• Steel and Composite Structures
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• 제25권3호
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• pp.327-335
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• 2017

To gain more knowledge of aluminum foam sandwich structure and promote the engineering application, aluminum foam sandwich consisting of 7050 matrix aluminum foam core and 304 stainless steel face-sheets was studied under three-point bending by WDW-T100 electronic universal tensile testing machine in this work. Results showed that when aluminum foam core was reinforced by 304 steel face-sheets, its load carrying capacity improved dramatically. The maximum load of AFS in three-point bending increased with the foam core density or face-sheet thickness monotonically. And also when foam core was reinforced by 304 steel panels, the energy absorption ability of foam came into play effectively. There was a clear plastic platform in the load-displacement curve of AFS in three-point bending. No crack of 304 steel happened in the present tests. Two collapse modes appeared, mode A comprised plastic hinge formation at the mid-span of the sandwich beam, with shear yielding of the core. Mode B consisted of plastic hinge formation both at mid-span and at the outer supports.

• International Journal of Korean Welding Society
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• 제4권1호
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• pp.46-52
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• 2004

To combine the mechanical advantages of ceramics with those of metals, one often uses both materials within one composite component. But, as known, they have different material properties and fracture behaviors. In this study, a four-point bending test is carried out on $Si_3N_4$ joined to ANSI 304L stainless steel with a Ti-Ag-Cu filler and a Cu interlayer at room temperature to evaluate their longitudinal strain behaviors. And, to detect localized strain, a couple of strain gages are pasted near the joint interfaces of the ceramic and metal sides. The normal strain rates are varied from $3.33{\times}10^5$ to $3.33{\times}10^{-1}s^{-1}$ Within this range, the experimental results showed that the four-point bending strength and the deflection of the interlayer increased with increasing the strain rate.

• 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.

• Journal of Welding and Joining
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• 제35권3호
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• pp.7-14
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• 2017

The effect of high temperature-moisture on corrosion and mechanical properties for Sn-0.7Cu, Sn-3.0Ag-0.5Cu (SAC305) solders on flexible substrate was studied using Highly Accelerated Temperature/Humidity Stress Test (HAST) followed by three-point bending test. Both Sn-0.7Cu and SAC305 solders produced the internal $SnO_2$ oxides. Corrosion occurred between the solder and water film near flexible circuit board/copper component. For the SAC305 solder with Ag content, furthermore, octahedral corrosion products were formed near Ag3Sn. For the SAC305 and Sn-0.7Cu solders, the amount of internal oxide increased with the HAST time and the amount of internal oxides was mostly constant regardless of Ag content. The size of the internal oxide was larger for the Sn-0.7Cu solder. Despite of different size of the internal oxide, the fracture time during three-point bending test was not significantly changed. It was because the bending crack was always initiated from the three-point corner of the chip. However, the crack propagation depended on the oxides between the flexible circuit board and the Cu chip. The fracture time of the three-point bending test was dependent more on the crack initiation than on the crack propagation.

• Journal of the Korean Wood Science and Technology
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• 제46권5호
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• pp.486-496
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• 2018

4점 휨 시험에서 지간 길이에 따른 낙엽송 제재목의 휨 성능 변화를 알아보기 위하여 연구를 진행하였다. 연구에 사용된 시험편의 크기는 38(너비) ${\times}$ 89(깊이) ${\times}$ 3,600(길이) $mm^3$이며, 평균 기건 밀도와 함수율은 각각 $543.5kg/m^3$, 10.5%이었다. 낙엽송 육안 등급 1등급 248본을 두 그룹으로 나눠, 지간 거리 1,650 mm와 3,000 mm에서 휨 실험을 진행하여 휨 강도와 휨 탄성계수를 도출하였다. 휨 탄성계수는 유의 수준 5%에서 지간 거리에 따라 차이가 없다고 판단된 반면 휨 강도는 차이가 있었으며, 지간에 반비례하였다. 지간 거리 1,650와 3,000 mm에서 휨 강도의 5% 하한치는 각각 28.65와 25.70 MPa로 확인되었다. 지간 거리에 따른 휨 강도 차이는 백분위 수가 증가함에 따라 커지는 것으로 확인되었으며, 이는 와이블 최약 링크 파손 이론에 의한 치수 효과 때문으로 사료된다. 따라서 지간 대 깊이 비가 15 이상으로만 제한되어 있는 목구조용 실대재 휨 시험법(KS F 2150)에 치수 효과를 고려할 수 있는 방법이 포함되어야 할 것으로 판단된다. 이를 통해 다양한 치수의 제재목에서 얻어지는 강도를 설계 값에 반영할 수 있을 것으로 기대된다.

• 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.

• 대한기계학회논문집A
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• 제24권10호
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• pp.2451-2460
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• 2000

In order to minimize straightness error of deflected shaft, a geometric adaptive straightness controller system is studied. A multi-step straightening and a three-point bending process have been developed for the geometric adaptive straightness controller. Load-deflection relationship, on-line identification of variations of material properties, on-line springback prediction, and real-time hydraulic control methodology are studied for the three-point bending process. By deflection pattern analysis and fuzzy self-learning method in the multi-step straightening process, a straightening point and direction, desired permanent deflection and supporting condition are determined. An automatic straightening machine has been fabricated for rack bars by using the developed ideas. Validity of the proposed system is verified through experiments.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 춘계학술대회 논문집
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• pp.139-148
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• 1994

An experimental study on material characterization and mechanical properties of SMC(Sheet Molding Compounds) compression molding 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, 45mm/min were used for preparing the specimen of SMC compression molding 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.

• 한국가스학회지
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• 제3권3호
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• pp.1-8
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• 1999

Membrane용 오스테나이트계 304 스테인리스강 판재의 3점 굽힘피로 특성에 관한 연구를 상온 및 LNG 온도인 $-162^{\circ}C$, 변형량 $0.43{\~}1.70\%$ 범위에서 수행하였다. 저온에서의 굽힘피로 특성이 상온보다 우수한 것으로 나타났고, 이는 변형유기 마르텐사이트 변태에 필요한 구동력이 적어서 보다 많은 양의 마르텐사이트를 함유했기 때문으로 판단된다. 상온 및 저온 모두에서 반복경화 현상이 관찰되었으며, 이러한 반복경화는 상온의 경우 피로주기가 반복됨에 따라 점진적으로 증가되지만 저온의 경우 초기 피로주기에서 급격히 증가된 후 점차로 감소하거나 일정한 값을 나타내었는데 이러한 차이는 저온의 경우 초기에 급격히 변형유기 마르텐사이트가 생성되지만 상온의 경우 변형유기 마르텐사이트 생성에는 일정한 소성변형의 축적이 필요하기 때문으로 생각된다. 기존의 JGA 연구결과와 비교해 볼 때 본 연구에서 사용된 국산소재의 굽힘피로 특성이 우수한 것으로 나타났다.

• Journal of Mechanical Science and Technology
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• 제16권9호
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• pp.1078-1083
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• 2002

Ceramics are significantly used in many industrial applications due to their excellent mechanical and thermal properties such as high temperature strength, low density, high hardness, low thermal expansion, and good corrosion resistive properties, while their disadvantages are brittleness, poor formability and high manufacturing cost. To combine advantages of ceramics with those of metals, they are often used together as one composite component, which necessiates reliable joining methods between metal and ceramic. Direct brazing using an active filler metal has been found to be a reliable and simple technique, producing strong and reliable joints. In this study, the fracture characteristics of Si$_3$N$_4$ ceramic joined to ANSI 304L stainless steel with a Ti-Ag-Cu filler and a Cu (0.25-0.3 mm) interlayer are investigated as a function of strain rate and temperature. In order to evaluate a local strain a couple of strain gages are pasted at the ceramic and metal sides near joint interface. As a result the 4-point bending strength and the deflection of interlayer increased at room temperature with increasing strain rate. However bending strength decreased with temperature while deflection of interlayer was almost same. The fracture shapes were classified into three groups ; cracks grow into the metal-brazing filler line, the ceramic-brazing filler line or the ceramic inside.