基于光滑粒子流体动力学方法的镁及镁合金ECAP过程数值模拟研究
发布时间：2018-09-07 17:39
【摘要】：近年来,国内外学者致力于研究改善镁及镁合金的强度和室温变形能力。细晶强化是提高镁合金室温综合性能最有效的途径。经过等径角挤压(ECAP)加工的镁及镁合金室温综合性能明显提高。但由于镁合金室温塑性变形能力差且再结晶温度低的特性,限制了ECAP工艺细化晶粒的效果。包套ECAP工艺是一种新型ECAP工艺有效解决了纯镁室温下ECAP变形过程发生开裂的问题。但该工艺影响因素众多,且模具内部加工过程封闭,借助计算机仿真技术在很大程度上有效反映工件的变形行为。对于镁合金ECAP过程的数值模拟研究,必须要准确地预测工件的损伤程度,但现阶段的模拟方法难以实现动态的损伤演化过程。本文使用光滑粒子流体动力学(SPH)方法来处理动态损伤演化问题,通过建立基于SPH方法含损伤预测模型的计算程序,对室温下纯镁的ECAP过程和包套ECAP过程进行模拟研究。主要研究工作和结论如下:首先,基于弹塑性力学的SPH方法建立了镁及镁合金ECAP变形过程的数学模型。通过修正SPH基本控制方程来保证计算过程的稳定性,并采用罚函数排斥力来处理固壁边界问题,移动边界实现挤压运动过程。编写了基于sph方法计算程序,通过计算经典算例验证了本文所建计算程序的正确性,对200℃下az31镁合金的ecap变形过程进行了模拟计算,获得了与有限元商业软件基本一致的计算结果。为基于sph方法含损伤预测模型计算程序的建立奠定基础。其次,针对材料的动态损伤演化问题,在上文已建程序的基础上,加入损伤演化本构模型和失效粒子法,编写了基于sph方法含损伤预测模型的计算程序。通过对室温下纯镁在不同挤压速度下ecap损伤演化过程的模拟研究,并与已有试验结果的对比表明本文程序可以准确模拟纯镁的损伤演化过程。模拟研究表明,高变形速率导致纯镁发生韧脆转变,宏观裂纹萌生之前,试样中形成束状高应变率区逐渐汇聚于剪切面,并在裂纹扩展至断裂后消失;较低变形速率下纯镁呈片层状开裂,损伤演化过程具有周期性,塑性变形区应变率分布均匀性提高,裂纹扩展缓解高应变集中趋势,裂尖周围产生塑性变形阻碍裂纹扩展。最后,使用本文所建基于sph方法含损伤预测模型的计算程序,对室温下纯镁在两种包套材料的ecap变形过程进行了模拟研究。研究表明,同等挤压条件下,以2024铝合金为包套的组合工件发生片层状开裂;以工业纯铁为包套的组合工件保持完整且挤压过程中纯镁的变形均匀性明显提高。
[Abstract]:In recent years, scholars at home and abroad have focused on improving the strength and room temperature deformability of magnesium and magnesium alloys. Fine grain strengthening is the most effective way to improve the comprehensive properties of magnesium alloys at room temperature. The comprehensive properties of magnesium and magnesium alloys processed by equal-diameter angular extrusion (ECAP) at room temperature are improved obviously. However, due to the poor plastic deformation at room temperature and low recrystallization temperature, the grain refinement effect of ECAP process is limited. The coated ECAP process is a new type of ECAP process which effectively solves the problem of cracking during ECAP deformation at room temperature of pure magnesium. However, there are many factors affecting the process, and the internal processing process of the die is closed, so the deformation behavior of the workpiece can be reflected to a great extent by computer simulation technology. For the numerical simulation of magnesium alloy ECAP process, it is necessary to accurately predict the damage degree of the workpiece, but the present simulation method is difficult to realize the dynamic damage evolution process. In this paper, the smooth particle hydrodynamics (SPH) method is used to deal with the dynamic damage evolution problem. The ECAP process and the wrapped ECAP process of pure magnesium at room temperature are simulated by establishing a program based on the SPH method with damage prediction model. The main work and conclusions are as follows: firstly, the mathematical model of ECAP deformation process of magnesium and magnesium alloys is established based on the SPH method of elastoplastic mechanics. The stability of the calculation process is guaranteed by modifying the SPH basic governing equation, and the penalty function repulsion force is used to deal with the problem of the solid wall boundary, and the moving boundary is used to realize the extrusion process. The calculation program based on sph method is compiled, and the correctness of the program is verified by calculating the classical example. The ecap deformation process of az31 magnesium alloy at 200 鈩，
本文编号：2228957
[Abstract]:In recent years, scholars at home and abroad have focused on improving the strength and room temperature deformability of magnesium and magnesium alloys. Fine grain strengthening is the most effective way to improve the comprehensive properties of magnesium alloys at room temperature. The comprehensive properties of magnesium and magnesium alloys processed by equal-diameter angular extrusion (ECAP) at room temperature are improved obviously. However, due to the poor plastic deformation at room temperature and low recrystallization temperature, the grain refinement effect of ECAP process is limited. The coated ECAP process is a new type of ECAP process which effectively solves the problem of cracking during ECAP deformation at room temperature of pure magnesium. However, there are many factors affecting the process, and the internal processing process of the die is closed, so the deformation behavior of the workpiece can be reflected to a great extent by computer simulation technology. For the numerical simulation of magnesium alloy ECAP process, it is necessary to accurately predict the damage degree of the workpiece, but the present simulation method is difficult to realize the dynamic damage evolution process. In this paper, the smooth particle hydrodynamics (SPH) method is used to deal with the dynamic damage evolution problem. The ECAP process and the wrapped ECAP process of pure magnesium at room temperature are simulated by establishing a program based on the SPH method with damage prediction model. The main work and conclusions are as follows: firstly, the mathematical model of ECAP deformation process of magnesium and magnesium alloys is established based on the SPH method of elastoplastic mechanics. The stability of the calculation process is guaranteed by modifying the SPH basic governing equation, and the penalty function repulsion force is used to deal with the problem of the solid wall boundary, and the moving boundary is used to realize the extrusion process. The calculation program based on sph method is compiled, and the correctness of the program is verified by calculating the classical example. The ecap deformation process of az31 magnesium alloy at 200 鈩，
本文编号：2228957
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