• Tribology and Lubricants
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• v.31 no.4
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• pp.157-162
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• 2015

In this study, an ultrasonic nanocrystalline surface modification (UNSM) technique is applied to tungsten carbide-cobalt (WC-Co) to extend the service life of carbide parts used in press mold. The UNSM technique modifies the structure, reduces the surface roughness, increases the surface hardness, induces the compressive residual stress, and increases the wear resistance of materials by introducing severe plastic deformation. The surface roughness, hardness, and compressive residual stress of WC after UNSM treatment improve by about 42, 10, and 71%, respectively. A wear test under dry conditions is used to assess the effectiveness of the UNSM technique on the friction and wear behavior of WC. The UNSM technique is found to reduce the WC friction coefficient by approximately 21% and enhance the wear resistance by approximately 85%. The improved friction and wear behavior of WC may be mainly attributed to the increased hardness and compressive residual stress. Moreover, the WC specimen is treated by UNSM technique using three different WC, silicon nitride (Si₃N₄) and stainless steel (STS304) balls. The surface treated by WC balls shows the highest hardness when compared with treatment by stainless steel and silicon nitride balls. According to the obtained results, the UNSM technique is believed to increase the durability of the carbide component by improving the friction and wear behavior.

• Bulletin of the Korean Chemical Society
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• v.30 no.10
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• pp.2227-2232
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• 2009

Novel polythiol materials of urethane lens series for plastic optical lens were synthesized from polyol materials via thioisouronium of thiourea with c-HCl in refluxing aqueous solution, in which polythiol material was carried out from hydrolysis of thioisouronium by ammonia water. Their structure properties were identified by EA, EI-MS, FT-IR, $^1H\;and\;^{13}C$ NMR spectroscopies and TGA. Their ophthalmic lenses as polythiourethane material were prepared by thermal curing to an injected glass mold using the evenly solutions of diisocyanates series (TDI, XDI, HDI or IPDI) with polythiols. Polythiourethane shows that the strong stretching mode for SH group of polythiol disappeared in FT-IR spectra after thermosetting polymerization. Thermal deformation starting temperature of ophthalmic lenses was determined by TMA. Ophthalmic lenses made from characteristic polythiol and diisocyanate series have transparency, colorless and good impact strength, in which thermal resistance and impact strength of ophthalmic lenses were influenced by diisocyanate series. Physical properties of ophthalmic lens have contrast thermal resistance with impact strength. The property of thermal resistance and impact strength for respective ophthalmic lenses was examined by TMA and drop ball test.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.2
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• pp.243-257
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• 2003

The purpose of this study was to search the influences of the increase of the contents of sodium alginate in the experimental alginates on the some mechanical properties. 3 commercial alginates were selected for the purpose of comparison of the results of experiments. 7 experimental alginates were manufactured with the rise of contents of sodium alginate from 8.8% to 18.3% with the decrease of contents of diatomaceous earth and with the constant contents of calcium sulfate 12.5%. sodium phosphate 2.2%, zinc fluoride 2.0%. Splitable metal mold with 12.5mm diameter and 20.0mm height was filled with mixed alginate to prepare the cylinder shaped specimens. Strain in compression, elastic recovery, compressive strength were tested using the ISO specification number 1563, alginate impression material. Experimental groups were 7, and 10 specimens were used for each test items and each groups. Following results were obtained ; 1. Strain in compression was decreased with the increase of sodium alginate contents (p=0.0077, r2 = 0.6302). 2. Elastic recovery was decreased with the increase of sodium alginate contents but was not significant(p=0.0639, r2=0.7449). 3. Compressive strength was increased with the increase of sodium alginate contents (p<0.0001, r2 = 0.9617). These results mean that the increase of sodium alginate contents make alginate harder but may result the increased permanent deformation.

• Journal of the Korea Convergence Society
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• v.11 no.9
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• pp.169-173
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• 2020

The structural analysis was performed at this study when the axle was loaded by using a total of three automotive support beam models, models A, B and C. Comparing with three models A, B, and C, the equivalent stress is considered to be good for its durability because model C is less than the yield stress of the material. The maximum equivalent stresses happening at models A and B are 1.8 times and 2.5 times higher than the yield stress, respectively, indicating that the material is fractured. So, it does not seem to be efficient as a support beam. Model C can be applied efficiently to the improvement design of axle support beams in terms of durability compared to models A and B. The strength of automotive support beam can be evaluated by applying this research result to the automotive part. And it is seen that this study is adequate at the efficient design and aesthetic convergence practically.

• Journal of the Korea Convergence Society
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• v.9 no.11
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• pp.271-276
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• 2018

When the driver riding in a bicycle goes on board, the load of driver is shown differently according to the position loaded on the frame of bicycle. The load is applied most at the joint of bike frame and the load at the mid-part of frame is applied least than the other parts. So, the weight of frame is decreased as the part not applied with a lot of load is manufactured into the thin thickness. As the part applied with high load is manufactured into the thick thickness, it can be endured through this load. The configurations of general frame, double butted and triple butted were modelled by using CATIA program. The durabilities of each model due to the load of passenger were investigated by carrying the structural and fatigue analyses. As this study result investigated with the analysis program of ANSYS, the deformation of general frame happened most and that of triple butted became least. These simulation analysis data are intended to be used to design the actual bicycle frame in the most efficient way at design and manufacture.

• Journal of the Korea Convergence Society
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• v.10 no.7
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• pp.149-154
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• 2019

This paper is to study the durability through structural analysis on the front undercover of SUV car for offroad. It was investigated which model became structurally best by analyzing three kinds of models which are similar to the configuration of undercover for the protection of the part under car body which has been used really. The models of undercover were designed through CATIA program and analyzed by using ANSYS program as three kinds of models A, B and C. Through the analysis results, model B was expressed to have the best durability as model B has the least equivalent stress and the longest fatigue life among three models. As the design data with the durability of undercover obtained on the basis of this study result are utilized, the esthetic sense can be shown by being grafted onto the machine or structure at real life.

• Journal of the Korea Convergence Society
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• v.11 no.12
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• pp.155-159
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• 2020

In this study, the structural analyses were performed on the number of leaf springs in large truck. The deformations were small for all four models. The maximum stress of model A was found to be the largest, and that of model D was the smallest. Model A was seen about 1.87 times larger than model D and about 1.52 times larger than model B. The maximum stresses of models C and D were seen to be less. In terms of the effect to reinforce one more overlapping spring, The effect of the enhancement of the strength of model D was shown to be small by comparing with model C. Therefore, model C with three overlapping springs is thought to be efficient in design and good in strength. The structural strength of leaf spring can be evaluated by applying this study result to the leaf spring at large truck. And it is seen that the result can be the design of the leaf spring with durability at large truck and the aesthetic convergence.

• Design & Manufacturing
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• v.16 no.3
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• pp.9-15
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• 2022

In order to reduce the manufacturing costs of the glass lens, it is necessary to manufacture a lens using a UV curable resin or a thermosetting resin, which is a curable material, in order to replace a glass lens. In the case of forming a lens using a thermosetting material, it is necessary to form several lenses at once using the wafer-level lens manufacturing technologies due to the long curing time of the material. When a lens is manufactured using a curable material, an error in the shape of the lens due to the shrinkage of the material during the curing process is an important cause of defects. The major factors for these shape errors and deformations are the shrinkage and the change of mechanical properties in the process of changing from a liquid material during curing to a solid state after complete curing. Therefore, it is necessary to understand the curing process of the material and to examine the shrinkage rate and change of physical properties according to the degree cure. In addition, it is necessary to proceed with CAE for lens molding using these and to review problems in lens manufacturing in advance. In this study, the viscoelastic properties of the material were measured during the curing process using a rheometer. Using the results, Rheological investigation of cure kinetics was performed. At the same time, The shrinkage of the material was measured and simple mathematical models were created. And using the results, the molding process of a single lens was analyzed using Comsol, a commercial S/W. In addition, the experiment was conducted to compare and verify the CAE results. As a result, it was confirmed that the shrinkage rate of the material had a great influence on the shape precision of the final product.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.3 s.55
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• pp.188-196
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• 2009

In Concrete, shrinkages occur like plastic shrinkage and drying shrinkage in the early age because of evaporation and transfer of moisture. Within the country, the crack test standardized by KS is used to test the drying shrinkage of the concrete by using the restricted drying shrinkage of Dumbbell type mold, but this test is for the cracking-point and the restricted shrinkage stress. Thus it is difficult to valuate the crack quantitative test. In this study, it is intended to develop the Flat-ring type restrained test method for the shrinkage deformation movement of the concrete and to provide the quantitative data for evaluating the cracks in concrete. And it suggest the proper specimen diameter and quantitative test method about shrinkage crack properties on Flat-ring type restrained test method. And Verified the suitability.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.5
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• pp.3286-3291
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• 2014

A study on the crack protection and thermal insulation properties of the expanded perlite inorganic composites was performed. Mixed expanded perlite with a water glass was stabilized for 24 hrs at room temperature in the mold and, thereafter, converted into a massive foamed body through complete drying process at $150^{\circ}C$. Aluminum phosphate and micron size mica powder were used as a reaction accelerator and a stabilizer for thermal crack, respectively. Especially, use of mica exhibited a remarkable effect on the protection of thermal crack at higher temperature over $500^{\circ}C$, and thermal conductivity of the composites was enhanced with higher perlite contents, showing ca. 0.09 W/mK for the sample of 100/200/10/1.5 water glass/perlite/mica/Al phosphate by weight. A severe dimensional deformation of the composite materials was observed over $600^{\circ}C$, however, showing a temperature limitation for a practical application. The facts were considered as the results from the glass transition temperature of the water glass, of which main component is sodium silicate.