Photoelastic evaluation of stress fields and fracture during dynamic splitting experiments

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Dynamic tensile-splitting experiments were conducted on brittle polyester disks, manufactured from Homalite®-100, to photoelastically visualize stress field development in the specimens and, ultimately, specimen fracture. A Split Hopkinson Pressure Bar (SHPB) was used to load the specimen dynamically and record load data as a function of time. Images of the stress field were captured with high-speed photography and interpreted using photoelastic analysis. The experiments determined that the specimens reached an equilibrium state relatively quickly, and remained in equilibrium until fracture. Fracture began with in-plane cracks forming on either side of the specimen. Transverse cracks emanated from the in-plane cracks, then propagated across the specimen midplane at velocities up to 60% of the shear wave velocity in the material. Contact loads calculated from photoelasticity agreed favorably with SHPB results. These experiments also allowed for the determination of the dynamic splitting strength of the Homalite®-100 as a function of strain rate. The dynamic splitting strength of the material increased with the increasing strain rate, reaching a maximum value of about twice the static splitting strength.

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Journal of Testing and Evaluation