the radiused surface were the second radius.

6. A method described in any one of claims 1 to 5, wherein the array sensor having transducer elements is either curved or linear.

7. Prior to the step of placing the probe body (40) in position relative to the radiused part, (a) generating a cross-sectional model of a probe (30, 40, 46) in contact with a radiused part (10, 22) having a first surface (24) and a second surface (28) connected by a radiused surface (26), the probe comprising an array sensor (30, 46) of transducer elements (32), the cross-sectional model comprising first and second lines representing the contours of the first and second surfaces, respectively, and a plurality of circular arcs spanning an expected range of variation in radius of the radiused surface of the radiused part, each of the circular arcs terminating at the first and second lines; (b) calculating a set of transmit focusing methods that, when executed, cause the array sensor to emit a plurality of beams (36) converging at a plurality of foci positioned at various distances from a center of the array sensor, the foci corresponding to respective centers of the plurality of arcs positioned at various distances from a center of the simulated array sensor of transducer elements; and 7. The method of claim 1, further comprising: (c) calculating a set of receive focusing laws designed to cause the array sensor to derive a plurality of parameter values ​​characterizing the intensity of echoes received after impingement of the plurality of beams on the radiused surface of the radiused component.

8. 8. The method of claim 1, wherein the radiused surface is concave.

9. 8. The method of claim 1, wherein the radiused surface is convex.

10. 1. An apparatus for inspecting radiused parts, comprising: an array sensor (30) having a plurality of transducer elements (32); a probe body (40) that holds the array sensor; and a pulser / receiver device (82) programmed to perform operations, said operations comprising: pulsing the apertures of each of the transducer elements of the array sensor to transmit a first plurality of beams centered at a first focal point and steered at respective steering angles within a scan plane; processing transducer output signals from the transducer elements of each aperture to derive respective parameter values ​​characterizing the intensity of respective echoes returning to the array sensor after each beam of the first plurality of beams is emitted; pulsing the apertures of each of the transducer elements of the array sensor to transmit a second plurality of beams focused at a second focal point and steered at respective steering angles within the scan plane; and processing transducer output signals from the transducer elements of each aperture to derive respective parameter values ​​characterizing the intensity of respective echoes returning to the array sensor after each beam of the second plurality of beams is emitted; the first focal point is located at the same location as a first center of curvature of a first arc having a first radius, and the second focal point is located at the same location as a second center of curvature of a second arc having a second radius different from the first radius.

11. The device described in claim 10, wherein the array sensor having transducer elements is curved.

12. The device described in claim 10, wherein the array sensor having transducer elements is linear.

13. 13. The apparatus of claim 10, wherein the probe body is designed for the largest radius of the radiused surface to allow inspection of smaller radii of the radiused surface without any mechanical adjustment.

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