Experimental and Theoretical Behavior of Self-healing Bolted Joints

This article focuses on improving the experimental behavior of a self-healing bolted joint using shape memory alloys (SMAs). Self-healing bolted joints are used to reduce the likelihood of failure of structures due to loosening of bolted joints. The clamping force (CF) in a bolted joint assembly plays an important role in maintaining the integrity of the structure. Controlling the preload in a bolted joint assembly by external heating activates the heat-to-recover (HTR) SMA washer. The SMA washer is initially in the martensitic state. When the bolt is loosened to a certain amount of preload, a heater enveloping the ring is activated allowing an axial constrained recovery of the SMA and a control of the preload in the bolt. Several experiments are conducted to ascertain the effect of heating rate, cooling rate, relaxation of assembly, and initial preload, on the preload-temperature relationship. Experimental results indicate that the use of SMA rings is promising for retightening and controlling preload in bolted joint assemblies. Two analytical models are established; one is based on the Liang-Rogers model (Liang, C. and Rogers, C.A. 1990. “One-dimensional Thermo-mechanical Constitutive Relations for Shape Memory Materials,” Journal of Intelligent Materials Systems and Structures, 1:207-234) and the other draws on the analogy between the cyclic stress-strain curves.