DAMAGE BEHAVIOR OF INSERTS EMBEDDED IN CARBON FIBER REINFORCED PLASTICS UNDER NEAR-SERVICE LOADS

摘要

Mechanical fasteners offer the opportunity to allow for a detachable connection of thin-walled carbon fiber reinforced plastics (CFRP) parts to metal-based structures in the context of multi-material design. Commercially available fasteners are always related to drilling before fastening which leads to inevitable bearing stress concentrations. Embedded metal elements, so-called inserts, can also be used to introduce loads into thin-walled CFRP structures and have distinctive benefits. It is possible to realize connections without drilling of the components - hence fiber continuity can be maintained leading to an increase of strength. They usually consist of a boundary plate with a welded bushing as investigated in this paper. A second, shape-optimized insert variant was additionally investigated. The specimens were finally cured in the RTM process. This paper is comprised of a systematic comparison of both insert types under near-service loads such as quasi-static, dynamic and cyclic loads. Furthermore, the influence of thermal and mechanical pre-damage on the quasi-static and cyclic strength was evaluated. It turned out that quasi-static and cyclic strength were significantly increased due to the shape-optimization. The benefits of the welded inserts are the damage tolerance after pre-damage and high strain-rate sensitivity leading to increasing strength. In addition, a lifetime prediction is feasible due to coherent damage behavior under cyclic loading conditions.