The effects of the yield surface curvature and anisotropy constants on the axial crush response of circular crush tubes

In this paper, the effects of the yield surface curvature and anisotropy constants on the predicted crush response of aluminum tubes are investigated. The yield function proposed by Plunkett et al. (2008) with two linear transformations is employed in the commercial finite element software LS-DYNA to predict the crush response of the aluminum alloy AA5754-O circular tubes. This yield function represents anisotropy of aluminum alloys accurately by simultaneously capturing the variation of both the yield stress and the R-value with orientation. Dynamic crush simulations of tubes are performed using this yield function with four different yield surface shapes. The same sets of experimental uniaxial yield stresses and R-values along with various sample orientations are considered for determining the anisotropy coefficients of the yield function for each case (the coefficients are different even though the input experimental data is the same). Simulations of axial crush show that the yield surface shape affects the collapse mode and predicted energy absorption characteristics of the crush tube. The analysis shows that the deformation is predominately controlled by balanced biaxial deformation. However, characterization of both the plane strain and pure shear points on the yield surface for energy absorption are also important. The shape and the area of the yield function govern the loading condition, which dictates the deformation and energy absorption. The results demonstrate the importance of the shape of the yield surface in axial crush simulations of structural components using aluminum.