预应力超声冲击成形数值模拟研究

Numerical Simulation of Prestressing Ultrasonic Impact Forming

目的以2024铝合金薄板件为研究对象,结合有限元仿真分析,探讨超声冲击成形过程中预应力对材料残余应力和变形量的影响规律,预测成形结果。方法基于Johnson-Cook本构关系,建立超声冲击处理模型和冲击成形模型,针对无预弯以及预弯半径1000、3000、5000 mm情况,分析不同方向上试件的残余应力和成形量之间的差异性,并进行实验验证。结果经超声冲击处理后,试件表面呈现压应力层,试件中间区域呈现拉应力层,且随着预弯半径的减小,预弯方向上的表层残余压应力层逐渐减小,最大残余应力逐渐增大,中间拉应力逐渐增大,而预弯垂直方向上残余应力的变化规律呈现相反的状态。试件表层的压应力层有利于弯曲变形,中间区域的拉应力层能抑制弯曲变形。在设备偏移方向上试件可以获得更大的变形量,随着预弯半径的减小,预弯方向上的变形量逐渐增大,垂直预弯方向上的变形量逐渐减小。结论通过实验和模拟获得的弧高值的差异性较小,验证了所建立的有限元模型的准确性,通过该方法可以预测试件超声冲击成形结果,为制定合理的工艺参数提供理论基础。

The work aims to analyze the influence of prestressing on the residual stress and deformation of the 2024 aluminum alloy in ultrasonic impact forming through the finite element method and apply it to predict the forming results.An ultrasonic impact treatment model and an impact forming model were established according to the Johnson-Cook constitutive relation.The residual stress and deformation in different directions of the plate were analyzed with no prebending,1000 mm,3000 mm and 5000 mm prebending radii.The numerical results were verified by the experimental results.In the ultrasonic impact forming process,residual compressive stress was produced in the plate top layer and residual tensile stress was produced in the plate middle layer.With the decrease of the prebending radius,the depth of the top residual compressive stress decreased,the maximum residual compressive stress increased and the residual tensile stress increased in the plate prebending direction.And the changes regulations of the residual stress in the plate vertical direction of prebending were reversed.The compressive stress in the top surface was beneficial to the bending deformation,and the tensile stress in the middle region inhibited the bending deformation.More deformation could be produced in the prebending direction.With the decrease of the prebending radius,the deformation increased in the prebending direction and decreased in the prebending vertical direction.In conclusion,the small difference of the arc height between the numerical experimental results verifies the accuracy of the numerical model.This method can be used to predict the ultrasonic impact forming results and provides a theoretical basis for the design of optimal process parameters.