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On the role of dissipative hardening in predicting indentation size effects

Prabhat Agnihotri (University of Groningen), Eduardo Bittencourt (), Erik Van der Giessen (University of Groningen)

Discrete Dislocation Plasticity

Mon 4:20 - 5:40

Barus-Holley 157

The failure of continuum models in predicting indentation size effects (ISE) has provided an impetus for the development of strain gradient plasticity (SGP) theories in which an intrinsic material length scale is incorporated to model the nonlocal effects arising from geometrically necessary dislocations (GNDs). In this work, we have used the nonlocal crystal plasticity theory proposed by Gurtin which explicitly uses a free energy that depends on the net Burgers vector. Two sources of hardening are accounted for in this theory; dissipative hardening associated with an increase in slip resistance and energetic hardening associated with a change in free energy due to a density of GNDs. Even though Gurtin's theory has been successfully applied to capture various size effects in the plastic regime when, the nonlocal effects are dominated by the energetic hardening. However, nonlocal effects can also be included in the dissipative hardening and present study aims at studying the contribution of both to the ISE. Since discrete dislocation plasticity (DDP) provides a more detailed description of plastic flow by naturally accounting for the non local effects, the results of Gurtin’s theory are compared with the discrete dislocation plasticity (DDP) predictions to improve our understanding of role of different hardening mechanisms in capturing ISE. Moreover, different forms of defect energy in Gurtin’s theory are examined to assess their ability in predicting ISE.