Adhesion under a shear load parallel to the contact interface is a common issue in engineering and biological systems, such as when insects and adhesion devices crawl on vertical walls. A question of interest is whether and how the shear load influences the adhesion behavior between an elliptical flat punch and an elastic medium. Here, we derive lower- and upper-bound limiting analytical solutions to this problem based on the local and global energy balances. Numerical results based on our analytical solution indicate that the lower- and upper-bounds are very close to each other, and their ratio depends only on the ellipse eccentricity in the absence of shear load. The lower-bound solution yields the location of the initial detachment, which is influenced by the contact area, ellipse eccentricity, shear load, and Poisson’s ratio, but not Young’s modulus. The presence of a shear load reduces the pull-off force and can also alter the position where the detachment is nucleated. Furthermore, there exists an optimal elliptical shape that gives rise to the maximum adhesion strength in the presence of a shear load. The theoretical findings are validated through experiments involving the pull-off of a rigid punch from an adhesive polymer substrate subjected to a shear load. The present study sheds insight and may provide helpful guidelines for designing biomimetic adhesive systems.

中文翻译：

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椭圆度增强了剪切载荷下触点的粘合强度

平行于接触界面的剪切载荷下的粘附是工程和生物系统中的常见问题，例如当昆虫和粘附装置在垂直墙壁上爬行时。一个令人感兴趣的问题是剪切载荷是否以及如何影响椭圆形平冲头和弹性介质之间的粘附行为。在这里，我们根据局部和全球能量平衡得出该问题的下限和上限限制解析解。基于我们的解析解的数值结果表明，下限和上限彼此非常接近，并且它们的比率仅取决于没有剪切载荷时的椭圆偏心率。下界解产生初始脱离的位置，该位置受接触面积、椭圆偏心率、剪切载荷和泊松比的影响，但不受杨氏模量的影响。剪切载荷的存在会降低拉脱力，并且还会改变脱离成核的位置。此外，存在一个最佳的椭圆形状，该形状在存在剪切载荷的情况下产生最大的粘合强度。该理论结果通过实验得到了验证，实验涉及将刚性冲头从承受剪切载荷的粘性聚合物基材上拉出。本研究提供了见解，并可能为设计仿生粘合剂系统提供有用的指导。