• 항공우주시스템공학회지
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• 제4권1호
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• pp.23-26
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• 2010

In this study, it was performed damage assesment of small scale composite aircraft developing. This aircraft adopted the sandwich structure to skin of wing. This study aims to investigate the residual strength of sandwich composites with Nomex honeycomb core and carbon fiber face sheets after the open hole damage by the experimental investigation. The 4-point bending tests were used to find the bending strength, and the open hole was applied to introduce the simulated damage on the specimen. The bending strength test results after open hole was compared with the results of no damaged specimen test. The FEM analysis is assessed via an experimental 4-point bending test.

• 마이크로전자및패키징학회지
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• 제21권4호
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• pp.33-39
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• 2014

To establish the reliability of a packaging structures, adhesion testing of key interfaces is a critical task. Due to the material mismatch, the interface may be prone to delamination failure due to conditions during the manufacturing of the product or just from the day-to-day use. To assess the reliability of the interface adhesion strength testing can be performed during the design phase of the product. One test method of interest is the four-point bending (4PB) adhesion strength test method. This test method has been implemented in a variety of situations to evaluate the adhesion strength of interfaces in bimaterial structures to the interfaces within thin film multilayer stacks. This article presents a review of the 4PB adhesion strength testing method and key implementations of the technique in regards to semiconductor packaging.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.173-174
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• 2008

The four-point bending test is a widely used method to determine material parameters. The aim of the present study was to evaluate the flexural strength (or modulus of rupture) and the Weibull modulus of cordierite ceramic substrate by means of four-point bending tests. The strength data from experiments followed Weibull statistics. These data indicate that the fatigue effects are more severe when the substrate temperature in the peripheral region is near $200^{\circ}$. At temperatures well above $200^{\circ}C$ the available design strength can be as high as 65% as substrate's initial strength.

• 대한토목학회논문집
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• 제31권5A호
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• pp.389-397
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• 2011

본 논문에서는 이방향 휨인장강도 시험 시 시험체에 작용하는 등방성 휨인장거동의 구현여부를 실험적으로 증명하기 위해 시험체의 변형률 측정 실험과, 시험체에 등방성 휨인장응력이 작용할 수 있도록 시험법 개선을 위한 연구를 수행하였다. 또한, 개선된 시험법을 적용하여 이방향 휨인장강도와 4점 휨인장강도 시험에 의한 일방향 휨인장강도를 측정하여 비교하였다. 실험 결과, 시험체에 발생하는 등방성 휨인장응력은 시험체의 표면 조건과 뒤틀림 정도에 많은 영향을 받는 것으로 나타났으나, 시험법 개선으로 인해 시험체에 등방성 휨인장응력상태를 확보할 수 있었다. 개선된 이방향 휨인장강도 시험에 의한 이방향 휨인장강도가 일방향 휨인장강도 보다 32% 더 큰 것으로 나타났으며, 분산성은 동일한 것으로 나타났다.

• Composites Research
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• 제27권2호
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• pp.77-81
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• 2014

본 연구에서는 전기체 복합재가 적용되어 설계된 소형 항공기의 손상 평가 및 유지 보수 연구를 수행하였다. 본 연구에서 개발 중인 항공기의 스킨 부위는 샌드위치 구조가 적용되었다. 본 연구에서는 노멕스 허니컴코어와 카본 면재가 적용된 샌드위치 복합재 구조에 대해 구멍 손상 이후의 잔류 강도 평가에 대한 연구를 수행하였다. 4점 굽힘 시험을 통해 시편의 굽힘 강도를 확인하고, 시편에 손상을 모사하기 위하여 시편의 중앙 부위에 구멍 손상을 가하였다. 손상된 시편을 손상 전 시편과 동일한 시험을 통해 손상 전의 강도와 비교하였다. 또한 손상된 복합재 구조는 손상 부위 제거 후 패치 수리 기법을 적용하고 손상된 시편과 보수된 시편의 굽힘 강도 시험결과를 비교하였다. 샌드위치 복합재 구조 시편의 유지 보수 후 굽힘 강도 시험 결과 손상 전 시편의 강도와 비교하여 강도의 95%까지 회복되는 것으로 분석되었다.

• 한국생산제조학회지
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• 제6권1호
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• pp.59-68
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• 1997

Recently, the cases of using bonded dissimiliar materials which have each of the different components tend to increase for the purpose of developing new materials and using the special objects in the field of industry. Among the cases the strength evaluation of the joining materials of vehicle engine and the structural materials with ceramic/metal bonded joints becomes more important. But the residual stress occurs, because the joining of ceramics and metals is performed in extremely high temperature. It becomes a dominant cause to reduce the strength of the ceramic/metal bonded joints. In this paper, strength evaluation method of ceramic/metal bonded joints considering stress singularity was investigated by boundary element method and 4-point bending test. An advanced method of quantitative strength evaluation for ceramin/metal bonded joints is to be suggested.

• Journal of Welding and Joining
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• 제32권4호
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• pp.34-38
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• 2014

Carburizing treatments are the important way to developing fatigue strength and wear resistance. It is well known that the case depth is one of the most significant parameters determining fatigue strength. In this study, 3-point bending fatigue test was conducted to evaluate fatigue strength for the carburized depth with 18CrNiMo7-6 steel. As a result, fatigue strength increased with effective case depth decreased. It is shown that hardness in case hardened layer played principal role in the fatigue strength.

• 마이크로전자및패키징학회지
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• 제18권1호
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• pp.15-21
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• 2011

전자기기의 고집적화를 위해 실리콘 웨이퍼의 두께가 점점 얇아지고 있으며 이로 인해 제조공정 중 균열이나 파손이 발생할 가능성이 높아지고 있다. 본 연구에서는 300 ${\mu}m$~100 ${\mu}m$ 두께의 반도체용 단결정 실리콘 웨이퍼의 파단 강도 및 파괴특성을 평가하였다. 기계적 연마를 통해 두께 (300, 200, 180, 160, 150, 100 ${\mu}m$)가 다른 실리콘 웨이퍼를 준비하였다. 하나의 웨이퍼에서 40개의 실리콘 다이(크기 : 62.5 mm${\times}$4 mm)를 얻어 4점 굽힘시험을 통해 평균 강도값을 구하였다. 강도분포의 통계적 해석을 위해 와이블 선도를 이용하여 형상인자(와이블 계수)와 크기인자(확률적 파괴강도)를 얻었다. 취성 실리콘 다이의 시편 크기(두께)효과와 파단 확률이 고려된 통계적 파단강도 값을 실리콘 다이 두께의 함수로 얻었다. 관찰된 파괴양상을 측정된 파단강도와 관련하여 고찰하였다.

• 대한기계학회논문집A
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• 제20권6호
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• pp.1836-1842
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• 1996

In this paper, static and fatigue bending strengths of CFRP(carbon fiber reinforced plastic laminates having impact damage(FOD) are evaluated. Composite laminates used for this experiment are CF/EPOXY and CF/PEEK orthotropy laminated plates, which have two-interfaces[${0^0}_4{90^0}_4}$]$_sym$. A steel ball launched by the air gun colides against CFRP laminates to generate impact damages. The damage growth during bending fatigue test is observed by the scanning acoustic microscope(SAM). When the impacted side is compressed, the residual fatigue bending strength of CF/PEEK specimen P is greater that that of CF/EPOXY SPECIMEN B. On the other hand, when the impacted side is in tension, the residual fatigue bending strength of CF/PEEK speicemen P is smaller than that of CF/EPOXY specimen B. In the case of impacted-side compression, fracture is proposed from the transverse crack generated near impact point. On the other hand, fracture is developed toward the impact point from the edge of interface-b delamination in the case of impacted-side tension.

• The Journal of Advanced Prosthodontics
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• 제9권6호
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• pp.439-446
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• 2017

PURPOSE. To evaluate the effects of different surface treatments on the bond strength of novel CAD/CAM restorative materials to resin cement by four point bending test. MATERIALS AND METHODS. The CAD/CAM materials under investigation were e.max CAD, Mark II, Lava Ultimate, and Enamic. A total of 400 bar specimens ($4{\times}1.2{\times}12mm$) (n=10) milled from the CAD/CAM blocks underwent various pretreatments (no pretreatment (C), hydrofluoric acid (A), hydrofluoric acid + universal adhesive (Scotchbond) (AS), sandblasting (Sb), and sandblasting + universal adhesive (SbS)). The bars were luted end-to-end on the prepared surfaces with a dual curing adhesive resin cement (Variolink N, Ivoclar Vivadent) on the custom-made stainless steel mold. Ten test specimens for each treatment and material combination were performed with four point bending test method. Data were analyzed using ANOVA and Tukey's test. RESULTS. The surface treatment and type of CAD/CAM restorative material showed a significant effect on the four point bending strength (FPBS) (P<.001). For LDC, AS surface treatment showed the highest FPBS results ($100.31{\pm}10.7MPa$) and the lowest values were obtained in RNC ($23.63{\pm}9.0MPa$) for control group. SEM analyses showed that the surface topography of CAD/CAM restorative materials was modified after treatments. CONCLUSION. The surface treatment of sandblasting or HF acid etching in combination with a universal adhesive containing MDP can be suggested for the adhesive cementation of the novel CAD/CAM restorative materials.