Activation volume and its relation with plastic instability (original) (raw)
Related papers
Modeling of Severe Plastic Deformation: Evolution of Microstructure, Texture, and Strength
Integral Materials Modeling, 2007
Severe plastic deformation processes involve large grain rotations due to the action of different modes of plastic deformation and other microstructural changes which lead to characteristic texture formation. The present review deals with the evolution of texture during the most important severe plastic deformation processes, namely Equal Channel Angular Pressing (ECAP), High Pressure Torsion (HPT), Friction Stir Processing (FSP), Accumulative Roll Bonding (ARB) and Multi-Axial Forging (MAF). First three of the processes are shear based, while the latter two are plane-strain based. The textures formed during ECAP are visually different from simple shear textures due to (i) the inclination of the shear plane, (ii) additional contribution of non-shear based deformation. The relative intensities of texture components are function of deformation micro-mechanisms, amount of straining and configuration of the strain path. The texture evolved during HPT is very similar to simple shear texture, with additional consequences of microstructural changes that occur due to very large deformations. The textures formed in FSP process also resemble shear textures. On the other hand, texture evolution during ARB and MAF can be described using plane strain deformation. The present review deals with texture evolution during severe plastic deformation as a function of nature of processes and type of materials.
Metals, 2018
In this study, for the first time, the effect of large non-monotonic simple shear strains on the uniformity of the tensile properties of pure Cu specimens was studied and justified by means of microstructural and textural investigations. A process called simple shear extrusion, which consists of two forward and two reversed simple shear straining stages on two different slip planes, was designed in order to impose non-monotonic simple shear strains. Although the mechanism of grain refinement is continuous dynamic recrystallization, an exceptional microstructural behavior and texture were observed due to the complicated straining path results from two different slip planes and two pairs of shear directions on two different axes in a cycle of the process. The geometry of the process imposes a distribution of strain results in the inhomogeneous microstructure and texture throughout the plane perpendicular to the slip plane. Although it is expected that the yield strength in the periphe...
Analysis of shear banding in twelve materials
1992
Abstract The problem of the initiation and growth of shear bands in 12 different materials, namely, OFHC copper, Cartridge brass, Nickel 200, Armco IF (interstitial free) iron, Carpenter electric iron, 1006 steel, 2024-T351 aluminum, 7039 aluminum, low alloy steel, S-7 tool steel, Tungsten alloy, and Depleted Uranium (DU− 0.75 Ti) is studied with the objectives of finding out when a shear band initiates, and upon what parameters does the band width depend.
Shear bands formation in different engineering materials subjected to dynamic compression
PROCEEDINGS OF THE 22ND INTERNATIONAL ESAFORM CONFERENCE ON MATERIAL FORMING: ESAFORM 2019
During dynamic compression tests, different mechanisms occur at the micro-structural level, resulting in a competition among strain hardening, strain rate hardening and thermal softening. The softening effect is due to dynamic recovery and dynamic recrystallization. If the hardening effects become less effective than softening ones, the material could become unstable, forming narrow bands in which the deformation concentrate involving (quasi) adiabatic conditions and an unpredicted catastrophic failure occurs. These narrow bands are called Adiabatic Shearing Bands (ASB). This type of instability can be observed in different type of materials: polymeric materials due to combination between temperature and strain rate, and in Titanium alloy and Aluminum alloy due to strain rate effects. In this work, an analysis about adiabatic shear bands on three different types of materials is described. Compression tests of Titanium alloy (Ti-4Al-6V), Aluminum alloy (AA 7075-T6) and Polymeric material (Polypropylene) have been carried out in quasi-static and dynamic condition, the lasts ones by a Split Hopkinson Bar.
Macroscopic effects of micro-shear banding in plasticity of metals
Acta Mechanica, 1998
Mathematical idealization of a micro-shear bands system by means of the theory of singular surfaces of order one, related to a physical model of shear strain-rate produced by active micro-shear bands and a certain averaging procedure over the representative volume element, is studied. Theoretical description of small elastic and large plastic deformations within the framework of a two-surface plasticity model, with the internal yield surface connected to kinematic hardening anisotropy and the external surface related to micro-shear banding, is proposed. The idea of the multiple potential surfaces forming a vertex on the smooth external surface is applied to display the connection with the geometric pattern of micro-shear bands. A new physical insight is given into the linear and nonlinear flow laws, in rates of deformation and stress, known in the theory of plasticity.