등이축 굽힘강도를 이용한 중고 자동차용 앞창유리의 안전성 평가

조석수,이성룡,홍성왕 한국기계기술학회 2017 한국기계기술학회지 Vol.19 No.4

Recycling is required for all disused vehicle since 2015. The resource recycling act also recommends that most disused vehicle parts have to be reused except for steering and brake parts. Since vehicle windshields should provide protection for drivers and passengers, they need high structural strength and reliability. However, the vehicle windshields themselves contain many defects arising from glass production process. Because the vehicle windshields are exposed to harsh road conditions, they are expected to experience the formation and growth of surface cracks, which can result in sudden failure. In this study, equibiaxial flexural strength tests are performed on used vehicle windshields to examine whether or not the parts can endure high impact stress due to foreign flying objects. The following conclusions can be drawn: (1) The equibiaxial flexural strength of used vehicle windshields fits the two-parameter Weibull distribution. The equibiaxial flexural strength with a 99.9% failure probability is 69MPa for used vehicle windshields. (2) The equibiaxial flexural strength with six sigma quality level and maximum principal stress at vehicle windshield under high impact load are 8.05MPa and 23MPa respectively. Therefore, Structural safety factor of used vehicle windshields is 0.35 and so we should prohibit used vehicle windshields from keeping in reuse.

손상된 소다라임 유리의 굽힘강도 평가

오상엽,강성황 한국기계기술학회 2001 한국기계기술학회지 Vol.3 No.2

치과 CAD/CAM 절삭가공용 하이브리드 복합 레진블록의 굴곡강도에 미치는 광중합 효과

박민주,김희중,김병훈 대한치과재료학회 2023 대한치과재료학회지 Vol.50 No.1

The purpose of this study is to evaluate the effect of photo-polymerization on the mechanical strength of the hybrid resinblock. Hybrid composite resin was fabricated by polymer matrix mixed with inorganic filler and various additive. Visible light(460 nm) LED curing device for photo-polymerization was designed and fabricated. Photo-polymerization of resin block wasperformed under 3 hrs at 1200 mW/cm2, 2 hrs at 1600 mW/cm2, 3 hrs at 1600 mW/cm2, and 4 hrs at 1600 mW/cm2 of irradiationintensities and time. Mechanical strength was measured using flexural strength. In addition, the sample treated for 2 hrs at1600 mW/cm2 was performed post-treatment under conditions of plasma surface treatment (100 W, 5 min) and light curingfor 15 min in order to improve the degree of polymerization. And then specimen was measured for flexural strength again. After the photo-polymerization, surface morphology was analyzed by SEM. The flexural strength of the composite resin blockwas significantly increased as the irradiation time was increased. Especially, post-treated sample showed higher flexural strengththan that of the other samples. In the SEM analysis, surface morphology was no significant difference regardless of thephoto-polymerization conditions. Light irradiation and plasma treatment could be a powerful technique to improve the polymerizationof hybrid composite resin block for CAD/CAM-processed prosthesis.

Effect of speed sintering on flexural strength, density, and linear shrinkage of monolithic zirconia

권우창,박미경 대한치과재료학회 2023 대한치과재료학회지 Vol.50 No.3

The purpose of this in vitro study was to evaluate the effect of speed sintering on flexural strength, density, and linear shrinkage of monolithic zirconia. Four hundred Ø18.7×1.7-mm presintered zirconia specimens were divided into 8 groups (n=50) based on the sintering times (speed (60, 90, and 120 min) or normal (540 min)) and temperatures (1400, 1450, 1500, and 1550 ℃). The mechanical properties (Vickers hardness, biaxial flexural strength, and fracture toughness) and physical properties (linear shrinkage, density, and porosity) were examined. The crystallite size of zirconia was calculated using scherer’s formula. The mechanical properties (biaxial flexural strength, Vickers hardness, and fracture toughness) of all specimens increased with increasing sintering times and temperatures. The biaxial flexural strength of the SS groups sintered 1500 ℃ and 1550 ℃ with 120 min showed similar value compared with NS groups. The SS 120 and NS groups showed similar the linear shrinkage percentages at all temperatures. The porosity decreased with increasing sintering times and temperatures in all specimens. The sintered and relative density and the average crystallite size increased with increasing sintering times and temperatures in all specimens. The average crystallite size ranged from 70.1 nm to 129.8 nm. XRD analysis showed the presence of a tetragonal metastable phase in all groups before and after sintering. The biaxial flexural strength values under speed sintering (1500 ℃ and 1550 ℃, 120 min) were similar to those of normal sintering groups.

Slim Multi-Layer Printed Circuit Boards의 굽힘 강도 개선에 관한 실험적 연구

김상목(Sang-Mok Kim),구태완(Tae-Wan Ku),송우진(Woo-Jin Song),강범수(Beom-Soo Kang) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5

Recently, demands on thin multi-layer printed circuit boards(PCB) have been rapidly increased with broad spread of personal portable digital appliances such as multi-media. In case of mobile phone, however, the fact that PCBs have low flexural strength might cause defects. The purpose of this study is to improve the flexural strength by substituting the well-known GFRP(glass fiber reinforced plastic) for CFRP(carbon fiber reinforced plastic). Firstly, finite element simulation was carried out using ABAQUS to find out a unique CFRP layer that has a role to sustain the applied forces mainly in PCB. Secondly, three point bending tests were conducted with the newly designed CFRP PCB model to verify the improvement of the flexural strength. Consequently, it is shown that PCB layered with the CFRP on both outer sides of the board can be used to improve the flexural strength effectively.

Y3Al5O12 첨가가 질화규소 세라믹스의 제조 및 그 기계적 특성에 미치는 영향

노상훈,김부안,문창권,정해용,서원찬,윤한기 한국해양공학회 2007 韓國海洋工學會誌 Vol.21 No.6

In the present work, silicon nitride was fabricated with Y3Al5O12 as a sintering additive and its mechanical properties were investigated. Silicon nitride with 3, 5, and 7 wt% of Y3Al5O12 was prepared and sintered by a Hot Pressing (HP) technique at 1750 and 1800℃ for 2 h. The process was performed under different process pressures of 30 and 45 MPa. Mechanical properties (density, strength, hardness, and fracture toughness) were investigated as a function of the Y3Al5O12content in Si3N4. Si3N4 -Y3Al5O12 ceramics showing similar mechanical properties compared with Si3N4-Y2O3-Al2O3 ceramics. But its high temperature strength was considerably higher than that of Si3N4-Y2O3-Al2O3 ceramics.1. 서 론 산업이 고도화되고 이용되는 부품소재가 더욱 가혹한 환경에 노출됨에 따라 기존의 금속이나 고분자소재보다 높은 기계적 특성을 지니는 구조세라믹스에 대한 요구가 증대되고 있다. 그러나 실제 응용에 있어서 구조세라믹스는 자체의 신뢰도와 취성 때문에 많은 제한이 있으며, 이를 극복하기 위해 가혹한 환경에서의 높은 강도와 파괴인성을 확보하는 것이 가장 중요한 과제로 대두되고 있다(Tsuge et al., 1975; Sanders and Mieskowski, 1985).대표적인 구조세라믹스인 질화규소는 강도, 내열성, 내열충격성, 내화학성, 내마모성 등이 매우 우수한 재료이다. 이러한 특성으로 자동차 엔진부품, 가스 터빈, 절삭 공구, 베어링, 펌프용 실링(Sealing)재로 산업전반에 걸쳐 활용되고 있다. 하지만 Si3N4는 소결 시 충분한 소결강도를 가지기 전에 분해할 뿐만 아니라, 난소결성이며 파괴인성 또한 낮은 것이 단점으로 지적되고 있다. 이러한 단점을 극복하기 위하여 일반적으로 질화규소는 Al2O3, Y2O3, MgO, ZrO2 등의 소결조제를 첨가하여

316 스테인레스강의 열충격 특성

이상필(Sang-Pill Lee),김영만(Young-Man Kim),민병현(Byung-Hyun Min),김창호(Chang-Ho Kim),손인수(In-Soo Son),이진경(Jin-Kyung Lee) 한국해양공학회 2013 韓國海洋工學會誌 Vol.27 No.5

The present work dealt with the high temperature thermal shock properties of 316 stainless steels, in conjunction with a detailed analysis of their microstructures. In particular, the effects of the thermal shock temperature difference and thermal shock cycle number on the properties of 316 stainless steels were investigated. A thermal shock test for 316 stainless steel was carried out at thermal shock temperature differences from 300℃ to 1000℃. The cyclic thermal shock test for the 316 stainless steel was performed at a thermal shock temperature difference of 700℃ up to 100 cycles. The characterization of 316 stainless steels was evaluated using an optical microscope and a three point bending test. Both the microstructure and flexural strength of 316 stainless steels were affected by the high-temperature thermal shock. The flexural strength of 316 stainless steels gradually increased with an increase in the thermal shock temperature difference, accompanied by a growth in the grain size of the microstructure. However, a thermal shock temperature difference of 800℃ produced a decrease in the flexural strength of the 316 stainless steel because of damage to the material surface. The properties of 316 stainless steels greatly depended on the thermal shock cycle number. In other words, the flexural strength of 316 stainless steels decreased with an increase in the thermal shock cycle number, accompanied by a linear growth in the grain size of the microstructure. In particular, the 316 stainless steel had a flexural strength of about 500 MPa at 100 thermal-shock cycles, which corresponded to about 80% of the strength of the as-received materials.

압력/진공 릴리프 밸브 스테인레스 강의 내열특성

조경서(Kyung-Seo Cho),이상필(Sang-pill Lee),이진경(Jin-Kyung Lee),이향준(Hyang-Jun Lee),이민원(Min-Won Lee),기동환(Dong-Hwan Ki) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

The present work dealt with the high temperature properties of STS 316 steels for disk or sheet materials, in order to develop the safe relief valve of oil or gas storage tank. Especially, the critical temperature difference for the strength degradation of STS 316 steels has been investigated by the high temperature thermal shock test. The flexural strength of stainless 316 steels gradually increased with the increase of thermal shock temperature, accompanying the rapid reduction at the thermal shock temperature higher than 973 K. Especially, the stainless 316 steels represented an average flexural strength of about 540 ㎫ at the thermal shock temperature of 1273 K, corresponding to about 85 % of as-received materials.

액상소결 SiC 재료의 특성 평가

조경서(Kyung-Seo Cho),이문희(Moon-Hee Lee),이상필(Sang-Pill Lee),이진경(Jin-Kyung Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

The mechanical and microstructure properties of liquid phase sintered (LPS) SiC materials have been investigated, in conjunction with a nondestructive technique by the ultrasonic wave. The thermal shock damage behaviors of LPS-SiC materials were also examined. LPS-SiC materials were fabricated at the temperature of 1820 ℃ using the additives of Al₂O₃, and Y₂O₃ particles. The compositional ratios of additive materials (Al₂O₃/Y₂O₃) for LPS-SiC materials were changed from 0.4 to 1.5. LPS-SiC materials represented the good density of about 3.2 Mg/㎥ and an average flexural strength of about 725 ㎫ at an additive composition ratio of 1.5. The attenuation coefficient related to the velocity of ultrasonic wave was greatly changed by different additive composition ratios of LPS-SiC materials. The flexural strength for LPS-SiC materials increased with the decrease of attenuation coefficient. In accordance with the increase of thermal shock cycle, the attenuation coefficient of LPS-SiC materials also increased, due to the creation of microcracks.

SiC 재료의 미세조직 및 열충격 특성

이상필(Sang-Pill Lee),조경서(Kyung-Seo Cho),이현욱(Hyun-Uk Lee),손인수(In-Soo Son),이진경(Jin-Kyung Lee) 한국해양공학회 2011 韓國海洋工學會誌 Vol.25 No.3

The thermal shock properties of SiC materials were investigated for high temperature applications. In particular, the effect of thermal shock temperature on the flexural strength of SiC materials was evaluated, in conjunction with a detailed analysis of their microstructures. The efficiency of a nondestructive technique using ultrasonic waves was also examined for the characterization of SiC materials suffering from a cyclic thermal shock history. SiC materials were fabricated by a liquid phase sintering process (LPS) associated with hot pressing, using a commercial submicron SiC powder. In the materials, a complex mixture of Al₂O₃ and Y₂O₃ powders was used as a sintering additive for the densification of the microstructure. Both the microstructure and mechanical properties of the sintered SiC materials were investigated using SEM XRD, and a three point bending test. The SiC materials had a high density of about 3.12 Mg/m3 and an excellent flexural strength of about 700 ㎫, accompanying the creation of a secondary phase in the microstructure. The SiC materials exhibited a rapid propagation of cracks with an increase in the thermal shock temperature. The flexural strength of the SiC materials was greatly decreased at thermal shock temperatures higher than 70 ℃, due to the creation of microcracks and their propagation. In addition, the SiC materials had a clear tendency for a variation in the attenuation coefficient in ultrasonic waves with an increase in thermal shock cycles.