Fatigue of selected GRP composite components and joints with damage evaluation

The paper summarises the most important results of selected experimental programmes on static and fatigue strength of heavy loaded components and joints made of glass reinforced plastic (GRP) composites, having been recently performed in fatigue laboratory of the SVÚM a.s. research and testing institute. Components like GRP trailer leaf springs, springs for railway freight vehicles are addressed, along with heavy loaded joints like stud connections in rotor blade roots at different loading and environmental conditions. It was confirmed during the different kind of tests that fatigue damage accumulation can be well monitored particularly when there are no defects or imperfections in the material. Then the damage curve usually had the typical three-stages sigmoidal shape. In case of fatigue tests of stud joints, where damage was located into the bonded area inside the specimen, temperature changes were considerably more sensitive than displacement and detailed temperature monitoring indicated weak areas in the full scale model specimens. Sudden break was mostly characteristic for defect material with insufficient wet out or with different bubbles and voids. After a more detailed analysis of fatigue tests, some further links like connections between total fatigue life and initial stiffness or initial temperature increase gradient were indicated.