Prevention of early edge delaminations of fatigue loaded flat composite specimen via aimed internal stresses

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The fatigue properties of fiber-polymer-composites are of high importance for the lightweight design with this material and there is no doubt that this will remain so in future. The necessary research cannot be done without experiments. For this reason every progress in experiments increasing the quality of the results is welcome.A well known problem testing flat laminate specimen arises from the so called edge effect. First cracks and delaminations start from the edges of the specimen. This makes it difficult to establish a clear correlation between on the one hand the specimen loading and on the other hand the failure evolution. For this reason some researcher change the specimen type from flat specimen to tubes, in spite the fact tubes are much more expensive and more difficult to handle.It is a new idea to lower the stress state of the edge effect in a narrow region of the specimen edges by introducing aimed internal stresses. By this the edges should no longer be the starting point of failure. First FE-calculations and tests validated the new concept. For this the aim of the research project is to develop this promising method to a standard in composite testing.