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

在许多工程部件和结构中，在非对称应力循环(称为棘轮)上累积的塑性应变以及在疲劳循环中的逐渐损伤过程是导致失效的主要原因。据报道，工程结构的灾难性失效每年造成的损失超过1500亿美元，原因是部件/结构的几何形状复杂，以及它们在使用中所经历的严重载荷。当疲劳和棘轮现象结合在一起时，两者都会逐渐造成损害。安全问题和与工程材料失效相关的费用，需要通过开发一种强大的疲劳棘轮损伤方法，在材料失效的设计和分析中实现高度可靠性。 该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作用下的整体损伤。这项研究将利用Varvani-Topper疲劳损伤模型和修正的Ahmadzadeh-Varvani硬化准则，开发一种算法来同时评估不同多轴加载谱的非对称循环中的疲劳损伤和塑性应变累积。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，从而解决了早期建立的本构模型的不足。 未来五年，这项研究的最终目标是开发一种简单、准确和可靠的损伤框架，以预测工程构件在各种多轴阶跃加载历史下的寿命。这项研究旨在建立基于疲劳损伤和塑性应变累积的模型，以可靠地预测工程构件的寿命。使用申请者的NSERC资助的设备，将进行多轴测试，以评估拟议方法的能力。 申请人的长期目标和未来展望将是全面扩大材料在各种复杂载荷、恶劣环境和高温下的损伤评估研究，这些材料具有粘塑性性质，缺乏严谨的科学文献。 申请人相信，拟议研究的结果将在很大程度上有助于制定设计指南和安全规范，引领该领域的专业人员进行更安全、更可靠的承重部件故障设计。学生在申请者的监督下参与研究步骤，将培养能够在加拿大和世界各地的行业服务的HQP，包括汽车、航空航天、压力容器和管道。这将使使用安全可靠的制成品和零部件的加拿大社会受益。

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.