On the Use of Shape Memory Alloy Studs to Recover Load Loss in Bolted Joints

Creep is an important factor that contributes to the clamp load loss and tightness failure of bolted joints with and without gaskets over time. Retightening of the joint can be expensive and time consuming; therefore, it 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 (SMAs). However, very few experimental studies are available, which demonstrate the feasibility of these alloys. The objective of this study is to explore the benefit of shape memory and superelasticity behavior of an SMA stud to recover 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 thermomechanical behavior 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. Based on 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 standard flanges is used, with and without gaskets to demonstrate the ability of the SMA stud to recover load losses due to gasket creep.