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Investigating plastic yielding across the strain rates

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The yield point of a material is often used in design applications as the upper limit of acceptable mechanical stress within the material. Although sometimes regarded as a unique value, the yield point is known to be heavily dependent on the strain rate the material is loaded with. In this talk, dislocation dynamics will be employed to explore some of the factors affecting this strain rate dependence of the yield point, for strain rates ranging from 100/s to 10 9/s. This will set two fundamentally different regimes: a quasi-static, low strain range regime (below ~10 6/s) and a dynamic, shock loading regime. In the quasi-static regime, traditional dislocation dynamics and line dynamics are employed to explore the impact the strain rate has on the bowing of dislocation segments leading to plastic yielding. For higher strain rates, Dynamic Discrete Dislocation Plasticity (D3P) will be employed to simulates plasticity as a result of the collective motion of individual dislocations. In D3P , dislocations are modelled as discontinuities in a elastodynamic continuum, so unlike traditional discrete dislocation methods, time is included as a true field variable, and dislocations are described as sources of elastodynamic wavelets emanating from their cores. This introduces a new dimension to the classical study of dislocation-mediated phenomena. By studying the collective response of the dislocations in shocked systems under varied boundary conditions we are able to study in detail the effect dislocations have on phenomena ranging from the attenuation of the dynamic yield point to plastic shielding of dynamic crack tips.

This talk is part of the Engineering - Mechanics and Materials Seminar Series series.

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