Application of Fatigue Life Prediction Methods for GMAW Joints in Vehicle Structures and Frames 2011-01-0192
In the North American automotive industry, various advanced high strength steels (AHSS) are used to lighten vehicle structures, improve safety performance and fuel economy, and reduce harmful emissions. Relatively thick gages of AHSS are commonly joined to conventional high strength steels and/or mild steels using Gas Metal Arc Welding (GMAW) in the current generation body-in-white structures. Additionally, fatigue failures are most likely to occur at joints subjected to a variety of different loadings. It is therefore critical that automotive engineers need to understand the fatigue characteristics of welded joints.
The Sheet Steel Fatigue Committee of the Auto/Steel Partnership (A/S-P) completed a comprehensive fatigue study on GMAW joints of both AHSS and conventional sheet steels including: DP590 GA, SAE 1008, HSLA HR 420, DP 600 HR, Boron, DQSK, TRIP 780 GI, and DP780 GI steels. Dissimilar metal welds were made between DP590 GA and SAE 1008, DP 600 and SAE 1008, TRIP 780 and SAE 1008, DP 780 and SAE 1008, and Boron and HSLA. Fatigue behavior was evaluated for several different specimen geometries: single lap-shear, double lap-shear, butt weld, start-stop, and perch mount.
Currently, many fatigue life prediction methods, such as structural stress approach, hot spot structural stress approach, notch stress approach, and local strain approach, are available to analyze GMAW joints. This study reviews two structural stress methods for fatigue life prediction of the welded joints, and it also assesses the two methods with previous A/S-P Sheet Steel Fatigue Committee fatigue test results.