Environmental effects on bolted composite joints subjected to preload
Résumé
Bolted joints are among most commonly used mechanical connection types in various domains. Application of bolt preload favours "filtering" external forces acting on a structural unit. Nevertheless, this preloaded state tends to loosening over time. Being slightly noticeable in metallic joints, the loss is multiplied by numerous parameters in case of composite ones and can reach nearly 30% within two weeks. The influence of some parameters, like specimen thickness and moisture content, is studied experimentally. The experimental campaign is completed by a numerical analysis of the composite material properties with an application of a homogenisation methodology and finite element method. Experimentally computed matrix properties and reconstructed relative volume elements of a fibre bundle and composite serve as a basis for the evaluation of out-of-plane and in-plane mechanical parameters. The latter are validated by the experimental in-plane properties of the composite material. As demonstrated, the reduction in out-of-plane elastic modulus leads to the increase of part compliance, causing the disjunction of assembled parts due to the higher losses of preloading force.
