EAGER: The Surrogate System Hypothesis for Joint Mechanics

这个项目的目的是了解控制工程结构中机械连接行为的基本物理学。机械连接是工程系统中必不可少的组成部分，然而，控制机械连接的物理原理在很大程度上是未知的。这种知识的缺乏阻碍了工程师和设计师开发可以用来指导设计的接合结构的预测模型。因此，接缝结构经常被过度设计以防止失效的发生。在低影响的应用中，如办公椅、家用电器等，过度设计连接界面几乎没有实际意义。对于严重后果的应用，如喷气式飞机的航空涡轮机、火箭的机身、国防应用或汽车车架，过度设计可能会在燃油效率和安全性方面产生重大影响。如果存在接缝结构的预测模型(即预测接缝的刚度和能量消耗)，则可以适当地设计接缝，为结构贡献适当的重量，并有可能降低燃料消耗。第二个结果是，预测模型可以用于连接界面的设计，以耗散可能会损坏组件的其他部件的能量，例如火箭内的敏感电子设备。这个早期概念探索性研究补助金(AGER)项目试图通过开发一个严格的框架，即代理系统假说来解决预测能力上的差距，在该框架中，可以断章取义地描述连接的界面(避免与真实系统的高制造成本或测量中的多个污染源相关的复杂情况，例如来自系统内的其他关节)，然后用于高精度地预测感兴趣系统内的关节的响应。代理系统假说指出，可以使用包含与感兴趣的系统相同的关节的代理结构来推断关节的属性。这些属性一旦考虑了代理结构的属性，就可以作为空间离散的关节模型(而不是模式模型)直接替换到感兴趣的系统中。这个项目的目标是测试代理系统假说，以确定在不同的载荷条件下，在现实结构中，它是否得到了实验证据的支持。根据假设的性质，实验研究必须与数值建模工作相结合，数值建模工作将建立在动态子结构界最近成熟的降阶建模技术的基础上，用于研究节理结构的响应。这项工作分为几个目标：在新的制度下测试代理制度假设，以挑战其潜在的假设，确定假设限制的界限，并在具有更复杂几何形状的现实系统上演示概念证明。如果代理系统假说得到支持，除了组件的设计和优化外，它还将使接触力学有几个重大进展。这项研究将为基于特征良好的代理系统的关节预测模型提供一种新的方法。一旦开发出预测性方法，就有可能在硬件制造之前的设计阶段检测到潜在的故障。这项研究的分支是，如果成功，这一假说表明，微尺度和纳米尺度的效应，如粗糙度的分布，对于确定宏观尺度特征背后的结构动力学，如几何和平均粗糙度，是次要的。

This project is aimed at understanding the fundamental physics governing the behavior of mechanical joints in engineered structures. Mechanical joints are essential and integral parts of engineered systems and yet the physics governing them is largely unknown. This lack of knowledge prevents engineers and designers from developing predictive models of a jointed structure that can be used to guide its design. As a result, jointed structures are often overdesigned to prevent failure from occurring. In low consequence applications, such as an office chair, home electronic appliance, etc., overdesign of the jointed interface has little practical consequence. For high consequence applications, such as aero-turbines for passenger jets, the fuselage of rockets, defense applications, or the frame of an automobile, overdesign can have significant ramifications in terms of fuel efficiency and safety. If a predictive model of jointed structures existed (i.e. one that predicts both the stiffness of a joint and how much energy it dissipates), then joints could be properly designed contributing their appropriate weight to the structure, with the potential of reducing fuel consumption. A second outcome is that the predictive model could be used in design of jointed interfaces to dissipate energies that might otherwise damage other components of the assembly, such as sensitive electronics within a rocket. This EArly-concept Grant for Exploratory Research (EAGER) project seeks to address this gap in predictive capability by developing a rigorous framework, the surrogate system hypothesis, in which a jointed interface can be characterized out of context (avoiding complications associated with high manufacturing expenses for the real system or multiple sources of contamination in measurements such as from other joints within the system) and then used to predict the response of the joint within the system of interest with high accuracy.The surrogate system hypothesis states that a surrogate structure that contains the same joint as the system of interest can be used to deduce the properties of the joint. These properties, once accounting for the properties of the surrogate structure, can then be substituted directly into the system of interest as a spatially discrete joint model (as opposed to a modal model). The goal of this project is to test the surrogate system hypothesis to determine if, under varied loading conditions and in realistic structures, it is supported by experimental evidence. The experimental investigations must, by nature of the hypothesis, be in combination with numerical modeling efforts, which will be built upon recently matured reduced order modeling techniques from the dynamic substructuring community for studying the response of a jointed structure. The work is divided into several objectives: testing the surrogate system hypothesis in new regimes in order to challenge its underlying assumptions, determining the bounds of the hypothesis' limitations, and demonstrating proof-of-concept on a realistic system with more complex geometries. If the surrogate system hypothesis finds support, it will enable several significant advances for contact mechanics in addition to the design and optimization of assemblies. This research will enable a new approach for predictive models of joints based off of well-characterized surrogate systems. Once a predictive approach is developed, it will be possible to detect potential failures at the design phase before hardware is manufactured. The ramification of this research is that, if successful, this hypothesis indicates that micro- and nano-scale effects, such as the distribution of asperities, are secondary to determining the dynamics of a structure behind the macro-scale features such as geometry and mean roughness.