Wongsangam, Jittraporn

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Wongsangam, Jittraporn
Alternative Name
Wongsa-Ngam, Jittraporn
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Email
jittraporn.wo@kmitl.ac.th

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Now showing 1 - 10 of 17
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    Microstructural evolution and microhardness in a low carbon steel processed by high-pressure torsion
    (2014-10-01)
    Marulanda Cardona, Diana Maritza
    ;
    Wongsa-Ngam, Jittraporn
    ;
    Langdon, Terence G.
    A low-carbon triple-alloyed steel was processed by high-pressure torsion at room temperature for up to 5 turns under a pressure of 6.0 GPa. Microhardness, scanning electron microscopy and X-ray diffraction were used to investigate the hardness and microstructural evolution of the steel. Values of the Vickers microhardness were recorded across the sample diameters. The results show that there is a gradual evolution in both the hardness and the microstructure with increasing numbers of turns. However, the microhardness does not become fully homogeneous across the sample diameter after five turns and there remain significantly lower values in the center of the disk. These results indicate that complete homogeneity across the disks for this steel requires applied pressures higher than 6.0 GPa and/or torsional straining through more than 5 turns.
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    Advances in Superplasticity from a Laboratory Curiosity to the Development of a Superplastic Forming Industry
    (2022-11-01)
    Wongsa-Ngam, Jittraporn
    ;
    Langdon, Terence G.
    Superplasticity refers to the ability of some materials to pull out to tensile elongations of 400% or more when the strain rate sensitivity is ~0.5. The first report of true superplastic flow was published in 1934 in experiments conducted in England. However, this remarkable result attracted little interest among western scientific researchers and the result remained a laboratory curiosity for many years. Later, following extensive research on superplasticity in the Soviet Union, interest developed in the west, and superplasticity became a topic of extensive scientific research. This research was further enhanced with the demonstration that the application of severe plastic deformation provided an opportunity for achieving grain refinement to the submicrometer or even the nanometer level, and these small grains were especially attractive for achieving good superplastic properties. It is now recognized that superplastic alloys provide an excellent forming capability, especially in making high quality curved parts that are not easily fabricated using more conventional processes. This has led to the development of a large superplastic forming industry that currently processes many thousands of tons of sheet metals. This report traces these developments with an emphasis on the scientific principles behind the occurrence of superplastic flow.
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    Enhancing ductility of sintered Fe-Ni-Mo-Mn-Si-C alloy by Co addition
    (2024-05-17)
    Putsaccada, Viseth
    ;
    Wongsa-Ngam, Jittraporn
    ;
    Ohtake, Naoto
    ;
    Morakotjinda, Monnapas
    ;
    Krataithong, Rungtip
    This research aims to investigate the effect of cobalt (Co) on accelerating the bainitic transformation in sintered Fe-Ni-Mo-Mn-Si-C alloys. Experimental sintered specimens were prepared from the mixtures of pre-alloyed Fe-4.00Ni-0.50Mo-0.2Mn powder with a fixed 4.00 wt% silicon carbide and varied Co contents (0.50 to 3.00 wt%) using a traditional press and sinter process. Sintering was conducted in a vacuum furnace at 1250 °C for 45 minutes and under slow cooling in the sintering furnace. It was found that Co strongly influenced the kinetics of bainite transformation in sintered Fe-Ni-Mo-Si-C-(Co) alloys. Tensile strength and hardness of sintered alloys increased with Co content. High elongation values were obtained in sintered specimens with high Co contents. The increases of tensile strength and ductility with Co content were attributed to accelerated bainitic ferrite formation and retained austenite stability, respectively.
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    Effect of bearing materials on journal bearings under TEHL with lubricant based on Carreau model
    (2020-02-17)
    Gunnuang, Waleephan
    ;
    Aiumbhornsin, Chatchai
    ;
    Wongsa-Ngam, Jittraporn
    ;
    Mongkolwongrojn, Mongkol
    This work presents a transient analysis of journal bearings under thermal elastohydrodynamic lubrication (TEHL) based on the Carreau model. The effects of the elastic modulus of the bearing liner have been investigated using numerical simulations. A time-dependent modified Reynolds equation and an adiabatic energy equation based on the Carreau model have been formulated and numerically solved to examine the performance of the journal bearings. The results show that the minimum film thickness and the friction coefficient both increase with decreasing bearing liner elastic modulus. In contrast, the dimensionless load carrying capacity, dimensionless maximum film temperature, and dimensionless maximum film pressure all decrease with decreasing bearing liner elastic modulus. The stability regions tend to decrease in size for journal bearings under TEHL, especially for journal bearings composed of soft materials.
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    An examination of the saturation microstructures achieved in ultrafine-grained metals processed by high-pressure torsion
    (2014-10-01)
    Sabbaghianrad, Shima
    ;
    Wongsa-Ngam, Jittraporn
    ;
    Kawasaki, Megumi
    ;
    Langdon, Terence G.
    Experiments were conducted on two commercial alloys, a Cu-0.1%Zr alloy and an Al-7075 aluminum alloy, to investigate the significance of the saturation microstructure which is achieved after processing by high-pressure torsion (HPT). Samples were processed by HPT and also by a combination of equal-channel angular pressing (ECAP) followed by HPT. The results show that the saturation conditions are dependent upon the grain size in the material immediately prior to the HPT processing. Additional grain refinement may be achieved in HPT by initially processing the material to produce an ultrafine-grain size before conducting the processing by HPT.
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    The influence of HPT on microstructure and wear resistance of Al-7wt%Si-2wt%Fe Alloy
    (2021-01-01)
    Wongsa-Ngam, Jittraporn
    ;
    Xu, Jie
    ;
    Phongphisutthinan, Chakkrist
    ;
    Langdon, Terence G.
    An aluminum silicon-based alloy (Al-7wt%Si-2wt%Fe) was subjected to severe plastic deformation by the high-pressure torsion (HPT) method. This HPT processing was conducted at room temperature up to five revolutions under a pressure of 6.0 GPa and rotation speed of 1.0 rpm. Observations of microstructure evolution, especially intermetallic phases, was carried out by an optical microscope (OM) and a scanning electron microscope (SEM). It was found that the ironintermetallic particles decreased in size with numbers of turns. This is due to the large strain introduced during HPT processing which produced a degree of fragmentation of intermetallic phases which increased with the imposed strain. In addition, wear behaviors of the as-cast and samples deformed by HPT were also investigated using micro-tribometer UMT-2 (CETR Co., USA) following the ASTM G99-05 (2010) standard. The friction coefficient and wear volume loss were measured to evaluate the effect of imposed strain during HPT processing on wear resistance. It was found that the values of the average friction coefficient were slightly lower in deformed samples and the wear volume loss decreased with increasing numbers of turns.
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    Assessing the Structural Performance of Bolted Rail Joints Employing Various Fishplate Models via Finite Element Analysis
    (2026-01-01)
    Le, Sai Kham
    ;
    Wongsa-Ngam, Jittraporn
    In railway tracks, fishplates are attached to each side of two rail ends and secured with four bolts, providing what is known as a bolted rail joint (BRJ). This rail joint is involved in complex interactions between multiple components under wheel loads, leading to stress and deformation of each component, potentially resulting in failures of the railway track. In this study, the different roles of selected fishplate models in the structural performance of a BRJ under static load are investigated using finite element analysis with ABAQUS CAE. Three fishplate models are examined: a thin cross-section, a thick cross-section, and a modified design. The first two models are currently used in rail transportation, while the novel modified version is designed to enhance the structural performance of BRJs. Preliminary results indicate that using the modified fishplate significantly reduces stress on the upper rail fillet and fishplate. Additionally, vertical displacement in both the rail and fishplate is diminished. These improvements are expected to increase the service life and reliability of BRJs, thereby contributing to safer and more cost-effective railway operations.
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    A study of die parameters influencing the plastic deformation for 3D finite element simulations of equal-channel angular pressing
    (2025-08-01)
    Wongsa-Ngam, Jittraporn
    ;
    Noraphaipaksa, Nitikorn
    ;
    Kanchanomi, Chaosuan
    ;
    Langdon, Terence G.
    Equal-channel angular pressing is an effective method of severe plastic deformation that is employed to produce materials with ultrafine grain structures. This study aimed to systematically investigate the influence of the die parameters, specifically the channel angle and the outer curvature angle, on the induced plastic strain, strain inhomogeneity and the reaction force during processing of a round section copper-zirconium alloy workpiece. Three-dimensional finite element simulations were developed using ABAQUS/ Explicit to model single-pass deformation with varying channel angles of 90°, 110°, 120° and 150° and outer curvature angles of 20°, 30° and 60°. The results demonstrate that the channel angle is the dominant factor controlling the average equivalent plastic strain, which decreased from approximately 1.04 at 90° channel angle with 20° outer curvature angle to about 0.31 at 150° channel angle regardless of the outer curvature. In contrast, the outer curvature angle significantly influences the strain homogeneity at low channel angles, with the coefficient of variance increasing from 0.06 to 0.22 when the outer curvature angle increases from 20° to 60° at a 90° channel angle. Additionally, the maximum reaction force declined markedly with an increasing channel angle, dropping from 58 kN at 90° to 12 kN at 150°, thereby highlighting a strong interplay between imposed strain and forming load. These findings provide clear guidelines for optimizing the die design to balance high strain, uniform deformation and manageable pressing forces in the industrial processing of ultrafine-grained materials.
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    Microstructural Evolution and Properties of a Hot Extruded and HPT-Processed Resorbable Magnesium WE43 Alloy
    (2017-03-01)
    Liu, Dexue X.
    ;
    Pang, Xin
    ;
    Li, Denglu L.
    ;
    Guo, Chenggong G.
    ;
    Wongsa-Ngam, Jittraporn
    Disks of an extruded magnesium WE43 alloy are processed by high-pressure torsion (HPT) and the evolutions of microstructure and mechanical properties are investigated in detail. Excellent grain refinement is achieved by HPT processing with a reduction in grain size from an initial value of ≈12 μm to a final value of ≈200–300 nm after 10 turns. The microhardness increases significantly with HPT processing but low hardness values are recorded at the centers of the disks. The tensile strength initially increases and then decreases while the elongation decreases. Observations of the fracture surfaces reveal a corresponding transition of the fracture mode from ductile to brittle.
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    Numerical investigation of plastic strain homogeneity during equal-channel angular pressing of a Cu-Zr Alloy
    (2021-12-01)
    Wongsa-Ngam, Jittraporn
    ;
    Noraphaiphipaksa, Nitikorn
    ;
    Kanchanomai, Chaosuan
    ;
    Langdon, Terence G.
    A three-dimensional finite element method (3D FEM) simulation was carried out using ABAQUS/Explicit software to simulate multi-pass processing by equal-channel angular pressing (ECAP) of a circular cross-sectional workpiece of a Cu-Zr alloy. The effective plastic strain distri-bution, the strain homogeneity and the occurrence of a steady-state zone in the workpiece were investigated during ECAP processing for up to eight passes. The simulation results show that a strain inhomogeneity was developed in ECAP after one pass due to the formation of a corner gap in the outer corner of the die. The calculations show that the average effective plastic strain and the degree of homogeneity both increase with the number of ECAP passes. Based on the coefficient of variance, a steady-state zone was identified in the middle section of the ECAP workpiece, and this was numerically evaluated as extending over a length of approximately 40 mm along the longitudinal axis for the Cu-Zr alloy.