Basil M. Darras

Finite element modeling and optimization of superplastic forming using variable strain rate approach

Detailed finite element simulations were carried out to model and optimize the superplastic blow forming process using a microstructure-based constitutive model and a multiscale deformation stability criterion that accounts for both geometrical instabilities and microstructural features. Optimum strain rate forming paths were derived from the multiscale stability analysis and used to develop a variable strain rate forming control scheme. It is shown that the proposed optimization approach captures the characteristics of deformation and failure during superplastic forming and is capable of significantly reducing the forming time without compromising the uniformity of deformation. In addition, the effects of grain evolution and cavitation on the superplastic forming process were investigated, and the results clearly highlight the importance of accounting for these features to prevent premature failure.

A Model to Predict the Resulting Grain Size of Friction-Stir-Processed AZ31 Magnesium Alloy

One of the most important issues that hinder the widespread use of friction stir (FS) processing, an effective microstructural modification technique, is the lack of accurate predictive tools that enable the selection of suitable processing parameters to obtain the desired grain structure. In this study, a model that is capable of predicting the resulting average grain size of a FS-processed material from process parameters is presented. The proposed model accounts for both dynamic recrystallization and grain growth. Several AZ31 magnesium samples were FS processed in different combinations of rotational and translational speeds. The thermal fields and resulting average grain size were measured, and the effective strain rates were approximated analytically. The results show that the proposed model is capable of predicting the resulting grain size of FS-processed materials.

Experimental investigation of underwater friction-stir welding of 5083 marine-grade aluminum alloy

Friction-stir welding has emerged as an effective technique for the challenging task of welding aluminum alloys. This article presents a detailed experimental study on underwater friction-stir welding of 5083 marine-grade aluminum alloy. The effects of submersion, rotational speed, and translational speed were investigated. The thermal histories, void fractions, microhardness, and tensile properties of the welded alloy samples, as well as power consumption of the process, were measured and analyzed. The results showed that underwater friction-stir welding produced good tensile properties and led to a significant reduction in the void fraction.

Performance Evaluation of TiAlN-PVD Coated Inserts for Machining Ti-6Al-4V under Different Cooling Strategies

Titanium alloys are labeled as difficult to materials because of their low machinability rating. This paper presents an experimental study of machining Ti-6Al-4V under turning operation. All machining tests were conducted under dry, mist and flood cooling approaches by using a TiAlN coated carbide cutting inserts. All cutting experiments were conducted using high and low levels of cutting speeds and feed rates. The study compared surface finish of machined surface and flank wear at cutting edge under dry, mist and flood cooling approaches. Scanning electron microscopy was utilized to investigate the flank wear at cutting edge under various cooling approaches and cutting conditions. Investigation revealed that TiAlN coated carbides performed comparatively better at higher cutting speed.

Micro-hardness prediction of friction stir processed magnesium alloy via response surface methodology

Purpose The purpose of this paper is to present a model to predict the micro-hardness of friction stir processed (FSPed) AZ31B magnesium alloy using response surface methodology (RSM). Another objective is to identify process parameters and through-thickness position which will give higher micro-hardness values. Moreover, the study aims at defining the factor that exhibits the most effect on the micro-hardness. Friction stir processing (FSP) machine can then be fed with the optimized parameters to achieve desirable properties. Design/methodology/approach An experimental setup was designed to conduct FSP. Several AZ31B magnesium samples were FSPed at different combinations of rotational and translational speeds. The micro-hardness of all the combinations of process parameters was measured at different through-thickness positions. This was followed by an investigation of the three factors on the resulting micro-hardness. RSM was then used to develop a model with three factors and three levels to predict the micro-hardness of FSPed AZ31 magnesium alloy within the covered range. The analyses of variance in addition to experimental verification were both used to validate the model. This was followed by an optimization of the response. Findings The model showed excellent capability of predicting the micro-hardness values as well as the optimum values of the three factors that would result in better micro-hardness. The model was able to capture the effects of rotational speed, translational speed, and through-thickness position. Results suggest that micro-hardness values were mostly sensitive to changes in tool rotational speed. Originality/value FSP is considered to be one of the advanced microstructural modification techniques which is capable of enhancing the mechanical properties of light-weight alloys. However, the lack of accurate models which are capable of predicting the resulted properties from process parameters hinders the widespread utilization of this technique. At the same time, RSM is considered as a vital branch of experimental design due to its ability to develop new processes and optimize their performance. Hence, the developed model is very beneficial and is meant to save time and experimental effort toward effective use of FSP to get the desired/optimum micro-hardness distribution.

Design Maps and Shape Optimization of a Prototype Vehicle Chassis

This paper focuses on optimizing the design of an eco-car chassis cross-section. This is done by constructing design maps and by carrying out a parametric study on the relative stiffness and mass of three different cross-sections: round-tubular, square-tubular and I-section. The objective is to determine the section that yields the desired safety factor while maintaining the lowest possible mass. An iterative approach is employed and the safety of the final design is verified both numerically and experimentally.