AN EFFECT OF MICROSTRUCTURE DEFECTS ON SHEAR FATIGUE RESISTANCE OF GLASS REINFORCED POLYMERS

摘要

Long fibre glass reinforced polymers (GRP) are materials with a great potential for the use in wide range of machinery components and structures due to some specific favourable properties. An example of an advanced application of GRP is for a manufacture of environmentally friendly leaf springs, because of very suitable values of E-modulus, low specific weight, damping, sufficient static strength and generally excellent fatigue properties. In comparison with metal alloys, new design approaches have to be used, taking account of different fatigue damage mechanisms and modes. In the paper, fatigue properties of GRP materials and components are discussed with a particular emphasis on scale and microstructure effects. Results of an experimental investigation of fatigue damage mechanisms under bending and shear cyclic loading and effects of microstructural defects resulting from an insufficient wetting are presented and analysed. It was shown that if microstructural defects are present in the component, initiation of fatigue damage is localised into these areas, resulting in sudden, premature failure. Fatigue life can be then reduced by more than three orders in comparison with the perfect material. The presence of defects is affected particularly by properties of the constituents and moulding parameters. Suitable changes of the process parameters resulted in a significant improvement of fatigue resistance.