Surface contact and design of fibrillar ‘friction pads’ in stick insects (Carausius morosus): mechanisms for large friction coefficients and negligible adhesion.

Many stick insects and mantophasmids possess tarsal ‘heel pads’ (euplantulae) covered by arrays of conical, micrometre-sized hairs (acanthae). These pads are used mainly under compression; they respond to load with increasing shear resistance, and show negligible adhesion. Reflected-light microscopy in stick insects (Carausius morosus) revealed that the contact area of ‘heel pads’ changes with normal load on three hierarchical levels. First, loading brought larger areas of the convex pads into contact. Second, loading increased the density of acanthae in contact. Third, higher loads changed the shape of individual hair contacts gradually from circular (tip contact) to elongated (side contact). The resulting increase in real contact area can explain the load dependence of friction, indicating a constant shear stress between acanthae and substrate. As the euplantula contact area is negligible for small loads (similar to hard materials), but increases sharply with load (resembling soft mat...

诸多竹节虫与螳䗛（Mantophasmatodea）物种均生有跗节“跟垫”（euplantulae），其表面覆盖着阵列排布的圆锥形微米级毛发（acanthae）。此类跟垫主要在受压工况下发挥作用：其抗剪强度随载荷增大而提升，且粘附性可忽略不计。针对卡氏细枝竹节虫（Carausius morosus）开展的反射光显微镜观测显示，跗节跟垫的实际接触面积会在三个层级上随法向载荷发生变化。其一，载荷施加使更多凸面垫体区域进入接触状态；其二，载荷增大提升了参与接触的棘毛密度；其三，更高载荷会使单根毛发的接触形态逐渐从圆形（尖端接触）变为长条形（侧面接触）。实际接触面积的上述增长可解释摩擦力的载荷依赖性，表明棘毛与基底之间的剪切应力保持恒定。由于低载荷下euplantulae的接触面积可忽略不计（与硬质材料类似），但随载荷增大则会急剧增长（类似软质垫...