Variation in Functional Properties of Shape Memory Materials under Use of Long Duration

本文研究了形状记忆合金(SMA)和形状记忆聚合物(SMP)的功能性能、SMA的疲劳性能和SMP长时间保持一定形状的变形性能。主要研究结果如下：(1)在应力控制条件下，形状记忆合金的子循环加载过程中，出现了恒应变应力松弛和恒应力蠕变变形。卸载压力机出现应力恢复和蠕变恢复。这些伪粘弹性行为是由基于温度变化的马氏体相变引起的。(2)研制了一台形状记忆合金钢丝交变平面弯曲疲劳试验机。对于形状记忆合金钢丝的旋转弯曲、脉动弯曲和交变弯曲疲劳，用最大应变系统地表达了应变比对疲劳寿命的影响。一种新型超弹性薄壁…的疲劳寿命更多的管子比金属丝短。薄壁圆管的疲劳裂纹在内表面萌生。(3)对于新研制的高弹性细丝，在应力水平为1400 Mpa、应变量为4%时，应力-应变曲线基本为直线。疲劳性能不依赖于温度和频率。弹性模数是不锈钢的四分之一。这种高弹性细丝具有很高的医用导丝性能。(4)如果SMP泡沫在高温下加载，变形后的形状在低温下保持，其形状固定率和形状恢复率都大于98%，而不依赖于保持6个月后的最大应变。(5)如果SMP泡沫在高温下保持变形后的形状，则会发生二次成形，导致形状恢复不完全。板形不可恢复率与保形温度、保形应变和保形时间成正比。较少

In the present study, functional properties of shape memory alloy (SMA) and shape memory polymer (SMP), fatigue properties of SMA and deformation properties of SMP held at the fixed shape for a long duration were investigated. The results obtained can be summarized as follows.(1)In the subloop loading of SMA under the stress-controlled conditions, stress relaxation under constant strain and creep deformation under constant stress appear in the loading process. Stress recovery and creep recovery appear in the unloading press. These pseudoviscoelastic behaviors are induced due to the martensitic transformation based on variation in temperature.(2)An alternating-plane bending fatigue testing machine for an SMA wire was newly developed. The influence of strain ratio on fatigue life is systematically expressed by using maximum strain for rotating-bending, pulsating-plane bending and alternating-plane bending fatigue of an SMA wire. Fatigue life of a newly developed superelastic thin-walled … More tube is shorter than that of a wire. Fatigue crack of a thin tube initiates on an inner surface. The ratio of fracture surface due to fatigue in a thin tube is small.(3)With respect to a newly developed highelastic thin wire, the stress-strain curve is almost straight till a stress level of 1400 MPa and an amount of strain of 4%. The fatigue property does not depend on temperature and frequency. Modulus of elasticity is one fourth of that of stainless steel. The highelastic thin wire has high performance for a medical guide wire.(4)If an SMP foam is loaded at high temperature and the deformed shape is held at low temperature, both ratios of shape fixity and shape recovery are larger than 98 % without depending on maximum strain after holding for six months.(5)If the deformed shape of an SMP foam is held at high temperature, secondary shape forming occurs, resulting in imperfect shape recovery. The ratio of shape irrecoverableness increases in proportion to shape-holding temperature, shape-holding strain and shape-holding time. Less