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2018 Research Highlight: A Continuum Constitutive Model for Amorphization in Boron Carbide

A Continuum Constitutive Model for Amorphization in Boron Carbide

 

CMEDE Researchers
Dr. Qinglei Zeng 
Johns Hopkins University
Dr. Andrew L. Tonge 
U.S. Army Research Laboratory
Professor K.T. Ramesh 
Johns Hopkins University

Boron carbide is well known as the third hardest material in nature. Benefitting from its high Hugoniot elastic limit (HEL), low density and high thermal stability, it should be an ideal candidate as protection material. However, boron carbide was found to lose shear strength under high impact velocities, which has been attributed to the formation of amorphization bands observed in different experiments (e.g. ballistic impact, indentation, diamond anvil cell). In this work, we proposed a continuum constitutive model for amorphization in boron carbide and implemented it in the integrative model based on Tonge-Ramesh model.

The proposed model comprises the onset of amorphization bands and the subsequent sliding along these bands. We define an equivalent amorphization stress as the initiation criterion for amorphization, which combines the contribution from shear stress and hydrostatic pressure. There’s compaction deformation inside amorphization bands. When the shear stress reaches a critical shear resistance, sliding will occur along bands, which will introduce additional damage to the material.

With this proposed model, we have investigated the deformation mechanisms in plate impact experiments and calibrated material parameters based on the experiments performed by Vogler et al. The simulated particle velocity histories are in good agreement with the experimental results. We have also performed preliminary simulations of sphere-cylinder impact experiments and observed the competition between microcracking and amorphization during the failure process. Further parametric study based on experiments is in progress.