Friction Stir Welding Cracks In The Weld Zone Stability To Extend The Numerical Analysis

Currently,the friction stir welding for aluminum alloy 2024-T351(AA2024-T351) is widely used in key structural engineering.But the literature on stable crack extension mechanism for FSW joints is rare.By researching on the mechanism,the rule of stable crack extension and the fracture parameters can be predicted,the effective fracture criterion can be found.It is most significant in the engineering application and the academic study to optimize the parameters of FSW,improve the weld strength,design the anti-fatigue and anti-fracture welding structure,estimate the residual life,etc.This paper's thread is:based on lots of experimental data,researching the stable extension of FSW cracks and the change of mechanical parameter during crack extension;reflecting the change of stress filed at crack tip,plastic zone and load carrying capacity;combining with the micro-structures to analyze the results of experiment and numeric calculation;and modifying the fracture criterion.Planar numeric analyses on stable crack extension for Mode I(0~0 loading)and mixed mode(30~0 or 60~0 loading)fracture for 2024-351 FSWs are completed by using code Franc2D/L:1.The stable extension of Mode I crack is studied and it is suggested that code Franc2D/L is reliable.1)The maximum load and load-crack extension curve(P-Δa curve)are simulated by Franc2D/L and compared with the results of experiment.Results indicate that FSW joint is a low strength matching.2)The dynamic effective stress and Y directional stress fields are analyzed, which shows that numeric calculation is prior to experimental method because stress field is difficult to be obtained by experiment.Therefore the rule of crack extension can be analyzed accurately and comprehensively by numerical analysis.3)Critical COD criterion is modified.Modified critical COD curve is obtained and applied to the calculation of FSW crack from initiation to stable extension.4)During crack stable extension,the real size and shape of crack tip plastic zone are analyzed,which is tough in experiment.2.The stable extension of Mixed ModeⅠ—Ⅱ(30~0 or 60~0 loading)crack is studied by linear elastic method.Result shows that code Franc2D/L is viable.1)The loading angle and welding parameters will change crack path in the a stable crack extension of ModeⅠ—Ⅱ.2)The different behaviors of K factor in elastoplastic and elastic materials are analyzed.3)The study on mixed degree of 300 and 600 crack extension shows that Mode I dominates all the process except for the crack initiation.4)The numerical analysis on stable crack extension of ModeⅠ—Ⅱabout crack extension path and mixed degree shows that Franc2D/L is viable.