Abstract
Weld fatigue performance is a critical aspect for application of advanced high-strength steels
(AHSS) in automotive body structures. A comparative study has been conducted to evaluate
the fatigue life of AHSS welds. The material studied included seven AHSS of various strength
levels - DP 600, DP 780, DP 980, M130, M220, solution annealed boron and fully hardened
boron steels. Two conventional steels, HSLA 590 and DR 210, were also included for baseline
comparison. Lap fillet welds were made on 2-mm nominal thick sheets by the gas metal arc
welding process (GMAW). Fatigue test was conducted under a number of stress levels to
obtain the S/N curves of the weld joints.
It was found that, unlike in the static and impact loading conditions, the fatigue performance of
AHSS is not influenced by the HAZ softening in AHSS. There are appreciable differences in the
fatigue lives among different AHSS. Changes in weld parameters can influence the fatigue life
of the weld joints, particularly of these of higher strength AHSS. A model is developed to predict
the fatigue performance of AHSS welds. The validity of the model is benchmarked with the
experimental results. This model is capable to capture the effects of weld geometry and weld
microstructure and strength on the fatigue performance experimentally observed. The
theoretical basis and application of the newly developed fatigue modeling methodology will be
discussed.
