Search Results

In present paper, the process of joining aluminum alloy 6111T4 and steel HSLA340 sheets by self-piercing riveting (SPR) is studied. The rivet material properties were obtained by inverse modeling approach. Element erosion technique was adopted in the LS-DYNA/explicit analysis for the separation of upper sheet before the rivet penetrates into lower sheet. Maximum shear strain criterion was implemented for material failure after comparing several classic fracture criteria. LS-DYNA/implicit was used for springback analysis following the explicit riveting simulation. Large compressive residual stress was observed near frequent fatigue crack initiation sites, both around vicinity of middle inner wall of rivet shank and upper 6111T4 sheet.

Due to magnesium alloy's poor weldability, other joining techniques such as laser assisted self-piercing rivet (LSPR) are used for joining magnesium alloys. This research investigates the fatigue performance of LSPR for magnesium alloys including AZ31 and AM60. Tensile-shear and coach peel specimens for AZ31 and AM60 were fabricated and tested for understanding joint fatigue performance. A structural stress - life (S-N) method was used to develop the fatigue parameters from load-life test results. In order to validate this approach, test results from multijoint specimens were compared with the predicted fatigue results of these specimens using the structural stress method. The fatigue results predicted using the structural stress method correlate well with the test results.

The use of die cast magnesium for automobile transmission cases offers promise for reducing weight and improving fuel economy. However, the inferior creep resistance of magnesium alloys at high temperature is of concern since transmission cases are typically assembled and joined by pre-loaded bolts. The stress relaxation of the material could thus adversely impact the sealing of the joint. One means of assessing the structural integrity of magnesium transmission cases is modeling the bolted joint, the topic of this paper. The commercial finite element code, ABAQUS, was used to simulate a well characterized bolt joint sample. The geometry was simulated with axi-symmetric elements with the exact geometry of a M10 screw. Frictional contact between the male and female parts is modeled by using interface elements. Material creep is described by a time hardening power law whose parameters are fit to experimental creep test data.