Department of Mechanical & Aerospace Engineering, Field of Theoretical and Applied Mechanics, Cornell University, Ithaca, NY 14853, USA.
Soft Matter. 2019 Mar 6;15(10):2223-2231. doi: 10.1039/c8sm02579g.
Recent experiments have reported that the surface stress of soft elastic solids can increase rapidly with surface strain. For example, when a small hard sphere in adhesive contact with a soft silicone gel is slowly retracted from its rest position, it was found that the retraction force versus displacement relation cannot be explained either by the Johnson-Kendall-Roberts (JKR) theory or a recent indentation theory based on an isotropic surface stress that is independent of surface strain. In this paper, we address this problem using a finite element method to simulate the retraction process. Our numerical model does not have the restrictions of the aforementioned theories; that is, it can handle large nonlinear elastic deformation as well as a surface-strain-dependent surface stress. Our simulation is in good agreement with experimental force versus displacement data with no fitting parameters. Therefore, our results lend further support to the claim that significant strain-dependent surface stresses can occur in simple soft elastic gels. However, significant challenges remain in the reconciliation of theory and experiments, particularly regarding the geometry of the contact and substrate deformation.
最近的实验表明，软弹性固体的表面应力会随表面应变快速增加。例如，当一个小硬球与软硅胶凝胶处于胶着接触，并从静止位置缓慢缩回时，人们发现，回缩力与位移的关系既不能用 Johnson-Kendall-Roberts（JKR）理论，也不能用最近基于各向同性表面应力且与表面应变成正比的压痕理论来解释。在本文中，我们使用有限元方法来模拟回缩过程，从而解决了这一问题。我们的数值模型没有上述理论的限制，也就是说，它可以处理大的非线性弹性变形以及与表面应变成正比的表面应力。我们的模拟与无拟合参数的实验力与位移数据吻合良好。因此，我们的结果进一步支持了这样的观点，即在简单的软弹性凝胶中会出现显著的应变成分的表面应力。然而，在理论与实验的协调方面仍然存在重大挑战，特别是在接触几何形状和基底变形方面。
