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The article concerns the injection manufacturing process of molded foam sheets and their intrinsic shock and noise performances. The main goal is to optimize the physical performances of molded plastic foams at an early stage in their design and manufacturing. The effects of injection process parameters on the properties of molded LDPE foams are investigated. The input optimization parameters considered are: injection temperature, mold temperature, injection speed, plasticization back pressure, and screw rotation speed during the plasticization phase. The output optimization parameters considered are: density, shock absorption, and acoustic absorption. The experimental design method made use of the Taguchi table and central composition design. This allows us to identify simplified mathematical models for input/output and to detect the most influential input in the injection process. We conclude by validating the models and their robustness. POLYM. ENG. SCI., 48:2305-2316, 2008. [C] 2008 Society of Plastics Engineers, INTRODUCTION Plastic foams are made up of scattered cavities. These cavities enhance lightness and softness, while adding to the soundproofing and heatproofing qualities. Polymer foams are increasingly used in industrial [...]

A new energetic approach is proposed to predict the time-varying dynamic response in the vibroacoustic field. This approach is based on the derivation and development of a hyperbolic type energy equation. It can be derived from the transport theory, or obtained by applying fundamental energy balance equation. The focus of this paper is to compare this new energy equation with the time-varying vibrational conductivity equation used extensively in recent study of energy approaches in mid-high frequency domain. The new energy equation is evaluated numerically by comparing its solutions with the diffusion equation and exact energy results. The comparative studies are applied to a beam subjected to a transverse unit impulse, and the dispersive effect is considered. [DOI: 10.1115/1.1687399]

Byline: F. Bouchoucha, M. Akrout, T. Fakhfakh, M.N. Ichchou, M. Haddar In this paper, we present an inexpensive and robust tool for the vibratory monitoring of cylindrical pipes. The tool will be based on the analysis of the anomalies which affect the elastic waves travelling in the pipe. We develop a numerical approach to study the guided elastic wave propagation in tubular structures. Wave finite element method (WFEM) based on the characterisation of the elastic waves is introduced to investigate the dispersion and wave scattering in pipes. Dynamic reduction technique is employed to improve the computational efficiency. Through WFEM and using a modal decomposition, we develop the dynamical behaviour of the pipe. We study the detection of some defects which affect the junction between two adjacent pipes. The question of the mode sensitivity to the defect's detection is considered.