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UBC Theses and Dissertations

Improving load sharing efficiency in dry fibrillar adhesives with interfacial curvature and the asymptotic solution to optimal compliance distribution Khungura, Harman


This thesis explores two investigations into improving the detachment strength and load distribution at the interface of dry bio-inspired fibrillar adhesives subjected to normal loading. The first is in how interfacial curvature affects the load sharing efficiency of engineering prototypes. Previous investigations unraveled the benefits of backing layer (BL) thickness in counteracting the detrimental load concentration created by interfacial misalignment. However, little attention was dedicated to the role of interfacial curvature on load distribution and the resulting adhesive strength. Based on the concavity of the curvature, the adhesive can detach more easily or develop stronger adhesion, compared to a flat-on-flat interface. This suggests the possibility to actuate curvature and better control adhesion. The curvature-induced strengthening/weakening of the adhesive was analyzed in combination to BL thickness, interfacial misalignment, and imperfections in the fibril length distribution. Detrimental load concentrations, created by BL interaction and interfacial misalignment, drastically reduce when the curvature prompts larger stretch to the central fibrils. This also mitigates load concentrations created by uneven fibril length distribution. These beneficial effects are reverted when the curvature prompts larger stretch to the peripheral fibrils. The quantitative analysis provides a design tool for stronger and more controllable adhesives. The second investigation is into an asymptotic solution to the optimal compliance distribution attributable to fibrils within the array. The optimal compliance distribution allows the adhesive to achieve equal load sharing (ELS) which is its theoretical maximum strength i.e all fibrils carry the same load and detach simultaneously. The array of fibrils is modelled as a continuum of linear elastic material that cannot laterally transmit load (analogous to a Winkler soil). Ultimately, the closed form solution for the continuum distribution of fibril compliance is obtained and compared to the data from a discrete model. The results show improving accuracy for an incremental number of fibrils and smaller center to center spacing. Surprisingly, the approximation introduced by the asymptotic models shows reduced sensitivity of the adhesive strength with respect to misalignment and improved adhesive strength for large misalignment angles.

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