Fibers made from shape memory alloys perform strain recovery during phase transformation of crystal structure. Controlled parameters such as heating time, holding temperature, and cooling time dominate the micro deformation of shape memory alloy fiber (SMAF). Mechanical contraction occurs at high temperature (austenitic phase), and strain-relief happens at low temperature (martensitic phase). But the rapid change of temperature causes unfinished or incomplete phase transformation, which induces residual strain within the SMAF. The accumulated defects shorten the specimen’s life during cyclic loading and lower the limit of fatigue failure. This study uses digital image correlation to provide the in-situ response temperature-strain relations during the phase transformation and quantizes the residual strain within the SMAF. Experiments accurately control the holding temperature of SMAF in three conditions, which are (a) under, (b) around, and (c) beyond the phase transformation temperature of the specimen, and systematically analyzes the self-accommodation and strain-recovery of SMAF in the three experiments. The in-situ measurement of microscale deformation can help the end-user optimize the control parameters and increase the life and performance of SMAF.

由形状记忆合金制成的纤维在晶体结构的相变过程中进行应变恢复。加热时间、保温温度和冷却时间等受控参数决定了形状记忆合金纤维 (SMAF) 的微变形。机械收缩发生在高温（奥氏体相），而应变释放发生在低温（马氏体相）。但是温度的快速变化会导致未完成或不完全的相变，从而在 SMAF 内产生残余应变。累积的缺陷缩短了试样在循环加载过程中的寿命，降低了疲劳失效的极限。本研究使用数字图像相关来提供原位相变期间的响应温度-应变关系并量化 SMAF 内的残余应变。实验准确控制SMAF在试样相变温度(a)以下、(b)附近、(c)超过三种状态下的保温温度，系统分析了SMAF的自调节和应变恢复在三个实验中。该原位微尺度变形的测量可以帮助最终用户优化控制参数和增加SMAF的寿命和性能。