Defect-free joints were friction stir welded (FSW) from AZ31 Mg alloy sheets by employing optimum welding parameters for the tool geometry used. Microstructure, texture and mechanical response of the welded joints were studied to identify... more
Defect-free joints were friction stir welded (FSW) from AZ31 Mg alloy sheets by employing optimum welding parameters for the tool geometry used. Microstructure, texture and mechanical response of the welded joints were studied to identify susceptibility of crack initiation in the different weld zones and to understand the overall fracture behavior of these welds. Uniaxial tensile testing conducted orthogonal to the welding direction at temperatures of 25, 100, 200, and 300 °C revealed that cracks initiated mainly on the tool’s advancing side (AS) of the weld between thermo-mechanically affected zone (TMAZ) and stir zone (SZ). Such cracks were found to propagate preferentially along this interfacial region leading to complete fracture. This finding may be linked to the inhomogeneous plastic deformation in the weld resulting in strong texture and microhardness gradients at the interface region between the TMAZ (AS) and the SZ. On the other hand, in tensile samples machined along the welding direction and containing stir zone microstructure, second phase particles were identified as the preferred sites for cracks initiation.
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In the present contribution, the relationship between the fatigue life of styrene-butadiene rubber (SBR) and the stretch amplitude was established. Focusing on the multiaxial loading effect on the life duration of SBR, experimental tests... more
In the present contribution, the relationship between the fatigue life of styrene-butadiene rubber (SBR) and the stretch amplitude was established. Focusing on the multiaxial loading effect on the life duration of SBR, experimental tests were conducted using cylindrical specimens subjected to tension and torsion loadings under constant and variable amplitudes. Based upon the continuum damage mechanics approach, a three-dimensional model
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Polyethylene-based polymers as biomedical materials can contribute to a wide range of biomechanical applications. Therefore, it is important to identify, analyse, and predict with precision their mechanical behaviour. Polyethylene... more
Polyethylene-based polymers as biomedical materials can contribute to a wide range of biomechanical applications. Therefore, it is important to identify, analyse, and predict with precision their mechanical behaviour. Polyethylene materials are semi-crystalline systems consisting of both amorphous and crystalline phases interacting in a rather complex manner. When the amorphous phase is in the rubbery state, the mechanical behaviour is strongly dependent on the crystal fraction, therefore leading to essentially thermoplastic or elastomeric responses. In this study, the finite deformation stress-strain response of polyethylene materials is modelled by considering these semi-crystalline polymers as two-phase heterogeneous media in order to provide insight into the role of crystalline and amorphous phases on the macro-behaviour and on the material deformation resistances, i.e. intermolecular and network resistances. A hyperelastic-viscoplastic model is developed in contemplation of representing the overall mechanical response of polyethylene materials under large deformation. An evolutionary optimization procedure based on a genetic algorithm is developed to identify the model parameters at different strain rates. The identification results show good agreement with experimental data, demonstrating the usefulness of the proposed approach: the constitutive model, with only one set of identified parameters, allows reproducing the stress-strain behaviour of polyethylene materials exhibiting a wide range of crystallinities, the crystal content becoming the only variable of the model.
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The mechanical stress–strain behaviour of polyethylene (PE) materials under finite strains is studied both experimentally and theoretically. In order to gain insight into the structure and physical properties of investigated PE materials,... more
The mechanical stress–strain behaviour of polyethylene (PE) materials under finite strains is studied both experimentally and theoretically. In order to gain insight into the structure and physical properties of investigated PE materials, a series of thermal (DSC and DMTA) and microstructural (small-angle X-ray scattering and AFM) characterizations have been undertaken. The influence of crystallinity on the various features of the
Research Interests: Materials Engineering, Mechanical Engineering, Civil Engineering, Plasticity, Small Angle X Ray Scattering, and 13 moreStrain Rate, Polyethylene, Large Deformation Mechanics, Mechanical Stress, Microstructures, Constitutive model, Constitutive Modelling, Finite Strain, Strain Hardening, Physical Properties, Constitutive Equation, Tensile Test, and Large Strain
Research Interests: Materials Engineering, Mechanical Engineering, Civil Engineering, Plasticity, Strain Rate, and 14 moreStress relaxation, Large Deformation Mechanics, Cyclic Loading, Mechanical Testing, Glass Transition, Glass Transition Temperature, Room Temperature, Time Dependent, Constitutive model, High Density Polyethylene, Finite Strain, Poly (Ethylene Terephthalate), Experimental Data, and Large Strain
ABSTRACT A study was conducted to evaluate the effectiveness of step-feed in a rotating biological contactor (RBC) system consisting of two three-stage units (one control and one step-feed) treating synthetic wastewater. The performance... more
ABSTRACT A study was conducted to evaluate the effectiveness of step-feed in a rotating biological contactor (RBC) system consisting of two three-stage units (one control and one step-feed) treating synthetic wastewater. The performance of the system was evaluated in terms of organic rates, applied and removed. The impact on sCOD, sBOD(5) removals, and stage-dissolved oxygen (DO) conditions over a range of hydraulic and organic loading rates (HLR = 0.032 to 0.125 m(3)/m(2)-day and OLR = 11.03 to 111.6 g sCOD/m(2)-day) was evaluated. The results indicate a linear relationship with excellent correlation between the organic loading and removal rates. Varying the HLR and the substrate concentration within the tested range had negligible effect on the removal efficiency of the process. Similarly, the overall removal efficiency with varying OLR showed very limited improvement except at the highest OLR tested (111.6 g sCOD/m(2)-day) where removal increased by 5.2 and 2.4% for COD and BOD5, respectively. Increasing the HLR and the OLR resulted in a decrease in DO in all the stages of the two units. However, DO values in the step-feed system were higher than those recorded for the control system. In addition, O-2 limiting conditions (DO < 2 mg/L) and heavy bacterial mass growth and possible growth of Beggiatoa were detected in the first stage of the control at high loading rates.
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Investigated in this paper is the mechanical and microstructural response of specimens cut from rolled AA 6061-T6 alloy subjected to uniaxial loading at different temperatures (25, 100, 200, and 300 °C) and strain rates (10–4, 10−3, 10−2,... more
Investigated in this paper is the mechanical and microstructural response of specimens cut from rolled AA 6061-T6 alloy subjected to uniaxial loading at different temperatures (25, 100, 200, and 300 °C) and strain rates (10–4, 10−3, 10−2, 10−1 s−1). It was found that the material exhibits a strain rate and temperature dependent behavior. Microstructure observations reveal grains elongated in the loading direction with the average grain size being independent of loading conditions. However, it was observed that loading conditions influence the distribution and shape of the intermetallic phase particles. Micro cracks are observed to occur and are linked to observed damage and, consequently, decrease of ductility. Investigating the root cause of this damage mechanism reveals that particles of intermetallic phase composition are the likely sites of crack initiation. The crack-initiation mechanism at temperatures less than 200 °C is identified as crack initiation emanating from these particles while at temperatures of about 300 °C the mechanism is identified as interfacial decohesion.