Understanding the physics of non-linear unloading-reloading behavior of metal for springback prediction.

Finite element simulation technique is extensively useful nowadays for die designing by optimizing the springback from the formed state of sheet metal panel. The magnitude of springback is normally calculated in finite element simulation by assuming a completely elastic recovery in non-linear kinematic hardening law. Constant values of elastic modulus and Poisson's ratio are required to estimate the elastic recovery by non-linear kinematic hardening law. Cleveland and Ghosh (Int J Plast 18:769-785, 2002), Li and Wagoner (Int J Plast 1827:1126-1144, 2011), and many other research groups have reported that inelastic strain release during unloading is the main source of extra strain recovery and as a result poor springback prediction by commercial finite element software. In this regard, many theoretical postulates have been proposed to explain such inelastic strain release during unloading. In this work, we show from atomistic simulation that irreversible movement of dislocation, i.e., microplasticity, is the source of inelastic strain release during unloading.

Monotonic and cyclic plastic deformation behavior of nanocrystalline gold: atomistic simulations.

Monotonic and cyclic plastic deformation behavior of nanocrystalline gold was investigated at room temperature using molecular dynamics simulation. Yielding starts in nanocrystalline gold by initiation of 1/6 〈1 1 2〉 Shockley partial dislocation from the grain boundary. A stacking fault is created between the grain boundary and moved Shockley partial dislocation. With the progression of further deformation, increase in dislocation density inside the grain, the formation of dislocation locks such as Stair-rod 1/6 〈1 1 0〉 and Hirth 1/3 〈1 0 0〉 dislocations, generation and removal of stacking fault tetrahedron are observed. Grain coarsening and a rise in the number of dislocation inside the grains were noted with an increasing number of cycles.