Thermo-Electric Detection of Early Fatigue Damage in Metals

There are numerous nondestructive inspection methods which can be used to detect and quantitatively characterize advanced fatigue damage following crack initiation. However, crack nucleation occurs at a much smaller microstructural scale following a more or less extended period of gradual material degradation which remains beyond the reach of known eddy current, ultrasonic, and other inspection methods. Before crack initiation, fatigue degradation remains an elusive process leading to distributed crystal defects on the scale of individual grains and grain boundary imperfections. This gradual evolution of early fatigue damage first results in increasing dislocation density, formation of slip bands, microplasticity, cold work, etc., then leads to crack nucleation at multiple sites. Following crack nucleation the growing microcracks ultimately coalesce into larger detectable fatigue cracks, but current NDE methods cannot detect the often quite serious preexisting fatigue damage in the material before this point

The effect of setting velocity on the static and fatigue strengths of self-piercing riveted joints for automotive applications

In order to reduce vehicle weight to increase fuel efficiency and reduce CO2 emission, more and more automotive manufacturers are now using lightweight materials, such as aluminium, to build part of or the whole body-in-white structure. Due to the advantages over other joining techniques, self-piercing riveting (SPR) is a main joining technique for aluminium structures. In this paper, the effect of setting velocity/force on the joint quality and performance was studied. It was found that in the range studied, the increase of setting velocity increased the static lap shear strength but reduced the static T peel strength of the SPR joints. The results also suggested that the setting velocity did not have significant influence on the lap shear fatigue strength, but the T peel fatigue strength of the joints was increasing with the increase of setting velocity until it reached certain value. An increase in the setting velocity led to a decrease in the rivet head height and an increase in the interlock. In this study, the results showed that the static lap shear strength of SPR joints increased after corrosion and the setting velocity in the range studied did not have obvious influence on the change of lap shear strength after corrosion