Improved support for impact measurements

Abstract

The present invention relates to an impact excitation measurement system comprising a test chamber, an impactor, a sensor system, and a support system, wherein the impactor is configured to impact a test specimen supported by the support system at a predetermined height, the sensor system is configured to acquire the vibration response of the test specimen to the impact applied to the test specimen by the impactor, the support system is configured to support a solid test specimen at the predetermined height within the test chamber, the support system comprises a set of support bars having a thermal expansion coefficient essentially equal to the thermal expansion coefficient of the impactor, the set of support bars comprises at least three support bars each having a support end, the three support ends being positioned non-collinearly.

Description

[Technical Field]

[0001] Technical Field The present invention relates to a non-destructive method and system for performing measurements on solid specimens using impact excitation techniques. The invention is particularly useful for performing tests on specimens at different temperatures. The measurements are useful for detecting defects and anomalies in solids and for characterizing the E modulus, G modulus, Poisson's constant, and damping parameters. [Background technology]

[0002] background Testing of solids can be done in several ways. The first test usually consists of a visual inspection to ensure the solid has the correct size and shape and check for surface defects. However, in many cases, the properties of a solid depend heavily on its internal structure, which may not be visible to the naked eye. For example, the strength of metals and alloys depends heavily on the specific type and amount of bulk defects. These defects can be both small and large and can occur due to natural causes, manufacturing methods, wear and tear, accidents, etc.

[0003] Regardless of how a defect occurs, in some cases it is important to know the state of the solid with respect to the defect. To analyze a solid for defects, invasive or non-invasive methods can be used on a specimen of the solid. Non-invasive methods thereby allow analysis without destroying or altering the specimen. Therefore, non-invasive methods are typically used on specimens that still need to be used later or that need to undergo further testing (which may themselves be invasive or non-invasive).

[0004] One type of non-invasive testing method for solids uses vibration to analyze a test specimen. This involves subjecting the test specimen to controlled vibrations that can propagate through the solid and be transmitted, reflected, or absorbed. Controlled vibrations can be induced using impulse excitation techniques (IET), whereby the test specimen is positioned so that it can vibrate substantially unimpeded when impacted. In impulse excitation techniques, the specimen is then impacted by a specialized tool or projectile, and the material properties of the test specimen are determined by analyzing the resulting vibrations as they are picked up by a vibration signal measurement sensor, such as a piezoelectric sensor, microphone, laser vibrometer, or accelerometer. Vibrations that pass through a solid are also referred to as sound or sound waves, and the measurement is also referred to as acoustic measurement. Therefore, vibration signal measurement sensors are also referred to as "acoustic sensors" in the context of this application.

[0005] An apparatus for testing solids using sound is described in WO 2019 / 020825. This document discloses an apparatus for analyzing the mechanical vibration response of a solid material sample, comprising an array of impactors configured to impact respective distinct points on the surface of the solid material sample, a sensor configured to capture the mechanical vibration response as a time-varying signal following impact of at least one impactor, and processing means configured to analyze the time-varying signal to determine frequencies and damping constants of sine waves constituting the time-varying signal. The invention also relates to a corresponding method for characterizing a solid material sample.

[0006] Analysis of the response of a solid specimen to vibrational excitation typically involves the analysis of the following parameters: - Young's modulus (E), which indicates the tensile elasticity of the specimen; - shear modulus (G), which indicates the response of the specimen to shear stress; - Poisson's ratio (ν), which describes the deformation of the specimen in the direction perpendicular to the applied uniaxial stress; - Signal attenuation or dimming caused by internal friction The present invention includes extracting one or more, preferably all, of the above.

[0007] These properties typically depend on the frequency or frequency range of the vibration excitation. This allows a test specimen to have several resonant frequencies that depend on the different vibration modes of the specimen. The important modes here are bending and torsion. The parameter values ​​at these resonant frequencies are important for describing the condition of the specimen.

[0008] In many applications, solid components, for example in machinery, are used at different temperatures. This can cause operating temperatures to fluctuate rapidly and / or over a wide temperature range. For example, a vehicle brake disk can heat up significantly and rapidly during operation (from essentially ambient temperature to over 500°C in just a few seconds). Another example is a kerosene injection nozzle for an aircraft jet, which can heat up to over 1500°C during operation. High temperature ranges can significantly affect the material properties of components, particularly elastic properties such as the Young's modulus, shear modulus, and Poisson's ratio mentioned above. For example, solids can generally be expected to become more flexible at higher temperatures due to weakening of internal bonds on average, which essentially means that E and G are expected to gradually decrease with increasing temperature.

[0009] At different temperatures, solid components may have different material properties. This can affect the function of the component. It is important to find the temperature or temperature range where the normal or intended function of the component is disrupted. This can be due to bulk properties of the material, defects that can be induced by modifying temperature, defects that may become more significant at higher temperatures, variability in expansion of different parts of the component, etc. Specific examples of temperature dependence of material properties of a part are as follows:

[0010] - A general change in elastic properties, which reduces the stiffness of the component and thereby hinders its proper functioning; for example, a brake disc may become too elastic at high temperatures to allow proper braking.

[0011] - Phase transitions at certain temperatures or within certain temperature ranges can significantly change the material properties of the component.

[0012] - Chemical reactions can equally modify the material properties of the components. - For example, precipitation of different stoichiometric phases in an alloy may be present in the material, for example due to poor manufacturing methods, leading to internal material boundaries between materials with different temperature-dependent expansions. Clearly, this can lead to serious problems.

[0013] - Laminates or other layered components, whereby the adhesion of one layer to the next can decrease with increasing temperature.

[0014] To test the proper function of a solid component at different temperatures and / or over the entire temperature range of its intended operation, it is necessary to measure the material properties of a test specimen at different temperatures. Here, the test specimen can be, for example, the entire component, a portion of the component, or a piece of the same material of the component. The test is preferably performed in a controlled environment that allows at least temperature control. The material properties are then measured at different temperatures.

[0015] The inventors have found that measuring the material properties of a test specimen over a wide temperature range, potentially extending from below -50°C to over 2000°C, can be very difficult in practice. Creating a temperature-controlled environment for such a temperature range typically requires an oven, which may include multiple vibration-generating components. Clearly, background vibrations generated by the oven can interfere with the measurement process. These background vibrations typically worsen at higher temperatures. Furthermore, some material properties (e.g., E and G) can be expected to decrease with increasing temperature, so the signal also decreases. Both effects result in a lower signal-to-noise (STN) ratio at higher temperatures.

[0016] WO 2020 / 254698 discloses a method for acoustically measuring material properties of a test specimen at elevated temperatures, the method comprising: a) heating the test specimen within a test temperature range; b) performing a background measurement within the test temperature range by capturing a vibration signal from the test specimen within a calibration period to obtain a noise signal; c) performing an acoustic measurement on the test specimen within the test temperature range and within the test period by: c1. applying a vibration excitation to the test specimen; c2. capturing a vibration signal of the test specimen within a test period to obtain a vibration response signal to the vibration excitation; and d) analyzing the vibration response signal to obtain the material properties of the test specimen by taking the noise signal into account. This document also discloses a system for acoustically measuring material properties of a test specimen at elevated temperatures. Summary of the Invention [Problem to be solved by the invention]

[0017] Although the above prior art documents disclose methods and systems for obtaining acoustic responses to impacts at different temperatures, the inventors have found that accuracy can still be improved, especially for tests performed at different temperatures.

[0018] The present invention aims to solve the problem of poor STN ratios for acoustic measurements on test specimens at high temperatures, thereby obtaining more accurate attenuation measurements at any temperature. Furthermore, the present invention provides a new and inventive support system for supporting a test specimen within a test chamber, which is capable of supporting the test specimen stably at different temperatures in a manner that reduces errors. [Means for solving the problem]

[0019] Summary of the Invention The present invention relates to an impact excitation measurement system comprising a test chamber, an impactor, a sensor system, and a support system. The test chamber is preferably a heated chamber equipped with a temperature control system configured to control the temperature within the chamber. The support system is configured to support a solid test specimen at a predetermined height within the test chamber. The impactor is configured to impact the test specimen supported by the support system at the predetermined height. The sensor system is configured to acquire a vibration response of the test specimen to the impact applied to the test specimen by the impactor.

[0020] The inventors have found that the accuracy of measurements obtained with existing support systems can be improved. In doing so, the inventors have realized that the accuracy can be temperature dependent, and that the thermal expansion of the support system plays an important role in obtaining accurate measurements. This effect is particularly pronounced when measurements are performed over a large temperature interval. Therefore, the present invention Support The support system includes a set of support bars made of a thermally stable material, preferably made entirely of the thermally stable material. Additionally or alternatively, the support bars are made of the same material as the impactor, preferably made essentially entirely of the same material as the impactor. Also additionally or alternatively, the support bars include a coefficient of thermal expansion essentially equal to the coefficient of thermal expansion of the impactor.

[0021] The term "thermally stable material" refers to a material that has a very small thermal expansion over a large temperature interval. Preferably, the material has a thermal expansion coefficient of at most 30.0 x 10 -6 K -1 , more preferably up to 20.0 × 10 -6 K -1 , and even more preferably up to 10.0 × 10 -6 K -1 , and even more preferably up to 9.0 × 10 -6 K -1 , and even more preferably up to 8.0 × 10 -6 K -1 , and even more preferably up to 7.0 × 10 -6 K -1, and even more preferably up to 6.0 × 10 -6 K -1 , and even more preferably up to 5.0 × 10 -6 K -1 , and even more preferably up to 4.0 × 10 -6 K -1 , most preferably up to 3.0 × 10 -6 K -1 Preferably, the material has such a low thermal expansion over the entire temperature interval over which the measurements are carried out.

[0022] The coefficient of thermal expansion of the support bar may be essentially equal to the coefficient of thermal expansion of the impactor, the term "essentially equal" being used herein to refer to the coefficients of thermal expansion being the same to a small relative difference in the coefficient of thermal expansion of the impactor, typically up to 25%, more preferably up to 20%, even more preferably up to 15%, even more preferably up to 10%, even more preferably up to 5%, for example 5%, 4%, 3%, 2%, 1% or less.

[0023] The support bar preferably has a support end capable of supporting the part, the support end having a point-like shape. The point-like shape of the support end allows for a small contact surface between the support end and the test piece, preferably 2 mm 2 Less than 1.5 mm, preferably 2 less than, and even more preferably about 1 mm 2 For example, the support end may preferably comprise a point-like shape in the form of a spherical cap with a height (h) of up to 3 mm, preferably 2 to 3 mm, and a radius (a) at the base of the cap of up to 0.5 mm.

[0024] The set of support bars comprises at least three support bars, each having a support end, and the three support ends are non-collinearly positioned. Three non-collinear support points tend to provide stable support. Indeed, in a preferred embodiment, the set of support bars comprises exactly three support bars. In another preferred embodiment, the set of support bars comprises exactly four support bars, at least three of which have non-collinearly positioned support ends. Thus, the three non-collinear support points preferably provide stable support during testing. Piece The test specimen defines an essentially horizontal support surface capable of supporting the test piece. This is particularly preferred when the test piece has an essentially flat base surface. Note that the test specimen may typically include a beam-like shape.

[0025] The present invention also relates to a kit comprising an impact excitation measurement system as described above and further herein and at least one test specimen, the test specimen having a base surface, the base surface comprising a set of at least three non-collinear recesses, whereby the at least three non-collinear recesses are positioned corresponding to the non-collinear support ends of the at least three support bars, preferably each recess being positioned at a node of the test specimen for a predetermined vibration mode of the test specimen.

[0026] The present invention also provides a method for acoustically measuring material properties of a test specimen, preferably at one or more temperatures, comprising: a. placing a test specimen on a support system within a test chamber of a system according to the invention and preferably heating the test specimen to within a test temperature range; b. preferably performing a background measurement, preferably within the test temperature range, by capturing a vibration signal from the test specimen within a calibration period, thereby obtaining a noise signal; c. c1. Applying vibration excitation to the test specimen; c2. Capture the vibration signal of the test piece during the test period, thereby obtaining the vibration response signal to the vibration excitation. performing acoustic measurements on the test specimen within the test temperature range and test duration by d. analyzing the vibration response signal, preferably by taking noise signals into account, to obtain material properties of the test specimen; The present invention relates to a method, comprising:

[0027] Drawing Overview [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 illustrates a naming convention for describing spherical caps. [Figure 2A] FIG. 10 shows the node locations of vibration nodes of a beam-shaped test specimen. [Figure 2B] FIG. 10 shows the node locations of vibration nodes of a beam-shaped test specimen. [Figure 3] 1 illustrates a system according to the present invention; [Figure 4] FIG. 1 illustrates a method for measuring acoustic responses at different temperatures and deriving material properties from these measurements, in accordance with the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] Detailed Description of the Invention The present invention relates to an impact excitation measurement system as described above and further described herein, a kit comprising such an impact excitation measurement system and at least one test specimen, and a method for acoustically measuring material properties of a test specimen as described above and further described herein.

[0030] Measurements that can be performed using the system or method of the present invention are preferably performed over a temperature interval including a lower limit and an upper limit. This temperature interval preferably includes a lower limit of up to 50°C, more preferably up to 30°C, even more preferably up to 20°C, even more preferably up to 0°C, even more preferably up to -18°C, and even more preferably up to -80°C. A particularly preferred lower limit of the temperature interval is room temperature. The temperature interval preferably includes an upper limit of at least 20°C, more preferably at least 50°C, even more preferably at least 100°C, even more preferably at least 200°C, even more preferably at least 400°C, even more preferably at least 600°C, even more preferably at least 800°C, and even more preferably at least 1000°C or higher, such as 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, and any value therebetween or above. The material of the support bar is preferably thermally stable over the above temperature interval. Taking into account the potentially large temperature interval from -80°C to 1500°C, the support bar is preferably made from a ceramic or glass-like material, for example glass, borosilicate, fluorophlogopite mica in a borosilicate glass matrix (e.g. Macor® containing 46% by weight of silica (SiO2), 17% by weight of magnesium oxide (MgO), 16% by weight of aluminum oxide (Al2O3), 10% by weight of potassium oxide (KO), 7% by weight of boron trioxide (BO3), 4% by weight of fluorine (F)), quartz, fused silica, silicon carbide, silicon, crystalline glass ceramics (e.g. Sitall), lithium aluminosilicate glass ceramics (e.g. Zerodur®).

[0031] Preferably, the test specimen comprises a predetermined shape and / or a predetermined size, which makes measurements easier to perform as the same support system can be used to measure different test specimens having the same predetermined shape and / or size.

[0032] Preferably, the impactor is or at least comprises a mechanical impactor. The mechanical impactor can be actuated in a number of ways, for example mechanically or electromechanically. A mechanical impactor may be preferred as mechanical systems tend to be usable over a wide temperature range.

[0033] Preferably, the recesses are each located at a node of the test specimen for a predetermined vibration mode of the test specimen, whereby the support system preferably comprises support bars having support ends, the positions of which correspond to the positions of the recesses of the test specimen, i.e. the positions of the support ends preferably correspond to the positions of the nodes of the vibration mode of the test specimen.

[0034] The use of three or more support bars with point-like support points, also known as "needles," significantly reduces the damping caused by the support. Therefore, precise measurements of damping can be made that are caused solely by the internal friction of the test specimen and essentially unimpeded by external friction from the support system. This makes the present invention also extremely useful for very basic, even manual excitation, room temperature impulse excitation measurements, or measurements at any available temperature.

[0035] This is illustrated in Figures 2A and 2B. Figure 2A shows the locations of two nodes (dashed lines) of a bending mode on a beam-shaped specimen. This means that when the specimen is subjected to an impact, preferably an impact delivered at the antinode location of the bending mode, the specimen will vibrate primarily according to this bending mode. This means that the amplitude of the bending mode vibration at the node location disappears or is at least very small in the specimen's center of gravity system. This means that if the specimen is supported at the node location, it will be supported throughout the entire test. If the support were positioned in a random location, the specimen may tend to bounce off the support point due to non-zero amplitude of vibration at the support location. Furthermore, locating the support end on the bending mode node further ensures that the bending mode vibration is much less damped (essentially undamped) than other modes, allowing for an increased signal-to-noise ratio of the bending mode vibration response. This also results in highly accurate measurement of bending mode damping. The present invention relates to a support system comprising a set of support bars. In Figure 2A, the support system comprises exactly three support bars (201, 202, 203) that can be fixed on a support plate (204), each with a support end that contacts and supports the test specimen (205). The support ends of two support bars (201, 202) support the specimen at a first node (206), while the support end of the third support bar (203) supports the specimen at a second node (207). In the case of a bending mode, this means that the three support ends are positioned non-collinearly, thereby defining a stable support surface for the specimen. The natural frequency f of this bending vibration mode is f denotes the dynamic Young's modulus E of the sample. For the illustrated beam with mass m, length L, width b, and thickness t, the following relationship can be used:

[0036]

number

[0037] Here, when L / t≧20, the correction coefficient T is

[0038]

number

[0039] is defined as: Figure 2B shows the locations of two nodes (dashed lines) of the torsional mode on a beam-shaped specimen. This means that when the specimen is subjected to an impact, preferably an impact delivered at the antinode location of the torsional mode, the specimen will vibrate primarily according to this torsional mode. This means that the amplitude of the torsional mode vibration at the node location disappears or is at least very small in the specimen's center of gravity system. This means that if the specimen is supported at the node location, it will be supported throughout the entire test. If the supports were positioned in random locations, the specimen may tend to bounce off the support point due to non-zero amplitude of vibration at the support location. Furthermore, locating the support end on the torsional mode node further ensures that the torsional mode vibration is damped much less than other modes, making it possible to increase the signal-to-noise ratio of the torsional mode vibration response and obtain very accurate measurements of the damping of this mode. The present invention relates to a support system comprising a set of support bars. In FIG. 2B, the support system includes exactly four support bars (210, 211, 212, 213) that can be fixed on a support plate (214), each with a support end that contacts and supports the test specimen (205). The support ends of two support bars (210, 213) support the specimen at a first node (216), while the support ends of the third and fourth support bars (211, 212) support the specimen at a second node (217). For torsional modes, this means that each subset of three support ends is non-collinearly positioned. While exactly three non-collinearly positioned support ends may generally be preferred because they automatically and uniquely define the support plane, it should be noted that additional support bars can prevent at least one support end from contacting the specimen. Nevertheless, for certain modes, such as the torsional mode shown in FIG. 2B, using four support bars may be more stable due to their nodes. This typically occurs in modes that have nodes that intersect in the center of the specimen.

[0040] The natural frequency of this torsional vibration mode is f tdenotes the shear modulus of the sample. For the beam shown with mass m, length L, width b, and thickness t, the following relationship can be used:

[0041]

number

[0042] Here, the correction coefficient R is

[0043]

number

[0044] is defined as: FIG. 3 illustrates a system according to the present invention. This figure shows a heating chamber (301) equipped with a set of heating elements (302, 303, 304, 305, 306) capable of bringing the heating chamber and / or test specimen to a desired temperature or temperature range. The heating elements (302, 303) are attached to the heating chamber walls and can supply heat to the heating chamber walls, for example, by heat exchange with a high-temperature, high-pressure fluid, electrical resistance heating, magnetic induction, etc. The heat from these wall heating elements can be dispersed within the heating chamber, for example, by ventilation devices (304, 305). The ventilation devices (304, 305) may also be configured to supply a warm fluid, such as heated air or steam, to the heating chamber. The heating elements may also include radiant heating elements, such as a microwave element (306). The heating chamber preferably also includes one or more thermometers for measuring the actual temperature of the heating chamber and / or test specimen, and preferably also includes control circuitry configured to control the temperature of the test specimen and / or heating chamber.

[0045] The test specimen (307) is suspended by a support structure comprising a set of support bars (308a, 308b, 309), which preferably support the specimen at the locations of its vibration nodes, thereby allowing the specimen to vibrate as freely as possible. The support bars are preferably needle-shaped in nature, with non-collinearly positioned support ends, preferably with a small contact surface with the specimen. Optionally, very small depressions can be created in the sample to prevent the sample from vibrating during long measurement cycles, during which many impulses are applied to the specimen. These depressions should be very small, preferably less than 1 / 100,000 of the mass of the sample, so as not to affect the dynamic properties of the material. An acoustic sensor (310) or multiple acoustic sensors, which may comprise a microphone or laser interferometer, can be brought into contact with the specimen (311), preferably at a well-defined location, or a waveguide can be used to guide the acoustic response to the acoustic sensor, preferably with one end of the waveguide brought close to or in direct contact with the specimen within the heating chamber, and the other end preferably located outside the heating chamber. The latter embodiment allows the sensor to be located outside the heating chamber.

[0046] In a preferred embodiment, the acoustic sensor comprises a laser interferometer, which is particularly useful for measurements in a vacuum and allows for contactless measurements. Alternatively or additionally, the acoustic sensor may comprise, for example, - SR.Huang, RMLerner, KJParker "Time domain Doppler estimators of the amplitude of vibrating targets" (.J.Acous.Soc.Am.,91(2),965-974(1992)), - J. Tapson "High precision, short range ultrasonic sensing by means of resonance mode-locking" (Ultrasonics, 33, 6, 441-444 (1995)), and - R. Kazys, R. Sliteris, L. Mazeika "Ultrasonic technique for Vibration Measurements" (Proceedings of the 15th World Conference on Non-Destructive Testing, 15-21 October 2000 in Rome, https: / / www.ndt.net / article / wcndt00 / papers / idn246 / idn246.htm) The sensor may comprise an ultrasonic measurement sensor and / or a time-of-flight sensor and / or a Doppler type sensor, as described in

[0047] These types of sensors may also be used for non-contact measurements. In one embodiment, the method of the present invention is practiced in which the heating chamber contains a pressure below atmospheric pressure, preferably 0.5 bar or less, more preferably 0.2 bar or less, and most preferably essentially a vacuum pressure. This preferably allows a laser interferometer to be used to enable non-contact vibration measurements at low to zero pressure. Measurements down to zero pressure attenuate ambient noise, thereby increasing the signal-to-noise ratio.

[0048] The impactor preferably includes a ballistic impactor (312) capable of applying an impulse via an impactor actuator (313). The ballistic impactor (312) is preferably a ceramic rod that can withstand high temperatures and whose properties do not change significantly with temperature, i.e., the impactor preferably consists essentially of a thermally stable ceramic material. It can be fired upward (314) towards the specimen using the impactor actuator (313), which: - a guide tube (315) through the bottom of the heating chamber for guiding the ballistic impactor preferably along the vertical direction; - an electromechanically operated hammer (316) configured to impart a preferably vertical impulse (317) to the impactor (312); The hammer (316) may include an electric coil (318) and a movable rod or projectile (319) that can move in response to an electric current flowing through the coil (318). An example of such a system is presented in U.S. Patent No. 6,782,970, whereby in the present invention, the projectile of the impactor actuator applies an impulse to the ceramic impactor (312) rather than directly to the test specimen. Alternatively, a pressure-driven impactor or pressure-driven impact actuator (380) may be used to apply the impulse to the impactor.

[0049] Preferably, the support bar is made from the same material as the impactor and / or guide tube. Preferably, this means that the support bar consists essentially of a thermally stable ceramic material. Alternatively or additionally, the support bar has a coefficient of thermal expansion that is essentially equal to the coefficient of thermal expansion of the impactor and / or guide tube.

[0050] In one embodiment of the method of the present invention, step b. of performing background measurements within the test temperature range is preferably performed by capturing a vibration signal from the test specimen within a calibration period, thereby obtaining a noise signal. By considering the background noise of the environment when performing an analysis of the vibration response, material properties can be better determined. Furthermore, by considering the background noise within the same test temperature range as the acoustic measurement, the inventors have found that a much better analysis of the vibration response can be performed. This is because noise can be highly dependent on the temperature range, for example, due to heating elements, ventilation systems, or any other equipment or equipment components used to perform the measurement, each of which may behave differently in different temperature ranges.

[0051] The inventors have further found that best results are achieved when background measurements are performed by performing all steps of acoustic measurements except for applying vibrational excitation to the test specimen. Thus, in a preferred embodiment, step b of performing background measurements includes performing all steps of step c of performing acoustic measurements except for step c1 of applying vibrational excitation to the test specimen. This applies to all embodiments of the method described above, as well as the methods described later in this specification and claims.

[0052] In a preferred embodiment, the test chamber of the impact excitation measurement system of the present invention includes a heating element for bringing the test specimen within the test temperature range.

[0053] In a preferred embodiment, the impact excitation measurement system includes an impactor actuator for actuating an impactor when applying vibrational excitation to a test specimen located within the test chamber.

[0054] In a preferred embodiment, the impact excitation measurement system comprises a control system associated with the test chamber, the sensor, and the impactor, the control system comprising: optionally instructing the test chamber to bring the test specimen within a test temperature range; instructing the impact system to operate the impactor using the impactor actuator such that a vibration excitation is mechanically applied by the impactor to a test specimen located within the heating chamber during a test period, and to acquire a vibration response signal to the vibration excitation from a sensor; optionally, during a calibration period, instructing the impact system to actuate the impactor using the impactor actuator and acquire a noise signal from the sensor such that the impactor does not mechanically impart vibrational excitation to the test specimen located within the heating chamber; configured to obtain material properties of the test specimen by analyzing the vibration response signal, preferably thereby taking noise signals into account;

[0055] In a further aspect, the present invention relates to a dilatometric method for obtaining thermal expansion parameters of a test specimen, the method comprising the steps of: - extracting at least two resonant frequencies from experimental data at a first temperature; - obtaining a first value of a first dimensional parameter from the at least two resonant frequencies at the first temperature; - comparing the first value of the first dimensional parameter at the first measurement temperature with a second value of the first dimensional parameter at a second temperature; - calculating thermal expansion parameters from said comparison; Includes:

[0056] The at least two resonant frequencies at the first temperature are thereby a material property of the test specimen, which can preferably be obtained by the acoustic measurement method described above and further described herein. The impact excitation measurement system described above and further described herein can preferably be used to obtain the at least two resonant frequencies.

[0057] 4 illustrates one embodiment of a method according to the present invention. In a first step a, the temperature is set within a first temperature range (1021). Then, step b is performed (1002), taking care not to shock the test specimen (1001), preferably by activating an impact system but avoiding impact. Then, step c is performed, impacting the test specimen (step c1, 1010), and capturing a vibration response signal (step c2, 1020). The signal is then analyzed (step d, 1030), whereby E, G, ν, and / or other properties (particularly the damping constant) are obtained within the temperature range of step a. The impact avoidance activation step (1001), noise capture step (1002), impact step (1010), and response capture step (1020) may be performed repeatedly (as shown, for example, if the apparatus has multiple impactors operating in series) before the signals are analyzed (1030), or alternatively, each captured signal may be analyzed separately, so that noise signals and / or vibration response signals at different temperatures or temperature ranges can be combined in the analysis of step d to obtain more accurate values ​​of material properties and / or determine the temperature dependence of these material properties.

[0058] Depending on the excitation mode selected, analysis 1030 may further include determining the dynamic Young's modulus (E) or shear modulus (G) from the frequencies of the spectrum of responses, particularly by identifying peak frequencies and applying equations such as those described above.

[0059] Preferably, the analysis further comprises comparing 1040 the decay constant with a reference value. This step allows the method according to the invention to be used for quality control purposes. In fact, a method for controlling the quality of a manufactured article comprises characterizing at least a portion of the manufactured article as said solid material sample using the above-described method, and signaling a "pass" condition 1040 / YES if the decay constant is within a predetermined margin of said reference value, and declaring a "fail" condition 1040 / NO if the decay constant is outside said predetermined margin of said reference value. Thus, according to one aspect of the invention, there is provided a method for controlling the quality of a manufactured article, comprising characterizing at least a portion of the manufactured article as said test piece using the above-described method, and signaling a "pass" condition if the decay constant is within a predetermined margin of said reference value, and declaring a "fail" condition if the decay constant is outside said predetermined margin of said reference value.

[0060] In one embodiment of the present invention, steps a-d are preferably repeated multiple times at the same temperature, at different temperatures, or within different temperature ranges. In a preferred embodiment, the test specimen is heated sequentially, whereby steps a-d are performed within successive temperature ranges.

[0061] For example, a test specimen can be heated continuously at a rate of 1°C / sec starting from room temperature (20°C). Steps a-d can then be performed periodically every 20 seconds, meaning that a first set of steps a-d is performed in a temperature range of 20-40°C, a second set of steps a-d is performed in a temperature range of 40-60°C, and so on up to a maximum temperature range of, say, 1780-1800°C. Note, however, that the temperature ranges do not have to be equally large and can, for example, be smaller relative to the temperature range of interest. For example, if it is known that a test specimen or a component made from the same material as the test specimen will primarily be used at temperatures between 700-800°C, a smaller temperature range, say, 5°C, can be determined to more accurately measure material properties between these temperatures.

[0062] It should also be noted that measurements performed in steps b and / or c can be combined with measurements performed in steps b and / or c at other temperatures to obtain more accurate noise and / or vibration response signals. For example, assume that steps a through d are performed in a temperature range of 80°C to 100°C and also in a temperature range of 100°C to 120°C. Thus, step b may be performed once in a subrange of 82°C to 87°C and once in a subrange of 102°C to 107°C, while step c may be performed once in a subrange of 92°C to 97°C. In such a case, the analysis of step d can be performed taking into account two noise signals obtained in two iterations of step b. Thus, in a preferred embodiment, steps a, b, c, and / or d are performed more than once within one temperature range. Alternatively or additionally, steps a, b, c, and / or d may be performed multiple times in different, potentially overlapping, temperature ranges.

[0063] In one embodiment, the control system comprises processing means configured to analyze the vibration response signal taking into account the noise signal to determine material properties of the test specimen.

[0064] Thereby, the processing means may be preferably configured to subtract the noise signal from the vibration response signal in the time domain, or more preferably in the frequency domain, by using a Fourier transform or fast Fourier transform or harmonic decomposition on the captured signal. The subtraction may also be performed in a combination of the time and frequency domains. The processing means is preferably configured to analyze the time-varying signal to determine the frequencies and decay constants of the sinusoids that make up the time-varying signal, i.e., to solve the harmonic inversion problem. The harmonic inversion problem, which more generally consists of determining the frequencies, decay constants, amplitudes, and phases of the sinusoids that make up a discrete-time, finite-length signal consisting of the sum of a finite number of such sinusoids in a given bandwidth, is well known in the literature but has not been associated to IET to date. In their paper "Harmonic inversion of time signals and its applications" (The Journal of Chemical Physics 107, 6756 (1997)), Vladimir A. Mandelshtam and Howard S. Taylor describe the use of the general filter diagonalization method of Wall and Neuhauser to solve the harmonic inversion problem by reassessing it as one of small matrix diagonalization. Computer-based implementations of this technique are known in the art, including the "Harminv" program by Steven G. Johnson of the Massachusetts Institute of Technology. The results of the analysis can be output to a screen 140 or to any other suitable interface for storage or further processing by other devices.

[0065] The processing means may consist of one or more dedicated hardware components (e.g., ASICs), appropriately configured configurable hardware components (e.g., FPGAs), microprocessors with appropriate software, or a combination of the above. The same components may also perform other functions.

[0066] In a preferred embodiment of the invention, the test specimen is a workpiece, a device, or a component of a device. In another preferred embodiment of the invention, the test specimen comprises a well-defined shape, preferably a beam shape, and is made from the same material or using the same manufacturing techniques as the workpiece, device, or component of a device.

Claims

1. an impact excitation measurement system comprising a test chamber, an impactor, a sensor system, and a support system, the impactor configured to impact a test specimen supported by the support system at a predetermined height, the sensor system configured to acquire a vibration response of the test specimen to the impact applied to the test specimen by the impactor, and the support system configured to support a solid test specimen at the predetermined height within the test chamber; The support system comprises a set of support bars having a thermal expansion coefficient essentially equal to a thermal expansion coefficient of the impactor, the set of support bars comprising at least three support bars each having a support end, the three support ends being non-collinearly positioned.

2. The impact excitation measurement system of claim 1 , wherein the support bar is made from the same material as the impactor.

3. 3. The impact excitation measurement system according to claim 1, wherein the support bar is made of a thermally stable material.

4. The impact excitation measurement system according to any one of claims 1 to 3, wherein the support end includes a point-like shape.

5. 5. The impact excitation measurement system of claim 4, wherein the support end includes a point-like shape in the form of a spherical cap with a height (h) of up to 3 mm and a radius (a) at the base of the cap of up to 0.5 mm.

6. 6. The impact excitation measurement system according to claim 1, wherein the test chamber is a heated chamber comprising a temperature control system configured to control the temperature within the chamber.

7. The material of the support bar is up to 30.0 x 10 －６ K －１ The impact excitation measurement system according to any one of claims 1 to 6, wherein the impact excitation measurement system comprises a linear expansion coefficient of

8. The material has a maximum of 10.0 x 10 －６ K －１ 8. The impact excitation measurement system of claim 7, wherein the coefficient of linear expansion is:

9. An impact excitation measurement system according to any one of claims 1 to 8, wherein the impactor comprises a ballistic impactor (312) arranged to apply an impulse via an impactor actuator (313).

10. 10. The impact excitation measurement system of claim 9, wherein the impactor consists essentially of a thermally stable ceramic material.

11. The impactor actuator (313) a guide tube (315) through the bottom of the test chamber for guiding the ballistic impactor along a vertical direction; and an electromechanically operated hammer (316) configured to impart a normal impulse (317) to the ballistic impactor (312).

12. A kit comprising an impact excitation measurement system as described in any one of claims 1 to 11 and at least one test piece, wherein the test piece has a base surface, the base surface having a set of at least three non-collinear recesses, whereby the at least three non-collinear recesses are positioned corresponding to the non-collinear support ends of the at least three support bars.

13. 13. The kit of claim 12, wherein each of the recesses is positioned at a node of the test specimen for a predetermined vibration mode of the test specimen.

14. A method for acoustically measuring material properties of a test specimen at one or more temperatures, comprising: a) placing a test specimen on the support system in a test chamber of the impact excitation measurement system according to any one of claims 1 to 11; b. performing a background measurement by capturing a vibration signal from the test specimen within a calibration period to obtain a noise signal; c. c1. Applying a vibration excitation to the test specimen; c2. Capturing a vibration signal of the test piece during the test period, thereby obtaining a vibration response signal to the vibration excitation. performing acoustic measurements on the test specimen within the test period by d. analyzing the vibration response signal to obtain the material properties of the test specimen by taking into account the noise signal; A method comprising:

15. The method of claim 14 including the step of heating the test specimen within a test temperature range.

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