Effect of Temperature and Viscoelastic Creep on the Clamp-Up Load in Hybrid Composite/Metal Bolted Joints

摘要

Hybrid composite to metal bolted joints are the focus of much research due the inherent advantages that they present. In particular, they are very attractive to designers and engineers alike due to their simplicity and ease of disassembly. However, hybrid connections are particularly susceptible to metal fatigue, stress relaxation primarily due to viscoelastic creep of the composite, thermal effects due to coefficient of thermal expansion mismatch, galvanic corrosion between the dissimilar constituents of the joint and moisture absorption causing differential strain between the metal and composite. The study presented in this report focuses in an investigation of the effects of temperature and primary creep in hybrid metal to composite bolted connections. The study's relevance stems from the desire to apply this technology to naval applications, where watertight integrity must be maintained. It was then decided to examine this type of connection at the subcomponent level. Therefore, EGlass/vinyl ester plates (exclamation point)4' thick were bolted to aluminum and steel plates of the same thickness with instrumented steel bolts to determine the primary stress relaxation response. Special attention was placed on the effects of temperature change on the stress relaxation that hybrid connections are particularly susceptible from. A model was developed with the sole purpose of integrating the existing coefficient of thermal expansion mismatch between all the joint parts in the scheme of analysis. Experiments were carried out to obtain the CTE of the composite material used in the hybrid connection tests, and a computer program, GASmooth, was specifically written to correct the thermal effects on the stress relaxation data.