Mechanical properties determined by nanoindentation tests of polypropylene modified by He+ particle implantation

In this paper the changes are studied of the mechanical properties of polypropylene for various alpha irradiation fluences in nanoindentation tests. The material's mechanical properties vary significantly for fluences above 5 x 10(13) He+ cm(-2), and increase sharply beyond 10(16) He+ cm(-2). The hardness and Young's modulus both increase in the first micrometer of the irradiated sample. This behavior might be explained by reticulation of the amorphous regions between the crystalline zones, The variations in both hardness and Young's modulus with fluence. and depth penetration were modeled as an equivalent hard thin film on a soft non-irradiated substrate. This allowed us to estimate the hardness and Young's modulus for various penetration depths and fluences, describe the increase in hardness and Young's modulus versus the fluence, and report an exponential decrease versus penetration depth. (C) 2001 Elsevier Science B.V. All rights reserved.