Collaborative Research: New Nonlinear Modal Analysis Framework for Multi-Scale Modeling of Structures with Bolted Interfaces

许多行业的工程师使用有限元方法将结构划分为小单元，以便计算机可以找到并求解控制每个单元的方程。这使得人们可以计算具有复杂形状的结构(如飞机、机器、生物医学植入物等)的应力和变形，并预测结构是否能够经受住运行中将遇到的载荷。虽然这种方法在许多情况下都被证明是非常有效的，但即使是现代计算机也不足以准确地对部件之间的接口进行建模。因此，每年要花费数十亿美元测试结构，以确定螺栓连接等界面的刚度，以便调整模拟模型，以便更好地捕捉结构的真实行为。这使得新机器变得更加昂贵，并经常导致设计过早损坏，可能危及生命。当飞机等结构由于机翼上方的空气湍流而承受动态载荷时，预测尤其困难。这项工作将探索一种模拟具有螺栓界面的结构运动的新方法，并将进行实验以试图了解如何模拟节点中的摩擦和微观滑移及其对减振的影响。该方法可以很容易地集成到现有的有限元软件中，便于其过渡和广泛采用。作为这项研究的补充，PIS机构将开展外展活动，并举办一个短期课程，让学生和研究人员了解作为项目一部分制定的技术。负责机械接头能量耗散的物理学是复杂的，跨越了各种长度尺度。虽然近年来人们对纳米和介观接触界面的性质有了很多了解，但摩擦是极其复杂的，可能受到局部弹性、化学、塑性、表面粗糙度和氧化物或薄层磨损颗粒提供的润滑的影响。这项工作提出了一个新的降阶建模框架，允许人们将小范围接触的物理与组件的全局运动联系起来。这是对模态分析的一种扩展，可用于深入了解结构在各种加载条件下的响应。该方法将通过对各种结构的模拟和对具有螺栓接口的组件的实验来验证，为了解接口对结构响应的作用提供了新的见解。将进行模拟，以了解各种摩擦规律的特征/参数如何在全局动力响应的阻尼和非线性中表现出来。

Engineers in many industries use the finite element method to divide structures into small elements so that the equations governing each can be found and solved by computers. This allows one to compute the stresses and deformation of structures with complicated shapes such as airplanes, machines, biomedical implants, etc. and to predict whether the structure can survive the loads it will experience in operation. While this method has proven very effective in many scenarios, even modern computers are not powerful enough to model the interfaces between parts accurately. As a result, billions of dollars are spent annually testing structures to determine the stiffness of interfaces, such as bolted connections, in order to adjust the simulation models so that they better capture the real behavior of the structure. This makes new machines much more expensive and often leads to designs that break prematurely, potentially endangering lives. Prediction is particularly difficult when a structure, such as an aircraft, experiences dynamic loads due to turbulence in the air passing over the wings. This work will explore a new means of simulating the motion of structures with bolted interfaces and will perform experiments to seek to understand how to model friction and microscopic slip in the joints and its effect on vibration damping. The methodology can be easily integrated in existing finite element software, to facilitate its transition and broad adoption. The research will be complemented by outreach activities at the PIs institutions and a short course exposing students and researchers to the technique formulated as part of the project.The physics that are responsible for energy dissipation in mechanical joints are complicated and span the full range of length scales. While much has been learned in recent years about the nature of nano- and meso-scale contact interfaces, friction is exceedingly complicated and may be influenced by local elasticity, chemistry, plasticity, surface roughness and lubrication provided by oxides or thin layers of wear particles. This work posits a new reduced order modeling framework that allows one to connect the physics of small scale contacts to the global motion of the assembly. An extension to modal analysis that can then be used to obtain a wealth of insight into the response of the structure under a variety of loading conditions. The methodology will be validated through simulations on various structures and through experiments on assemblies with bolted interfaces, providing new insights into the role of interfaces on a structure's response. Simulations will be performed to understand how the features/parameters of various friction laws manifest themselves in the damping and nonlinearity of the global dynamic response.