Ultrasonic velocity measurement is a well-established method to measure properties and estimate strength as well as detect and locate damage. Determination of accurate and repeatable ultrasonic wave velocities can be difficult due to the influence of environmental and experimental factors. Diffuse fields created by a multiple scattering environment have been shown to be sensitive to homogeneous strain fields such as those caused by temperature variations, and Coda Wave Interferometry has been used to measure the thermally induced ultrasonic velocity variation in concrete, aluminum, and the Earth's crust. In this work, we analyzed the influence of several parameters of the experimental configuration on the measurement of thermally induced ultrasonic velocity variations in a carbon-fiber reinforced polymer plate. Coda Wave Interferometry was used to determine the relative velocity change between a baseline signal taken at room temperature and the signal taken at various temperatures. The influence of several parameters of the experimental configuration, such as the material type, the receiver aperture size, and fiber orientation on the results of the processing algorithm was evaluated in order to determine the optimal experimental configuration.
Variations in build process parameters, post-processing parameters, and feedstock have a significant impact on the structural integrity and performance of components made with additive manufacturing (AM). Effective nondestructive testing (NDT) is critical for ensuring the structural integrity of components. Complex geometries, nonequilibrium microstructures, new process variables, and lack of clear accept or reject criteria for AM components present new challenges to NDT. Quantitative, volumetric NDT methods that can detect material defects of interest in complex geometries are required. Process compensated resonance testing (PCRT) is an NDT method that uses a swept sine input to excite the component's resonance modes of vibration. The resonance frequencies are recorded, analyzed statistically, and compared to acceptability limits established using a database of training components. The swept sine input excites whole-body vibrational modes in nearly any geometry, and the component's resonance frequencies correlate directly to its structural integrity. In this study, PCRT evaluations were performed on titanium alloy (Ti-6Al-4V) populations made with electron beam PBF and aluminum alloy (AlSi10Mg) populations made with laser PBF. The evaluations were conducted in support of ASTM round-robin testing. In the Ti-6Al-4V population, PCRT showed clear resonance frequency differences between nominal specimens and off-nominal specimens with defective material states. PCRT also quantified the effects of hot isostatic pressing (HIP). PCRT pass/fail NDT of the Ti-6Al-4V population in the pre-HIP and post-HIP states demonstrated 100% accuracy. Computed tomography scans of the post-HIP specimens showed no clear indications of porosity. Follow-up tensile testing of a subset of nominal and off-nominal specimens in the post-HIP state showed that the off-nominal specimens had lower yield stresses and ultimate tensile stresses than nominal specimens. In the AlSi10Mg population, PCRT detected differences between recycled and virgin feedstock powder. PCRT pass/fail NDT of AlSi10Mg specimens exposed to nominal and off-nominal heat treatment demonstrated 100% accuracy.
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