Strain gradients and size effects in nonhomogeneous plastic deformation
- Washington State Univ., Pullman, WA (United States). Dept. of Mechanical and Materials Engineering
Phenomenological constitutive equation for plastic deformation in metallic alloys are usually developed with the basic assumption of uniformity of the deformation field, or by the homogenization of the field over a macroscopic representative element. This, in turn, coupled with simple nondimensional analysis within the classical continuum theory of plasticity, leads to the development of homogeneous constitutive equations that relate the flow stress to some internal variables, such as strain hardening, strain rate, and volume fraction of second phase particles in metal matrix composites. However, there are circumstances where the size of the microstructure significantly influences the overall mechanical properties of the material. This becomes even more crucial when the size of the plastic deformation zone and the magnitude of the strain gradient within it become comparable to the size of the underlying dislocation structure. For example, predicting the width of the shear band in metallic alloys and its scaling with the size of the microstructure is an important issue from a fundamental point of view. A constitutive model that can capture this phenomenon can also provide an explanation of other observed phenomena such as the size of the plastic zone near a crack tip, the dependence of flow stress on particle size in metal matrix composite, the effect of specimen size on the stress-strain curve in pure copper, and the significant increase in flow stress observed in indentation tests when the size of the indenter is in the nanometer range. The objective of this paper is to provide a possible explanation of how a local microscopic strain inhomogeneity resulting from a heterogeneous microstructure can generate a strain gradient effect when the deformation field is averaged over a macroscopic representative element, leading to a specific predictive relation for the strain gradient coefficient c in terms of the materials elastic-plastic moduli and grain size.
- OSTI ID:
- 5187119
- Journal Information:
- Scripta Metallurgica et Materialia; (United States), Vol. 30:9; ISSN 0956-716X
- Country of Publication:
- United States
- Language:
- English
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