• 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.

• 한국가구학회지
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• 제19권3호
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• pp.211-218
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• 2008

This experiment was carried out to investigate the effect of internal holes on the bending strength of PB. The diameters of holes are 0mm to 13mm. The locations of holes are 1/8 to 4/5 point horizontally from sample end and are 1/5 to 4/5 vertically from sample surface, the numbers of holes are 1 to 4 pcs. In the size of internal holes, the bending strengths of PB were decreased significantly with the increase of diameter of holes, and the relationship between diameters(D) of holes and bending strength (${\sigma}_b$) of PB was ${\sigma}_b=-11D+168.8$ ($r^2=-0.99^{**}$). The effects of hole-locations and hole-numbers on the bending strengths of PB were large. and so they should be considered as major factors for the jointing design of PB.

• 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.

• 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.

• 대한기계학회논문집
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• 제17권11호
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• pp.2752-2761
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• 1993

The purpose of this study is to confirm the decreasing problems of residual bending strength, and the fracture machanism experimentally when CFRP composite laminates are subjected to Foreign Object Damage. Composite laminates used for this experiment are CFRP orthotropy laminated plates, which have two-interfaces [O/sub 6//sup o//90/sub 6//sup o/]sub sym/ and four-interfaces [O/sub 3//sup o//90/sub 6//sup o//O/sub 3//sup o]/sub sym/. When the specimen is subjected to transverse impact by a steel ball, the delamination area generated by impact damage is observed by using SAM(Scanning Acoustic Microscope). also, Thefracture surfaces obtained by three-point bending test were observed by using SEM (Scanning Electron Microscope). Then, fracture mechanism was investigated based on the observed delamination area and fracture surface. The results were summarized as follows; (1) It is found that for the specimen with more interface, the critical delamination energy is increased while delamination-development energy is decreased. (2) Residual bending strength of specimen A is greater than that of Specimen B within the impact range of impact energy 1. 65J (impacted-side compression) and 1. 45J (impacted-side tension). On the other hand, when the impact energy is beyond the above ranges, residual bending strength of specimen A is smaller than that of specimen B. (3) In specimen A and B, residual strength of CFRP plates subjected to impact damage is lower in the impacted-side compression than in the impacted-side tension. (4) In the case of impacted-side compression, fracture is propagated from the transverse crack generat-ed 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.

• 한국세라믹학회지
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• 제35권3호
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• pp.219-230
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• 1998

Various interlayer materials have been tested for active metal(Cusil ABA) brazing of Si3N4/S. S316 joint. In general multilayer joint had higher strength(80-150 MPa) and better reliability than monolayered one. The joint with Cu(0.2)/Mo(0.3)/Cu(0.2mm) interlayer showed the highest bending strength of abou 490 MPa and the joint with Cu(0.2)/Mo(0.3mm) interlayer the best reliability (14.6 Weibull modulus). The stresses distributed in joint materials during 4-point bending test were estimated by CAE von Mises analysis; the estimated stresses were In good agreement with the measured data. In multilayer joint Cu was though to reduce the residual stresses induced by the difference in thermal expansion coefficient between the ceramic Mo and metal It apperared that a Cu/Mo was optimum interlayer material for Si3N4/S. S316 joint with high bending strength (420 MPa) and reliability. In addition the various shapes and types of compound were examined by EPMA in joining interface.