CAREER: Modeling the Loosening of Bolted Joints due to Nonlinear Dynamics of Structural Assemblies

这项教师早期职业发展计划（Career）拨款将资助研究，阐明螺栓连接完整性的丧失如何影响对安全性和可靠性至关重要的机械结构的弹性和进展，并应用于车辆，工业设备，生物医学植入物，太空望远镜和游乐场设备，从而促进科学进步，促进国家繁荣和福利。螺栓和螺丝松动是美国基础设施的常见问题。结构故障通常会带来灾难性的后果，例如，导致车辆碰撞或火车出轨，从而导致人员伤亡、经济损失和环境破坏。很少有人知道结构的动力如何影响松动螺栓连接在长时间的操作。使用装配时的数据校准的模型无法在结构的生命周期内实现优化的预防性维护。该项目通过开发预测建模方法来克服这些挑战，该方法可以捕捉结构动力学和螺栓连接完整性之间的耦合，并与结构的使用寿命保持一致，从而改善老化基础设施的健康监测，增强对极端天气影响的设计，以及更可靠的可再生能源发电。该项目通过“为发现而教”的方法推进STEM学习，增强多样性，通过基于游戏的学习和虚拟现实体验吸引学生的天然好奇心。来自行业和国家实验室的建议和外联确保研究活动符合行业需求，结果可获得并有效评估。本研究旨在为预测具有松动螺栓连接的组合结构的长期非线性动力学建立建模和验证框架的基础。它通过结合新的实验和建模技术来实现这一目标，将拧紧螺栓头周围的应变映射到界面内随着关节动态演变的潜在接触条件，例如，为了测试松动速率与界面上的相对位移无关的假设。然后，从实验测量中推导出螺栓张力与关节刚度和阻尼有关的模型以及控制张力演变的微分方程。最后，将非线性正态模态理论扩展为包含螺栓张力作为因变量，并用于表征内部共振对局部损伤进展的影响。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This Faculty Early Career Development Program (CAREER) grant will fund research that clarifies how loss of integrity of bolted joints affects the resilience and progression to failure of safety- and reliability-critical mechanical structures, with application to vehicles, industrial equipment, biomedical implants, space telescopes, and playground equipment, thereby promoting the progress of science, and advancing the national prosperity and welfare. Loose bolts and screws are a common problem in US infrastructure. Structural failures often have catastrophic consequences, for example, resulting in vehicle crashes or train derailments that lead to casualties, economic loss, and environmental damage. Little is known about how a structure’s dynamics influences the loosening of bolted joints over long periods of operation. Models calibrated using data from the time of assembly fail to enable optimized preventative maintenance over a structure’s lifetime. This project overcomes these challenges by developing predictive modeling approaches that capture the coupling between structural dynamics and the integrity of bolted joints over timespans consistent with the structure’s service life, leading to improved health monitoring of aging infrastructure, toughened designs against the impacts of extreme weather, and more reliable energy generation from renewable sources. The project advances STEM learning and enhances diversity through a “Teach for Discovery” approach that engages students’ natural curiosity through game-based learning and virtual reality experiences. Advise from, and outreach to, industry and national labs ensures that the research activities are informed by industry needs and that results are accessible and effectively assessed.This research aims to develop the foundations of a modeling and validation framework for predicting the long-term nonlinear dynamics of assembled structures with loosening bolted joints. It achieves this aim partly by combining new experimental and modeling techniques to map the strains around a tightened bolt head to the underlying contact conditions inside the interface as the joint evolves dynamically, for example, to test the hypothesis that the rate of loosening is independent of the relative displacement across the interface. Models relating bolt tension to joint stiffness and damping and differential equations governing the evolution of the tensions are then derived from experimental measurements. Finally, the theory of nonlinear normal modes is expanded to incorporate bolt tension as a dependent variable and used to characterize the influence of internal resonances on the progression of local damage.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.