AI 中文总结
本文通过实验探究扭转方向与大变形对软PDMS扭转接触的影响，明确大变形可驱动剪切诱导的接触面积减小，为软界面摩擦接触模型提供了基准。
AI 中文摘要
在软接触中，剪切诱导的接触面积减小现象被广泛观测到，但近期的扭转实验揭示了更复杂的非单调演化规律：接触面积随扭转角先增大后减小。导致初始面积增大的机制，以及大变形在整体面积演化中的作用仍不明确。本研究中，我们通过结合正-反扭转测试与系统改变固化剂-基体比例来调节材料软度和变形程度，实验研究了软聚二甲基硅氧烷（PDMS）球的扭转接触响应。加载-卸载测试表明，扭转界面具有强不可逆性：卸载过程中，接触面积遵循减小-增大-减小的路径，而非回溯加载分支，且出现可重复的花瓣状边缘，表明存在褶皱诱导的表面不稳定性。通过降低混合比例，我们发现更大的变形会增强面积减小的贡献，最终抑制初始面积增大，使足够软的PDMS在加载过程中出现单调的面积减小。更软的PDMS还表现出更低的剪切强度、更弱的扭矩振荡以及更好的可重复性。研究结果提供了实验证据，证明大变形可驱动剪切诱导的接触面积减小，而初始面积增大的起源仍未解决。这些发现缩小了导致初始面积增大的可能机制（如摩擦起电）的范围，并为软界面的摩擦接触模型提供了严格的基准。
英文摘要
Shear-induced contact area reduction is widely observed in soft contacts, yet recent torsional experiments have revealed a more complex non-monotonic evolution in which the contact area first increases and then decreases with twist angle. The mechanism responsible for this initial area increase and the role of large deformation in the overall area evolution remain unclear. In this study, we experimentally investigate the torsional contact response of soft Polydimethylsiloxane (PDMS) spheres by combining forward-backward twist tests with a systematic variation of the curing-agent-to-base ratio to tune material softness and deformation level. The loading-unloading tests show that the torsional interface is strongly irreversible: during unloading, the contact area follows a decrease-increase-decrease path rather than retracing the loading branch, and repeatable petal-like edges appear, indicating a wrinkle-induced surface instability. By decreasing the mixing ratio, we find that larger deformation strengthens the area-reduction contribution and eventually suppresses the initial area increase, leading to a monotonic area decrease during loading for sufficiently soft PDMS. Softer PDMS also exhibits lower shear strength, weaker torque oscillations, and improved repeatability. The results provide experimental evidence that large deformation can drive shear-induced contact area reduction, while the origin of the initial area increase remains unresolved. These findings narrow the possible mechanisms (e.g., triboelectrification) responsible for the initial area increase and provide a stringent benchmark for frictional contact models of soft interfaces.
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