Study On Fatigue Performance Of Aluminum Alloy Welded Joint For High-speed Train

Fatigue is the most usual failure mode of welded joints in mechanical structures. Aluminum alloy welded joint is wildly used on car body of high speed-train, so it is very urgent to research the fatigue performance of aluminum alloy welded joint.First of all, the concept of S-N curve and the procedures of p-S-N curve fatigue test, data processing were introduced. And then, these procedures were taken into practice on 4 kinds of aluminum alloy welded joints: corner joint, butt joint, cruciform joints and double-sided lap joint. As the results, median S-N curve and p-S-N curve with confidence 95%, fraction surviving 90%, 99% of the welded joints were gotten. Afterwards, basing on recommendation method of Eurocode 9, all the mid-long fatigue life S-N curves and p-S-N curves were prolonged to long fatigue life regime.Basing on fluctuation method fatigue test existing mean tensile stress and stress ratio r=0.3 were taken on corner joint to investigate the influence, which the mean tensile stress acts on fatigue limit amplitude. After this, the results from the test and calculation results of several common mean stress translation methods were analyzed.Fatigue cumulative damage is an important part of determination of structures fatigue life. Basing on test data, suitable cumulative damage model for aluminum alloy welded joint were sought from both linear and nonlinear. Basing on linear cumulative damage, the rule of critical damage value was researched. The Hypothesis that critical damage value accords with logarithm normal distribution was put forward and verification by test data. The suggested values of modified miner ruleαwith certain confidence, fraction surviving was given. Basing on nonlinear cumulative damage, feasible math model was given and its feasibility and accuracy was proved by test data. After all, a series of random load spectrum obtaining from CRH2 car body was using for analyzing fatigue life between different premise, including considering mean stress or not, using linear cumulative damage model or nonlinear cumulative damage model.