Figure 8-4 (a) In an undeformed thermoplastic polymer tensile bar,(a)the polymer chains are randomly oriented. (b)When a stress is applied,a neck Polymer chains develops as chains become aligned before deformation locally.The neck continues to grow until the chains in the entire gage length have aligned.(c)The strength of the polymer is increased. (b) Stress Alignment of chains by deformation2、高分子材料的机械性能 2） 高分子材料的机械性能特点 塑性 塑性： 1、屈服应变高 达20% 2、颈缩变形阶 段长，断裂 前变形高达 1000% 1.3.2 高分子材料的性能 Necking and crystallization