Journal of the Korean Society for Precision Engineering

Performance Study of Dielectric Elastomer Actuators with Varying Thickness of Carbon Nanotube Electrodes and Pre-stretch Ratios: Mingyu Kang, Joong-Hyun Park, Jong-An Choi, Jingu Jeong, Soonjae Pyo; J. Korean Soc. Precis. Eng. 2025;42(10):817-823.
Published online October 1, 2025; DOI: https://doi.org/10.7736/JKSPE.D.25.00004

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This study examines how two key design parameters—the pre-stretch ratio and the thickness of the carbon nanotube (CNT) electrode—affect the actuation performance of dielectric elastomer actuators (DEAs). DEA samples are created with varying pre-stretch levels (50% and 125%) and different amounts of CNT spray coating (4 and 8 mg), and their threshold voltages and areal strains are quantitatively assessed. The experimental results indicate that higher pre-stretch ratios result in lower threshold voltages and greater areal deformations, while increased CNT thickness typically reduces actuator deformation due to enhanced mechanical stiffness. The combination of a high pre-stretch ratio and low CNT loading demonstrates improved electro-mechanical responsiveness at moderate voltages. These findings underscore the interconnected effects of structural and electrode design on DEA performance, offering practical design guidelines for optimizing soft actuator systems. This research lays a solid foundation for future applications of DEAs in haptic interfaces, wearable actuators, and soft robotics.

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Study on Repair of SKD 61 Using Directed Energy Deposition with H13 and P21 Powders: Bit-na Yun, Min-seong Ko, Hyo-jeong Kang, Do-Sik Shim; J. Korean Soc. Precis. Eng. 2024;41(11):849-856.
Published online November 1, 2024; DOI: https://doi.org/10.7736/JKSPE.024.073

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In this study, we investigated characteristics and mechanical properties of SKD61 repaired using the direct energy deposition (DED) process. Mechanical properties of the repaired product can vary depending on the base material and powder used in the DED process. To prepare for DED repairing for a damaged part, we conducted experiments using two different powders (H13 and P21). Experimental results showed that both powders were deposited without defects in the surface or interface between the deposited zone and the substrate. Hardness measurements indicated that the repaired region of the Repaired-H13 sample exhibited higher hardness than the base material, while the Repaired-P21 sample showed a sharp increase in hardness in the heat-affected zone (HAZ). Additionally, tensile test results revealed that the Repaired-H13 sample had lower tensile strength and elongation than the base material, whereas the Repaired-P21 sample demonstrated higher tensile strength and yield strength with a higher elongation than the Repaired-H13 sample. In case of Repaired-H13, it was confirmed that interfacial crack occurred due to a high hardness difference between the repaired part and the substrate.

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Microstructure and mechanical properties of P21 tool steel fabricated via laser powder bed fusion
A. Rajesh Kannan, V. Rajkumar, S. Maheshwaran, N. Siva Shanmugam, Wonjoo Lee, Jonghun Yoon
Materials Letters.2025; 398: 138930. CrossRef

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A Numerical Investigation of Deformed Region in Plate Specimen of Split-Hopkinson Tensile Bar: Byeongjin Park, Yeon-Bok Kim, Jeong Kim; J. Korean Soc. Precis. Eng. 2024;41(8):607-615.
Published online August 1, 2024; DOI: https://doi.org/10.7736/JKSPE.024.025

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In Hopkinson bar theory, stress, strain, and strain rate can be determined by analyzing the dimensions of the specimen. When conducting Split-Hopkinson Pressure Bar (SHPB) experiments, the stress-strain curve is obtained by considering the entire length and width of the specimen. However, in Split-Hopkinson Tensile Bar (SHTB) experiments, it is important to only consider the regions where deformation occurs in order to accurately determine the dynamic material properties. This study introduces a method for selecting the dimensions of the deformed region (LD and WD) in plate specimens for SHTB experiments using Finite Element Analysis (FEA). The analysis involved varying the length and width of a 1 mm thick SUS430 specimen, and the deformed region was determined using the proposed method. The stress-strain curves obtained from this region were then compared with the input Cowper-Symonds model. The validity of the proposed approach was confirmed, as the percentage error between them ranged from 2.54 to 6.62%.

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Study on Mechanical Properties of MWCNT Reinforced Photocurable Urethane Acrylate for Additive Manufacturing: Hyunjun Jo, Bum-Joo Lee; J. Korean Soc. Precis. Eng. 2024;41(3):199-206.
Published online March 1, 2024; DOI: https://doi.org/10.7736/JKSPE.023.133

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During its early development stages, 3D printing was primarily used for rapid prototyping, whereas it is currently employed to fabricate products in various fields, including aerospace, automobile production, dentistry, architecture, and food. The photopolymerization of the polymer used for 3D printing is precise and provides excellent surface roughness but has lower mechanical strength than traditional manufacturing methods. In this study, Multi-walled Carbon Nanotubes (MWCNTs) were blended with urethane acrylate-based resin as a filler. Mechanical strength enhancement was confirmed using a DLP 3D printer. The stabilities of MWCNT dispersions in resin were verified, and viscosity and curing depth measurements were conducted to establish 3D printing parameters. Tensile and flexural strengths were higher for an MWCNT length of 50 μm than one of 100 μm, and maximum values were obtained at an MWCNT content of 0.1 phr. Under optimal conditions, tensile and flexural strengths increased by 2.1 and 1.8-fold, respectively.

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Effect of Cross Section of Glass Fiber and Injection Conditions on the Tensile Strength in GFRP Injection Molding: Il Yong Han, Sung Hyun Park, Min Soo Cheong, Tae Kyun Kim, Dong Sam Park; J. Korean Soc. Precis. Eng. 2022;39(12):947-954.
Published online December 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.109

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SFT, which has a high glass fiber content, is one of the effective methods to replace metal and secure weight reduction and price competitiveness. This study evaluated the effect of glass fiber shape on mechanical properties in injection molding by fabricating SFT with a glass fiber content of 60%. Three types of SFTs were manufactured by adding round glass fibers of Φ7 μm and Φ10 μm and flat glass fibers of 27 × 10 μm. DOE (Design of Experiment) conducts to confirm the change in tensile strength due to changes in significant injection conditions. As a result of the experiment, Φ7 μm SFT and flat SFT have similar tensile strength and Φ10 μm SFT showed the lowest tensile strength value. As for the standard deviation of strength value, the Φ7 μm SFT had the largest standard deviation, and the Φ10 μm SFT showed the slightest change in the injection conditions. In flat SFT, it confirms that the tensile strength increased as the molding temperature increased. The fracture surface observes using SEM. It founds that the tensile strength lowers due to the small glass fiber density and many pullouts at the fracture surface of Φ10 μm with weak strength.

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Enhancing Adhesive Strength between Metal and Plastic in Smartphone Applications
Moon-Soo Kim, Jin-Hyung Park, kang-Suk Choi, Seon-Mi Park, Seong-Dae Choi
Journal of the Korean Society of Manufacturing Process Engineers.2025; 24(9): 82. CrossRef

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Practical Blended Flow Models for Bulk Metal Forming Using the Cylindrical Tensile Test with Its Related Flow Behavior at Large Strain: Chang Woon Jee, Su Min Ji, Jong Bok Byun, Man Soo Joun; J. Korean Soc. Precis. Eng. 2022;39(8):583-593.
Published online August 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.037

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The fundamental flow models of metallic materials at room temperature, including the Ludwik, Hollomon, Swift and Voce models, were evaluated in terms of tensile test with an emphasis on the necking phenomena and post-necking behavior, to emphasize their limitation in satisfying tensile strength and Considère condition as well as the pre-necking and post-necking strain hardening. To resolve this limitation and enhance the applicability of the new proposed flow model to typical strain hardening materials, the Ludwik-Swift blended flow model is proposed after investigation into three blended flow models among the Ludwik, Voce and Swift models. Results revealed that there is no interpolation-based blended flow model of the fundamental flow models for the example flow curve exhibiting typical strain hardening but that the extrapolation-based combination of them can provide an engineering solution when the Ludwik and Swift models are blended. It was revealed that the reason for their good matching lies in the distinct difference in the strain hardening exponent, between the Ludwik and Swift models in the case of metallic materials with typical strain hardening.

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Novel finite element model of analyzing wall thickness during tube drawing considering raw tube’s thickness non-uniformity and die misalignment
N. A. Razali, J. B. Byun, M. S. Joun
International Journal of Material Forming.2024;[Epub] CrossRef

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A Study on the Strength Characteristic of Compact Tension Specimen due to Internal Holes and Material: Jung-Ho Lee, Sung-Ki Lyu, Jae-Ung Cho; J. Korean Soc. Precis. Eng. 2019;36(7):623-629.
Published online July 1, 2019; DOI: https://doi.org/10.7736/KSPE.2019.36.7.623

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Majority of deformation and ruptures as a result of severe deformation of mechanical structures are due to the existence of cracks or cracks generated through specific situations. These cracks causes stress concentration and eventually ruptures under lower load conditions than they are designed to withstand. In this study, simulation tensile analysis was done by designing compact tension specimen models with the number of holes that existed inside and the materials of the test specimens by focusing on the effects of the cracks. The study results from all the analysis (deformations, equivalent stress and strain energy) confirmed that the specimen models having two holes had better strength characteristics than those with only one hole. Additionally, the durability and strength characteristics of specific mechanical structures against the load improved through appropriate arrangement of holes thereby reducing stress generation. As such the results of this study could be utilized as the basic data for future researches on composite materials and sandwich type homogenous materials. Furthermore, the study results can assist in designing more durable products.

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A Study on the Impact Test Analysis of Specimens for Designing the Housing of Precision Guided Projectile: Jun bok Ko, So dam Yi, Eun joo Park, Ki bong Baek, Myeong seop Kim, Suhk hoon Suh; J. Korean Soc. Precis. Eng. 2019;36(6):575-582.
Published online June 1, 2019; DOI: https://doi.org/10.7736/KSPE.2019.36.6.575

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The precision-guided projectile is a weapon system for precision attacks, and the cannon-launched projectile is guided by a control device. The electrical actuator system is a subsystem of the control device, and the whole projectile undergoes high axial and lateral impact force for 1 to 10mseconds. In this study, a charpy, and a tensile impact analysis were conducted, using specimens made in the materials of SUS630 and Al7075-T6 to understand fracture mechanics and impact property, such as energy change rate. The impact analysis and gas-gun impact test were conducted, to validate the optimized housing model.

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Evaluation of Structural Stability of Small Wind Turbine Blade by Blade Test and Structural Analysis and Improvement of Blade Design: Youn Gi Choi, Shin You Kang, Jong Il Kim; J. Korean Soc. Precis. Eng. 2018;35(9):893-899.
Published online September 1, 2018; DOI: https://doi.org/10.7736/KSPE.2018.35.9.893

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This paper examines the stability of the blades that convert the wind kinetic energy into the mechanical energy among the small wind power-generation systems, and proposes the design improvement for blades with a higher rigidity and a lighter weight than the conventional blades. The composite-specimen tensile test and static-load test are conducted to verify the reliability. To design the lightweight blade with the high stiffness, the displacement and the safety factor of the blade composed of the composite material are calculated from the structural-analysis results, and the optimal dimensional and material designs are performed. The optimal design parameters are selected by the shear-web lamination angle and the lamination thickness. The objective function is selected by the safety factor and the weight. For the optimum material design, the GFRP is converted into the CFRP. In this paper, the structural improvement is performed by optimizing the dimensional and material designs, the blade stiffness and weight are redesigned and compared with those of the designed blades, and the structural stability of the redesigned blades is also examined.

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The Suitability of Substructures of the Offshore Wind Power Complex
Dae Kyung Kim, Dong Soon Kang, Jong Hak Lim, Young Il Byun, Chul Ki Song
Journal of the Korean Society for Precision Engineering.2022; 39(4): 299. CrossRef
Evaluation of Structural Integrity for Lifting-and-Lowering-Type Drone Station Using Fluid-Structure Interaction Analysis
Sang Ho Kim, Jae Youl Lee, Sung-Ho Hong, Jehun Hahm, Kap-Ho Seo, Jin-Ho Suh, Young Sik Joung, Se Hoon Jeung
Journal of the Korean Society for Precision Engineering.2021; 38(11): 841. CrossRef

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FE Analysis of Self-Piercing Rivet (SPR) Process and Tensile Behaviours: Chan Hee Jeong, Dae Yeong Kim, Hyun Seok Oh, Seong Sik Cheon; J. Korean Soc. Precis. Eng. 2018;35(9):875-880.
Published online September 1, 2018; DOI: https://doi.org/10.7736/KSPE.2018.35.9.875

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In this paper, we focus on the numerical modeling of the reliability of the self-piercing rivet process. Tensile tests were conducted on SPR joining Al (ECO Al7021-T7) specimens. In addition, a 2D axisymmetric FE model was generated to characterise the SPR joining process on the extruded Al sheets. The simulations were carried out using the LS-DYNA, one of the representative explicit finite element codes. A tensile simulation of the riveted two Al plates was performed to investigate the tensile behaviour of self-piercing rivet parts. An FE analysis results showed comparatively good agreement with experiments.

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Strength Prediction by Simulating the Cross-Tension Test for Triple Riveted Joints of Aluminum Dissimilar Materials Using 9 mm Self-Piercing Rivet
Seung-Min Yuna, Hyeong-seok Jang, Dae-guk Lee, Hee-soo Park, Sang-Yeol Kim
Journal of the Korean Society of Manufacturing Technology Engineers.2024; 33(1): 11. CrossRef
Validation of the Joinability of 9 mm SPR for Automotive Dissimilar Material Three-Joint Configurations Using Joining Parameters
Hyeongseok Jang, Seungmin Yun, Heesoo Park, Daeguk Lee, Sangyeol Kim
Transaction of the Korean Society of Automotive Engineers.2024; 32(4): 387. CrossRef
Comparative Study on J-Integrals of SM45C, Short Fiber GFRP and Woven Type CFRP Shown at Crack through Analytical Method
Jae Woong Park, Sung Ki Lyu, Jae Ung Cho
Journal of the Korean Society for Precision Engineering.2019; 36(6): 567. CrossRef

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The Effects of Grid Shape on Flexibility and Durability of Flexible Transparent Metal Grid Films: Oh Young Kwon, Yo Sep Lee, Won Jae Lee, Young Moon Jang, Sung-Hoon Choa; J. Korean Soc. Precis. Eng. 2018;35(5):551-559.
Published online May 1, 2018; DOI: https://doi.org/10.7736/KSPE.2018.35.5.551

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Recently, the metal grid electrode drew attention as a flexible transparent conductive electrode for touch screen panels. In metal grid electrodes, various shapes of grid patterns were used to avoid the moiré phenomenon. In this study, we investigated the effects of the metal grid shapes - such as the honeycomb, diamond, and square - on the flexibility and durability of the metal grid film using an experimental and numerical analysis. The flexibility of the metal grid film was evaluated via the following: bending, cyclic bending fatigue and stretching tests; it was compared with the numerical stress analysis. In the bending test, the resistance of the honeycomb grid sample increased by 10% at a bending radius of 10 mm. On the other hand, the diamond grid showed almost no change in resistance up to a bending radius of 6 mm. When the substrate was stretched to 5%, many cracks appeared on the surface of the honeycomb pattern sample. On the other hand, no cracks were found in the diamond pattern sample. Therefore, the diamond pattern exhibited superior flexibility and durability to the honeycomb pattern. The numerical stress analysis also showed that the honeycomb pattern had the highest stress and the diamond pattern had the lowest stress during bending and stretching, which corresponded with the experimental results.

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Experimental Investigation on Fatigue Characteristics of SPR (Self-Piercing Rivet) and Hybrid Joints: Dae Yeong Kim, Dong Ok Kim, Seong S. Cheon; J. Korean Soc. Precis. Eng. 2018;35(3):335-340.
Published online March 1, 2018; DOI: https://doi.org/10.7736/KSPE.2018.35.3.335

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In this paper, fatigue life of extruded aluminium single lap joints, both by self-piercing rivet (SPR) and by hybrid joining (Adhesive-SPR), were characterised based on the quasi-static and fatigue tests. The rivet tail pull-out fracture occurred in the SPR joint specimen under the quasi-static tensile test because the peel stress caused the rivet to separate from the joint. Therefore, adhesive joining was considered to effectively prevent the rivet in the joint specimen from separation. As a result, 68% higher tensile strength of the hybrid joint specimen was observed, compared to that of the SPR joint specimen. From the fatigue tests, the fatigue limit load of SPR joint specimen was found to be 4.8 kN i.e.35% of tensile strength load. The fatigue limit load of the hybrid joint specimen was revealed to be 5.6 kN, i.e., 20% of tensile strength load. Over the fatigue limit load conditions, fracture in base material was shown in the case of SPR joint specimen. Also, fractures in base material and transient failure in adhesives were observed in hybrid joint specimen.

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A Study on the Improvement of Bonding Strength of Heterojunctions by Applying Laser Surface Treatment to Carbon Fiber Reinforced Plastics
Huan Wang, Seong Cheol Woo, Chung-Ki Sim, Seong-Kyun Cheong, Joohan Kim
Journal of the Korean Society for Precision Engineering.2022; 39(9): 683. CrossRef
Optimal Stiffness Design of Self-Piercing Riveting's C-Frame for Multimaterial Joining
Chang-Yeul Shin, Jae-Jin Lee, Ji-Hun Mun, Soon-Deok Kwon, Min-Seok Yang, Jae-Wook Lee
Journal of the Korean Society of Manufacturing Process Engineers.2021; 20(5): 76. CrossRef
Investigating the Tensile-Shear of Dissimilar Materials Joined Using the Hybrid SPR Technique
Kwan-jong Yu, Du-bok Choi, Jae-yeol Kim
Journal of the Korean Society of Manufacturing Process Engineers.2020; 19(9): 33. CrossRef
Study on the 3-layer Joining of Aluminum Alloy and Steel Plate Using Self-piercing Riveting
You-Sung Kang, Ji-Hyoung Park, Yongho Jeon, Minsung Hong
Journal of the Korean Society of Manufacturing Technology Engineers.2018; 27(4): 307. CrossRef