Damage detection method for composite laminates using in-situ thermal gradients and differential expansion across damage

Abstract

The subject of the present invention is a composite laminate damage detection method using in-situ thermal gradients and expansion differences across damage. An example system for in-situ inspection of a composite structure includes a surface strain imaging device and a controller. The surface strain imaging device is configured to image an area of ​​an outer surface of a composite structure when the temperature of the composite structure is warmed to thermal equilibrium with the surrounding environment and a temperature gradient exists within the composite structure. The controller includes a processor and a memory and is configured to use data received by the surface strain imaging device to detect out-of-plane displacements of the outer surface in an area caused by the temperature gradient. The controller is also configured to determine that the out-of-plane displacement meets a threshold condition, and based on determining that the out-of-plane displacement meets the threshold condition, mark the area of ​​the outer surface for further inspection.

Description

Technical Field

[0001] The present disclosure relates generally to nondestructive inspection, and more particularly to systems and methods for nondestructively inspecting composite structures based on differential thermal expansion. Background Art

[0002] Modern aerospace structures are susceptible to mechanical damage. For example, hail or thunderstorms can damage the skin (e.g., fuselage, wings, or other structures) of an aircraft while the aircraft is in flight or on the ground. Similarly, accidental contact with various ground objects or debris can also damage the skin of an aircraft. Therefore, the ability to detect damage to the skin of an aircraft is very useful to operators of those aircraft.

[0003] Composite materials are increasingly being used as a replacement for conventional materials, such as aluminum and steel alloys, in aircraft skins. The use of composite materials is due in part to the generally high strength-to-weight ratio inherent in composite materials. Composite materials typically include a network of reinforcing fibers applied in layers and a resin that substantially wets the reinforcing fibers to form intimate contact between the resin and the reinforcing fibers.

[0004] Due to high energy impacts to the aircraft skin, delamination or separation of adjacent layers may occur beneath the surface of the aircraft skin. In some instances, the delamination may be greater than any external visual indication of potential damage. Summary of the invention

[0005] In one example, a system for in-situ inspection of a composite structure is described. The system includes a surface strain imaging device and a controller. The surface strain imaging device includes a detector and is configured to image an area of ​​an outer surface of a composite structure when the temperature of the composite structure is warmed to thermal equilibrium with the surrounding environment and a temperature gradient exists between the inner surface of the composite structure and the outer surface of the composite structure. The inner surface of the composite structure and the outer surface of the composite structure are separated by a plurality of inner layers. The controller includes a processor and a memory and is configured to use data received by the surface strain imaging device to detect an out-of-plane displacement of the outer surface in an area caused by the temperature gradient. The controller is also configured to determine that the out-of-plane displacement satisfies a threshold condition, and to mark the area of ​​the outer surface for further inspection based on determining that the out-of-plane displacement satisfies the threshold condition.

[0006] In another example, a system for in-situ inspection of a composite structure is described. The system includes a surface strain imaging device and a controller. The surface strain imaging device includes a detector and is configured to image a region of an outer surface of a composite structure when the temperature of the composite structure is warmed to thermal equilibrium with the surrounding environment and a temperature gradient exists between an inner surface of the composite structure and an outer surface of the composite structure. The inner surface of the composite structure and the outer surface of the composite structure are separated by a plurality of inner layers. The controller includes a processor and a memory and is configured to receive data indicating a shape of an outer surface of the composite structure from the surface strain imaging device. Additionally, the controller is configured to determine whether the data indicates delamination between inner layers of the plurality of inner layers of the composite structure.

[0007] In another example, a method for in-situ inspection of a composite structure is described. The method includes imaging a region of an outer surface of a composite structure using a surface strain imaging device when the temperature of the composite structure is warmed to thermal equilibrium with the surrounding environment and a temperature gradient exists between an inner surface of the composite structure and an outer surface of the composite structure. The inner surface of the composite structure and the outer surface of the composite structure are separated by a plurality of inner layers. The method also includes detecting, by a controller, an out-of-plane displacement of the outer surface in the region caused by the temperature gradient using data received by the surface strain imaging device. Additionally, the method includes determining, by the controller, that the out-of-plane displacement satisfies a threshold condition, and marking, by the controller, the region of the outer surface for further inspection based on determining that the out-of-plane displacement satisfies the threshold condition.

[0008] The features, functions, and advantages that have been discussed can be achieved independently in various examples or may be combined in yet other examples, further details of which can be seen with reference to the following description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The novel features which are believed to be characteristic of the illustrative examples are set forth in the appended claims. However, the illustrative examples together with the preferred mode of use, further objects and description thereof will be best understood by reference to the following detailed description of illustrative examples of the disclosure when read in conjunction with the accompanying drawings, in which:

[0010] Figure 1 A system according to an example is shown.

[0011] Figure 2 is a conceptual illustration of the effect of temperature gradients on aircraft skin based on an example.

[0012] Figure 3 is another conceptual illustration of the effect of temperature gradients on aircraft skin based on an example.

[0013] Figure 4 A surface strain imaging device according to an example is shown.

[0014] Figure 5 Another surface strain imaging device according to an example is shown.

[0015] Figure 6 Another surface strain imaging device according to an example is shown.

[0016] Figure 7 is a conceptual illustration of an in-situ inspection of an aircraft according to an example.

[0017] Figure 8 is another conceptual illustration of an in-situ inspection of an aircraft according to an example.

[0018] Fig. 9 is another conceptual illustration of an in-situ inspection of an aircraft according to an example.

[0019] Fig.10 A flow chart of a method according to an example is shown.

[0020] Fig.11 Shows the Fig.10 The methods shown are used together with additional operations. DETAILED DESCRIPTION

[0021] The disclosed examples will now be described more fully below with reference to the accompanying drawings, in which some but not all of the disclosed examples are shown. In fact, several different examples may be provided, and they should not be construed as limited to the examples set forth herein. Rather, these examples are provided to make the present disclosure thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0022] Because composite aircraft skins are susceptible to mechanical damage during operation, inspection techniques are needed to assess the structural health of composite aircraft skins. In examples, systems and methods for inspecting composite structures, such as composite aircraft skins, are described. The systems and methods facilitate inspecting aircraft composite skins for damage in situ, in other words, while the aircraft is in service. Further, the systems and methods allow for identification of damage, such as delamination, that may be hidden during visual inspection.

[0023] In an example method, a surface strain imaging device is used to inspect a composite structure having a temperature gradient between an inner surface of the composite structure and an outer surface of the composite structure. The method includes imaging an area of ​​the outer surface of the composite structure using the surface strain imaging device when the temperature of the composite structure is warmed to thermal equilibrium with the surrounding environment. Due to the temperature gradient, defects within the composite structure can produce anomalies on the outer surface of the composite structure. For example, due to the temperature gradient, delamination within the composite structure may cause out-of-plane displacements in the outer surface of the composite structure. Using data received by the surface strain imaging device, a controller can detect such out-of-plane displacements of the outer surface caused by the temperature gradient. In addition, the controller can determine that the out-of-plane displacement meets a threshold condition and mark the area of ​​the outer surface for further inspection.

[0024] The method can be used to examine an aircraft skin that is exposed to temperature fluctuations during the transition from cruise to landing. An aircraft may cruise for a long period of time at an altitude of approximately 10,000 meters. At this altitude, the average temperature is around -56°C. Therefore, while cruising, the aircraft skin can cool to thermal equilibrium with the surrounding environment. During descent, the temperature of the surrounding environment will increase to a temperature that is greater than the temperature at the cruising altitude. Therefore, the temperature of the aircraft skin may begin to rise during descent, with the outer layer of the aircraft skin heating up faster than the inner layer of the aircraft skin. As a result, upon landing and for some time after landing, the aircraft skin will have a naturally occurring temperature gradient between the inner surface of the aircraft skin and the outer surface of the aircraft skin.

[0025] Advantageously, the systems and methods described herein can be used to inspect aircraft skin without requiring extended downtime. For example, the systems and methods can be used to inspect aircraft skin during downtime between flights. Further, the inspection techniques are non-invasive techniques that can be performed without removing panels or physically contacting the aircraft skin. Thus, the systems and methods provide a solution for rapid, in-situ damage detection of aircraft skin and other composite structures.

[0026] Various additional features of these systems and methods are described below with reference to the accompanying drawings.

[0027] Reference now Figure 1 , Figure 1 A system 100 according to an example is shown. Figure 1As shown in , the system 100 includes a surface strain imaging device 102, a controller 104, and an output component 106. The controller 104 and / or the output component 106 can be connected to the surface strain imaging device 102 or positioned in the surface strain imaging device 102. The surface strain imaging device 102, the controller 104, and / or the output component 106 can also communicate with each other or with a central computing device by way of one or more communication links. Further, the surface strain imaging device 102, the controller 104, and the output component 106 can be components of a common device. The device can be a portable device.

[0028] As shown, the surface strain imaging device 102 includes a detector 108. For example, the detector 108 may include a charge coupled device (CCD) camera. The surface strain imaging device 102 is configured to image an area of ​​an outer surface of a composite structure 110 using the detector 108. An example of a composite structure is an aerospace composite structure, such as an aircraft skin. The system 100 may also be used to image other composite structures.

[0029] The surface strain imaging device 102 can take various forms depending on the desired implementation. As an example, the surface strain imaging device 102 can include a shearography system. As another example, the surface strain imaging device 102 can include a D-Sight system having a light source and a retroreflective screen. As still another example, the surface strain imaging device 102 can include a three-dimensional (3D) scanner.

[0030] The surface strain imaging device 102 may be a handheld measuring instrument. Optionally, the surface strain imaging device 102 may be attached to a robot crawler ( Figure 1 Not shown) or UAV ( Figure 1 Further, in some examples, system 100 may include a plurality of surface strain imaging devices configured to image different respective regions of composite structure 110 from different respective viewpoints.

[0031] The controller 104 may take the form of a control unit, a laptop computer, a mobile computer, a wearable computer, a tablet computer, a desktop computer, or other type of computing device. Thus, the controller 104 includes a processor 112 and a memory 114. The processor 112 may be any type of processor, such as a microprocessor, a digital signal processor, a multi-core processor, etc. The memory 114 may include a non-transitory computer-readable medium storing program instructions that can be executed by the processor 112 or a group of processors to perform any controller functions described herein. The controller 104 may further include a display, an input device, and one or more communication ports, and the controller 104 is configured to communicate with other components of the system 100 or other devices external to the system 100 through the one or more communication ports.

[0032] The controller 104 may be configured to receive data indicating the shape of the outer surface of the composite structure 110 from the surface strain imaging device 102. The data may include the height of various points of the outer surface within the area imaged by the surface strain imaging device 102. For example, the points of the outer surface may be represented using x, y, and z coordinates of a three-dimensional coordinate system. Using this approach, the height may be the z value of the point.

[0033] Further, the controller 104 may be configured to determine whether the data indicates delamination between inner layers of the composite structure 110. For example, the controller 104 may be configured to detect out-of-plane displacement of the outer surface and determine whether the out-of-plane displacement satisfies a threshold condition.

[0034] Detecting out-of-plane displacements may involve detecting displacements relative to the plane of the outer surface, such as bumps. For example, to detect out-of-plane displacements, the controller 104 may identify a point on the surface as a local maximum in the z dimension and compare the z value of the maximum with the z values ​​of points around the point. The comparison may involve calculating one or more surface gradients for the identified maximum. If one or more of the surface gradients is greater than a threshold, the controller 104 may identify the point as indicating an out-of-plane displacement. Other techniques for detecting out-of-plane displacements using data received by the surface strain imaging device 102 are also possible.

[0035] Determining whether the out-of-plane displacement satisfies the threshold condition may involve determining at least one property of the out-of-plane displacement and comparing the at least one property to a threshold value. For example, determining whether the out-of-plane displacement satisfies the threshold condition may involve determining a height of the out-of-plane displacement and determining whether the height exceeds a threshold height.

[0036] In one example, the height of the out-of-plane displacement can be defined as the distance in the z-dimension between the point representing the out-of-plane displacement and the average z-value of all points in the region (the average z-value of a set of points surrounding the point). Further, the threshold height can be a few thousandths of an inch (e.g., six thousandths of an inch (equivalent to 0.1524 mm), ten thousandths of an inch (equivalent to 0.254 mm), etc.). The threshold value can vary depending on the desired configuration of the system 100. For example, the operator can configure the threshold value based on an assessment of the range of temperature gradients within the composite structure 110.

[0037] As another example, determining whether an out-of-plane condition satisfies a threshold condition may involve determining whether a size (e.g., area) of an out-of-plane displacement satisfies a threshold size. For example, the threshold size may be a diameter of one inch (equivalent to 25.4 millimeters). An out-of-plane displacement with a diameter less than the threshold size may not require maintenance. However, an out-of-plane displacement with a diameter exceeding the threshold size may require scheduling of temporary or permanent maintenance. Alternatively, the threshold size may be a threshold area, such as 500 square millimeters.

[0038] Upon determining that the out-of-plane displacement satisfies the threshold condition, the controller 104 may mark the area of ​​the exterior surface for further inspection.Marking the area of ​​the exterior surface for further inspection may involve causing the output component 106 to provide a visual indication or an audible indication.

[0039] The output component 106 may include a speaker, and the auditory indication may be an audible tone or other sound. Additionally or alternatively, the output component 106 may include a light source, and the visual indication may include illumination of the light source. Similarly, the output component 106 may include a display, and the visual indication may include text and / or graphics displayed on the display. An operator of the system 100 may interpret the visual indication or auditory indication provided by the output component 106 to indicate that the data analyzed by the controller 104 indicates potential delamination between the inner layers of the composite structure 110.

[0040] In some examples, marking the area of ​​the exterior surface for further inspection may involve highlighting a region corresponding to the region on a diagram of the composite structure 110. For example, the controller 104 may cause the output component 106 to display a diagram of the composite structure, wherein the region corresponding to the region is highlighted by a color difference of the region relative to other portions of the diagram, a border surrounding the region, an arrow pointing to the region, etc. Additionally or alternatively, the controller 104 may send the diagram with the highlighted region to another device. The controller 104 may use the relative position and orientation of the surface strain imaging device 102 relative to the position of the composite structure 110 as a basis for determining the region to be highlighted. Alternatively, the controller 104 may determine the region based on input received from an operator of the system 100. For example, the system 100 may prompt the operator to designate the region after determining that the out-of-plane displacement satisfies a threshold condition.

[0041] Figure 2 2 is a conceptual illustration 200 of the effect of a temperature gradient on an aircraft skin according to an example. The conceptual illustration 200 includes a first cross-sectional view 202 of the aircraft skin and a second cross-sectional view 204 of the aircraft skin. Figure 2 As shown in , the aircraft skin includes an innermost layer 206 , a plurality of inner layers 208 , and an outermost layer 210 .

[0042] The first cross-sectional view 202 represents a stress-free state of the aircraft skin when the temperature of the innermost layer 206 and the outermost layer 210 are both approximately equal to the temperature T0. Based on the above discussion, the temperature T0 may be a steady-state temperature of the aircraft skin at a cruising altitude, such as about -55° C. In the stress-free state, the layers of the aircraft skin are relatively parallel.

[0043] The second cross-sectional view 204 shows the stress state of the aircraft skin due to the temperature gradient within the layer of the aircraft skin. Due to the principle of thermal expansion, the length of some materials changes as the temperature of the material changes. The fraction of change in a material per degree of temperature change is called the coefficient of thermal expansion (CTE). For example, the CTE of carbon fiber at temperatures between 25°C and 60°C is 2.42×10 -6 m / (m·℃) and is 1.73x10 between -30℃ and 0℃ -6 m / (m·℃).

[0044] During descent, the temperature of the outermost layer 210 increases as the outside temperature increases. The innermost layer 206 is closest to the interior of the aircraft, and the insulation layer separates the interior of the aircraft from the innermost layer 206. As a result, during descent and after landing, the inner layer 208 and the innermost layer 206 heat up more slowly than the outermost layer 210. Therefore, after landing, a temperature gradient exists within the aircraft skin.

[0045] The temperature gradient is shown in graph 212, which depicts the approximate temperature of each layer. The innermost layer 206 has a temperature T0 and the outermost layer has a temperature T1, where T1 is greater than T0. Typically, the difference between the temperature T0 of the innermost layer 206 and the temperature T1 of the outermost layer may be at least 20°C.

[0046] Due to the temperature gradient and the principle of thermal expansion, in the stressed state, the length of the outermost layer 210 is longer than the length of the inner layer 208, which in turn is longer than the length of the innermost layer 206. Due to the length difference, in the stressed state, the aircraft skin expands from the center outward, as evidenced by the curved shape of the outermost layer 210.

[0047] Figure 3 is another conceptual illustration 300 of the effect of a temperature gradient on a composite structure according to an example. Figure 2 300 . Similar to conceptual illustration 200 of , conceptual illustration 300 includes a first cross-sectional view 302 of an aircraft skin and a second cross-sectional view 304 of an aircraft skin. Further, the aircraft skin includes an innermost layer 306, a plurality of inner layers 308, and an outermost layer 310. Still further, first cross-sectional view 302 represents a stress-free state of the aircraft skin when the temperature of the innermost layer 206 and the outermost layer 210 are both approximately equal to temperature T0. And second cross-sectional view 304 represents a stress state of the aircraft skin due to a temperature gradient between temperature T0 and temperature T1 within a layer of the aircraft skin. The temperature gradient is shown by graph 312.

[0048] However, conceptual illustration 300 differs from conceptual illustration 200 in that the aircraft skin includes several delaminations 314 between the layers of the aircraft skin. As shown in second cross-sectional view 304, in the stressed state, the temperature gradient causes an out-of-plane displacement 316 having an out-of-plane displacement height H. This can be detected by using a surface strain imaging device such as Figure 1 The surface strain imaging device 102 images the outermost layer 310 and uses the controller to analyze the resulting image data to detect the out-of-plane displacement 316.

[0049] Out-of-plane displacement 316 may be attributed to delamination 314. For each delamination between the lower and upper layers, the presence of the delamination allows the upper layer to expand upward (i.e., outward from the interior of the aircraft) within the delamination region as the upper layer stretches. In addition, due to the separation between the layers, the rate of heat transfer between areas of the aircraft skin having delaminations is slower than the rate of heat transfer between areas of the aircraft skin without delaminations. In other words, each delamination acts as an insulating layer. Because each delamination acts as an insulating layer, the delamination causes portions of the layer below the delamination (i.e., closer to the interior of the aircraft) to remain cooler longer than other portions of the layer that are not insulated by the delamination.

[0050] Figure 4 FIG. 4 shows a surface strain imaging device 400 according to an example. Figure 1 An example configuration of the surface strain imaging device 102 is shown. Figure 4 As shown in FIG. 4 , the surface strain imaging apparatus 400 includes a shear pattern interferometry system 402. The shear pattern interferometry system 402 further includes a light source 404, a shearing element 406, a detector 408, and a computing device 410, all of which are linked together via a system bus, network, or other connection mechanism 412.

[0051] In one example, light source 404 may be a laser, shearing element 406 may be a Michelson interferometer, and detector 408 may be a camera. To image a region of an exterior surface of a composite structure, computing device 410 may cause light source 404 to illuminate the region while detector 408 images the region through shearing element 406. The use of shearing element 406 allows detector 408 to capture two superimposed images, referred to as sheared images, representing the exterior surface. In operation, staggered speckle interferometry system 402 may capture a first sheared image at a first time and then subsequently (e.g., seconds or minutes later), capture a second sheared image. Based on a comparison between the first sheared image and the second sheared image, computing device 410 may determine data indicative of an exterior surface shape of the composite structure.

[0052] Those skilled in the art will appreciate that other sheared speckle interferometry systems with other configurations and operating principles may also be used. For example, the sheared speckle interferometry system 402 may further include a load element configured to provide an acoustic or mechanical load to the composite structure. Using this configuration, the sheared speckle interferometry system 402 may obtain a first sheared image corresponding to an unloaded state and a second sheared image corresponding to a loaded state. The computing device 410 may then compare the first sheared image with the second sheared image to determine data indicating the shape of the outer surface of the composite structure.

[0053] Figure 5 Another surface strain imaging device according to an example is shown. The surface strain imaging device 500 represents Figure 1 Another example configuration of the surface strain imaging device 102 is shown in FIG. Figure 5 As shown in FIG. 5 , surface strain imaging apparatus 500 includes a light source 502 , a retroreflective screen 504 , a detector 506 , and a computing device 508 , all linked together via a system bus, network, or other connection mechanism 510 .

[0054] The surface strain imaging device 500 can use an optical double-pass retroflection surface inspection technique to image an area of ​​the outer surface of the composite structure. For example, the light source 502 can be a divergent light source, the retroreflection screen 504 can include a plurality of semi-silvered glass beads, and the detector 506 can be a camera. In operation, the computing device 508 can cause the light source 502 to illuminate an area of ​​the composite structure. The light from the light source 502 is then reflected by the composite structure and illuminates the retroreflection screen 504. The retroreflection screen 504 then redirects any incident light back to the composite structure, and the light is again reflected by the composite structure and collected by the detector 506. If the area of ​​the composite structure is uniformly flat, the detector 506 can observe and output data indicating uniform light intensity on the surface. However, if there is an out-of-plane displacement on the outer surface of the composite structure, the detector 506 will observe a local intensity difference on the area. The computing device 508 can analyze the intensity difference and output data indicating the shape of the outer surface.

[0055] Figure 6 Another surface strain imaging device according to an example is shown. The surface strain imaging device 600 represents Figure 1 Another example configuration of the surface strain imaging device 102 is shown in FIG. Figure 6 As shown in FIG. 6 , the surface strain imaging apparatus 600 includes a 3D scanner 602 . The 3D scanner 602 further includes a light source 604 , a scanning element 606 , a detector 608 , and a computing device 610 .

[0056] 3D scanner 602 can take various forms. For example, 3D scanner 602 can be a laser line scanner. Using this configuration, light source 604 can be a laser, and scanning element 606 can scan the laser beam output by light source 604 over an area of ​​the outer surface of the composite structure. Further, detector 608 can be a camera that captures an image of the laser beam appearing on the outer surface. By triangulating between the position of the laser, the position of the camera, and the point on the outer surface where the laser beam appears, computing device 610 can determine the distance to various points on the outer surface.

[0057] As another example, the 3D scanner can be a time-of-flight camera (e.g., LIDAR) that uses time-of-flight technology to determine the distance between the detector 608 and various points on the exterior surface by measuring the round-trip time of laser pulses output by the light source 604. As still another example, the 3D scanner 602 can be a structured light 3D scanner. Using this approach, the light source 604 projects a light pattern onto the exterior surface of the composite structure, which is then detected by the detector 608 and analyzed by the computing device 610 to determine the shape of the exterior surface.

[0058] Figure 7 7 is a conceptual illustration of an in-situ inspection of an aircraft 702 according to an example. Figure 7 , the surface strain imaging device 704 is attached to a robotic crawler 706. The robotic crawler 706 may include a locomotive system (e.g., wheels and / or tracks) such that the robotic crawler 706 can move the surface strain imaging device 704 to different locations and corresponding viewpoints of an aircraft skin 708 of the aircraft 702. Additionally, the robotic crawler 706 may include one or more actuators configured to pan, tilt, and / or rotate the surface strain imaging device 704.

[0059] Figure 8 8 is another conceptual illustration 800 of an in-situ inspection of an aircraft 802 according to an example. Figure 8 , the surface strain imaging device 804 is attached to the UAV 806. The UAV 806 may include multiple motors and propellers so that the UAV 806 can fly the surface strain imaging device 704 to different locations and corresponding viewpoints of the aircraft skin 808 of the aircraft 802. In addition, the UAV 806 may include one or more actuators configured to shake, tilt and / or rotate the surface strain imaging device 804.

[0060] Fig. 9 900 is another conceptual illustration of an in-situ inspection of an aircraft 902 according to an example. Fig. 9 , a first surface strain imaging device 904a is attached to a first support 906a and is configured to image a first region of an aircraft skin 908 of an aircraft 902 from a first viewpoint, a second surface strain imaging device 904b is attached to a second support 906b and is configured to image a second region of the aircraft skin 908 from a second viewpoint, and a third surface strain imaging device 904c is attached to a third support 906c and is configured to image a third region of the aircraft skin 908 from a third viewpoint. Each of the first support 906a, the second support 906b, and the third support 906c may include one or more actuators configured to pan, tilt, and / or rotate the first surface strain imaging device 904a, the second surface strain imaging device 904b, and the third surface strain imaging device 904c, respectively. In some examples, the first, second, and third surface strain imaging devices 904a, 904b, and 904c can image the aircraft skin 908 as the aircraft 902 is driven past the first, second, and third supports 906a, 906b, and 906c.

[0061] Fig.10A flow chart of a method 1000 according to an example is shown. Fig.10 The method 1000 shown in FIG. 1 presents, for example, a method that can be used with Figure 1 , 7 , 8 and 9, or, for example, an embodiment of a method for use with any system disclosed herein. Any example device or system described herein, such as Figure 1 The components of the system 100 may be used or configured to perform Fig.10 The logical functions presented in .

[0062] The method 1000 may include one or more operations, functions, or actions as shown by one or more of blocks 1002-1008. Although the blocks are shown in sequence, the blocks may also be performed in parallel and / or in a different order than those described herein. Moreover, multiple blocks may be combined into fewer blocks, divided into additional blocks, and / or removed based on the desired implementation.

[0063] It should be understood that for this and other processes and methods disclosed herein, the flow chart shows the functions and operations of a possible implementation of the present embodiment. In this regard, each box can represent a module, segment or portion of a program code, which includes one or more instructions that can be executed by a processor to implement a specific logical function or step in the process. The program code can be stored in any type of computer-readable medium or data storage, for example, such as a storage device including a disk or hard drive. The computer-readable medium may include a non-temporary computer-readable medium or memory, for example, such as a computer-readable medium that stores data in a shorter period of time, such as a register memory, a processor cache, and a RAM. The computer-readable medium may also be any other volatile or non-volatile storage system. For example, a computer-readable medium may be considered to be a tangible computer-readable storage medium.

[0064] Initially, at block 1002, method 1000 includes imaging an area of ​​an outer surface of a composite structure using a surface strain imaging device. The surface strain imaging device may image the outer surface of the composite structure when the temperature of the composite structure is warmed to thermal equilibrium with the surrounding environment and a temperature gradient exists between the inner surface of the composite structure and the outer surface of the composite structure. The inner surface of the composite structure and the outer surface of the composite structure are separated by a plurality of inner layers. For example, the composite structure may include an aircraft skin having a temperature difference of at least 20° C. between an innermost layer of the aircraft skin and an outermost layer of the aircraft skin. In some instances, the surface strain imaging device may include a staggered speckle interferometry system. In other instances, the surface strain imaging device may include a 3D scanner.

[0065] At block 1004, method 1000 includes detecting, by a controller, out-of-plane displacements of the outer surface in a region caused by a temperature gradient using data received by the surface strain imaging device. For example, the controller may detect out-of-plane displacements relative to the plane of the outer surface, such as bumps. In one example, the received data may be expressed as x, y, z coordinates in three-dimensional space for a plurality of points on the outer surface. To detect the out-of-plane displacements, the controller may identify a local maximum in the z dimension and compare the surface gradient of the local maximum to a threshold value.

[0066] At block 1006, the method 1000 includes determining, by the controller, that the out-of-plane displacement satisfies a threshold condition. For example, the controller may determine at least one property of the out-of-plane displacement and compare the at least one property to a threshold value corresponding to the at least one property. For example, the at least one property may include a height of the out-of-plane displacement, a diameter of the out-of-plane displacement, and / or an area of ​​the out-of-plane displacement.

[0067] And at block 1008, method 1000 includes, based on determining that the out-of-plane displacement satisfies the threshold condition, marking, by a controller, the area of ​​the exterior surface for further inspection.Marking the area of ​​the exterior surface may involve causing an output component to output a visual indication and / or an audible indication.

[0068] Fig.11 Shows the Fig.10 Additional operations that can be used together with the methods shown in Fig.11 The block 1102 can be used as Fig.10 At block 1102, Fig.11 Including determining that the height of the out-of-plane displacement exceeds a threshold height. For example, the height of the out-of-plane displacement can be defined as the distance in the z dimension between the point representing the out-of-plane displacement and the average z value of all points in the area (or the average z value of a group of points surrounding the point). After determining the height, the controller can compare the height to the threshold height.

[0069] Further, the present disclosure includes the following embodiments:

[0070] Embodiment 1. A system for in-situ inspection of a composite structure, the system comprising: a surface strain imaging device including a detector, the surface strain imaging device configured to image a region of an outer surface of a composite structure when the temperature of the composite structure is warmed to thermal equilibrium with the surrounding environment and a temperature gradient exists between the inner surface of the composite structure and the outer surface of the composite structure, wherein the inner surface of the composite structure and the outer surface of the composite structure are separated by a plurality of inner layers; and a controller including a processor and a memory, the controller configured to: use data received by the surface strain imaging device to detect out-of-plane displacements of the outer surface in the region caused by the temperature gradient, determine that the out-of-plane displacements satisfy a threshold condition, and based on determining that the out-of-plane displacements satisfy the threshold condition, mark the region of the outer surface for further inspection.

[0071] Embodiment 2. The system of embodiment 1, wherein determining that the out-of-plane displacement satisfies a threshold condition comprises determining that a height of the out-of-plane displacement of the outer surface exceeds a threshold height.

[0072] Embodiment 3. The system of embodiment 1 or 2, further comprising an output component, wherein marking the area of ​​the outer surface for further inspection comprises causing the output component to output a visual indication.

[0073] Embodiment 4. The system of any of embodiments 1 to 3, wherein marking the area of ​​the exterior surface for further inspection comprises highlighting a region corresponding to the area on a drawing of the composite structure.

[0074] Embodiment 5. The system of any of Embodiments 1 to 4, wherein the composite structure comprises an aircraft skin, and wherein the temperature gradient comprises a temperature difference of at least 20° C. between an innermost layer of the aircraft skin and an outermost layer of the aircraft skin.

[0075] Embodiment 6. The system according to any one of embodiments 1 to 5, wherein the surface strain imaging device comprises an offset speckle interferometry system.

[0076] Embodiment 7. The system according to any one of embodiments 1 to 5, wherein the surface strain imaging device further comprises a light source and a retroreflective screen.

[0077] Embodiment 8. The system of any one of embodiments 1 to 5, wherein the surface strain imaging device comprises a three-dimensional (3D) scanner.

[0078] Embodiment 9. The system according to any one of embodiments 1 to 8, wherein the surface strain imaging device is a handheld measuring instrument.

[0079] Embodiment 10. The system of any one of embodiments 1 to 9, further comprising a robotic track, wherein the surface strain imaging device is attached to the robotic track.

[0080] Embodiment 11. The system according to any one of embodiments 1 to 9, further comprising an unmanned aerial vehicle (UAV), wherein the surface strain imaging device is attached to the UAV.

[0081] Embodiment 12. A system according to any one of embodiments 1 to 11, wherein: the surface strain imaging device is configured to image an area of ​​the outer surface from a first viewpoint, and the system further includes another surface strain imaging device, which is configured to image another area of ​​the outer surface of the composite structure from a second viewpoint different from the first viewpoint.

[0082] Embodiment 13. A system for in-situ inspection of a composite structure, the system comprising: a surface strain imaging device including a detector, the surface strain imaging device configured to image a region of an outer surface of a composite structure when the temperature of the composite structure is warmed to thermal equilibrium with the surrounding environment and a temperature gradient exists between the inner surface of the composite structure and the outer surface of the composite structure, wherein the inner surface of the composite structure and the outer surface of the composite structure are separated by multiple inner layers; and a controller including a processor and a memory, the controller configured to: receive data indicating a shape of the outer surface of the composite structure from the surface strain imaging device, and determine whether the data indicates delamination between inner layers of the multiple inner layers of the composite structure.

[0083] Embodiment 14. The system of Embodiment 13, wherein determining whether the data indicates delamination between inner layers of the composite structure comprises determining whether the data indicates an out-of-plane displacement of an outer surface of the composite structure that satisfies a threshold condition.

[0084] Embodiment 15. The system of embodiment 13 or 14, further comprising an output component configured to provide a visual indication of whether the data indicates delamination between inner layers of the composite structure.

[0085] Embodiment 16. The system of any of Embodiments 13 to 15, wherein the composite structure comprises an aircraft skin, and wherein the temperature gradient comprises a temperature difference of at least 20° C. between an innermost layer of the aircraft skin and an outermost layer of the aircraft skin.

[0086] Embodiment 17. The system according to any one of embodiments 13 to 16, wherein the surface strain imaging device is a handheld measuring instrument.

[0087] Embodiment 18. A system according to any one of Embodiments 13 to 17, wherein: the surface strain imaging device is configured to image an area of ​​the outer surface from a first viewpoint, and the system further includes another surface strain imaging device, which is configured to image another area of ​​the outer surface of the composite structure from a second viewpoint different from the first viewpoint.

[0088] Embodiment 19. A method for in-situ inspection of a composite structure, the method comprising: using a surface strain imaging device to image an area of ​​an outer surface of a composite structure when the temperature of the composite structure is warmed to thermal equilibrium with the surrounding environment and a temperature gradient exists between the inner surface of the composite structure and the outer surface of the composite structure, wherein the inner surface of the composite structure and the outer surface of the composite structure are separated by a plurality of inner layers; using data received by the surface strain imaging device to detect, through a controller, out-of-plane displacements of the outer surface in the area caused by the temperature gradient; determining, through the controller, that the out-of-plane displacement satisfies a threshold condition; and based on determining that the out-of-plane displacement satisfies the threshold condition, marking, through the controller, the area of ​​the outer surface for further inspection.

[0089] Embodiment 20. The method of embodiment 19, wherein determining that the out-of-plane displacement satisfies a threshold condition comprises determining that a height of the out-of-plane displacement exceeds a threshold height.

[0090] For the purpose of illustration and description, descriptions of different advantageous arrangements have been presented, and are not intended to be exhaustive or limited to examples of the disclosed form. After reading and understanding the foregoing disclosure, many modifications and variations will be apparent to those of ordinary skill in the art. In addition, different examples may provide different advantages compared to other examples. The selected one or more examples are selected and described in order to best explain the principles, practical applications, and to enable other persons of ordinary skill in the art to understand the various examples of the present disclosure with various modifications suitable for the intended specific use.

Claims

1. A system for in-situ inspection of a composite structure, the system comprising: a surface strain imaging device including a detector, the surface strain imaging device configured to image a region of the outer surface of the composite structure when the temperature of the composite structure warms to thermal equilibrium with a surrounding environment and a temperature gradient exists between the inner surface of the composite structure and the outer surface of the composite structure, wherein the inner surface of the composite structure and the outer surface of the composite structure are separated by a plurality of inner layers; A controller comprising a processor and a memory, the controller being configured to: detecting an out-of-plane displacement of the outer surface in the region caused by the temperature gradient using data received by the surface strain imaging device, determining that a height of the out-of-plane displacement of the outer surface exceeds a threshold height, and based on determining that the height of the out-of-plane displacement exceeds the threshold height, marking the area of ​​the exterior surface for further inspection; and An output component, wherein marking the area for further inspection includes causing the output component to output a visual indication. 2 . The system of claim 1 , wherein marking the area of ​​the exterior surface for further inspection comprises highlighting a region corresponding to the area on a diagram of the composite structure.

3. The system of claim 1, wherein the composite structure comprises an aircraft skin, and wherein the temperature gradient comprises a temperature difference of at least 20°C between an innermost layer of the aircraft skin and an outermost layer of the aircraft skin.

4. The system of claim 1, further comprising a robotic track, wherein the surface strain imaging device is attached to the robotic track.

5. The system of claim 1, further comprising an unmanned aerial vehicle (UAV), wherein the surface strain imaging device is attached to the UAV.

6. A system according to any one of claims 1 to 5, wherein: The surface strain imaging device is configured to image the region of the outer surface from a first viewpoint, and The system further includes another surface strain imaging device configured to image another region of the outer surface of the composite structure from a second viewpoint different from the first viewpoint.

7. A method for in-situ inspection of a composite structure, the method comprising: imaging a region of the outer surface of the composite structure using a surface strain imaging device when the temperature of the composite structure warms to thermal equilibrium with the surrounding environment and a temperature gradient exists between the inner surface of the composite structure and the outer surface of the composite structure, wherein the inner surface of the composite structure and the outer surface of the composite structure are separated by a plurality of inner layers; detecting, by a controller, an out-of-plane displacement of the outer surface in the region caused by the temperature gradient using data received by the surface strain imaging device; determining, by the controller, that a height of the out-of-plane displacement of the outer surface exceeds a threshold height; and Based on determining that the height of the out-of-plane displacement of the outer surface exceeds the threshold condition, marking, by the controller, the area of ​​the outer surface for further inspection, wherein marking the area for further inspection includes causing an output component to output a visual indication.

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