轻薄型金属反平面撕裂机理研究

MECHANISM INVESTIGATION OF OUT-OF-PLANE TEARING ON LIGHT METAL

"轻薄型金属(厚度≤10mm)反平面撕裂机理研究"旨在为报废汽车及家用电器的破碎回收处理提供理论依据。通过对轻薄型金属破碎过程分析及试验研究,发现Ⅲ型裂纹起到了主要破坏作用;根据拉伸试验应力-应变关系曲线变化趋势与理想弹塑性材料基本一致的现象,将材料简化为理想弹塑性模型;裤形撕裂试验所获得的载荷-位移曲线变化趋势表明试样起裂前后所需载荷较大,扩展过程中载荷逐渐减小;对反平面撕裂过程研究可知,在载荷作用下裂尖塑性区逐渐向外扩展,当其达到最大尺寸后,随着载荷继续增加,裂纹则开始扩展,而塑性区也逐渐向前推移直至试样断裂。裂纹尖端场的解表明起裂前及扩展过程中尖端应力-应变场均存在奇异性,且扩展过程中尖端场奇异性比起裂前弱,即起裂前裂尖的应力-应变集中程度比扩展过程中要大,这表明裂纹在起裂阶段比扩展阶段所需载荷更大。

The objective of ＂mechanism investigation of out-of-plane tearing on light metal （wall thickness less than or equal to 10mm）＂ is to provide the theoretical foundation for shredding and recovery processing of end-of-life vehicles and household appliances. The research and analysis on the shredding process of light metal indicates that the mode Ⅲ crack contributes mostly in the shredding process. The material used is simplified as an ideal elastic-plastic model based on the phenomenon that the stress-strain curves of a tensile test have an identical variable trend with the ideal elastic-plastic material. The variable trend of load-displacement curves obtained by a trousers tearing test shows that a greater load is required at a crack initiation stage, comparing with a propagation stage. The study on the process of out-of-plane tearing has found that the crack tip plastic zone expands gradually under loading, when the plastic zone reaches the maximum size, the crack begins to propagate as the loading increasing, meanwhile the plastic-zone moves ahead gradually until fracture. The solution to the crack tip field indicates that singularity exists in the crack tip stress-strain fields, and the singularity is weaker at the stage of propagation than that of the crack initiation stage, namely, the stress-strain concentration level of the crack initiation stage is much higher than that of the propagation stage, which means that a greater load is required at the crack initiation stage.