Shear Band Characteristics of Metals with Porosity and Viscosity

Author(s):

John D. Clayton

Abstract:

Initial defects such as voids or material imperfections increase susceptibility to adiabatic shear failure in ductile metals as demonstrated in prior experimental, analytical, and numerical investigations. Viscosity in the shear band, manifesting macroscopically as strain-rate sensitivity, inhibits localization. An analytical shear band process zone model is advanced to account for porous and viscous phenomena. The material contains an average defect measure (e.g., porosity) and a concentrated defect measure at a spatial location where shear banding is most likely to initiate after an instability threshold is attained. Shearing resistance and certain physical properties are reduced commensurately with local defect concentration. Non-Newtonian viscosity increases dissipative resistance. Viscous dissipation, if strong enough, is shown to prevent an infinitesimal-width shear band even in a non-conductor. A pseudo-quadratic viscosity widens the band similarly to heat conduction, and akin to quadratic shock viscosity used in hydrocodes to resolve widths of planar shock waves. The model captures simulation data showing reduced localization strain and shear band width with increasing maximum initial pore size in additively manufactured titanium and HY-100 steel. Predictions for shear band width, local strain, and temperature are more accurate versus experimental data on steel than prior analytical modeling. A quantitative framework is established by which processing defects (e.g., as arising in additive manufacturing) and slip-band strength dependence on shearing rate can be related to shear band characteristics.