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

纤维-聚合物-复合材料的疲劳性能对于这种材料的轻量化设计非常重要，毫无疑问，这在未来将继续如此。没有实验就不能进行必要的研究。因此，在实验中提高结果质量的每一个进步都是受欢迎的。测试平板层合板试样的一个众所周知的问题来自于所谓的边缘效应。首先裂纹和分层从试样的边缘开始。这使得很难建立一个明确的相关性，一方面的试样加载和另一方面的故障演变。为此，尽管管形试样价格昂贵、操作困难，但一些研究者将试样类型从平板试样改为管形试样。通过引入有针对性的内应力来降低试样边缘狭窄区域的边缘效应应力状态是一种新的思路。这样，边缘就不再是故障的起点。首先，有限元计算和测试验证了新的概念。为此，该研究项目的目的是将这种有前途的方法发展成为复合材料测试的标准。

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.