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

该学院早期职业发展计划（CAREER）拨款将资助研究，阐明螺栓连接的完整性损失如何影响安全性和可靠性关键机械结构的恢复力和故障进展，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，推进国家繁荣和福利。螺栓和螺钉松动是美国基础设施的常见问题。结构故障通常会造成灾难性的后果，例如，导致车辆碰撞或列车脱轨，从而导致人员伤亡、经济损失和环境破坏。很少有人知道如何结构的动态影响松动的螺栓连接在长期的运作。使用组装时的数据校准的模型无法在结构的使用寿命内实现优化的预防性维护。该项目通过开发预测建模方法克服了这些挑战，这些方法可以捕获结构动力学之间的耦合以及与结构使用寿命一致的时间跨度内螺栓连接的完整性，从而改善对老化基础设施的健康监测，强化设计以应对极端天气的影响，以及更可靠的可再生能源发电。该项目通过“发现教学”的方法推进STEM学习并增强多样性，该方法通过基于游戏的学习和虚拟现实体验激发学生的自然好奇心。来自行业和国家实验室的建议和推广确保了研究活动符合行业需求，并且结果可以访问和有效评估。本研究旨在为预测螺栓连接松动的装配结构的长期非线性动力学建立建模和验证框架。它实现了这一目标的一部分，结合新的实验和建模技术，以映射周围的应变拧紧螺栓头的基本接触条件内的接口作为联合动态演变，例如，测试的假设，松动的速度是独立的相对位移的接口。模型螺栓张力联合刚度和阻尼和微分方程的张力的演变，然后来自实验测量。最后，扩展了非线性简正模态理论，将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NSF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.