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是非常重要的，而且毫无疑问，这种情况将在未来保持下去。没有实验，就不能进行必要的研究。由于这个原因，实验中的每一次进步都是值得欢迎的，提高了结果的质量。一个众所周知的问题是测试平板叠层试件是由所谓的边缘效应引起的。首先，裂纹和分层从试件的边缘开始。这使得很难在一方面试件加载和另一方面破坏演化之间建立明确的关联。为此，一些研究人员将试件类型从扁平试件改为管状试件，尽管管状试件的成本更高，操作也更困难。通过引入目标内应力来降低试件边缘狭窄区域内边缘效应的应力状态是一种新的想法。这样，边缘应该不再是失败的起点。首先，有限元计算和试验验证了这一新概念。为此，研究项目的目的是将这种有希望的方法发展成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.