Hardness and Young's modulus of transcrystalline polypropylene by Vickers and Knoop microindentation

A study of the anisotropic microhardness and Young's modulus of transcrysta lline isotactic polypropylene grown from the surface of high modulus carbon fibers is described. Static microindentation experiments were performed wi th Knoop and Vickers tips. The Young's moduli of the transcrystalline regio n were estimated from Knoop microindentation data by using a method recentl y developed in our laboratory. Data for the different lamellar directions w ere generated using the Knoop tip, which is sensitive to material anisotrop y. We found that the hardness and Young's modulus of the transcrystalline l ayer are higher by up to 30% when the longer diagonal of the probing Knoop tip is perpendicular to the transcrystalline growth direction, compared to when the diagonal is parallel to that direction. (C) 1999 John Wiley & Sons , Inc.