Experimental Analysis of Shear Band Deformation State in Bulk Metallic Glasses
Ashraf Bastawros (), Hui Wang (), Antonia Antoniou (Georgia Institute of Technolog)
Plasticity at Different Length Scales
Mon 10:45 - 12:15
CIT 219
Damage evolution in materials is typically driven by microscopic inhomogeneous deformation, leading to slip bands and textures in crystalline materials, shear bands in amorphous materials and compaction bands in cellular and granular materials. Measuring the strain evolution within these localized deformation bands is critical for the development and calibration of proper constitutive framework. However such measurements are bounded by many experimental limitations; the shear strain may reach several orders within a band of sub-micrometer width. We have developed an experimental protocol, utilizing digital image correlation (DIC) technique to measure the deformation history of shear band evolution in bulk metallic glasses under the constrained deformation field of wedge like cylindrical indentation. The severity of deformation is represented as strain maps at each loading increment by the in-plane maximum shear strain. The strain maps can be used for visualization purpose only, since the strain levels within the shear bands are biased by the disparity in gage length for strain calculation within the shear bands (o(100nm)) and that utilized for the continuum strain map (o(10microns)). By measuring the displacement jumps of two selected points on the shear bands, Lagrangian strain components are estimated over the entire shear band thickness at different stages of the whole loading cycle. The corresponding Lagrangian strain components within the shear band surrounding are evaluated by bi-linear surface fitting local displacement distribution. The strain evolution shows that shear band deformation is highly discontinuous. The strain increment remarkably remains approximately in the same direction of the total macroscopic strain vector at every loading stage, extending to a very large level of plastic deformation. The measured strain level of a newly developed shear band during first activation is comparable to strain levels predicted by continuum models.