Microhardness studies of chain-extended PE: III. Correlation with yield stress and elastic modulus

The correlation between microhardness, H, yield stress, Y, and Young's modu lus, E, has been explored on various chain-extended polyethylene (PE) sampl es and compared to chain-folded PE. Mechanical properties have been derived from tensile and compressive experiments. The tensile yield stress, Y-t, i s shown to correlate with hardness following H similar to 3Y(t) while H sim ilar to E-t/10 (E-t is Young's modulus derived from tensile experiments). O n the other hand, the compressive yield stress, Y-c, is shown to correlate to H following the mechanical models of elastoplastic indentation. Hence, H /Y-c increases with decreasing elastic strain tending towards H similar to 3Y(c) for a fully plastic deformation. The atmospheric pressure compression -moulded samples show the lowest H/Y-c ratios as a consequence of the large st fraction of compliant phase. Moreover, the H/E-c ratio (E-c being the el astic modulus under compressive force) is shown to diminish with the decrea se of Y-c/E-c. Chain extended PE provides the lowest values for the H/E-c r atio from all the PE samples investigated. (C) 2000 Elsevier Science Ltd. A ll rights reserved.