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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    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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    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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    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.
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    Wear resistance of an ultrafine-grained Cu-Zr alloy processed by equal-channel angular pressing
    (2015-03-05)
    Li, Jianwei
    ;
    Wongsa-Ngam, Jittraporn
    ;
    Xu, Jie
    ;
    Shan, Debin
    ;
    Guo, Bin
    A Cu-0.1 wt.% Zr alloy was processed by equal-channel angular pressing (ECAP) through 8 passes at room temperature to produce an ultrafine grain size of ~350 nm with an average Vickers microindentation hardness (200 gf) of ~140. Ball-on-disc dry sliding tests were conducted on an annealed material and on the ECAP-processed alloy using applied normal loads from 1 to 15. N. The coefficient of friction (COF), surface topography and wear volume loss were examined to evaluate the micro-wear resistance. The results show that samples processed by ECAP have lower average values for the COF than the unprocessed alloy and there is also a decrease in the wear depth and wear volume loss with increasing numbers of ECAP passes. The ultrafine-grained alloy processed by ECAP has a higher wear resistance than the annealed and unprocessed material due to the significant grain refinement and improved mechanical properties.
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    The effect of microstructure heterogeneity on the microscale deformation of ultrafine-grained aluminum
    (2014-01-01)
    Kammers, Adam D.
    ;
    Wongsa-Ngam, Jittraporn
    ;
    Langdon, Terence G.
    ;
    Daly, Samantha
    A combined approach of scanning electron microscopy and digital image correlation was used to examine microstructure-scale strain localization and active deformation mechanisms in ultrafine-grained (UFG) high purity (99.99%) aluminum processed by equal-channel angular pressing (ECAP). The results from tensile tests demonstrate a strong relationship between the heterogeneous microstructure and strain localization. The localized deformation was investigated in areas that contain significantly different microstructural features typical of ECAP processed aluminum. It was found that areas of the UFG microstructure containing primarily low angle grain boundaries deformed by dislocation slip and behaved similarly to a coarse-grained material. The greatest strain localization occurred at high angle grain boundaries (HAGBs) separating distinct microstructure regions and with median surface trace angles of approximately 26.6°. In areas of banded microstructure, shear strain localization as high as 30% and shear displacements of up to 500 nm occurred at the HAGBs separating bands, suggesting grain boundary sliding. Copyright © 2014 Materials Research Society.
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    Effects on hardness and microstructure of AISI 1020 low-carbon steel processed by high-pressure torsion
    (2017-10-01)
    Marulanda Cardona, Diana Maritza
    ;
    Wongsa-Ngam, Jittraporn
    ;
    Jimenez, Hernando
    ;
    Langdon, Terence G.
    Low-carbon steel AISI 1020 was subjected to high-pressure torsion (HPT) with 6.0 GPa pressure through 1/4–5 turns. The microstructures of the samples in each turn were studied by means of X-ray diffraction (XRD) analyzing the changes in micro-strain, crystallite size and lattice parameter. Vickers testing was utilized to study the microhardness behavior of the samples subjected to HPT processing. The morphology evolution of the samples and especially the changes in ferrite and pearlite structures were studied for different numbers of turns using scanning electron microscopy (SEM).