Mechanical Engineering Department, University of California, Santa Barbara, CA 93106, USA.
INM - Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany.
J R Soc Interface. 2019 Jul 26;16(156):20190239. doi: 10.1098/rsif.2019.0239. Epub 2019 Jul 31.
Dry adhesives using surface microstructures inspired by climbing animals have been recognized for their potentially novel capabilities, with relevance to a range of applications including pick-and-place handling. Past work has suggested that performance may be strongly dependent on variability in the critical defect size among fibrillar sub-contacts. However, it has not been directly verified that the resulting adhesive strength distribution is well described by the statistical theory of fracture used. Using in situ contact visualization, we characterize adhesive strength on a fibril-by-fibril basis for a synthetic fibrillar adhesive. Two distinct detachment mechanisms are observed. The fundamental, design-dependent mechanism involves defect propagation from within the contact. The secondary mechanism involves defect propagation from fabrication imperfections at the perimeter. The existence of two defect populations complicates characterization of the statistical properties. This is addressed by using the mean order ranking method to isolate the fundamental mechanism. The statistical properties obtained are subsequently used within a bimodal framework, allowing description of the secondary mechanism. Implications for performance are discussed, including the improvement of strength associated with elimination of fabrication imperfections. This statistical analysis of defect-dependent detachment represents a more complete approach to the characterization of fibrillar adhesives, offering new insight for design and fabrication.
受爬行动物启发的表面微观结构的干式粘合剂因其潜在的新颖功能而受到关注，其相关应用包括拾取和放置处理。过去的工作表明，性能可能强烈依赖于纤维状次接触中关键缺陷尺寸的可变性。然而，尚未直接验证使用的断裂统计理论是否可以很好地描述由此产生的粘附强度分布。使用原位接触可视化，我们对合成纤维状粘合剂进行了逐纤维的粘附强度表征。观察到两种不同的分离机制。基本的、设计相关的机制涉及从接触内部的缺陷扩展。次要机制涉及周边制造缺陷处的缺陷扩展。两种缺陷群体的存在使统计特性的特征复杂化。通过使用平均顺序排序方法来隔离基本机制来解决此问题。随后在双峰框架内使用获得的统计特性，允许描述次要机制。讨论了对性能的影响，包括消除制造缺陷带来的强度提高。这种对缺陷相关分离的统计分析代表了对纤维状粘合剂的更完整的表征方法，为设计和制造提供了新的见解。
