Contact mechanics of isotactic polypropylene

Mechanical properties of semi-crystalline polymers are strongly determined by the structure that develops upon partial crystallization of the material, and therefore a product's lifetime is directly related to its chemical and thermo-mechanical history. In this respect, changing the crystal phase, the molecular\u3cbr/\u3eweight, the cooling rate or the thermodynamic state can lead to completely different deformation kinetics and along with that, dierent failure modes. The effects of specic structural changes on intrinsic material properties are isolated and compared to observations in the scratch response of that same structure. This methodology clearly shows that the scratch resistance of a material can be qualitatively determined solely by its deformation kinetics; the surface penetration proves to be governed by visco-elasticity and the yield stress, whereas the friction force depends on the subtle interplay of penetration depth, shape of bowwave in front of the indenter tip (large strain behaviour) and in some cases crazing or cracking behind the indenter tip (localization). Likewise, the elastic recovery and therewith the final scratch depth gives important structural information which is related to intrinsic properties