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

聚合物泡沫夹芯复合材料已被用于现代船舶、民用基础设施和大型风力涡轮机叶片。这些结构经历了连续的加载循环和持续暴露在恶劣环境中，这可能会导致材料退化和结构失效。我们的目标是预测全球失效开始的时间，以及它在夹层结构服役期间的关键位置。这将通过开发夹层结构的材料和结构模型来实现，该模型结合了随时间变化的机械载荷以及热和水分扩散，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，将对夹层复合材料及其组分进行包括加速疲劳试验在内的综合试验方案。实验结果将被用于表征夹层结构各部件的时变(蠕变)材料模型、水热扩散模型和退化模型中的材料参数，并验证对夹层结构疲劳破坏开始时间和模式的预测。夹层结构的厚度和多层特性导致了多种失效机制，从其表面很难检测到这些失效机制。目前，夹层复合材料的疲劳失效主要是通过计算重复加载次数来确定的，直到观察到复合材料的全部失效为止，没有对失效机理进行任何解释，也没有考虑环境条件。这一研究结果将极大地提高我们对许多聚合物夹层复合材料结构和基础设施在恶劣环境中承受机械载荷时的寿命性能和疲劳失效机理的理解。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，以避免灾难性的故障。这些信息还可以帮助制造商和研究人员设计更高质量的聚合物复合材料。拟议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.