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Abstract: In the present study, different series of High Density Polyethylene (HDPE)/carbon nano-composites were prepared using melt blending in a co-rotating intermeshing twin screw extruder. The morphological, thermal, rheological, viscoelastic, mechanical, and fracture toughness properties of the nano-composites were analyzed. The microscopic examination of the cryogenically fractured surface found a good distribution of carbon nano-particles in the HDPE matrix. The melting temperature was not significantly affected by the addition of nano-carbon. Whereas, the crystallization percentage was slightly affected by adding carbon nano-particles into the matrix. The complex viscosity increased as the percentage of carbon increased. The Dynamic Mechanical Analysis (DMA) showed that the storage modulus increased with increasing the carbon nano-particles ratio and with increasing the testing frequency. The tensile test results showed that with increasing the carbon nano-particles contents, the Young’s modulus, yield strength of HDPE nano-composite increased while the strain at fracture decreased. Similarly, the fracture toughness and the strain energy release rate decreased proportional to the carbon content. [Copyright &y& Elsevier]

Abstract: In the present work, both experimental work and Finite Element Modeling (FEM) have been used to study the effects of notch geometry on the stress/strain behaviour and fracture of the ultra-high molecular weight polyethylene (UHMWPE) at quasi static conditions. The effects of notch profile radii on UHMWPE fracture behaviour, predicted stress/strain distribution, triaxial state of stress and hydrostatic pressure across the neck have been studied. Different techniques have been used to study the effects of notch geometry on the UHMWPE properties. Differential Scanning Calorimetry (DSC) has been used to study the changes in the tested material crystallinity. The universal testing machine has been used to measure the changes in the tested material mechanical properties. The SEM has been used to examine the change in the tested material fracture surface. Finally, the Finite Element Code (ANSYS10) has been used to investigate the effects of notch geometry on the predicted stress/strain distribution across the neck. The results show a notch strengthening behaviour for the tested material, where the axial yield properties increased significantly with the reduction of notch radii, while the axial ultimate properties decreased significantly for the notched specimens compared with plain ones. Also the predicted stress/strain distribution and stress triaxiality show a strong dependence on the notch geometry. The remarkable effects of notch geometry on the predicted stress/strains distributions across the neck show the importance of careful design of UHMWPE artificial joint components with the aim to eliminate the presence of stress risers such as undercuts and fillets. [Copyright &y& Elsevier]

Abstract: The present work was undertaken to examine the effect of some environmental media (sodium hydroxide NaOH solution, water, ice, UV irradiation dose and pre-heat treatment) on the mechanical (quasi-static tensile creep-recovery and relaxation) and physical/thermal (melting and crystallinity) behaviour of the ultra high molecular weight polyethylene (UHMWPE-GUR 410-medical grade), that has several biomedical and engineering applications. The results show changes in the mechanical properties due to these environmental effects. The pre-heat treatment has significantly enhanced the tensile properties compared to virgin specimens’ properties. Improvement due to pre-heat treatment at 100°C is more than that at 50°C. Specimens’ storing in ice, NaOH and water has not affected significantly the tensile properties. All properties except fracture strain have enhanced due to specimens exposure to UV irradiation. The differential scanning calorimetry results indicate that environmental media have not any noticeable effects on the melting temperature. However, a significant increase in the degree of crystallinity was observed for all specimens versus that for virgin specimens. The creep and permanent strains of the tested virgin material increase with temperature and lineally increase with applied load. The specimens’ exposure to environmental media has improved the creep resistance and the permanent creep strain when compared with that for virgin ones. Remarkable increase was observed in the initial relaxation and residual stress of the exposed specimens against that for virgin specimens. [Copyright &y& Elsevier]

Abstract: In the present work, a dynamic thermo-mechanical analysis technique has been used to investigate the effect of pre-heat treatments on the visco-elastic properties of Ultra-High Molecular Weight Polyethylene (UHMWPE) as a function of frequency and temperature. These properties include storage modulus (E′) and loss modulus (E″). The UHMWPE specimens were pre-heated at 50, 80 and 100°C for periods of 2 and 4h, respectively. The effect of these pre-heat treatments on the quasi-static mechanical properties (Young''s modulus, yield strength, fracture strength, ductility and micro-hardness) has also been investigated. Finally, the degree of crystallinity of the UHMWPE has been measured as a function of pre-heat treatment time and temperature. The results show a strong dependence of most of these properties on the degree of crystallinity which is a function of pre-heat treatment temperature and duration. [Copyright &y& Elsevier]