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6 July 1998 Using a laser vibrometer for monitoring dynamic strain, modal analysis, and calculating damping
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With the renewed interest in hypervelocity vehicles, component testing in extreme thermoacoustic and thermovibration environments is now required. This requires new test facilities and new instrumentation techniques be developed to test and evaluate these new structures, components and sub- components. To collect data in these extreme environments new instrumentation is needed. In a dynamic test environment use of strain gages is limited to low temperature testing. This paper describes how room temperature and high temperature (greater than 2000 degrees F) strain data is collected, using a laser vibrometer, on cantilevered coupons. This paper also describes the use of a laser vibrometer to obtain mode shapes and damping information. With new structural components, many manufactured from new composite materials such as ceramic matrix composites (CMC), there is a need to acquire accurate mode shapes and damping information. Traditionally modal analysis is done using accelerometers to map out the responses of a structure. This is time consuming, expensive and on small structures the weight of the accelerometers could affect the results. Through the use of a laser vibrometer accurate mode shapes can be obtained quickly. This information can be used to validate finite element models and to determine instrumentation locations on test components. With complex structures it is essential to determine the correct locations to install instrumentation when performing high level dynamic testing, the vibrometer is ideally suited for this. While the mode shapes are being mapped using a vibrometer it is an easy and logical step to calculate the damping of the structural component. Damping is calculated using the half-power bandwidth method that provides accurate results when using a vibrometer.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Michael P. Camden and Larry W. Simmons "Using a laser vibrometer for monitoring dynamic strain, modal analysis, and calculating damping", Proc. SPIE 3479, Laser Interferometry IX: Applications, (6 July 1998);

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