Vibration assisted puncturing of a soft brittle solid

Resistance to fracture of a soft elastic gel by a sharp object like a hypodermic syringe needle depends upon the macroscopic geometry of the tool. While this subject has been examined to some detail, somewhat less explored issue is the effect of vibration on gel fracture, particularly the coupled effect of geometry and vibration. The topic is however important as it is encountered in many natural systems: for example, the hierarchical structure of mosquito proboscis and its vibratory motion, both are thought to influence the puncturing load. In this context we have carried out displacement controlled fracture of a soft gel using a syringe needle while also subjecting the gel to longitudinal vibration at controlled frequency and amplitude. These experiments show that vibration reduces maximum puncturing load and arrests also the occurrence of side cracks thereby allowing stress concentration to attain critical level ahead of the needle tip for fracture to occur.