Collaborative Research: Validated Complementarity Contact Conditions for Suction-Friction of Multiphasic Soft Materials

这个项目将研究粘着和摩擦，并开发一个基于物理的接触模型，在各种液体膨胀的软材料中。在工程和生物医学应用中，不断增长的软膨胀材料的使用催生了对其力学行为建模的需求。这些材料经历了大变形，表现出依赖于加载速率的非线性力学响应。在接触加载中，速率相关主要源于软固体网络中的液体扩散、膨胀液体的粘性剪切和固体网络的粘弹性变形。在最近的研究中，在人工和生物软膨胀材料的剥离和滑动开始过程中，观察到了粘着和摩擦的速率依赖性。目前的接触配方缺乏描述这些观察结果的方法。这项研究将通过探索导致粘着和摩擦的速率依赖和耦合物理的机制，并相应地修正当前的接触公式来填补这一空白。这种基于物理的接触配方将能够对肌肉骨骼关节、软机器人与环境交互、手术切割、缝合以及软组织和替代物中的创伤性和弹道冲击、柔性电子设备与人类皮肤接触以及其他承载重大机械载荷的坚韧凝胶应用中的多种接触应用中的摩擦-粘连进行建模。这一对接触力学的新贡献将在研究生水平的课程和高中生的实践研讨会中讨论。最后，为了确保研究产品广泛和快速地传播到社区，该公式将在开源和广泛使用的软材料有限元代码中实施。研究的具体目标是检验一个主要假设，即在软膨胀材料中，固体网络控制粘附力和摩擦力，因此修改后的有效牵引力公式将解决接触分离(剥离)过程中的速率依赖和非局部性。PI进一步假设非局部粘着(吸力)和摩擦响应的耦合由材料的本征松弛时间常数控制。这些假说将通过新颖的计算和实验工作进行检验。在计算程序中，将使用变分多尺度间断Galerkin方法推导出软膨胀材料界面的统一接触框架，该框架可以在没有数值调整参数的情况下沿界面弱地施加材料点的整个加载和卸载范围。实验程序将补充计算框架，验证数据将从合成软膨胀材料界面上的整体机械特性、附着力和摩擦测试中获得。除了全局力-位移响应外，先进的激光和粒子图像测速技术将在界面附近提供全场表征。这种时间分辨的全局和局部数据将使建模框架能够进行稳健的验证。验证后，该框架将提供第一个基于物理的接触模型，该模型具有可测量的整体和界面属性，完全可参数化。这一统一的表述将通过揭示本地和非本地界面机制协同作用的变革性知识来实现，并直接类似于土壤和颗粒材料中的整体响应(凝聚力和吸力)行为。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project will study adhesion and friction, and develop a physics-based contact model in various soft materials swollen by liquids. The ever-growing use of soft swollen materials in engineering and biomedical applications catalyzes demands for modeling of their mechanical behavior. Those materials experience large deformations and exhibit nonlinear mechanical response that depends on loading rate. In contact loading, rate-dependence stems primarily from liquid diffusion within soft solid network, viscous shearing of swelling liquid and viscoelastic deformation of the solid network. In recent studies, the rate-dependence of adhesion and friction were observed during the onset of peeling and sliding in synthetic and biological soft swollen materials. Current contact formulations lack a methodology to describe those observations. The research will fill this gap by exploring the mechanisms leading to rate-dependent and coupled physics of adhesion and friction, and by correcting current contact formulations accordingly. The physics-based contact formulation will enable modeling of friction-adhesion in numerous contact applications encountered in musculoskeletal joints; soft robots interacting with their environment; surgical cuts, suturing, and traumatic and ballistic impacts in soft tissues and surrogates; contact of flexible electronics with human skin; and other tough gel applications carrying significant mechanical loads. This novel contribution to contact mechanics will be discussed in graduate level courses and hands-on seminars for high school students. Finally, to ensure broad and quick dissemination of research products to the community, the formulation will be implemented in an open-source and widely used finite element code for soft materials.The specific goal of the research is to test a major hypothesis that in soft swollen materials, solid network controls the strength in both adhesion and friction, and therefore a modified effective traction-based formulation would resolve both rate-dependence and nonlocality in contact separation (peeling) processes. The PIs further hypothesize that the coupling of nonlocal adhesion (suction) and friction response is governed by the intrinsic relaxation time constants of the materials. Those hypotheses will be tested through novel computational and experimental efforts. In the computational program, a unified contact framework will be derived for the soft swollen material interfaces using the Variational Multiscale Discontinuous Galerkin method, which can weakly impose the entire range of loading and unloading of a material point along the interface without numerical tuning parameters. The experimental program will complement the computational framework with validation data to be obtained from bulk mechanical characterization, adhesion and friction tests on synthetic soft swollen material interfaces. Besides the global force-displacement responses, advanced laser and particle image velocimetry techniques will deliver full field characterization in the vicinity of interfaces. This time-resolved global and local data will enable robust validation of the modeling framework. After validation, this framework will deliver the first physics-based contact model that is fully parametrizable with measurable bulk and interface properties. This unified formulation will be achieved by exposing the transformative knowledge that local and nonlocal interfacial mechanisms act in tandem, with direct analogy to the behavior of bulk response (cohesion and suction) in soils and granular materials.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.