Morphology Of Shear Bands Research Articles

Deformation morphology underneath the Vickers indent in a Zr-based bulk metallic glass

Hardness and plastic deformation during Vickers indentation in as-cast, annealed, and fully crystallized Zr 57 Cu 27 Al 11 Ni 5 bulk metallic glass was examined. Subsurface deformation morphology under the indenter tip was studied at various loads and for different annealing time. Appreciable plastic deformation, through shear banding, occurs in the as-cast and annealed alloys. Two different types of shear bands are observed. Their occurrence depends upon the amount of annealing and hence on the extent of crystallization. The fully crystallized alloy exhibits extensive cracking. Trends in the deformation zone size with load are consistent with the expanding cavity model, while the shear band morphology, particularly for the as-cast sample, attests the qualitative applicability of the slip line field theory.

Morphology of adiabatic shear bands in cylindrical specimens of AISI 4340 steel impacted by Hopkinson pressure bar

Cylindrical specimens of AISI 4340 steel, which were heat treated by quenching in oil followed by tempering at either 315 or 425°C, were impacted in a Hopkinson pressure bar at different impacting speeds. It was found that when strain and strain rate reached certain values, adiabatic shear bands (or plastic deformation zones) were formed in the specimens. The adiabatic shear bands appeared either in a circle on the transverse section, a hyperbola on different longitudinal sections without the central axis of the cylinder, and a triangle on the longitudinal section through the central axis of the cylinder. From these observations, it can be concluded that the plastic deformation localisation zone is limited in a thin conical shell in three dimensions. It was further confirmed that the adiabatic shear bands initiated along the maximum shear stress directions. In addition, the adiabatic shear bands in the specimens tempered at 315°C appeared white, while those in specimens tempered at 425°C had deformation characteristics. This indicates that the appearance of adiabatic shear bands is related to the hardness and microstructure of the tested steel.

Effect of Alloying Elements on the Microstructure and Texture of Warm Rolled Steels

The effect of Cr, B and P addition on microstructure and texture formation was studied in warm rolled at 640 and 710°C interstitial free (IF) and low carbon (LC) steels. Samples were characterised using Electron Back Scattering Diffraction analysis, optical and electron microscopy. The LC steel showed a decrease in the number of grains with shear bands compared with IF steel that deteriorated the deformation texture. The addition of chromium to the LC steel reversed this tendency. The increase in shear band frequency in the LC(Cr) steel appears to be due to the formation of coarse Cr 23 C 6 carbides and fine strain-induced Cr 23 C 6 and Cr 3 C 2 carbides. Chromium addition also led to an increase in grain thickness and thus in the tendency to form shear bands. The addition of phosphorus to the LC(Cr) steel did not improve the deformation texture significantly. The addition of boron to the LC(Cr) steel decreased the number of γ-fibre grains and is therefore expected to reduce the formability after annealing. Short, long, intense short and intense long shear bands were observed. Their formation depended on grain size, as well as on the amount of work hardening and precipitation hardening. The long and short (but not the intense) shear bands were linked to the presence of the γ-fibre after rolling. The main outcome of this work is that the addition of alloying elements affects the volume fraction of grains containing shear bands, the grain thickness and the shear band morphology; these, in turn, affect the texture of the steel, particularly after annealing.

Shear band interactions with crystals in partially crystallised metallic glasses

The morphology of shear bands in two partially crystallised metallic glasses, Ni 80B 20 and Cu 50Zr 50, is deduced by transmission and scanning electron microscopy. A number of different types of crystal/shear band interaction have been characterised, providing evidence both for the dilatational model of shear band deformation and for long range interactions between an operating shear band and a stress raiser in the amorphous matrix. Qualitative differences in the mechanical properties of the two partially crystallised glasses examined are rationalised in terms of the interactions observed.

Morphology and annealing behaviour of thick shear bands in polystyrene

Shear bands of 0.1 to 0.6 mm thick were produced in polystyrene by compression. These bands were studied by optical microscopy and surface profilometry. Both the as-deformed bands and the bands developed after annealing were investigated. Parameters such as the shear strain, step height and the height-to-base ratio of the band cross-section (ridges or valleys) were recorded.

Similarity between craze morphology and shear-band morphology in polystyrene

The formation of shear bands and crazes in thin films as well as in bulk samples of polystyrene were examined in the electron microscope using a variety of replication techniques. The morphologies of shear bands and crazes are quite similar both depending initially upon the relative shear displacement of 400 to 1000 A domains. As deformation continues and orientation increases, fibrils varying from 50 to 700 A are formed within the deformation zone, lateral constraint of the normal Poisson contraction causing voids to form in the crazes but not in the shear bands. Shear-band width was found not to be a unique function of either temperature or strain-rate and both craze and shear-band morphologies were found not to be strong functions of molecular weight. Regardless of molecular weight, fibrils formed within the deformation zone were always on the order of a few hundred Angstroms in diameter. However, for thin films of molecular weight less than 20 000 insufficient numbers of tie molecules between fundamental structural units or domains made it difficult for these fibres to span the craze width.