title: Experimental investigation into the deep penetration of soft solids by sharp and blunt punches, with application to the piercing of skin.
abstract: An experimental study has been conducted on the penetration of silicone rubbers and human skin in vivo by sharp-tipped and flat-bottomed cylindrical punches. A penetrometer was developed to measure the penetration of human skin in vivo, while a conventional screw-driven testing machine was used to penetrate the silicone rubbers. The experiments reveal that the penetration mechanism of a soft solid depends upon the punch tip geometry: a sharp tipped punch penetrates by the formation and wedging open of a mode I planar crack, while a flat-bottomed punch penetrates by the growth of a mode II ring crack. The planar crack advances with the punch, and friction along the flanks of the punch leads to a rising load versus displacement response. In contrast, the flat-bottomed punch penetrates by jerky crack advance and the load on the punch is unsteady. The average penetration pressure on the shank cross section of a flat-bottomed punch exceeds that for a sharp-tipped punch of the same diameter In addition, the penetration pressure decreases as the diameter of the sharp-tipped punch increases. These findings are in broad agreement with the predictions of Shergold and Fleck [Proc. R. Soc. London, Ser. A (in press)] who proposed models for the penetration of a soft solid by a sharp-tipped and flat-bottomed punch.
authors.affiliation: Department of Engineering, Cambridge University, Trumpington Street, Cambridge, CB2 1 PZ, UK.
authors.forename: Oliver A
authors.initials: OA
authors.lastname: Shergold
authors.forename: Norman A
authors.initials: NA
authors.lastname: Fleck
mesh_terms: D019245:Compressive Strength; D003198:Computer Simulation; D004548:Elasticity; D006244:Hardness; D006245:Hardness Tests; D006801:Humans; D008954:Models, Biological; D010812:Physical Stimulation / Q000379:methods; D012867:Skin / Q000293:injuries* / Q000503:physiopathology*; D013314:Stress, Mechanical; D014949:Wounds, Nonpenetrating / Q000503:physiopathology*; D014951:Wounds, Stab / Q000503:physiopathology*