Collaborative Research: Fatique and Lifetime Performance of Polymer Sandwich Constructions -A Multi-Scale Experiment and Modeling Approach

聚合物泡沫芯夹层复合材料已用于现代船舶、民用基础设施和大型风力涡轮机叶片。这些结构经历连续的载荷循环和持续暴露于恶劣环境，这可能导致材料退化和结构故障。我们的目标是预测的时间时，全球故障开始，其关键位置的夹层结构在其服务。这将通过开发夹层结构的材料和结构模型来实现，该模型将随时间变化的机械载荷与热和水分扩散以及成分特性的退化相结合。一个全面的测试计划，包括加速疲劳试验将进行夹层复合材料及其组成部分在不同的负载历史和各种水分和温度条件。实验结果将被用来表征材料参数的时间依赖性（蠕变）材料模型，湿热扩散，和降解模型的每个组件的夹层结构和验证的时间和模式时，疲劳失效的预测开始在夹层结构。夹层结构的厚和多层性质导致多种失效机制，这可能难以从其表面检测到。目前，夹层复合材料的疲劳失效主要是通过计算重复加载循环的次数来确定的，直到在复合材料中观察到整体失效，而没有对失效机制进行任何解释，也没有考虑环境条件。这项研究的结果将显着提高我们对许多结构和基础设施的寿命性能和疲劳失效机制的理解，这些结构和基础设施是由聚合物夹层复合材料制成的，它们在暴露于恶劣环境中时承受机械载荷。研究成果将有助于工程师改进由这些复合材料制成的结构/基础设施的设计，以避免灾难性故障。这些信息也可以帮助制造商和研究人员设计更好的质量聚合物复合材料。所提出的建模概念将解决上述挑战，这将提高聚合物夹层结构的可靠性，从而提高公共安全。

Polymer foam core sandwich composites have been utilized for modern marine vessels, civil infrastructures and large wind turbine blades. These structures experience continuous cycles of loadings and continuous exposure to hostile environments, which could lead to degradation in the materials and structural failures. Our aim is to predict the time when global failure starts, and its critical location in the sandwich structures during their service. This will be achieved through the development of material and structural models for the sandwich structures that incorporate the time-dependent mechanical loadings coupled with thermal and moisture diffusion, and degradation in the properties of the constituents. A comprehensive testing scheme including accelerated fatigue tests will be conducted on the sandwich composite and its constituents at different loading histories and various moisture and temperature conditions. The experimental results will be used to characterize the material parameters in the time-dependent (creep) material model, hygro-thermal diffusions, and degradation model for each component of the sandwich structures and verify the prediction of the time and mode when fatigue failure initiates in the sandwich structures. The thick and multi-layered nature of sandwich structures lead to multiple failure mechanisms, which can be difficult to detect from their surfaces. Currently, fatigue failure in sandwich composites has been determined mainly by counting the number of repeated loading cycles until overall failure is observed in the composites without any explanation on the failure mechanisms and consideration of the environmental conditions. The results of this study will significantly improve our understanding on the life performance and fatigue failure mechanisms in many structures and infrastructures made of polymer sandwich composites undergoing mechanical loadings while being exposed to hostile environments. The research outcomes will help engineers in improving the design of structures/infrastructures made of these composites in order to avoid catastrophic failures. This information can also help manufacturers and researchers designing better quality polymeric composites. The proposed modeling concept will address the above challenges, which will enhance the reliability of polymeric sandwich structures and hence public safety.