Bending fracture strength of the pipe joint using iron-based shape memory alloy (Fe-SMA) subjected to different expansion methods at various deformation rates.

• Diameter expansion methods are applied to improve the strength of Fe-SMA pipe joint. • Strength can be improved effectively by changing merely expansion method up to 24.7%. • The bending fracture strength of pipe joint is evaluated at various deformation rate. • The rate sensitivity of the strength could be changed by the expansion method. • The strength after unidirectional pressing method is larger at high deformation rate. Pipe joints made of iron-based shape memory alloys (Fe-SMAs) are very promising because of the low cost of raw materials compared to other shape memory alloys. However, their development is limited to a certain extent due to their inferior shape memory effect, which result in lower shape recovery stress. To minimize this drawback, different diameter expansion methods are applied to improve tightening pressure. Furthermore, deformation rates differ depending on the actual application environment of pipe joints. Hence, an investigation into the bending fracture strength of Fe-SMA pipe joints at various deformation rates is urgently required. In this study, Fe-SMA pipe joints were prepared with three different diameter expansion methods: radial expansion, unidirectional pressing, and bi-directional pressing. Afterwards, the bending fracture strength of the pipe joint specimens was evaluated through three-point bending tests with different deformation rates and showed consistent negative rate sensitivity. In addition, the bending fracture strength was effectively improved by choosing a suitable expansion method. Through a series of thorough experiments, a systematic understanding of the influence of the diameter expansion method and deformation rates on the bending fracture strength was developed. [ABSTRACT FROM AUTHOR]