Scanning Laser Vibrometer Research Articles

Estimation of the effective range of PZT sensors for damage detection based on full wavefield measurements

Optimal location of sensors for enhanced damage detection capability is one of the key factors which needs to be considered when designing SHM system based on PZT sensors. However the sensitivity of a sensor to damage is not only dependent on its relative location with respect to elastic waves source and damage, but can also depend on structure geometry as well as particular signal features which are used for structure assessment. In the presentation, results of structure evaluation based on guided waves excited by PZT transducers and full wavefield measurements obtained by laser scanning vibrometer will be presented. The measurements were acquired for pristine state of test structure and with introduced damage, therefore it is possible to calculate spatial distribution of various signal characteristics and estimate effective range of PZT sensors for damage detection based on a given damage index. Various parameters affecting the damage detection range will be compared, in particular: type and the extent of damage, type of signal characteristic used, parameters of the excitation signal (e.g. frequency, duration), as well time interval used for damage index calculation. The obtained results may be useful for refining algorithms for sensor placement optimization as well as damage localization techniques, e.g. based on RAPID imaging algorithm.

Feasibility Study for Monitoring an Ultrasonic System Using Structurally Integrated Piezoceramics

This paper presents a new approach to monitoring ultrasonic systems using structurally integrated piezoceramics. These are integrated into the sonotrode at different points and with different orientations. The procedure for integrating the piezoceramics into the sonotrode and their performance is experimentally investigated. We examine whether the measured signal can be used to determine the optimal operating frequency of the ultrasonic system, if integrating several piezoceramics enables discernment of the current vibration shape, and if the piezoceramics can withstand the high strains caused by the vibrations in a frequency range of approximately 20–25 kHz. The signals from the piezoceramic sensors are compared to the real-time displacement at different points of the sonotrode using a 3D laser scanning vibrometer. To evaluate the performance of the sensors, different kinds of excitation of the ultrasonic system are chosen.

Experimental and numerical investigations on the dynamic response of a power transformer

In the manufacturing unit, there is a need of an accurate and reliable numerical tool to predict noise radiation from transformer. The first step to achieve this is to have a proper modal analysis of the active part (winding+core+clamping system). An impact test was performed on a 30 MVA power transformer unit and resonance peaks were identified from the FFT plots. Also, Operational Deflection Shapes (ODS) were extracted to visualize the displacement pattern of the test object. Moreover, the transformer unit was electrically energized, and vibration levels were measured with Polytec 3D scanning laser vibrometer. A detailed numerical model was developed in COMSOL Multiphysics, and very good agreement was seen between the numerical and measurement results.

Laser Vibrometry of Shear Waves in a Layer of a Gel-Like Medium

Abstract—A laser scanning vibrometer was used to measure the amplitudes and phases of the vibrational velocity of shear waves excited by a one-dimensional source in the form of a narrow rectangular bar in a gellike medium. The vibrations of 26 plates reflecting the laser beam and located inside an optically transparentphantom along a segment with a length of 84.5 mm at a distance of 20 mm from the source were measured.The angular distributions of the amplitude and phase of shear waves at discrete frequencies from 59 to 500 Hz were measured in continuous mode. In pulsed mode, the vibrator excited a pulse in the medium with a durationof 1.5 periods of the 300 Hz frequency. The amplitudes and phases of shear waves were calculated by fastFourier transform of the time profile of the vibration velocity of the plates with a duration of 50 ms. The angular amplitude distributions measured in the pulsed and continuous modes are qualitatively the same. At all frequencies, the distributions are symmetrical with respect to the vertical axis. The maximum oscillation amplitude is observed at angles close to ±45°. The velocity of shear waves, calculated from the measured phase distributions, increases from 2 to 2.5 m/s with a change in frequency from 50 to 500 Hz. It is shown that this velocity behavior is well described by a relaxation model of the medium with one relaxation time equal to 0.3 ms. Shear wave attenuation depends on frequency and exceeds 1 cm-1 for waves with frequencies above250 Hz. The maximum attenuation per wavelength is observed near the relaxation frequency of the medium in the 300–400 Hz range. The results can be used to optimize devices for measuring the elasticity of soft tissues.

Laser Doppler in Green Compact Density Inspection of Powder Metallurgy

The density of green compact in powder metallurgy (PM) is a critical characteristic to determine the strength and tenacity of the product. Due to the fragility and sensitivity to the humidity of green compact, detection method triggers by knocking or immersion cannot be applied. Current inspection method for green compact is to use a densitometer with Archimedes Principle, which has to immerse green compact into water. This action considers a destructive test due to the porosity of the PM product, and the oxidation reaction of metal particles inside products cannot be controlled. Since the current detection method is destructive, most of the inspection on forming process of PM only complies after setup of compaction machine. The next non-destructive test is executed after sintering, such as Acoustic emission testing (AE) and Magnetic Testing (MT), which require a solid object for knocking or liquid immersion. To reduce defective compaction flow into the manufacturing process, a Non-destructive test in forming process is a prerequisite. Laser Doppler Vibrometer (LDV) takes advantage of measuring without damaging the test object and obtaining characteristic spectrum signal from the sample for further analysis, which is preferable for green compact of PM. The LDV test setup included a Polytec PSV-400 scanning laser vibrometer with a crystal resonator attached to the test product to generate reference vibration. Integrate spectrum in the frequency range 0 - 5000 Hz was recorded from 30 points of an annular pattern. Comparison of the spectrum and statistical analysis from defective specimens demonstrate that velocity increases within a specific frequency, which is different from with normal samples. Increases in velocity refer to uneven density distribution with an absence of particles inside product decline. The study approves the possibility of density detection in green compact using an LDV. Further studies aim to construct a relational model of specimen and compaction machine and determine a fundamental database for Advance Process Control (APC) of forming process in PM.

Super-sensitivity full-field measurement of structural vibration with an adaptive incoherent optical method

Full-field measurements of structural vibrations have been achieved by incoherent optical methods with video cameras such as digital image correlation and optical flow. In contrast to coherent optical methods such as scanning laser vibrometers, incoherent optical methods are low-cost and easy to set up. However, the sensitivity (minimum measurable displacement) of incoherent optical methods is generally lower than that of coherent optical methods. Typically, the sensitivity of incoherent optical methods is essentially limited by the finite bit depth of the digital camera due to the quantization with round-off errors. Quantitatively, this theoretical sensitivity limit is determined by the bit depth B as δp=1/(2B−1) [pixel] which corresponds to a displacement causing an intensity change of one gray level. Fortunately, natural dithering may be leveraged to overcome the quantization and exceed the sensitivity limit, achieving super-sensitivity.In this work, we first study the mechanism of the sensitivity limit induced by the quantization and the critical limitation of existing super-sensitivity methods in the full-field measurement of structural vibration. Addressing such a limitation, we present a general adaptive weighted averaging method with dithering, achieving super-sensitivity incoherent optical measurement of full-field deformational vibration of flexible structures. Specifically, both spatial and temporal samplings of the pixels are leveraged simultaneously to adaptively identify the motion (deformation) shape of the structure by principal component analysis (PCA) of spatiotemporal pixel intensities. Then, the identified deformation shape is used to perform a deformation-shape-weighted averaging over spatial pixels with dithering, revealing the sub-sensitivity displacement while retaining spatial resolution at full field. Numerical simulations and laboratory experiments are performed for principle explanation and method validation. Particularly, we derive a mathematical model of the minimum measurable vibration amplitude A∗ for the developed super-sensitivity method, which is found to be determined by the number of spatial pixels for averaging Ns and the noise level σn in the imaging system. Thus, this work provides, for the first time, a rigorous quantification of the sensitivity of incoherent optical measurement for structural vibration, and a new quantitative method to achieve super-sensitivity full-field measurement of structural vibration.

Reconstruction of radial pseudo-forces on cylinders via mono-laser scanning: Concept and application to characterization of damage

Damage in a plate can cause perturbation to the equation of out-of-plane motion, which can be equivalently regarded as the transverse pseudo-force applied on the damage region. Thereby, the characterization of damage in the plate can be achieved by identifying the pseudo-force. Nevertheless, it is difficult to formulate the pseudo-force for the characterization of damage in a cylinder because its longitudinal, circumferential, and radial motions are coupled. Moreover, a conventional scanning laser vibrometer equipped with a single scanning head can measure the out-of-plane motions of a plate but is insufficient for measuring the 3D motions of a cylinder. The aforementioned limitation leads to a noticeable barrier to extending the pseudo-force approach from a plate to a cylinder. To overcome this barrier, a new concept of radial pseudo-force (RPF) is formulated to represent the damage-induced perturbation to the radial equilibrium of a cylinder, whose motions are dominated by its radial components. The RPF is applied on the lateral surface of the cylinder and is an ideal damage indicator because it appears in the damage region only and almost vanishes at intact locations. Furthermore, a novel method for reconstructing RPFs via mono-laser scanning is proposed. A correction matrix is formed to correct an undeflected-laser-axis mode shape component (MSC) that can be directly measured via mono-laser scanning, whereby the radial MSC of the cylinder can be obtained for the reconstruction of the RPF on the cylinder. The concept of the RPF is numerically proved using the finite element method. In addition, the applicability of the RPF approach is experimentally validated on a cylinder with internal damage. The numerical and experimental results reveal that the RPF approach can graphically characterize the occurrence, location, and approximate plane size of damage in cylinders.

Simultaneous non-contact identification of the elastic modulus, damping and coefficient of thermal expansion in 3D-printed structures

Thermoplastic-extrusion 3D printing has gained popularity for the fabrication of electrothermal soft actuators that can control shape in response to temperature changes generated by embedded 3D-printed heaters. However, the material properties, such as the coefficient of thermal expansion, elastic modulus, and damping, significantly impact the performance of these 3D-printed electrothermal actuators. The material properties can be temperature-dependent, and vary based on the print and fill orientation. Current experimental methods cannot simultaneously research these properties, resulting in partial research of the influencing parameters.This research introduces a simultaneous and non-contact identification method for the elastic modulus, damping, and coefficient of thermal expansion, utilizing optical and thermal cameras, a scanning laser vibrometer, IR heating, and electrodynamic shaker excitation. The method was applied to several materials, including composites. The introduced method can fully characterize the 3D prints and the materials used for 3D printing, leading to the faster and more predictable development of future 3D-printed electrothermal actuators.

Method using singular value decomposition and whale optimization algorithm to quantitatively detect multiple damages in turbine blades

Renewable energy has increased in recent years with a consequential increase in equipment maintenance. Maintenance costs can be reduced by structural health monitoring techniques especially for wind turbine (WT) blade damages. However, the majority are not suitable for on-line measurements and quantitative detections. A quantitative damage detection method is developed to identify multiple damages in a WT blade under in-service operation conditions. Firstly, singular value decomposition is applied to reveal singular information in the operating deflection shape (ODS), which can be treated as damage locations. Secondly, whale optimization algorithm is utilized for a damage severity decision about the natural frequency database between damage severities and natural frequencies, which are constructed by finite element method (FEM) simulations on the detected damage locations in the WT blade. The procedure is applied to FEM numerical simulations of a single WT blade with two and three damages. By adding a certain noise to the simulation dataset, the robustness of the present method is validated. Furthermore, the laser scanning vibrometer is employed to test the ODS as well as natural frequencies of WT blades to testify the performance of the multiple damage detection method. Results show that the present method is effective for the detection of multi-damage in WT blades with a certain noise robustness.

An automated sonic tomography system for the inspection of historical masonry walls.

Background: The conservation of the built masonry heritage requires a comprehensive understanding of its geometrical, structural, and material characteristics. Non-destructive techniques are a preferred approach to survey historical buildings, given the cultural value of their fabric. However, currently available techniques are typically operated manually, consuming much time at operational and processing level and thus hindering their use for the on-site inspection of heritage structures. Methods: A novel automated sonic tomography system was designed and built to inspect and obtain information about the inner structure and damage of historic masonry walls. The system consists of a hitting device mounted on a frame that can be placed adjacent to the wall under analysis. The hitting device can move along the surface within the frame area in X, Y and Z directions, generating the sonic wave. The receiving system is a scanning laser vibrometer, able to measure from the distance the displacement of a focused point over time, recording the wave when it reaches the opposite surface. Results: Six stone masonry walls with different interior geometries were constructed at the laboratory by a professional stonemason. The construction of the walls was carefully documented, including the generation of detailed photogrammetric models of each single stone. The system was applied to survey the six masonry walls. Since the inner morphology of the walls is known, the resulting tomographic images could be compared with the ground truth. Conclusions: Automating the inspection allowed to collect thousands of data in a few hours. New software was also developed to automate the processing of the data. Results are expected to highlight the potential of tomography to obtain quantitative information about the interior of heritage structures, while providing new tools that make the implementation of the technique more practical for professionals. Data, software and models have been made publicly available.

Quantitative detection of multiple damages in wind turbine blade based on the operating deflection shape and natural frequencies

Structural damage detection based on vibration signals has gained significant attention from researchers due to its ease of implementation. However, while the detection of damage using natural frequencies and mode shapes is effective for static structures, it is not directly applicable to structures in operation. To address this limitation, a two-stage multi-damage detection method has been developed to quantitatively detect damage in wind turbine (WT) blades during operation. This method utilizes the operating deflection shape (ODS) and random forest (RF) techniques. In the first stage, a two-dimensional (2D) wavelet transform is employed to decompose the ODS of the WT blade and reveal the multi-damage locations represented by the singularity points in the third detailed map. In the second stage, the finite element method (FEM) is applied to establish relationships between the natural frequencies and damage severities at fixed damage locations of the blade. This relationships form a natural frequency database, which is then used in conjunction with the RF algorithm to search for the damage severity when the natural frequency of a damaged blade is known. To verify the performance of the proposed two-stage multi-damage detection method, simulations of WT blades with two or three damages were performed. In addition, experimental tests were conducted using a laser scanning vibrometer to measure the ODS and natural frequencies of small WT blades in the two damage conditions. Both the numerical simulations and experimental investigations demonstrate that the proposed method can achieve acceptable damage-detection precision.

Intelligent defect inspection of flip chip based on vibration signals and improved gcForest

The defect inspection of flip chips has become a meaningful and challenging task with the decrease of size and distance of solder balls. In this paper, we proposed a novel defect diagnostic method for flip chips based on vibration signals and improved multi-grained cascade forest (gcForest). Firstly, the flip chip is excited by an air-coupled capacitive ultrasonic transducer, and the corresponding vibration signals of flip chip are captured by a laser scanning vibrometer. Then, the feature information of original vibration signals is extracted by muti-grained scanning (MGS) automatically. Finally, the extracted feature information is input into the cascaded forest for defect diagnosis. Considering the low data transmission efficiency and feature redundancy between MGS and cascaded forest, a feature extraction channel strategy based on kernel principal component analysis (KPCA) is introduced into the cascaded forest. Besides, in order to improve the generalization ability of the improved gcForest, the classifiers of each layer in cascade forest are upgraded. The results demonstrate the superiority of the improved gcForest over the traditional methods on experimental vibration data of flip chips, especially under small training sizes, which is very beneficial to practical engineering.

FE‐based modeling of a mesoscale piezoelectric motor

AbstractThe manufacturing of systems at the mesoscale on the order of millimeters to centimeters is costly and challenging. To simplify the development process, the finite element method (FEM) can be used to compare and evaluate different design variations at an early stage. This method also allows for gaining a more precise understanding of the system's behavior. In robotic applications it is the torque that is of the greatest interest as a sufficiently high torque mitigates the need for a gearbox, which is very difficult to manufacture and integrate at small scales. Given this background, the present work aims to develop a finite element model for the numerical representation of a class of rotational piezoelectric motors based on multiple unimorph arms. The influence of different design parameters on the resulting torque is analyzed utilizing this model. The motor design consists of a planar rotor and a flat spring, a stator with three unimorph arms, as well as a shaft. With a total integrated motor thickness of 0.8 mm, the weight is approximately 200 milligrams. The rotation is mainly caused by the tip contact between the arms of the stator and the rotor itself. Experiments with prototypes have shown that bidirectional rotation is possible with the design, which is then investigated in more detail using the numerical model. There are several challenges here in the non‐linearity due to the contact between the individual components and the high‐frequency excitation of the motor in the kHz range.The modeling also requires validation experiments to determine the resulting properties for the coupled system of structural and piezoelectric components. This includes both the measurement of the unimorph arms and the measurement of the natural frequencies of the stator with the piezoelectric unimorphs by a laser scanning vibrometer and displacement sensors. The scanning vibrometer also provides the opportunity to compare the vibration modes, as an important non‐local output quantity, in order to achieve good agreement between the numerical and experimental results.In the next stage, the model is to serve as the basis for multi‐objective optimization to achieve maximum torque in the smallest possible volume. Further miniaturization possibilities will also be investigated in future studies.

Operational Modal Analysis of Historical Buildings and Finite Element Model Updating Using α Laser Scanning Vibrometer

Without affecting the integrity or stability of the heritage monuments, vibration-based techniques provide useful solutions for acquiring global information about them. By studying the dynamic response to suitable excitation sources, it is feasible to define the mechanical characteristics of structures and identify and locate defects in their global behaviour. Laser Doppler vibrometry (LDV), which enables non-contact measurements of the vibration velocity of moving surfaces using a focused laser beam, is a highly desirable technique for qualitative dynamic characterisation and damage assessment. LDV is a simple and non-intrusive approach. It permits remote measurements and has a high degree of sensitivity and frequency adaptation. In addition, the system is entirely computer controlled, providing simple data storage, processing, and analysis. LDV has been originally researched and developed for structural and modal shape analysis of physical prototypes, in-service devices (e.g., machinery components), medical imaging applications, and damage detection and analysis relevant to small-scale non-destructive testing (NDT), and evaluation of micro to meso-targets (e.g., fracture detection and mapping in composites, modal shape and vibration analysis of objects, etc.). In spite of several successful applications in the case of bridges and thin structures, ambient vibration testing in an integrated form that includes dynamic identification, sensitivity analysis, and numerical modelling update employing modern sensor non-contact technologies is still uncommon. In this paper, the authors intend to explore further the possibility of combining ambient vibrations and OMA in combination with the non-contact LDV sensing technique in order to remotely acquire mechanical waves travelling in historical structures, track the actual behaviour of such structures, and calibrate their finite element numerical models.

A novel index for vibration-based damage detection technique in laminated composite plates under forced vibrations: experimental study

In this study, vibration modal analysis has been used to experimentally investigate the detection of fiber breakage (FB) and delamination in laminated composite plates. The modal analysis was performed on two arrangement styles of carbon fiber reinforced polymer (CFRP) laminated plates under forced vibrations. The main contribution in this study is that a new index named Improved Curvature Damage Factor (ICDF) was introduced to detect and localize damages in composite structures. It is a developed version of an earlier index based on the change in mode shape curvature (MSC) of dynamic response. To include the effect of more than one mode shape Cumulative Improved Damage Factor (CICDF) was proposed. The ICDF index was validated with a number of earlier studies that investigated the damage detection in different structures in order to approve the efficiency of this index. A scanning laser vibrometer was also used to experimentally examine the modal-based and forced responses for intact and damaged plates. Various experimental tests were used to verify the advantages of the proposed methodology and its use in structural health monitoring. In addition, the analysis of experimental results showed that the mutation caused by FB is almost double that of the value of delamination peaking.

Use of Scanning Laser Technology to Obtain the Erhu Vibroacoustic

The aim of this research is to develop and validate an experimental model testing method in the erhu instrument. The model analysis is dependent on the dynamic behavior of materials which results the relationships to be naturally excited due to the structure. There are three major factors which would directly affect the performance of erhu vibroacoustic: (1) string, (2) vibrating skin, and (3) wooden soundbox. However, the transducer mass effect is the significant impact factor in the membrane vibration measurement. The attention is focused on the erhu skin vibration modes by using the scanning laser method. The method for experimental mode shapes of erhu skin was notable in that the equipment assembled a loudspeaker, a signal point laser, and a scanning laser vibrometer. The mode shapes can be excited depending on the white noise with plane acoustic wave to push on the skin surface. The scanning laser method is content two types of laser doppler vibrometer for various purpose. The single point laser measured the driving point vibration as the reference in the center of the skin surface. The responses were measured by the scanning laser vibrometer with 276 measuring points on the surface. The results showed the vibroacoustic of erhu skin which the various mode shapes are dependent on the frequency diversifications. The mode shapes of the erhu skin can be characteristic into five vibroacoustic patterns by the various frequency ranges (20 to 5,000 Hz). Obviously, the scanning laser method is a convenient and readily reproducible setup to evaluate in the erhu vibroacoustic properties. As an engineering application, the proposed method can be served as a fundamental tool when predicting or even suppressing the possible excitations associated with particular vibration modes in the mechanical designs of the instruments.

Vibration of the horn affects the Rayleigh jet breakup

There have been a number of studies on the Plateau–Rayleigh instability and the influence of the initial jet perturbation on the jet breakup. Our study observed that the threshold lengths of jet breakup varied with the voltage applied to the piezoelectric sheets during the droplet generation for extreme-ultraviolet (EUV) source and wafer cleaning. Combining acoustics and fluid mechanics, we investigated the process and mechanism to interpret the impact of the horn vibration on the jet breakup. The whole process of the vibration delivery from the horn to the jet was summarized: generated by the horn, the vibration transmits into the water, spreads in the chamber, stimulates the jet through the orifice, and grows continuously, causing the jet breakup. In order to validate the analysis, a series of experiments were carried out and compared with the theoretical predictions. The vibration mode and amplitude of the horn were determined by the scanning laser vibrometer. With the hydrophone detection, the distribution of the vibration in the axial direction at the nozzle outlet was studied, and the delivery of the vibration in the chamber was discussed. To verify the influence of the vibration in the chamber on the jet breakup, we compared the results of jet breakup under different sound pressures. Besides, a theoretical model of the jet breakup length versus the piezoelectric sheet voltage was proposed. The study of the whole process provides guidance for changing the jet breakup length by adjusting the voltage and helps to investigate other parameters of the jet breakup process.

Damping performance of particle dampers with different granular materials and their mixtures

A particle damper is a passive vibration control technology that utilizes the high damping properties of granular materials for reducing the vibration amplitude of a structure over a wide frequency range. Energy dissipation of particle damper is a highly nonlinear and complex physical phenomenon [1]. Previous studies have shown that the damping mechanism of a particle damper depends on several factors, like particle size and shape, granular material, filling ratio, and the number of particles [2–5]. Out of these parameters, the type of granular material used in the particle damper plays a major role in reducing the vibration amplitude of a mechanical structure. Therefore, the current contribution aims to investigate the influence of 20 different granular materials on vibration attenuation. The granular materials under investigation are subdivided into two major groups, namely: soft particles, like rubber granulate, and hard particles, like steel balls. Furthermore, this paper proposes a hybrid particle damper in which two different types of granular material mixtures are used, i.e. a particle damper in which for instance soft particles are mixed with hard particles. Moreover, in this contribution, fine particles, like rubber powder are mixed with hard granular materials like lead shot, which can be seen as an extension of the fine particle impact damper concept [6]. The humidity-dependent behavior of particle dampers is also another important issue, which is addressed in this paper. To investigate the vibration attenuation efficiency of all the granular materials and their mixtures including the humidity-dependent behavior, a laser scanning vibrometer device is used. Generally, the relationship between the vibration response and the granular material mass is rarely addressed in the literature, which can restrict the industrial application of particle dampers. Hence, the additional mass of the granular material is also a focus of this paper. The experimental investigation shows that the vibration response of the test specimen is significantly lower for particles with lower densities in the low-frequency range. Furthermore, an excellent damping efficiency can be also observed for the particle damper with a granular material mixture. The results obtained in this study are not restricted to any special structure and can be implemented in several industrial applications, where vibration and noise attenuation plays a major role, like automotive, aerospace, wind turbine, medical technology, mining, etc.

Modal Analysis of a Lithium-Ion Battery for Electric Vehicles

The battery pack in electric vehicles is subjected to road-induced vibration and this vibration is one of the potential causes of battery pack failure, especially once the road-induced frequency is close to the natural frequency of the battery when resonance occurs in the cells. If resonance occurs, it may cause notable structural damage and deformation of cells in the battery pack. In this study, the natural frequencies and mode shapes of a commercial pouch lithium-ion battery (LIB) are investigated experimentally using a laser scanning vibrometer, and the effects of the battery supporting methods in the battery pack are presented. For this purpose, a test setup to hold the LIB on the shaker is designed. A numerical analysis using COMSOL Multiphysics software is performed to confirm that the natural frequency of the designed test setup is much higher than that of the battery cell. The experimental results show that the first natural frequency in the two-side supported and three-side supported battery is about 310 Hz and 470 Hz, respectively. Although these frequencies are more than the road-induced vibration frequencies, it is recommended that the pouch LIBs are supported from three sides in battery packs. The voltage of the LIB is also monitored during all experiments. It is observed that the battery voltage is not affected by applying mechanical vibration to the battery.

Experimental Study of Modal Characteristics for Heated Composite Structures

Aircrafts with high Mach speeds are exposed to severe thermal load, which affect the performance of aircraft components. Although several experimental studies have been performed on the mechanical behavior of aircraft structures subjected to high temperatures, the experimental research on dynamic characteristics of structures under thermal load is limited. In this work, a series of laboratory modal tests have been carried out on carbon fiber reinforced silicon carbide matrix (C/SiC) composite plates under various radiant-heating conditions. High temperatures are achieved using quartz lamps, and their dynamic responses are measured using a scanning laser vibrometer. The modal parameters are evaluated by PolyMAX at several static temperature distributions. The temperatures are acquired by both full-field noncontacting infrared thermography and contacting thermocouples. The flat plates are with both free and constrained boundary conditions and the high temperature modal survey are performed for two kinds of thickness. The stiffened plate with free boundary condition is further studied as a more practical structure. Both the changes of the modal frequency and modal shape as temperature rises are presented. The effects of the thermal loads on the modal characteristics are investigated by test. The results show that the thermal stresses have a much greater effect on the modal characteristics than the change of the material properties due to heating. The test results could provide technical material for the limited database of high-temperature modal testing results.