Analyses On Fatigue Cracking Of Hybrid Laser Arc Welded7075-T6Aluminium Alloys

In this paper, the fatigue crack propagation life of hybrid laser arc welded joints of7075-T6aluminum alloy was investigated in details. By experiments, we established adifferent functional relationship between the amount of heat input and the elastic modulus,and to predict the fatigue life under a given amount of heat input. In addition, the effect ofvarious welding defects on the fatigue life was investigated. Based on the improved Formanmodel, a coupling joint life prediction model was proposed in which the7075-T6hybridwelding head performance differences, the threshold value of the stress intensity factor, thecrack driving force and residual stress multifactor were considered. The proposed modelwas validated by finite element simulation with crack propagation and joint testing. Theresults show that the predicted life of the new model agrees well with the experimentalresults.In this paper, ABAQUS finite element software and numerical methods were used toevaluate the effect of the hybrid welding joint performance differences, the threshold valueof the stress intensity factor, the crack driving force as well as the impact of the residualstress on the fatigue life of7075-T6aluminum alloy:1. The weld joint go through the complex heat cycle process and metallurgicalprocesses, usually, there are more defects in welding joint such as crack, blowhole, slag.Therefore there are performance differences between the welded joint and the base metal.In the finite element simulation process, base metal and welded joints were compared withdifferent modeling.2. The study found that the crack will extend only when the stress intensity factoramplitude reaches a certain critical value. Directly using Paris formula to predict the fatiguelife will result in unreasonable results.3. Based on the classic Paris formula, it is widely acknowledged that the stressintensity factor range ΔK is the main driving force of the crack propagation. The studyshows that, under the same stress intensity factor range, the greater the external load is, thebigger the crack propagation rate is, which indicates that the crack growth rate is affectednot only by ΔK value but also by the maximum stress. Therefore, the impact of the externalmaximum load should not be ignored during the numerical simulation process.4. As we know, the metal material experiences a complex thermal cycle process andmetallurgical process in the welding process, leading to uneven phenomenon of composition and structure of the joints when cooled to room temperature, which result innonuniform joint performance and large welding residual stress The presence of residualstress would seriously reduce the fatigue life of the joints. However, in the CT test, thesample weld was machined a gap, resulting in the vast majority release of the weld residualstress, the effect of residual stress on tested fatigue life can be almost negligible.