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针对铝合金焊缝性能低于母材、现有成形极限分析方法不适宜分析铝合金搅拌摩擦焊板材成形极限的现状,提出了一种基于二次多项式新本构模型的铝合金拼焊板成形极限理论模型。核心思想为利用材料自身的性能差异替代经典M-K理论模型的沟槽假设。针对铝合金硬化指数低、幂指数回归精度差的问题,将二次多项式新本构模型应用于M-K理论模型,最终建立了适合于铝合金搅拌摩擦焊拼焊板的成形极限理论预测模型。对铝合金搅拌摩擦焊板材进行了成形极限实验,并通过XJTUDIC三维数字散斑应变变形测量系统实时测量变形过程中的应变值,得到了铝合金搅拌摩擦焊拼焊板的实验成形极限图。最后对实验结果和理论分析结果进行了对比。相比传统的幂指数本构模型,二次多项式对应力-应变曲线的回归,无论在初试屈服阶段或后期变形阶段均有很好的吻合精度。幂指数最大拟合误差超过12%,而二次多项式的拟合误差小于1%,二次多项式回归模型能很好地拟合铝合金搅拌摩擦焊接接头的应力-应变关系;采用二次多项式本构关系的理论模型能很好地预测铝合金搅拌摩擦焊板材的成形极限,第一主应变的预测误差小于0.01;而幂指数理论模型则导致平面应变状态下的极限应变预测结果明显不准,在相同应变路径下第一主应变的预测误差达0.14。
Aiming at the fact that the performance of aluminum alloy weld is lower than that of base metal and the existing forming limit analysis method is not suitable to analyze the forming limit of aluminum alloy friction stir plate, a new aluminum alloy welding tailboard based on quadratic polynomial model is proposed Limit Theory Model. The core idea is to replace the groove hypothesis of the classical M-K theory model by using the material’s own performance differences. Aiming at the problem of low aluminum alloy hardening index and poor exponential return precision, a new quadratic polynomial model was applied to the M-K theoretical model. Finally, a forming limit theoretical prediction model suitable for the aluminum alloy friction stir welding tailor welded plate was established. The forming limit experiment of aluminum alloy friction stir welding plate was carried out, and the experimental shaping limit map of the aluminum alloy friction stir welding tail welded plate was obtained by real-time measuring the strain value during the deformation process by XJTUDIC three-dimensional digital speckle strain measuring system. Finally, the experimental results and theoretical analysis were compared. Compared with the traditional constitutive model of power exponent, the regression of quadratic polynomial to stress-strain curve has a good coincidence accuracy both in the first test yield stage and the later stage of deformation. The maximum fitting error of power exponent is more than 12% and the fitting error of quadratic polynomial is less than 1%. The quadratic polynomial regression model can well fit the stress-strain relationship of aluminum alloy friction stir welded joints. The quadratic polynomial The theoretical model of the structure relationship can well predict the forming limit of the aluminum alloy friction stir welding plate. The prediction error of the first principal strain is less than 0.01. And the exponential theoretical model leads to the obvious uncertainty of the ultimate strain prediction under the plane strain. The prediction error of the first principal strain in the same strain path reaches 0.14.