Load Recovery of a Bolted Joint With a Shape Memory Alloy Stud

Abstract

Creep is an important factor that contributes to the clamp load loss and tightness failure of bolted joints. Retightening of the joint can be expensive, time consuming and therefore is an undesirable solution. Currently, most efforts are put towards reducing load losses directly by tightening to yield, improving material creep properties or making joint less rigid. An alternative solution of current interest is the use of bolts in Shape Memory Alloys (SMA). However very few experimental studies are available that demonstrates its feasibility. The objective of this study is to exploit the benefit of the shape memory and superelasticity behaviors of a SMA stud to recover the load losses due to creep and thermal exposure of a gasket in a bolted joint assembly. This paper explores several venues to investigate and model the thermo-mechanical properties of a bolted joint with a nickel-titanium SMA stud. A stiffness-based analytical model which incorporates the Likhachev model of SMA is used as a representation of an experimental bolted joint assembly. Using this model, the rigidity of the experimental setup is optimized to make the best use of the SMA properties of the stud. This analytical model is compared with a Finite Element Model which also implements the Likhachev’s material law. Finally an experimental test bench with a relatively low stiffness representative of EN and JIS flanges is used, with and without gaskets to demonstrate the ability of the SMA stud to recover load losses due to gasket creep.