Shock-Induced Pore Collapse in PMMA: Deformation Physics and Failure Mechanics

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• Professor Guruswami Ravichandran, Graduate Aerospace Laboratories, California Institute of Technology
• Friday 20 March 2026, 14:00-15:00
• Department of Engineering - LR4.

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Porous materials play a central role in various engineering applications, including the development of lightweight materials, energy-absorbing structures, and energetic solids. Porosity spans multiple scales and arises from manufacturing defects, engineered foams, and architected metamaterials. Under shock loading, rapid pore collapse induces intense local deformation, often leading to failure. However, experimental insights into this process remain limited to continuum-level measurements and post-mortem analyses. This study introduces a novel technique for full-field, internal strain measurements during shock compression of transparent materials, applied to PMMA with embedded spherical pores. Using a normal plate impact setup and high-speed imaging at 10 million frames per second, we visualize pore collapse and extract time-resolved strain fields via digital image correlation. Experiments reveal a critical shock stress at which adiabatic shear bands (ASBs) initiate, marking the first in-situ observation of ASB formation during pore collapse. At higher stresses, ASBs evolve into dominant shear bands, culminating in dynamic shear fracture. We also examine wave interactions between multiple pores using shadowgraphy and their influence on collapse and failure mechanisms. Complementary elasticity theory and dynamic finite element simulations provide further insight into the physics governing pore collapse under extreme conditions.

This talk is part of the Engineering - Mechanics Colloquia Research Seminars series.

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