Mokhtar Awang

Bio: Mokhtar Awang is an academic researcher from Universiti Teknologi Petronas. The author has contributed to research in topics: Welding & Friction stir welding. The author has an hindex of 15, co-authored 125 publications receiving 892 citations. Previous affiliations of Mokhtar Awang include West Virginia University.

Thermo-Mechanical Modeling of Friction Stir Spot Welding (FSSW) Process: Use of an Explicit Adaptive Meshing Scheme

Abstract: This paper presents on-going finite element modeling efforts of friction stir spot welding (FSSW) process by an explicit finite element code. Adaptive meshing and advection schemes, which makes it possible to maintain mesh quality under large deformations, is utilized to simulate the material flow and temperature distribution in FSSW process. The predicted overall deformation shape of the weld joint resembles that experimentally observed. Temperature and stress graphs in the radial direction as well as temperature-deformation distribution plots are presented. However, refinements of several modeling aspects are needed for more realistic prediction of the FSSW process.

A Comparison of Different Finite Element Methods in the Thermal Analysis of Friction Stir Welding (FSW)

Abstract: Friction Stir Welding (FSW) is a novel kind of welding for joining metals that are impossible or difficult to weld by conventional methods. Three-dimensional nature of FSW makes the experimental investigation more complex. Moreover, experimental observations are often costly and time consuming, and usually there is an inaccuracy in measuring the data during experimental tests. Thus, Finite Element Methods (FEMs) has been employed to overcome the complexity, to increase the accuracy and also to reduce costs. It should be noted that, due to the presence of large deformations of the material during FSW, strong distortions of mesh might be happened in the numerical simulation. Therefore, one of the most significant considerations during the process simulation is the selection of the best numerical approach. It must be mentioned that; the numerical approach selection determines the relationship between the finite grid (mesh) and deforming continuum of computing zones. Also, numerical approach determines the ability of the model to overcome large distortions of mesh and provides an accurate resolution of boundaries and interfaces. There are different descriptions for the algorithms of continuum mechanics include Lagrangian and Eulerian. Moreover, by combining the above-mentioned methods, an Arbitrary Lagrangian–Eulerian (ALE) approach is proposed. In this paper, a comparison between different numerical approaches for thermal analysis of FSW at both local and global scales is reviewed and the applications of each method in the FSW process is discussed in detail. Observations showed that, Lagrangian method is usually used for modelling thermal behavior in the whole structure area, while Eulerian approach is seldom employed for modelling of the thermal behavior, and it is usually employed for modelling the material flow. Additionally, for modelling of the heat affected zone, ALE approach is found to be as an appropriate approach. Finally, several significant challenges and subjects remain to be addressed about FSW thermal analysis and opportunities for the future work are proposed.

Energy generation during friction stir spot welding (FSSW) of al 6061-T6 plates

Abstract: Effective and reliable computational models would greatly enhance the study of energy dissipation during the friction stir spot welding (FSSW) process. Approaches for the computational modeling of the FSSW process, however, are still under development, and much work is still needed, particularly the application of explicit finite element (FE) codes for a verifiable simulation. The objectives of this work are to develop an FE modeling of FSSW of 6061-T6 aluminum alloy and analyze energy generation during the welding process. In this work, a three dimensional (3-D) FE coupled thermal-stress model of FSSW process has been developed in Abaqus/Explicit code. Rate dependent Johnson–Cook material model is used for elastic–plastic work deformations. Temperature profile and energy dissipation history of the FE model have been analyzed. The peak temperature at the tip of the pin and frictional dissipation energy are in close agreement with the experimental work done by Gerlich et al. [1], which is about 5.1% different.

Modeling the tensile stress–strain response of carbon nanotube/polypropylene nanocomposites using nonlinear representative volume element

Abstract: This paper presents a finite element model for predicting the mechanical behavior of polypropylene (PP) composites reinforced with carbon nanotubes (CNTs) at large deformation scale. Existing numerical models cannot predict composite behavior at large strains due to using simplified material properties and inefficient interfaces between CNT and polymer. In this work, nonlinear representative volume elements (RVE) of composite are prepared. These RVEs consist of CNT, PP matrix and non-bonded interface. The nonlinear material properties for CNT and polymer are adopted to solid elements. For the first time, the interface between CNT and matrix is simulated using contact elements. This interfacial model is capable enough to simulate wide range of interactions between CNT and polymer in large strains. The influence of adding CNT with different aspect ratio into PP is studied. The mechanical behavior of composites with different interfacial shear strength (ISS) is discussed. The success of this new model was verified by comparing the simulation results for RVEs with conducted experimental results. The results shows that the length of CNT and ISS values significantly affect the reinforcement phenomenon.

Evaluation of properties and FEM Model of the Friction welded mild Steel-Al6061-Alumina

Abstract: Evaluation of mechanical and interfacial properties of friction welded alumina-mild steel rods with the use of Al6061 sheet are presented in this work. SEM, EDX analysis, hardness and bending strength tests were conducted. The bonds were attained through interfacial interlocking and intermetalllic phase formation with average bending strengths in the range of 40 to 200 MPa and insignificant hardness change in the parent alumina and mild steel. A preliminary simulation was made to predict the deformation, stress, strain and temperature distribution during the joining operation using a fully coupled thermo-mechanical FE model. The aluminum alloy metal being rubbed was simulated using a phenomenological Johnson-Cook viscoplasticity material model, which suited for materials subjected to large strains, high strain rates and high temperatures. The highest stress, strain and deformation are found to be within the heat affected zone of the weld close to the periphery rubbing surface region and correspond to the highest temperature profiles observed.

반도체 공정 overview

Abstract: With digital equipment becoming increasingly networked, either on wired or wireless networks, for personal and professional use alike, distributed software systems have become a crucial element in information and communications technologies. The study of these systems forms the core of the ARLES' work, which is specifically concerned with defining new system software architectures, based on the use of emerging networking technologies. In this context, we concentrate on the study of distributed systems which bring to life the vision of ubiquitous computing systems, also known as ambient intelligence.

A review of numerical analysis of friction stir welding

Abstract: Friction stir welding is a relatively new solid-state joining technique which is widely adopted in different industry fields to join different metallic alloys that are hard to weld by conventional fusion welding. Friction stir welding is a highly complex process comprising several highly coupled physical phenomena. The complex geometry of some kinds of joints and their three dimensional nature make it difficult to develop an overall system of governing equations for theoretical analyzing the behavior of the friction stir welded joints. The experiments are often time consuming and costly. To overcome these problems, numerical analysis has frequently been used since the 2000s. This paper reviews the latest developments in the numerical analysis of friction stir welding processes, microstructures of friction stir welded joints and the properties of friction stir welded structures. Some important numerical issues such as materials flow modeling, meshing procedure and failure criteria are discussed. Numerical analysis of friction stir welding will allow many different welding processes to be simulated in order to understand the effects of changes in different system parameters before physical testing, which would be time-consuming or prohibitively expensive in practice. The main methods used in numerical analysis of friction stir welding are discussed and illustrated with brief case studies. In addition, several important key problems and issues remain to be addressed about the numerical analysis of friction stir welding and opportunities for further research are identified.

Friction stir welding: Process, automation, and control

Abstract: This article provides an introduction to the basic principles of friction stir welding (FSW) as well as a survey of the latest research and applications in the field. The basic principles covered include terminology, material flow, joint configurations, tool design, materials, and defects. Material flow is discussed from both an experimental and a modeling perspective. Process variants are discussed as well, which include self-reacting (SR-FSW), stationary shoulder, friction stir processing (FSP), friction stir spot welding (FSSW), assisted FSW, and pulsed FSW. Multiple aspects of robotic friction stir welding are covered, including sensing, control, and joint tracking. Methods of evaluating weld quality are surveyed as well. The latest applications are discussed, with an emphasis on recent advances in aerospace, automotive, and ship building. Finally, the direction of future research and potential applications are examined.

Friction stir welding/processing of metals and alloys: A comprehensive review on microstructural evolution

Abstract: The unique combination of very large strains, high temperatures and high strain rates inherent to friction stir welding (FSW) and friction stir processing (FSP) and their dependency on the processing parameters provides an opportunity to tailor the microstructure, and hence the performance of welds and surfaces to an extent not possible with fusion processes. While a great deal of attention has previously been focused on the FSW parameters and their effect on weld quality and joint performance, here the focus is on developing a comprehensive understanding of the fundamentals of the microstructural evolution during FSW/P. Through a consideration of the mechanisms underlying the development of grain structures and textures, phases, phase transformations and precipitation, microstructural control across a very wide range of similar and dissimilar material joints is examined. In particular, when considering the joining of dissimilar metals and alloys, special attention is focused on the control and dispersion of deleterious intermetallic compounds. Similarly, we consider how FSP can be used to locally refine the microstructure as well as provide an opportunity to form metal matrix composites (MMCs) for near surface reinforcement. Finally, the current gaps in our knowledge are considered in the context of the future outlook for FSW/P.