A mesoscale quantification method of cavitation in semicrystalline polymers using X-ray microtomography

The ability of X-ray microtomography to quantify the cavitation in highly strained semicrystalline polymers is investigated on polyvinylidene fluoride. The cavitation phenomenon is studied on Circumferentially Notched Round Bars tested in tension. The tensile deformation induces void formation as attested by the whitening of the notch and SEM observations. The aim of this paper is to highlight the interest of a non destructive method based on X-ray microtomography in order to quantify the developed porosity in the cavited area and to follow step by step after relaxation, or continuously the evolution of the porosity during a tensile test. As voids may have a submicrometric size, as attested by SEM images in PVF2, the X-ray microtomography does not intend to image all the voids but to quantify them as a whole, including the non resolved voids. The method is designed to be used either with a laboratory microtomograph or with a synchrotron microtomography device. The quantification uses the correlation between the attenuation coefficient of the material and the porosity developed in the material. The measure is first validated on synchrotron images. Then the method is adapted to the laboratory microtomography prone to beam hardening artefacts. The results obtained with both devices are compared to each other and compared to the results obtained from local SEM analysis. Finally, the analysis of notched tensile specimens with varying notch root radius is investigated after interrupted tests. The analyses of the in situ tensile tests and relaxation effects are described in another paper [16].