In this research wood-plastic composite (WPC) panels were produced from high density polyethylene, MDF, and particle-board waste at 60, 70, and 80 wt% fiber loadings using the dry blend/hot press method. Physical and mechanical properties of the panels were studied and compared with conventional MDF and particle-board panels. The results indicated that the studied properties of the composites were strongly affected by the kind and proportion of the wood fiber and polymer. Maximum values of the flexural modulus of the WPC panels were reached at 70% fiber content. The flexural strength and impact strength of the WPC panels declined when fiber content increased from 60 to 80%. The flexural modulus of the WPC panels was lower than that of the virgin MDF panels but the flexural modulus of the composites with 70% fibers was close to that of particle-board panels. Flexural strength of MDF panels was noticeably higher than those of wood-plastic composites whereas the flexural modulus of particle-board panels was comparable to that of the wood-plastic composites at 80% fiber content. Furthermore, water uptake of wood-plastic samples increased with the increase in fiber content; however, it was relatively low compared with virgin MDF and particle-board panels.

Detailed analysis of the effects of multiple extrusions on physical, mechanical, micro-structural as well as dynamic mechanical thermal properties of natural fiber high-density polyethylene (HDPE) composites is reported. Composite materials containing HDPE, wood flour, and Maleic Anhydride polyethylene (MAPE) were manufactured and subjected to a recycling process consisting of up to four times grinding and reprocessing under industrial conditions. A wide range of analytical methods including bending tests, modulus of elasticity, impact strength, Scanning electron microscopy (SEM), fiber length measurement, water absorption tests, and dynamic mechanical thermal analysis (DMTA) were employed to understand the effects of recycling on natural fiber-HDPE composites. The results revealed that the recycled composites had lower bending strength and modulus of elasticity values, as compared to the reference counterparts. Also, the once recycled composites showed higher impact strength. Results, as well, indicated that generally the recycled composites had lower water absorption values as compared to the reference ones. The results obtained from DMTA exhibited a decrease in storage modulus and an increase in mechanical loss factor (tan δ) for all composites subjected to recycling. Alterations in phase transition temperatures and intensities were also monitored and the possible reasons were analyzed.

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a b s t r a c tIn this paper, a modified explicit time integration scheme is proposed for simulating the propagation of discontinuous waves. The spatial domain is discretized by the finite element method. To obtain accurate results, the standard finite element method requires a very fine mesh, which is why the computational effort can be very time consuming. The use of high-order finite element methods -such as the spectral element method based on Lagrange polynomials through Gauss-Lobatto-Legendre points or the iso-geometric analysis using non-uniform rational B-splines -can reduce the enormous computational costs significantly, compared to the standard finite element method. However, explicit time integration schemes such as the central difference method cannot eliminate the spurious oscillation near the front wave. The procedure proposed here is basically similar to the explicit method of Noh and Bathe, but the semi-discrete equation of motion is modified by introducing a damping parameter to suit the high-order FEM analysis of the discontinuous wave propagation. The performance due to this modification is tested for one-dimensional wave propagation problems using both lumped and consistent mass matrices. Then, the idea of a combination of the consistent and row sum lumped mass matrices is evaluated. The proposed method is studied also in two-dimensions by considering the Lamb problem of wave propagation. The results are promising enough to provide a better simulation of the discontinuous wave propagation problem.

Grid dispersion is one of the criteria of validating the finite element method (FEM) in simulating acoustic or elastic wave propagation. The difficulty usually arisen when using this method for simulation of wave propagation problems, roots in the discontinuous field which causes the magnitude and the direction of the wave speed vector, to vary from one element to the adjacent one. To solve this problem and improve the response accuracy, two approaches are usually suggested: changing the integration method and changing shape functions. The Finite Element iso-geometric analysis (IGA) is used in this research. In the IGA, the B-spline or non-uniform rational B-spline (NURBS) functions are used which improve the response accuracy, especially in one-dimensional structural dynamics problems. At the boundary of two adjacent elements, the degree of continuity of the shape functions used in IGA can be higher than zero. In this research, for the first time, a two dimensional grid dispersion * : ‫ﺍﻟﻜﺘﺮﻭﻧﻴﻜﻲ‬ ‫ﭘﺴﺖ‬ ‫ﻣﻜﺎﺗﺒﺎﺕ،‬ ‫ﻣﺴﺌﻮﻝ‬ :hnahvi@cc.iut.ac.ir