Experimentally Verified Thermodynamic Framework for Fatigue in Composite Materials

传统纤维增强复合材料在工程产品和结构中的应用呈指数级增长。虽然复合材料具有许多理想的性能，但在循环或波动载荷作用下，它们极易发生疲劳破坏。复杂的失效机制是由于复合材料的精细组成或细观结构，这些复合材料由多层组成，每一层都有排列或随机分布的纤维嵌入主体材料中。几种物质组分的存在及其不同的行为导致了有利和不利的相互作用，特别是在材料界面上。现有的疲劳失效建模方法依赖于经验或特定于观察的假设来解释突发行为的全谱，除非在特殊情况下，否则这并不是一种可行的策略。这笔赠款将支持开发一个经过实验验证的热力学框架，用于严格、快速和准确地评估复合材料的疲劳性能和寿命。这一结果将影响汽车、航空航天、建筑、交通和可再生能源发电等行业的复合材料应用。该奖项还将支持对研究生、本科生和K-12学生水平的下一代熟练劳动力以及专业人员的培训，分别通过参与研究、在当地高中推广、组织行业日和开发关于疲劳的短期课程。与基质破裂、分层和纤维断裂相关的内在复杂性使传统复合材料疲劳的治疗变得非常困难。这项研究的目的是通过一个基于热像测量的广义热力学熵框架来解释这些失效机制。其假设是，与内耗和能量耗散有关的熵为复合材料的性能退化和老化提供了一个自然的时间尺度。也就是说，疲劳过程和失效可以用循环载荷过程中的累积熵产生来描述。该方法包括在加载过程中对复合材料试件进行原位热成像，以量化基于熵的疲劳寿命度量。对铺层布局、纤维分布、组成材料和循环加载参数的影响的广泛表征将构成基于热力学的损伤模型的基础，该模型将用于预测剩余使用寿命以及通过实验观察和验证来研究内部损伤机理。该项目由土木、机械和制造业创新部门(CMMI)和既定的激励竞争研究计划(EPSCoR)共同资助。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The application of traditional fiber-reinforced composites in engineering products and structures is growing exponentially. While composite materials have many desirable properties, they are significantly susceptible to fatigue failure when subjected to cyclic or fluctuating loads. Complex failure mechanisms arise because of the elaborate makeup or meso-structure of composites, which are composed of layers, each with aligned or randomly distributed fibers embedded in host material. The presence of several material components and their distinct behaviors give rise to favorable as well as unfavorable interactions, especially at material interfaces. Existing fatigue failure modeling methods rely on empirical or observation-specific assumptions to account for the full spectrum of emergent behaviors, which has not proven to be a viable strategy except in special cases. This grant will support the development of an experimentally verified thermodynamic framework for rigorous, rapid, and accurate evaluation of fatigue performance and life of composite materials. The outcome will impact composite applications in industries such as automobile, aerospace, construction, transportation, and renewable power generation. The award will also support training of the next generation of skilled workforce at the graduate, undergraduate, and K-12 student levels as well as professionals via research participation, outreach at local high schools, and organization of industry days and development of a short course on fatigue, respectively.Inherent complexities associated with matrix cracking, delamination, and fiber breakage are among the intricacies that render the treatment of traditional composite fatigue very difficult. The objective of this research is to account for these failure mechanisms through a generalized thermodynamic entropy-based framework based on thermographic measurements. The hypothesis is that entropy, being tied to internal friction and energy dissipation, provides a natural time scale of performance degradation and aging of composites. That is, fatigue progression and failure can be described in terms of cumulative entropy generation during cyclic loading. The approach consists of in-situ thermal imaging of composite specimens during loading to quantify the entropy-based measures of fatigue life. Extensive characterization of the influence of ply layout, fiber distribution, constituent materials, and cyclic loading parameters will form the basis of the thermodynamics-based damage model, which will be used to predict remaining useful life as well as to investigate internal damage mechanisms with the help of experimental observations and validation. This project is jointly funded by the Division of Civil, Mechanical and Manufacturing Innovation (CMMI) and the Established Program to Stimulate Competitive Research (EPSCoR).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.