Damage and life assessment of materials undergoing concurrent fatigue and cyclic plastic strain accumulation over asymmetric multiaxial stress cycles with various loading spectra

在非对称应力循环中累积的塑性应变，称为棘轮，以及在疲劳循环中逐渐的损伤过程是许多工程部件和结构失效的主要原因。据报道，由于部件/结构的几何复杂性以及它们在使用中经历的严重载荷，每年工程结构灾难性失效的成本超过1500亿美元。当疲劳和棘轮现象耦合在一起时，它们都会逐渐造成损伤。与工程材料失效相关的安全问题和费用，需要通过开发强大的疲劳棘轮损伤方法，在设计和分析材料失效时实现高度的可靠性。***本研究提供了一种新的疲劳棘轮模型来评估工程材料在非对称多轴应力循环下的整体损伤。提出了一种基于Varvani-Topper疲劳损伤模型和改进的Ahmadzadeh-Varvani硬化规则的多轴加载谱非对称循环疲劳损伤和塑性应变积累同时评估算法。该模型将通过修改循环塑性参数来考虑非比例加载路径和加载顺序，从而解决早期开发的本构模型的缺点，加载顺序是评估在用部件整体损伤的重要参数。***未来五年研究的最终目标是开发一种简单、准确、可靠的损伤框架，以预测各种多轴阶梯加载历史下工程部件的寿命。本研究旨在建立基于疲劳损伤和塑性应变积累的模型，以可靠地预测工程构件的寿命。使用申请人的NSERC资助的设备，将进行多轴试验，以评估拟议方法的能力。***申请人的长期目标和未来前景将是全面扩展具有粘塑性性质的材料在各种复杂载荷、恶劣环境和高温下的损伤评估研究，这些领域缺乏严谨的科学文献。***申请人认为，拟议的研究成果将在很大程度上有助于制定设计指南和安全规范，以领导该领域的专业人员，以更安全，更可靠的设计承重部件，防止失效。在申请人的指导下，学生参与研究的步骤将培养HQP能够服务于加拿大和世界范围内的工业，包括汽车，航空航天，压力容器和管道。这将有利于加拿大社会使用安全可靠的制成品和部件。

The accumulated plastic strain over asymmetric stress cycles, referred as ratcheting, and gradual damage progress over fatigue cycles are the principal causes of failure in many engineering components and structures. The reported cost of catastrophic failure in engineering structures annually exceeds $150 billion due to the complexity in geometry of components/ structures and the severe loads they experience in service. Both fatigue and ratcheting phenomena progressively cause damage when they are coupled. Safety issues and expenses associated with failure of engineering materials, necessitate implementing a high degree of reliability in design and analysis against failure of materials by developing a robust fatigue-ratcheting damage approach.***The proposed research offers a novel fatigue-ratcheting model to assess overall damage of engineering materials subjected to asymmetric multiaxial stress cycles. The proposed research will develop an algorithm to concurrently assess fatigue damage and plastic strain accumulation over asymmetric cycles of various multiaxial loading spectra by means of the Varvani-Topper fatigue damage model and the modified Ahmadzadeh-Varvani hardening rule. The proposed model will address shortcomings of earlier developed constitutive models by modifying cyclic plasticity parameters to account for non-proportional loading paths, and loading sequences which are influential parameters in assessing overall damage of components in-service.***The ultimate objective of the proposed research over the next five years is to develop a simple, accurate, and reliable damage framework to predict the life of engineering components under various multiaxial step-loading histories. The proposed research is geared to developing the model based on fatigue damage and plastic strain accumulation to reliably predict lives of engineering components. Using the applicant's NSERC funded equipment, multiaxial tests will be conducted to evaluate the capability of the proposed methodology. ***The applicant's long-term objective and future outlook will be to comprehensively expand research on the damage assessment of materials at various complex loadings, hostile environments, and elevated temperatures with viscoplastic nature where there is a shortage of rigorous scientific literature.***The applicant believes that the outcomes of the proposed research will largely contribute in developing design guidelines and codes of safety leading professionals in the field toward a safer and more reliable design of load-bearing components against failure. The involvement of students over steps of research under the applicant's supervision will train HQP capable of serving in Canadian and world-wide industries including automotive, aerospace, pressure vessel, and pipeline. This will benefit Canadian society employing safe and reliable manufactured goods and components.