Experimental investigation of fatigue of fiber reinforced plastics due to cryogenic thermal cycling

Abstract

In many industrial applications, structures made of fiber reinforced plastics are not only exposed to cyclic mechanical loading but also have to sustain cyclically varying temperature loads. Due to the cyclic thermally induced stresses damage can occur which leads to fatigue of the material. The aim of this contribution is to investigate the degradation of material properties of fiber reinforced plastics due to thermal cyclic loads and to observe the underlying damage mechanisms. Specimens made of unidirectional and multidirectional layers of carbon fiber reinforced plastic are thermally cycled between room temperature and 90 K up to 1000 times. Afterwards a comprehensive material characterization of the conditioned and of the unconditioned reference specimens is conducted to determine the degradation of modulus and strengths in the different material directions for both tension and compression. In order to understand the underlying damage mechanisms, microscopic investigations are performed using light microscopy, confocal laser scanning microscopy and scanning electron microscopy. With these methods fiber-matrix-debonding and matrix cracks shall be observed. The investigated material shows only a slight degradation of the material properties and only little crack formation is observed leading to the conclusion that the investigated material is not prone to significant fatigue damage in the range of 1000 temperature cycles in the temperature regime from room temperature to 90 K.