Papers by Keyword: Heterogeneous Deformation

Abstract: BCC wires macroscopically deformed by axisymmetric elongation (wire drawing) develop an intense <011> fibre texture and exhibit a characteristic non-uniform deformation of the grains evident in transverse sections (grain curling or “Van Gogh sky structure”). The extraordinary grain morphology induced by the <011> fibre texture is also accompanied by a peculiar constant strain hardening rate in single-phase BCC wires (exponentially increasing in case of BCC containing composite wires) that allows to reach very high strengths. Here we present a calculation of the elastoplastic axial elongation of such an aggregate of BCC grains with the ideal <011> fibre texture, using a slip-gradient dependent large-strain crystal plasticity constitutive equation incorporated into a finite element method (FEM) code, i.e., with proper account of the influence of the evolving shape and size of individual grains and of the local grain interactions. The results reproduce well the observed macroscopic behaviour (linear flow stress-strain curve at large strains) and the peculiar mesoscopic structural changes (grain curling in transverse sections). The simulation is focused on the analysis of strain and dislocation density heterogeneities and on the building up of mesoscopic (inter- and intra-granular) internal stresses during deformation. The computed average transverse tensile stresses acting normal to the axially oriented {100} planes approximately parallel to the boundaries of the flattened grains is close to 0.3 times the tensile flow stress of the aggregate, in good agreement with previous calculations based on the Taylor-Bishop-Hill model or on elasticplastic self-consistent calculations and with available neutron diffraction measurements. Such a high level of internal tensile stresses explains the well-known tendency of high strength BCC wires to fail by longitudinal splitting.

Abstract: Room-temperature deformation behavior in the localized regions of W-80vol%Cu composite was investigated in this study. Plastic strain of about 10 % was added to the specimen at room temperature using a three-point bend testing machine. Then deformation behavior in a localized region was investigated using a high-magnification SEM photograph before and after deformation. Results are summarized as follow. (1) In a localized region near a large pore, heterogeneous deformation had occurred as expected. (2) In a region apart from a pore, mostly homogeneous deformation occurred but occasionally heterogeneous deformation occurred.