Mohamed Bouazara

Effect of high temperature treatment on the mechanical properties of birch (Betula papyrifera)

The thermal treatment of wood is an alternative to the chemical treatment for preservation purposes. The heat treatment process improves wood’s resistance to decay and its dimensional stability. However, mechanical strength decreases as a result of heat treatment. Therefore, the treatment parameters have to be optimized to keep this loss at a minimum while improving other properties. Thermal treatment is new in North America, and its parameters are not yet adjusted for the Canadian species. Carrying out the parameter adjustment in an industrial furnace requires many trials which are costly in terms of material and man-power. A laboratory study was carried out to determine the effect of different parameters of the heat treatment on the mechanical properties of birch in order to optimize this process. A thermogravimetric analyzer was built to carry out the laboratory tests. The impact of the process parameters–such as maximum treatment temperature, holding time at this temperature, heating rate, and gas humidity–on the mechanical properties of birch was investigated. Temperature distributions in wood and in gas as well as the weight loss of wood were measured during the experiments. Afterwards, hardness, modulus of elasticity, modulus of rupture, and resistance to screw withdrawal of the samples were measured. The relation between the process parameters and the resulting mechanical properties was examined.

An optimization method designed to improve 3-D vehicle comfort and road holding capability through the use of active and semi-active suspensions

The primary purpose of this paper is to analyze the effects of vibrations on the comfort and road holding capability of road vehicles as observed in the variation of different parameters such as suspension coefficients, road disturbances, and the seat position. This study required the development of a mathematical model to simulate the dynamic behavior of a 3-D vehicle. With this model, various types of non-linear suspensions such as active and semi-active suspensions may be investigated. The results obtained from the simulation of the 3-D vehicle demonstrate that the use of active and semi-active suspension models on road vehicles prove to be beneficial for comfort without unduly compromising road holding capability.

Effect of heat treatment on the mechanical properties of North American jack pine: thermogravimetric study

Heat treatment improves dimensional stability of wood, reduces its decay, and darkens its color. However, mechanical properties of wood can deteriorate during the heat treatment. The effect of heat-treatment conditions (maximum treatment temperature, heating rate, exposure time at the maximum heat-treatment temperature, and the gas humidity) on the mechanical properties of North American jack pine (Pinus banksiana) was studied using thermogravimetric analyzer. This type of study permits the identification of the best treatment conditions which will minimize reduction of mechanical properties of jack pine. The results showed that the degree of change in bending strength, hardness, screw withdrawal strength, and dimensional stability of jack pine during heat treatment depends strongly on the treatment conditions used. Therefore, great care should be taken to select the treatment conditions. Thermogravimetric analysis can be used as a first step for selection.

Microstructural and mechanical features of aluminium semi-solid alloys made by rheocasting technique

The rheocasting process applied by Swirled Enthalpy Equilibration Device (SEED) technique relies on rapid extraction of a controlled quantity of heat from the liquid aluminium alloy via mechanical agitation to form the semi-solid slurry that can be formed under pressure. Microstructural characteristics of both conventional and semi-solid A357 castings under T6 heat treatment conditions were examined using optical and scanning electron microscopy. The fatigue and tensile experiments were applied to evaluate the effect of SEED technique on the mechanical properties of T6-A357 semi-solid alloys and conventional castings. The results showed that the rheocasting–SEED technique has proved successful in producing optimum microstructure of Al–Si–Mg semi-solid alloys providing an excellent combination of quality and mechanical performance as compared to conventional technique. This paper is part of a Themed Issue on Aluminium-based materials: processing, microstructure, properties, and recycling.

Characterization of Cracking Mechanisms of Carbon Anodes Used in Aluminum Industry by Optical Microscopy and Tomography

The objective of this work is to understand the different mechanisms of crack formation in dense anodes used in the aluminum industry. The first approach used is based on the qualitative characterization of the surface cracks and the depth of these cracks. The second approach, which constitutes a quantitative characterization, is carried out by determining the distribution of the crack width along its length as well as the percentage of the surface containing cracks. A qualitative analysis of crack formation was also carried out using 3D tomography. It was observed that mixing and forming conditions have a significant effect on crack formation in green anodes. The devolatilization of pitch during baking causes the formation and propagation of cracks in baked anodes in which large particles control the direction of crack propagation.

On the characteristics of automotive low arm-suspension system parts made of aluminum casting alloys

Stress behaviour of the vehicle suspension system has received much attention in recent years due to its effect on life time of different parts, especially lower suspension arm. These stresses can be reduced by optimizing and design variables of automotive lower arm suspension system as well as its materials metallurgical parameters. The high strength-to-weight ratio of aluminium casting alloys makes them materials of choice. The studied model is selected to be close to real operation of automotive suspension system. The main objectives of this study are to propose the proper variables required in design of suspension system parts and to reduce the stresses on lower arm-suspension system by materials and design optimum selection. The agreement of the vibration model of vehicle, design variables for optimization and the materials selection validates its positive effect on the mechanical and quality performance of applied parts made of aluminium alloys.

Fatigue Failure Study of the Lower Suspension Vehicle Arm Using a Multiaxial Criterion of the Strain Energy Density

The objective of this study is to evaluate the potential of light alloy mechanical part use in automobile industry by studying their fatigue life using various parameters such as effect of suspension dynamic, excitation type, geometry and mechanical part weight. The studied part is the lower suspension arm made from 7075-T6 aluminium alloy. The strain density energy approach enables us to compare two same order tensor: the multiaxial and uniaxial cases. The random displacement excitation is obtained analytically from the power spectral density PSD. The force excitation is obtained by a simple normalisation of spectrum displacement. To avoid the use of Newton-Raphson method during the partial fatigue life calculation step in all mesh elements, a Matlab interface to identify the critical elements is developed. The strain energy density (SENER) signal of the critical element is corrected to remove anomalies by WAFO Matlab interface algorithm. Rainflow cycles are extracted using Markov formulation in order to calculate the number of signal repetitions to failure, which is calculated from Miner law.

Materials Performance and Design Analysis of Suspension Lower-Arm Fabricated from Al-Si-Mg Castings

The diversity of physical and mechanical properties of aluminum alloys leads to develop a variety of manufacturing processes including the semi-solid casting process. Fatigue failure is considered the most common problem occurred in automotive engineering applications by which the vehicle components, mainly suspension system parts, fail under conditions of dynamic loading. It is well known that the fatigue life of aluminum castings, mainly A357, is very sensitive to casting design as well as to casting defects and microstructure constituents. The fatigue characteristics of automotive lower suspension arm made of semi-solid A357 aluminum castings have been investigated using metallurgical and analytical approaches. The critical stress areas capable of initiating cracks during fatigue tests are detected by using fatigue experimental design for real part materials by the installation of strain gages on the suspension arm to calculate maximum stress; further more, analytical approach is applied using modelling software. Microstructure characteristics of the semisolid A357 under T6 heat treatment conditions are examined using scanning electron microscope. The results show that using the SEED casting technology (Swirled Enthalpy Equilibration Device) has an efficient effect on the mechanical and metallurgical characteristics of real part materials that are also affected by castings design.

Dynamic and Fatigue Study of the Automotive Upper Arm Suspension System

Optimum design of an automotive part under random loading must satisfy two principal conditions: a safe fatigue life and a natural frequency far from the road power spectral density spectrum. Dynamic behaviour of the upper arm suspension was modelled solving the equation of motion. The quasi-static analysis was used in this study as it is highly efficient when the frequency of excitation is below the resonance frequency. The fatigue life was calculated from the multiaxial criterion equivalent to the uniaxial one based on Strain Energy Density. Finally, the critical elements were detected using a Matlab interface developed in previews work.