Friction behavior and preload relaxation of fastening systems with composite structures

Composite materials are rapidly replacing conventional materials and components need to be installed, maintained and repaired. Therefore they also have to be fastened mechanically e.g. with threaded fasteners for clamping components together. Threaded fasteners offer a high loading capacity along with untightening possibilities.Special criteria for design in the flow of preload have to be met. Very important are friction behavior during tightening and preload relaxation during operation in product life time. Friction coefficients are responsible for preload level and preload deviation. For established material combinations, standards with defined ranges are available. What about friction coefficients with composite materials in component contact? The contribution shows results from numerous measurements, such as different combinations of materials at various lubrication states, development of friction with preload magnitude, friction development with number of retightening, influence of tightening speed, deviations in the system.Furthermore every bolted joint, which has to transmit forces between components, can only work with a reliable and sufficient preload. This is critical due to the temperature dependency of the type of laminate matrix (yield point and thermal expansion; here carbon fiber reinforced Epoxy (EP) matrix and Polyether ether ketone (PEEK) matrix are investigated). Conclusions refer to improvement of related products.