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Shear strain localisation and fracture in high strength structural materials

Bassim M., Odeshi A.

Archives of Materials Science and Engineering

2008

Vol. 31, nr 2

69-74

Purpose: The purpose of this paper is to investigate the factors variables influencing the plastic deformation and failure in some high strength metallic materials under high velocity impact. Design/methodology/approach: The materials were tested in compression at strain rates ranging between 10³ and 10⁴ s-¹ using direct impact Hopkinson Pressure Bar. Microstructural evaluation before and after mechanical loading at high strain rates was carried out to determine the mechanisms of plastic deformation and failure of the materials under study at high strain rates. Findings: Plastic deformation in the materials is dominated by shear strain localization along adiabatic shear bands (ASBs). Cracks are initiated and propagated along these bands leading to failure. Occurrence of adiabatic shear bands and cracking tendency of these bands are significantly influenced by strength and microstructure. Whereas homogeneous materials show the least tendency for shear strain localization and adiabatic shear failure, the presence of hard precipitates or secondary phase particles promotes the occurrence of adiabatic shear bands. Other variables such as strain and strain rate also show considerable influence on shear strain localization and susceptibility of a material to adiabatic shear failure. Research limitations/implications: The results of these investigation provides an understanding of how various microstructural variables can influence adiabatic shear failure in metallic materials and are significant in enhancing a more efficient material design for use in high strain-rate related applications. Practical implications: This research is particularly significant in military applications where these materials are used as armour plates and can be subjected to extremely rapid loading condition as in ballistic impact or explosion fragmentation. Originality/value: Results of these investigations offers a qualitative model for predicting the conditions which promote occurrence of ASBs in metallic materials.