应力加载路径对板壳塑性起皱失稳极限的影响研究

Influence of Stress Loading Path on the Limit of Plastic Wrinkling and Instability of Plates and Shells

随着航天、航空、国防、汽车等制造技术领域对金属产品轻质化、强韧化的要求不断提高,塑性失稳成为制约其整体成形的难题之一,高效准确预测和预防薄壁构件成形过程中起皱失稳缺陷具有十分重要的意义。以楔形件拉伸试验作为研究对象,通过建立楔形件数值失稳起皱模型,结合分岔原理,提出一种板壳起皱极限图(Wrinkling limit diagram,WLD)数值求解及绘制方法。针对在金属板壳试件成形过程中应力加载路径对起皱失稳的显著影响,通过分析楔形件不同区域的应力加载路径,探究板壳变形时应力加载路径对临界起皱极限的影响。结果表明:对于存在彼此独立、不同受力状态起皱区域的试件,应对不同区域分别建立WLD。不同区域单元应力加载路径对WLD的影响可归纳为临界皱屈主应力比对主应变比的影响:当临界皱屈单元的主应力比越大时,临界皱屈主应变比就越大,即WLD斜率越大,工艺抗皱性越弱;同时,通过比较楔形件不同起皱失稳区域的承载变化过程可知,起皱单元的临界主压应力增加速率会影响板料的临界起皱失稳时刻。

With the increasing requirements for the lightness and toughness of metal products in the manufacturing technology fields such as aerospace,aviation,national defense and automobile,plastic instability has become one of the problems restricting the overall forming of metal products.Therefore,it is of great significance to predict and prevent the wrinkling and instability defects efficiently and accurately in the forming process of thin-walled components.Tensile test of wedge-shaped part is taken as the research object.By establishing numerical buckling model of wedge-shaped part and combining with bifurcation principle,a numerical solution and drawing method of WLD is proposed.In view of the significant influence of the stress loading path on the wrinkling instability of metal plate and shell specimens during the forming process,the stress loading path in different areas of the wedge is analyzed to explore the influence of the stress loading path on the critical wrinkling limit during plate and shell deformation.The results show that WLD should be built established in different regions for specimens with independent wrinkling regions under different stress states.The influence of stress loading path in different regions on WLD can be summarized as the influence of the critical wrinkling principal stress ratio on the principal strain ratio:when the critical wrinkling principal stress ratio is larger,the critical wrinkling principal strain ratio is larger,that is,the slope of WLD is larger,and the process resistance is weaker.At the same time,by comparing the load bearing histories of different wrinkling instability zones of the wedges,it can be seen that the increasing rate of critical principal compressive stress during wrinkling will affect the critical wrinkling instability moment of the sheet metal.