Defining an appropriate flight vibration specification is a critical issue at an initial design phase, for optimized design of components in a surface-to-air missile (SAM). As the related document (MIL-STD-810G) doesn’t provide detailed value, appropriate procedures for estimation of flight vibration specification are required for design of a surface-to-air missile. In this study, the method-making appropriate specification without an actual flight test is introduced. Comparison between a theoretical approach using the beam theory and FEA is conducted to attain a natural vibration frequency under thrust force. Transient response analysis using commercial S/W is conducted to establish an envelope curve for flight vibration.
Beyond conventional military products, technologies in the defense industry sectors around the globe are integrated and fused with newly emerging technologies such as three-dimensional printing (3DP) and smart material fabrication. Acknowledging these trends, this study proposes a miniature high-speed actuator whose fabrication process entails 3DP, smart materials, and shape memory alloy. The manufactured actuator is 25 mm long and 5 mm wide in and weighs 2.5 g, having the optimal frequency in the range of 35-40 Hz. Force and deformation measurement were also conducted, resulting in the lift force of 0.18 N per second with a bending deformation of 5 mm.
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Bidirectional rotational antagonistic shape memory alloy actuators for high-frequency artificial muscles Rawan Barakat, Susanne-Marie Kirsch, Felix Welsch, Paul Motzki Scientific Reports.2025;[Epub] CrossRef
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In this paper, a study on the effectiveness of micro-peening was accomplished for improvement of fatigue characteristics for reduction gear of manned and unmanned aircraft. The Almen saturation curve was obtained by various peening injection pressure supplied from a commercial air jet peening machine. The effective micro-peening process condition was adopted as five bar. The four points rotary bending fatigue test was conducted by using test specimen made of AISI alloy that was carburized based on AMS standard in this work. From the fatigue test result, the fracture life of specimen peened by nozzle pressure with five bar and six bar was higher than the un-peened specimen by approximately 323 percent and 146 percent respectively. However, the fracture life of specimen peened by the nozzle pressure with six bar was lower by approximately 221 percent than the peened specimen by five bar. For this reason, the peening nozzle pressure with five bar was decided as the optimum micro-peening condition. Effectiveness of micro-peening was validated and this micropeening technique will be used for real manned and unmanned aircraft gear parts or other durability mechanical parts.
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In this study, we analyzed wind torque from aerostatic force coefficients of radar structures according to the Reynolds number. The test was conducted in the KOCED Wind Tunnel Center at Chonbuk University, and the wind tunnel test model was at 1:8 scale. Wind speeds were in the range of 5-26 m/s to determine Reynolds number independence. Test results of the present radar system were not impacted by the Reynolds number. Maximum drag coefficient was 1.43 under an angle of attack of 0 degrees and angle of the vehicle was 135 degrees, while maximum positive pressure coefficient was 1.21 at the side of plane in angle of attack of 0 degrees. Maximum negative pressure coefficient was -2.06 at the corner front of the plane at an angle of attack of 90 degrees. To verify wind torque in the wind tunnel test, a drive system was designed and manufactured. A wind speed of 26 m/s, the maximum average operating wind speed condition, was applied to validate the radar was driven normally. Results of this study may be used as an evaluation method for wind speed tests of radar systems and large structures that cannot be used for wind tunnel tests.
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Recently, with the development of the IT industry, technology for satellite communication network systems using multichannel, high-capacity data is getting increasingly popular. Especially in the field of defense, experts emphasize the necessity for research and development (R&D) to improve communication quality in order to facilitate Network-Centric Warfare (NCW) and increase mission efficiency through the use of satellite communication network systems. High power is required for the implementation of this technology, and its quality is greatly affected by Passive InterModulation Distortion (PIMD). In order to improve PIMD levels, the leakage characteristics of the system were analyzed with knowledge of the strong influence of the state of the flange joint that has been confirmed by years of experience and previous studies. In this paper, we analyzed various problems from the mechanical point of view in order to improve the radio frequency (RF) performance by minimizing PIMD in the X band, which is used for the satellite communication. Based on our findings, we propose the flange shape to achieve the test result of -150 dBm, which is an improvement from the existing PIM performance and reference level.
This paper presents a method to predict the design allowable for composite laminates subjected to a tensile load with finite element analysis. The mechanical properties were obtained by conducting tensile and compressive lamina tests. The statistically-based properties were acquired using an in-house tool to calculate the design allowable. A tensile load was imposed on the FE model of the laminate, and each ply stress was compared to the design allowable of the lamina test. The load was considered as the failure load when the ply stress reached the allowable value. This load was applied to a laminate model to perform finite element analysis, and the laminate strength was calculated. The calculated strength and design allowable of the laminate were compared, and as a result, the difference between the results of analysis and test was found to be within 10%.
In this study, beam divergence through an optical fiber has been controlled through shaping of the optical fiber tip using a CO₂ laser, which make the beam divergence smaller than the conventional diamond wheel cleaving method. Precise length cleaving of an optical fiber inserted in a ferrule using a femtosecond laser has also been investigated with respect to changes of the laser pulse energy. A ribbon fiber composed of 12 optical fibers could be cut precisely at different lengths in a micrometer scale.
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Plating small sizes and quantities of workpieces requires their random loading in baskets, rather than individual loading manually. This random loading results in rubbing and collision amongst them, thereby making it impossible to conduct chemical reactions for plating, 4as the plating solution is unable to permeate to the overlapping workpiece surfaces. In this study, we developed a new plating technique under floating workpieces, by spraying high pressurized solution into a randomly loaded basket. In addition, this is accompanied by automatic optimization of the concentration through stirring of the plating solution. Experiments show that test samples were successfully floated at the optimized pressure of 50 kN/㎡. In addition, experiments in the plating parameter variation show the best plating performance at temperatures of 40℃, A and B chromate concentration at ratio = 1 : 2, an immersion time of 180 sec, and the pH value of 2.2, under optimized floated conditions.
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The present research investigates the wear analysis on SCM440 and SUS410 alloys for a high- load roller chain. In this wear analysis test, we concentrate on two wear factors: wear loss and coefficient of friction. For the wear test, reciprocating and block on ling analyses were used to assess the variation of wear characteristics. The applied normal loads were fixed at 10, 30, and 50 N in all tests. The test results showed that the Rockwell hardness average value of the SCM440 alloy is near 29.6 HRC, and the coefficient of friction and the wear loss are 0.62 and 3.8 mg, respectively. In addition, wear behavior was evaluated using lubricating oil.
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Study on Improvement of Catheter Tip Forming Process according to Plating Characteristics in Mold Han Chang Lee, Jinhyuk Jung, Gyu Ik Lee, Woojin Kim, Gyu Man Kim, Bong Gu Lee Journal of the Korean Society for Precision Engineering.2022; 39(9): 711. CrossRef
Elastomeric bushings are structural elements used in automotive suspension systems. A bushing is a hollow cylinder between an outer steel cylindrical sleeve and an inner steel cylindrical rod. The steel sleeve is connected to components of the suspension system and transfers forces from wheel to chassis. Force-Displacement relation for elastomeric bushings is critical for multi-body dynamics simulations. A boundary value issue for bushing response leads to force-displacement relation that requires extensive computation time to implement and therefore is unsuitable. Explicit force-displacement relation may be used in multi-body dynamics simulations. The relation is expressed in terms of a force relaxation function. Lianis model, Modified Lianis model, and Pipkin-Rogers model are introduced. Modified Pipkin-Rogers model was proposed and a boundary value issue was formulated for axial mode bushing response. Numerical solutions of the boundary value issue of Modified Pipkin-Rogers model were compared with results of the Pipkin-Rogers model. It is revealed that the method for determining bushing relaxation function and prediction of proposed force-displacement relation is in agreement with the original results.
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Frequency Related Verification of MPR Model of Elastomeric Bushing in Torsional Mode Seong Beom Lee Journal of the Korean Society for Precision Engineering.2021; 38(12): 959. CrossRef
Modified Pipkin-Rogers Modeling of Elastomeric Bushing in Torsional Mode Seongbeom Lee Journal of the Korean Society for Precision Engineering.2020; 37(12): 905. CrossRef
This paper studied the adhesive strength and electrolyte resistance of the pouch film according to the kind of the extruded resin, which is the basis of the numerous variables in extrusion lamination. After preparing a pouch film by using various extruded resins, we measured the adhesive strength and electrolyte resistance between the aluminum foil and the CPP film. The minimal difference was observed between the adhesive strength with the extruded resin. Also, the extruded resin used in the experiment did not satisfy the electrolyte resistance. An electrolyte resistance was obtained by addition of the functional resin to the extruded resin. The addition of functional resins resulted in improved adhesive strength and electrolyte resistance, that were measured to be approximately 1300 gf/15 mm and 800 gf/15 mm, respectively, at 85℃ for 7days.
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