Springback prediction of sheet metal forming is always an important issue in the industry, because it greatly affects the final shape of the product. The accuracy of simulation prediction depends on not only the forming condition but also the chosen material model, which determines the stress and strain redistributions in the formed parts. In this paper, a newly proposed elastoplastic constitutive model is used, in which the initial and induced anisotropies, combined nonlinear isotropic and kinematic hardenings, as well as isotropic ductile damage, are taken into account. The aluminum alloy sheet metal AA7055 was chosen as the studied material. In order to investigate springback under non-proportional strain paths, three-point bending tests were conducted with pre-strained specimens, and five different pre-straining states were considered. The comparisons between numerical and experimental results highlighted the hard effect of both kinematic hardening and ductile damage on the springback prediction, especially for a changed loading path case.

Cubic boron nitride (cBN)-based composites were prepared from cBN-Al and cBN-TiC mixtures, respectively, under high pressure and high temperature (HPHT). During sintering, Al reacted with cBN and produced AlN and AlB 2 , while TiC did not react with cBN. With increasing Al from 5-20 wt-%, the strength of the cBN-based composites decreased first, then increased. AlN and AlB 2 could strengthen the cBN-based composites to a certain extent. In the preparation from cBN-TiC, 10 wt-% addition of TiC was the optimal formulation to obtain the densest microstructure. Hardness of the two kinds of composites displayed different tendencies. On the other hand, cBN-based composites were treated at 1200°C for 1200 s. It was found that the isothermal oxidation process could be described by parabolic laws with slight oxidation scales formed on samples' surfaces in different morphologies.

No abstract