• 대한금속재료학회지
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• 제46권2호
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• pp.80-87
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• 2008

Many researches related to the reliability of Pb-free solder joints with PCB (printed circuit board) surface finish under thermal or vibration stresses are in progress, because the electronics is operating in hash environment. Therefore, it is necessary to assess Pb-free solder joints life with PCB surface finish under thermal and mechanical stresses. We have investigated 4-points bending fatigue lifetime of Pb-free solder joints with OSP (organic solderability preservative) and ENIG (electroless nickel and immersion gold) surface finish. To predict the bending fatigue life of Sn-3.0Ag-0.5Cu solder joints, we use the test coupons mounted 192 BGA (ball grid array) package to be added the thermal stress by conducting thermal shock test, 500, 1,000, 1,500 and 2,000 cycles, respectively. An 4-point bending test is performed in force controlling mode. It is considered that as a failure when the resistance of daisy-chain circuit of test coupons reaches more than $1,000{\Omega}$. Finally, we obtained the solder joints fatigue life with OSP and ENIG surface finish using by Weibull probability distribution.

• 한국기계가공학회지
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• 제19권6호
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• pp.80-87
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• 2020

The currently observed trend in car manufacturing is to increase energy-efficiency by producing lighter cars. This study examines the replacement of particular parts, specifically around the impact beam, with material composites 30% lighter than conventional steel currently used. The shape of the impact beam was determined as the trapezoidal cross-sectional area with central reinforcement, using three-point bending analysis. A prototype was fabricated based on the findings of our study and its performance was evaluated by the three-point bending analysis; 2 ply of aramid applied for its displacement. The performance of the final prototype for the door assembly was evaluated using a side-door strength test, which resulted to measured initial strength of 10.5 KN and intermediate strength of 15.6 KN. This research provides a promising solution for better impact beam manufacturing.

• 대한토목학회논문집
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• 제33권3호
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• pp.901-907
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• 2013

본 논문에서는 이방향 응력상태에서의 콘크리트 강도 특성과 크기효과 그리고 피로거동에 관한 연구를 수행하였다. 이를 위해 ASTM C 1550 시험법과 이방향 휨강도 시험(biaxial flexure test; BFT)을 적용하여 크기효과 및 피로시험을 실시하였으며, 단순보의 3등분점 하중에 의한 콘크리트 휨강도 시험(third-point bending test) 결과와 비교하였다. 실험 결과 3등분점 재하 휨강도 시험에 의한 일방향 응력상태의 강도보다는 ASTM C 1550 시험법과 이방향 휨강도 시험법에 의한 이방향 응력상태의 강도가 더 큰 것으로 측정되었다. 3등분점 재하 휨강도 시험, ASTM C 1550, 이방향 휨강도 시험법 모두 시편의 크기가 증가함에 따라 강도는 감소하는 것으로 관찰되었으며, 이방향 휨인장강도의 크기 효과가 일방향 휨인장강도의 크기효과보다 더 큰 것으로 확인되었다. S-N 곡선에 의한 일방향과 이방향 휨강도의 피로 수명은 유사한 것으로 분석되었다.

• 한국지반공학회논문집
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• 제36권3호
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• pp.25-36
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• 2020

동토의 세립분 함유량에 따른 파괴특성을 파악하기 위해 -10℃의 온도에서 다양한 세립분 함유량과 초기 노치(notch)의 위치를 조정한 직사각형 공시체를 제작하여 Three-point bending 시험을 수행하였다. 시험결과를 바탕으로 동토의 mode I 파괴인성(fracture toughness)을 산정하였으며, 하중-변형 곡선의 최대점까지의 fracture energy를 산정하여 동토의 mixed-mode(mode I + II) 파괴특성을 파악하였다. 시험결과, 최대하중 및 mode I 파괴인성은 세립분 함유량 10%까지 증가하다가 15%에서 다시 감소하는 경향을 나타내었다. 또한, 노치의 위치가 공시체 중심에서 멀어질수록 mode II 하중의 증가로 인해 균열이 진행하는데 필요한 fracture enenrgy가 증가하는 것으로 나타났으며, 세립분 함유량이 증가할수록 mode II 하중의 증가비율 또한 증가하는 것으로 나타났다.

• Composites Research
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• 제30권3호
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• pp.188-192
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• 2017

The mechanical properties of composites are significantly affected by external environment. It is essential to understand the degradation of material performance and judge the material's lifetime in advance. In the current research, changes in mechanical properties of glass fiber and unsaturated polyester composite materials (GFRP, Glass fiber reinforced plastic) were investigated under different bending stress and submerged in hot water at a temperature of $80^{\circ}C$. Loading time of 100 H (hours), 200 H, 400 H, 600 H, 800 H for testing under stresses equal to 0% (stress-free state), 30%, 50% and 70% of the ultimate strength was applied on the GFRP specimens. From the values of bending stress, obtained from three-point bending test, fracture energy, failure time, and life curve were analysed. Moreover, a normalized strength degradation model for this condition was also developed. It was observed that within 100 H, the decline rate of the bending strength was proportional to the pressure.

• Composites Research
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• 제26권5호
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• pp.295-302
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• 2013

본 연구에서는 차량용 Al5052/CFRP 복합재를 U-채널 몰드에서 컴프레션 몰딩 공정을 통해 제작하였다. Al5052는 샌드블라스팅을 통해 표면처리를 하였다. 표면처리를 하지 않은 판재와 표면거칠기(Ra)가 $1.85{\mu}m$ 및, $4.25{\mu}m$인 Al5052판재를 이용하여 실험을 수행하였다. 표면거칠기가 Al5052/CFRP 복합재의 접착성과 기계적 특성에 대한 영향을 전단시험과 굽힘실험을 통하여 평가하였다. 전단 시험에서는 표면거칠기가 $1.85{\mu}m$ 와 $4.25{\mu}m$ 시험편이 표면처리를 하지 않은 시험편보다 각각 3, 5배의 전단강도의 증가를 보였다. 굽힘시험에서는 표면처리를 하지 않았을 때 굽힘강도가 200 MPa에서 표면처리 후 400 MPa로 증가함을 알 수 있었다.

• 한국주조공학회지
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• 제34권2호
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• pp.60-66
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• 2014

A Zr-based amorphous alloy specimen was produced by vacuum die casting process. The salt spray test was carried out using the specimens in the as-cast, $Al_2O_3$ and $ZrO_2$ particle blasted state. Using these specimens, the SEM-EDX and XRD analyses, DSC measurement and bending strength test were conducted. After the salt spray test, the specimens were not experienced phase change and thermal characteristics of the alloys were remained unchanged. In the as-cast specimen, corrosion products were not observed. However, in the $Al_2O_3$ particle blasted specimen, pitting corrosion occurred and the detected corrosion products were $ZrCl_2$ and $NaZrO_3$. Due to the salt spray test, bending strength of the $Al_2O_3$ blasted specimens showed about 100 MPa lower strength than the other specimens. The bending fracture surface was vein pattern which was shown typically in the amorphous alloys.

• 한국세라믹학회지
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• 제36권10호
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• pp.1062-1068
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• 1999

상온 25$^{\circ}C$의 증류수에 단일 열충격을 시행한 후 ball-on-3 ball test로 강도를 측정하고 강도의 변화를 관찰하였다. 시편은 상용 알루미나 시편을 사용하였고, disc 형태의 시편에 대하여 열충격 후의 균열의 모양과 강도 시험 후의 균열의 모양을 잉크 침투법에 의해 관찰하였다. 통계적인 파괴 확률방법을 제시하였으며, thermal shock Weibull plot을 이용하여 3점 꺾임 강도와 비교하였다. ball-on-3 ball test 강도에 미치는 인자에 대해 통계학적인 접근을 통해 관찰한 결과, 시편중심에서 균열까지의 거리가 균열 밀도보다 더 큰 영향을 미치고 있음을 알 수 있었다.

• 대한기계학회논문집
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• 제18권9호
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• pp.2396-2403
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• 1994

An experimental study on material characterization and mechanical properties of SMC(Sheet Molding Compounds) compression method parts was carried out. Simple compression test using grease oil as a lubricant was carried out to characterize flow stress of SMC at elevated temperatures. Two different mold temperatures, $130^{\circ}C{\;}and{\;}150^{\circ}C$ and two different mold speeds, 15, 45 mm/min were used for preparing the specimen of SMC compression molded parts. Surface roughness, tensile, and 3-point bending tests were used to determine the effects of molding temperatures and speeds on mechanical properties of compression molded SMC parts. Orientation and distribution of glass fiber in the compression molded SMC parts were also investigated by photographing the burnt flat specimen and taking SEM(Scanning Electron Microscope) of cross-sectional T-specimen.

• International Journal of Automotive Technology
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• 제6권6호
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• pp.671-676
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• 2005

Spring is one of major suspension part of the light commercial vehicle (LCV). In the manufacturing process it is shot-peened to improve its fatigue strength. In this paper, residual stresses by shot peening were calculated through finite element analysis, and the effects of these residual stresses on fatigue strength of leaf spring were evaluated. Fatigue tests were performed with two kinds of specimens; one is actual leaf spring assembly, and the other is simulated 3-point bending specimen. Fatigue tests were performed under the loading condition that was measured on the proving ground. From the results, the maximum load-fatigue life relation of leaf spring was defined, and test results of 3 point bending specimen are in good agreement with those of leaf spring assembly. The effects of residual stresses by shot peening on fatigue strength of leaf spring is not large in the high load range, however, in the low load range, its effects were not negligible.