Publications

Abstract not provided.

The ability to measure full-field strains is desirable for analytical model validation or characterization of test articles for which there is no model. Of further interest is the ability to determine if a given environmental test’s boundary conditions are suitable to replicate the strain fields the test article undergoes in service. In this work, full-field strain shapes are estimated using a 3D scanning laser Doppler vibrometer and several post-processing methods. The processing methods are categorized in two groups: direct or transformation. Direct methods compute strain fields with only spatial filtering applied to the measurements. Transformation methods utilize SEREP shape expansion/smoothing of the measurements in conjunction with a finite element model. Both methods are used with mode shapes as well as operational deflection shapes. A comparison of each method is presented. It was found that performing a SEREP expansion of the mode shapes and post-processing to estimate strain fields was very effective, while directly measuring strains from ODS or modes was highly subject to noise and filtering effects.

3D scanning laser Doppler vibrometry (LDV) systems are well known for modal testing of articles whose excited dynamic properties are time-invariant over the duration of all scans. However, several potential test situations can arise in which the modal parameters of a given article will change over the course of a typical LDV scan. One such instance is considered in this work, in which the internal state of a thermal battery changes at different rates over its activation lifetime. These changes substantially alter its dynamic properties as a function of time. Due to the extreme external temperatures of the battery, non-contact LDV was the preferred method of response measurement. However, scanning such an object is not optimal due to the non-simultaneous nature of the scanning LDV when capturing a full set of data. Nonetheless, by carefully considering the test configuration, hardware and software setup, as well as data acquisition and processing methods it was possible to utilize a scanning LDV system to collect sufficient information to provide a measure of the time varying dynamic characteristics of the test article. This work will demonstrate the techniques used, the acquired results and discuss the technical issues encountered.

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Abstract not provided.

3D scanning laser Doppler vibrometry (LDV) systems continue to gain popularity for use in experimental modal analysis as the systems become more widespread. LDV is, by its nature, limited to measurements with line-of-sight visibility. This work presents an application of 3D scanning LDV to a test article with un-instrumented internal features that were not accessible to the lasers. The internal features, while not directly measurable, were known to contribute strongly to the modal characteristics of the test article. Initially, a traditional roving hammer test was conducted and modal parameters were extracted. The limited degrees of freedom inherent to this test method proved to be inadequate to correctly identify key mode shapes. It was found that by increasing the measurement point density and including all three translational degrees of freedom at each point, the key modal characteristics of the full system were able to be inferred from purely external measurements. These characteristics were essential in updating the mechanical behavior and material properties of the corresponding finite element model. The response measurements required for system identification were only practically achievable using the 3D LDV system. Comparisons of key experimental results to those of the calibrated analytical model are demonstrated.

Abstract not provided.