Background

Soft, biological, and bio-inspired materials are often compositionally heterogeneous and structurally anisotropic, and they frequently feature graded or layered organizations. This design complexity enables exceptional ranges in properties and performance yet complicates a fundamental understanding of the contact mechanics. Recent studies of soft gel layers have relied on Hertzian or Winkler foundation (“bed-of-springs”) models to characterize the mechanics but have found neither satisfactory.

Objective

The contact mechanics of soft gel layers are not yet fully understood. The aim of this work is to develop a simple contact mechanics model tailored for compositionally-graded materials with soft surface layers under high strains and deformations.

Methods

Concepts from polymer physics, fluid draining, and Winkler foundation mechanics are combined to develop a simple contact mechanics model which relates the applied normal force to the probe radius of curvature, elastic modulus, and thickness of soft surface layers subjected to high strains.

Results

This simple model was evaluated with two examples of graded surface gel layers spanning multiple length-scales, including commercially available contact lenses and stratified hydrogels. The model captures the nonlinear contact mechanics of highly strained soft aqueous gel layers more closely than either Hertz or Winkler foundation theory while simultaneously enabling a prediction for the thickness of the surface gel layer.

Conclusion

These results indicate that this simple model can adequately characterize the contact mechanics of highly strained soft aqueous gel layers.

中文翻译：

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高应变水凝胶的简单接触力学模型

背景

柔软，生物和受生物启发的材料通常在成分上是异质的，在结构上是各向异性的，并且通常具有渐变或分层的组织。这种设计上的复杂性可以在特性和性能上实现卓越的范围，但又使对接触力学的基本理解变得复杂。对软凝胶层的最新研究依赖于Hertzian或Winkler基础（“弹簧床”）模型来表征力学特性，但均未令人满意。

客观的

尚未完全了解软凝胶层的接触机理。这项工作的目的是开发一种简单的接触力学模型，该模型适用于在高应变和变形下具有软表层的成分渐变材料。

方法

结合了聚合物物理学，流体排放和Winkler基础力学的概念，以开发一个简单的接触力学模型，该模型将施加的法向力与探针的曲率半径，弹性模量和承受高应变的软表面层的厚度相关联。

结果

通过两个跨多个长度尺度的渐变表面凝胶层的示例（包括市售隐形眼镜和分层水凝胶）对这一简单模型进行了评估。与Hertz或Winkler基础理论相比，该模型更紧密地捕获了高度应变的软水凝胶层的非线性接触力学，同时能够预测表面凝胶层的厚度。

结论

这些结果表明，该简单模型可以充分表征高度应变的软水凝胶层的接触力学。