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Development of an image-based inertial impact test for the identification of polymeric material parameters at high rates
Matejunas, Andrew J.
Matejunas, Andrew J.
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2024
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2025-11-26
Abstract
The mechanical properties of polymers are becoming increasingly important both on their own and as matrix materials in composites for military, automotive, aerospace, medical applications, to name a few. At the same time, it is well-known that the mechanical properties of polymers are highly strain rate dependent. Traditional methods used to characterize material model parameters under dynamic conditions are limited by several restrictive assumptions. Generally, they investigate one deformation mode at one strain rate at a time. Therefore, traditional material characterization requires many experiments to fully identify mechanical properties. This dissertation leverages ultra-high-speed imaging and full-field metrology, including the grid method and digital image correlation, along with computational simulation to design an image-based inertial impact test (IBII) for polymers that utilizes the acceleration fields as loading information. An inverse technique, the virtual fields method (VFM) is used to extract stiffness sensitivity across strain rates in tension and compression for a model material of PMMA. Moreover, this work expands the existing VFM framework to account for viscoelastic material parameter identification. Using finite element simulations, the Maxwell form of the standard solid model is employed. The resulting model displacement fields are used to simulate the full-field images that would be produced from a physical experiment, and VFM is used to extract the constitutive parameters over a sweep of processing parameters. Specifically, the effects of image noise and the ideal processing settings for spatial and temporal resolution are quantified for optimal experimental configurations. The simulations reliably produce the bulk modulus, shear modulus, and associated time constant from a single IBII test. This ability to identify multiple constitutive parameters' evolution over time from a single experiment demonstrates considerable promise towards reducing the number of experiments required to fully describe the mechanical behavior of polymers at high strain rates.
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