Research

Deformation of the cavity in the J₂ voided cell (RMV) for effective strain Ee = 0.5 and triaxiality T = 0.8, and for effective strain E_e = 0.1 and triaxiality T = 2 when L = 1, 0 and -1 respectively. Initial void volumen fraction f₀ = 0.005.

Comparative analysis of the processes of dynamic necking and fragmentation in elasto-plastic and hyperelastic ductile rings subjected to rapid radial expansion. The elasto-plastic material and the hyperelastic material are modelled with constitutive equations which provide nearly the same stress-strain response during monotonic uniaxial tensile loading, and fracture is assumed to occur at the same level of deformation energy. Finite element computations have revealed that the number of necks nucleated in the elasto-plastic and hyperelastic rings is similar, but the proportion of necks that develop into fracture sites is much greater for the hyperelastic rings than for the elasto-plastic ones.

Contours of equivalent plastic strain for different specimen orientations. It is observed that the orientation of the specimen with respect to the in-plane symmetry axes of the material plays a key role in the location and characteristics of the neck(s) formed in the sample.

We have investigated the effect of the loading orientation on the inception of localization bands in orthotropic metallic sheets subjected to uniaxial tension. For that purpose, specimens with the loading axis oriented at different angles 0º ≤ θ ≤ 90º to the rolling direction of the sheet were investigated. The figure shows predicted values of the necking angles according to Cazacu (2018) criterion as a function of the specimen orientation with respect to the rolling direction for 2090-T3 Al alloy.

We have investigated both theoretically and using finite elements the elastoplastic field induced by a pressurized spherical cavity expanding dynamically in an infinite medium modelled using the Gurson–Tvergaard–Needleman porous plasticity approach. The theoretical model, which assumes that the porosity is uniformly distributed in the material and the cavitation fields are self-similar, incorporates artificial viscous stresses into the original formulation of Cohen and Durban (2013b) to capture the shock waves that emerge at high cavitation velocities. The finite element calculations, performed in ABAQUS/Explicit (2013) using the Arbitrary Lagrangian Eulerian adaptive meshing available in the code, simulate the cavity expansion process in materials with uniform and non-uniform distributions of porosity.

We have brought to light the effect of tension-compression asymmetry in flow stresses on the formation of dynamic necking instabilities in isotropic metallic plates subjected to plane strain stretching. This figure shows the energy dissipated when necking occurs for different cell sizes (L⁰/h⁰) calculated using finite elements (FEM) and linear stability analysis (LSA) for material 1 (von Mises material), material 2 (uniaxial tensile yield stress greater than uniaxial compressive yield stress) and material 3 (uniaxial tensile yield stress lower than uniaxial compressive yield stress). It is observed that the energy dissipated when  ecking occurs are significantly greater for the material 3. We have demonstrated that such behaviour is due to the larger plastic dissipation undergone, under plane strain stretching, by this material.