Tillier, Yannick (1998) Mechanical characterization of solid polymers using inverse analysis: application to high velocity and multiaxial tests. PhD thesis Sciences et Génie des Matériaux, ENSMP - CEMEF Centre de Mise en Forme des Matériaux, ENSMP.

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Abstract

Due to the cost and the complexity of real mechanical tests, simulation softwares are often used by manufacturers of polymer products. The quality of the predictions depends on the use of accurate constitutive equation and parameters. An experimental study using three different polymers (a semicrystallin polyethylene, an amorphous polycarbonate and a toughened polypropylene) shows that the hypotheses usually made when analytical methods are used, are only fulfilled under simple loading conditions and at low strain rates, far from real actual loading. For this reason, an inverse numerical model coupling a finite element simulation software (able to simulate rheological tests accounting complex loading conditions and temperature increase during high velocity tests) and a parameter identification module (based on an iterative Gauss-Newton method) was developed. The constitutive parameters are found minimising the discrepancy (the "cost function") between calculated and experimental forces, and optionally diameter in the case of the existence of a relative movement between the sample and the clamping device. This approach was validated by convergence and stability tests, and successfully applied to "average speed" tension tests. However the difficulty to extrapolate these results to very different loading conditions leads us to revisit the chosen constitutive equation when multiaxial loads are considered.

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