chedly Bradai

The increasing use of charged or not charged polymeric materials in the field of transport requires knowledge of their behavior in fast loading for the optimization of the structures. Such current studies are common in the case of metallic materials. But compared to metals, the particular behavior of polymers marked by a weak density, low Young modulus and visco-plastic behavior; makes the conventional experimental devices inoperative. Thus there doesn’t exist nowadays a unanimously recognized test allowing a fine investigation of the fast behavior of these materials. The objective of this work is the development of a fast tensile test reaching 100 to 500 s-1 strain rate inspired from Charpy device and the study of the polypropylene mechanical behavior under transitory dynamic loading. The major problem to be solved consists of the test duration which causes measurement difficulties by means of elastic wave like the case of Hopkinson bars technique.

For a long time, the design of the majority of structures subjected to dynamic solicitation was based only on the knowledge of mechanical characteristics established by quasi-static behaviour. A security coefficient is always used in order to take into account real operating conditions. As a consequence, structures are over dimensioned. The necessity to predict the dynamical behaviour of structures in presence of shock is in a great importance for their efficient dimensioning. Numerical simulation can help reaching this target. ln this paper, a polypropylene structure is considered. The quasi-static mechanical properties of this material are injected in LS DYNA software. The dynamical behaviour of a specimen subjected to shock under different strain rates following Norton-Hoff formula law is computed. The achieved time varying stresses and strains along the specimen, help us to extract the dynamic mechanical behaviour of the material. '!"

ABSTRACT In this paper, the influence of process parameters on the ductility during squeeze casting of 2017 A wrought aluminum alloy is studied. The Taguchi method of design of experiments was employed to optimize the process parameters and to increase the elongation percent. A 3-factor, 3-level casting experiment is conducted by Taguchi L9 orthogonal array through the statistical design method. Then, the input parameters are considered here including squeeze pressure, melt temperature, and die preheating temperature with three levels. The optimum casting parameters to acquire higher ductility were predicted, and the individual importance of each parameter was evaluated by examining the signal-to-noise (S/N) ratio and analysis of variance (ANOVA) results. The optimum levels of the squeeze pressure, melt temperature, and die preheating temperature were found to be 90 MPa, 700, and 200 °C, respectively. The ANOVA results indicated that the squeeze pressure has the higher statistical effect on the elongation percent, followed by the melt temperature and die preheating temperature. Optical microscopy and scanning electron microscopy (SEM) analysis were used to discuss the effect of pressure levels on the microstructure and the fracture characterization of the investigated alloy.

ABSTRACT In this paper, a testing method is developed to determine the dynamic stress-strain responses of the polypropylene (PP) under high strain rate uniaxial tension conditions. The main objective of this study is to determine the dynamical behaviour of PP materials under transitory loading. To this effect, an experimental machine using a mixed technique of Hopkinson tension bar and a sensing block system is developed in order to study the dynamic tensile stress-strain behaviour of the low-strength and low mechanical impedance specimen. A pendulum pulse technique is employed in dynamic tension experiments to ensure that valid experimental conditions are satisfied. Results show that, compared with quasi-static behaviour, dynamic tension causes smaller failure strains.