Mechanics-based Service-life Prediction of Natural-Fiber Composites

随着在汽车、包装和建筑行业的应用，在过去的几十年里，天然纤维复合材料作为合成纤维复合材料的可持续替代品得到了越来越多的关注。然而，天然纤维复合材料的广泛应用仍然受到限制，因为人们担心它们在高湿和潮湿环境中的耐用性。以往与湿度有关的耐久性研究本质上都是经验性的。该奖项将支持对天然纤维复合材料的环境辅助降解进行建模的基础研究。基于力学的建模方法将用于阐明复合材料组成、湿热暴露、机械降解和环境可持续性之间的关系。这些研究活动将推动在全球范围内完全生物可再生和经济可行的材料的科学和工程。相辅相成的教育和外联工作将有助于培养更具包容性的一代女工程师，她们将成为工程机械和材料可持续性方面的技术领袖。这项研究的主要目的是使用细观力学来预测暴露在波动的湿热条件下的短纤维和连续纤维天然纤维复合材料中的水分和霜冻引起的损伤。除了复合材料合成，实验工作还包括介观和纳米尺度的机械测试，以将水分含量和温度与纤维、基质和复合材料的机械性能降低联系起来。计算工作包括基于扩散的水分传输模型的建立；细观力学损伤模型的建立以考虑纤维软化和膨胀的内部应变；以及使用从复合材料样品的加速老化获得的数据来验证模型。一旦用实验数据校准，基于力学的寿命模型将被用来预测现场退化和估计在不同地理位置的几个应用中的功能老化(寿命结束)。这些使用寿命评估将被集成到概率生命周期评估建模框架中，以计算不同空间和时间域的真实环境影响。

With applications in the automotive, packaging, and construction industries, natural-fiber composites have gained in relevance over the past few decades as sustainable alternatives to synthetic-fiber composite materials. However, widespread application of natural-fiber composites remains limited due to concerns regarding their durability in high-humidity and wet environments. Previous moisture-related durability research has been empirical in nature. This award will support fundamental research to model the environmentally assisted degradation of natural-fiber composites. The mechanics-based modeling approaches will be used to elucidate relationships between composite composition, hygrothermal exposure, mechanical degradation, and environmental sustainability. The research activities will advance the science and engineering of materials that are fully biorenewable and economically viable on a global scale. The complementary education and outreach efforts will help foster a more inclusive generation of female engineers who will become technical leaders in engineering mechanics and materials sustainability. The primary objective of this research is to use micromechanics to predict moisture- and frost-induced damage in both short- and continuous-fiber natural-fiber composites that are exposed to fluctuating hygrothermal conditions. In addition to composite synthesis, the experimental work includes meso- and nano-scale mechanical testing to correlate moisture content and temperature with reductions in mechanical properties of fibers, matrices, and composites thereof. The computational work includes formulation of diffusion-based moisture transport models; formulation of micromechanical damage models to account for internal strains from fiber softening and expansion; and model validation using data obtained from the accelerated weathering of composite samples. Once calibrated with experimental data, the mechanics-based service-life models will be used to predict in-situ degradation and to estimate functional obsolescence (end of life) in several applications in a variety of geographic locations. These service-life estimates will be integrated into a probabilistic lifecycle assessment modeling framework to calculate true environmental impacts across variable spatial and temporal domains.