Xiaohua Hu

Modeling the influence of grain-level matrix inhomogeneity on strain localization in the presence of hard particles

The influence of grain-level matrix inhomogeneity on strain localization in sheet metals has been studied using a two-dimensional plane stress model containing two hard particles by finite element analysis. When the matrix material is treated as a homogeneous continuum, the localization strain decreases with interparticle spacing for particles aligned along the loading direction. In the case of an inhomogeneous matrix, consisting of grains of different Taylor factors corresponding to different crystallographic orientations, the position of the localization band and the value of localization strain seem to be insensitive to the interparticle spacing. Instead, localization forms preferentially in the softer grains within the matrix. The amount of post-localization deformation decreases significantly when the two particles straddle the shear band. It is concluded that the stress concentration that develops between two closely spaced particles does influence the shear localization process but the matrix inhomogeneity dominates localization behavior during sheet metal deformation.

Modeling Strain Localization Using a Plane Stress Two-Particle Model and the Influence of Grain Level Matrix Inhomogeneity

The role of dilute small particles on the development of strain localization under uniaxial tension has been studied by finite element analysis using a plane stress model with two small hard particles embedded in Al matrix. The influence of particle alignment and interparticle spacing in a homogeneous and inhomogeneous matrix are investigated. When the matrix material is a homogeneous continuum, there are small localization strains when close packed and aligned along the loading direction. In the case of an inhomogeneous matrix with grains of different strengths represented by their Taylor factors, the location of localization band is insensitive to the interparticle spacing, but mainly determined by grain-level inhomogeneity. This is because the particles are dilute and small compared with the matrix grains. The particles, however, can decrease the localization strains when they straddle the localization band.

Enhanced Formability in Sheet Metals Produced by Cladding a High Strain-Rate Sensitive Layer

The necking behavior of cladding sheets with a rate-sensitive layer cladding on a rateinsensitive core material has been studied. A nonlinear long-wavelength analysis, similar to the one proposed by Hutchinson and Neale (1977, “Influence of Strain-Rate Sensitivity on Necking Under Uniaxial Tension,” Acta Metal., 25, pp. 839–846) for monolithic ratesensitive materials, is developed to identify the onset of necking in a rate-sensitive clad sheet. This relatively simple analysis is validated by comparing its numerical results with those based on more complicated finite element analysis. It is demonstrated that for monolithic rate-sensitive materials the proposed nonlinear analysis reduces to the one developed by Hutchinson and Neale (1977). For cladding sheets, it is found that the necking strain increases monotonically by increasing the strain-rate sensitivity of the clad layer if the volume fraction of cladding is fixed. It is also revealed that, for fixed strain-rate sensitivity of the clad layer, necking localization is retarded by increasing the volume fraction of the cladding layer. [DOI: 10.1115/1.4024410]