In order to study the effect of the α, β crystalline structure of polypropylene (PP) on its mechanical properties, it is necessary to prepare samples with variable α/β-phase content but with constant crystallinity and constant spherulite size. With this objective, heat treatment was first defined to be applied to an isotactic PP containing a β nucleating agent in order to achieve these conditions. Then study of the effect of the β-phase content on the tensile properties and fracture behaviour has been done at room temperature. The mechanical properties at fracture were assessed by three-point bending tests and were analysed on the basis of the "Essential Work of Fracture" (EWF). The results show that the elongation at fracture under tensile stress and the "near" Plane-Strain Essential Work of Fracture, w Ie, increase substantially with the β-phase content. Besides, Young's modulus and the yield stress in tensile tests decrease slowly with the β-phase content. Finally, these results are analysed taking account the differences in structure of the α and β spherulites.
Since few years a 3D electric lines is developed. But new applications will be to expose this circuit to high variation of temperature and use them for electronic power. Circuits lines are made of tungsten and insulation in alumina. These materials have different behavior. That difference implies mechanics stress and stress singularities. Some stress concentration can fracture materials or interface between them. Alumina is a brittle material. We need to know his fracture behavior. A statistic model is already used: Weibull model. The idea is to break about hundred samples and to related the probabilities to break of alumina used in the circuit versus stress.
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