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UBC Theses and Dissertations

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UBC Theses and Dissertations

Mechanics of needle insertion and deep penetration in soft solids Fregonese, Stefano


This thesis examines the mechanical problem of piercing a soft solid body with a needle. This process is initiated by the critical condition of needle insertion and continued by deep penetration. This work describes both phenomena, in relation to material properties and needle size, with simple mechanical models and compares them against experiments. Needle insertion is characterized by physical and geometrical nonlinearities and a complex failure mechanism. To overcome the complexity of the problem, needle insertion is modelled as a sharp transition between two needle-specimen configurations, namely ‘indentation’ and ‘penetration’. The configurational transition is driven by minimum energy, where ’penetration’ becomes favoured over ’indentation’ at larger depths. The mechanism of penetration is strongly influenced by friction and adhesion, which provide a linear increase in penetration force with needle tip depth. This thesis finally reports some experimental observations related to the above phenomena, with some discussions about the stability of needle penetration.

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