Collaborative Research: Fatigue 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广泛应用于现代船舶、民用基础设施和大型风力发电机叶片。这些结构经历了连续的载荷循环和持续暴露于恶劣环境中，这可能导致材料退化和结构失效。我们的目标是预测整体故障开始的时间，以及其在夹层结构服务期间的关键位置。这将通过夹层结构的材料和结构模型的发展来实现，这些模型结合了与时间相关的机械载荷，加上热和水分扩散，以及成分性能的退化。在不同的加载历史和不同的湿度和温度条件下，对夹层复合材料及其组分进行了包括加速疲劳试验在内的综合试验方案。实验结果将用于表征夹层结构各组成部分的时间依赖（蠕变）材料模型、湿热扩散和退化模型中的材料参数，并验证夹层结构开始疲劳破坏的时间和模式的预测。夹层结构的厚度和多层性导致了多种破坏机制，这很难从其表面检测到。目前，夹层复合材料的疲劳破坏主要是通过计算重复加载循环的次数来确定的，直到复合材料出现整体破坏，而没有对破坏机制进行解释，也没有考虑环境条件。本研究的结果将大大提高我们对聚合物夹层复合材料在恶劣环境下承受机械载荷的许多结构和基础设施的寿命性能和疲劳失效机制的理解。研究成果将帮助工程师改进由这些复合材料制成的结构/基础设施的设计，以避免灾难性的故障。这些信息还可以帮助制造商和研究人员设计出质量更好的聚合物复合材料。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.