• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 추계학술대회 논문집
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• pp.272-276
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• 2001

Multicomponent $Zr_{41.2}Ti_{13.8}Cu_{12.5}Ni_{10}Be_{22.5}$ bulk matallic glass alloy shows good bulk glass forming ability due to its high resistance to crystallization in the undercooled liquid state.1) In this study, DSC and X-ray diffractometry have been performed to confirm the amorphous structure of the master $Zr_{41.2}Ti_{13.8}Cu_{12.5}Ni_{10}Be_{22.5}$ alloy. To investigate the mechanical properties and deformation behaviors of the bulk metallic $Zr_{41.2}Ti_{13.8}Cu_{12.5}Ni_{10}Be_{22.5}$ alloy, a series of compression tests has been carried out at the temperatures ranging from $351^{\circ}C$ to $461^{\circ}C$ and at the various initial strain rates from $2{\times}10^{-4}s^{-1}\;to\;2{\times}10^{-2}s^{-1}$. There are two types of nominal stress-strain curves. The one shows linear stress-strain relationship meaning fracture at maximum stress, the other shows plastic deformation including steady-state flow. Also DSC analysis for the compressed specimens has been performed to investigate the change of thermal stability and crystallization behavior for the various test conditions.

• 한국해양공학회지
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• 제7권2호
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• pp.19-29
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• 1993

The static tensile tests of GFRP, ID300, CFRID300 and CFRPEEK were made on the plain and notched specimens at room temperature. The results were discussed based on linear notch mechanics which was proposed by H.Nistani. The fracture of notched GFRP, ID300, CFRID300 and CFRPEEK specimens is controlled by the elastic maximum stress, $({\sigma}_max)$, and the notch root racius,$\rho$, alone, independently of the other geometrical conditions. The relation between fracture nominal stress,$({\sigma}_max)$, and stress concentration factor, $K_t$ and a part where $({\sigma}_c)$ is nearly constant independent of $K_t$. A similar phenomenon can be seen in the fatigue tests of notched specimes under rotating bending or push-pull. The almost constant $({\sigma}_c)$ values correspond to the nearly constant apparent stress intensity factor, $K_{1pc}$ values, obtained by assuming ,$\rho$=0. This can be attributed to the existence of the stable crack. Linear notch mechanics is very useful for analyzing the static tensile fracture behavior of notched GFRP, ID300, CFRPEEK specimens.

• 대한기계학회논문집
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• 제16권4호
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• pp.667-674
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• 1992

본 연구에서는 복합재료의 접착이음에 대한 강도 평가법을 확립하기 위한 기 초연구로써 접착이음의 가장기본적인 형태의 하나인 겹치기 이음(single-lap joint: SLJ)에 대한 응력해석과 정적 및 피로 강도시험을 실시하고, 종래의 강도평가법의 문 제점을 파악.검토하고 정량적이고 통일적인 접착이음의 강도평가법의 확립 및 설계 기 준의 설정에 대한 새로운 방향을 모색 하고저 한다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.290-294
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• 1997

In this study, the welded residual stresses test was carried out with pure titanium and TIG welded material using in chemical plants an airplane frames etc.. The relationship between process parameters and residual stresses is complex since a number of factors are involved. Extensive studies have been carried out to determine the effects of various process parameters on residual stress. The result of micro-hardness about butt welded spacemen was measured of low hardness value in the melting metal zone. The residual stress of welded zone on the Titanium plate by the sectioning method and finite element method was high measured in the spacemen of high current and voltage. Also, compressive residual stress in the range of distance about 15∼20mm from the middle of the deposited metal area is very change. The result of impact test about butt welded spacemen of pure titanium plate was measured of very difference in the welded bead, heat affect zone and base metal, and be measured of high impact value in the heat affect zone. The measure result of welded residual stresses about pure titanium is high measured hen nominal steel plate. The V-Type butt welded spacemen, that of the measurement result on the welded residual stress is high measure then X-Type butt welded spacemen.

• 대한기계학회논문집A
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• 제20권4호
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• pp.1275-1289
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• 1996

The plane elasticity problem of collinear cracks in a layered medium is investigated. The medium is modeled as bonded structure constituted from a surface layer and a semi-infinite substrate. Along the bond line between the two dissimilar homegeneous constituents, it is assumed that as interfacial zone having the functionally graded, nonhomogeneous elastic modulus exists. The layered medium contains three collinear cracks, one in each constituent material oriented perpendicular to the nominal interfaces. The stiffness matrix formulation is utilized and a set of homogeneous conditions relevant to the given problem is readily satisfied. The proposed mixed boundary value problem is then represented in the form of a system of integral equations with Cauchy-type singular kernels. The stress intensity factors are defined from the crack-tip stress fields possessing the standard square-root singular behavior. The resulting values of stress intensity factors mainly address the interactions among the cracks for various crack sizes and material combinations.

• Structural Engineering and Mechanics
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• 제50권5호
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• pp.605-616
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• 2014

When the periodic cellular structure is loaded or swelling beyond the critical value, the structure may undergo a pattern transformation owing to the local elastic instabilities, thus leading to structural collapse and the structure changing to a new configuration. Based on this deformation-triggered pattern, we have proposed the novel composite gel materials. This designed material is a type of architectural material possessing special mechanical properties. In this study, the mechanical behavior of the composite gel periodic structure with various gel inclusions is studied further through numerical simulations. When pattern transformation occurs, it results in a different elastic relationship compared with the material at untransformed state. Based on the obtained nominal stress versus nominal strain behavior, the Poisson's ratio and corresponding deformed structure patterns, we investigate the performance of designed composite materials and the effects of the uniformly distributed gel inclusions on composite materials. A better understanding of the characteristics of these composite gel materials is a key to develop its potential applications on new soft machines.

• Steel and Composite Structures
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• 제36권1호
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• pp.75-86
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• 2020

The grid structures with welded hollow spherical joint (WHSJ) have gained increasing popularity for use in industrial buildings with suspended cranes, and usually welded with steel tube (ST). The fatigue performance of steel tube-welded hollow spherical joint (ST-WHSJ) is however not yet well characterized, and there is little research on fatigue life prediction methods of ST-WHSJ. In this study, based on previous fatigue tests, three series of specimen fatigue data with different design parameters and stress ratios were compared, and two fatigue failure modes were revealed: failure at the weld toe of the ST and the WHSJ respectively. Then, S-N curves of nominal stress were uniformed. Furthermore, a finite element model (FEM) was validated by static test, and was introduced to assess fatigue behavior with the hot spot stress method (HSSM) and the effective notch stress method (ENSM). Both methods could provide conservative predictions, and these two methods had similar results. However, ENSM, especially when using von Mises stress, had a better fit for the series with a non- positive stress ratio. After including the welding residual stress and mean stress, analyses with the local stress method (LSM) and the critical distance method (CDM, including point method and line method) were carried out. It could be seen that the point method of CDM led to more accurate predictions than LSM, and was recommended for series with positive stress ratios.

• 한국건설순환자원학회논문집
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• 제3권1호
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• pp.58-63
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• 2015

현재까지 알칼리 활성화제를 사용한 무시멘트 콘크리트의 연구는 슬럼프, 강도 및 내구성 등 기본적인 재료성질에 대해서 주로 수행되어져 왔다. 그러나 알칼리 활성화제를 사용한 무시멘트 콘크리트의 구조부재에의 적용을 위해서는 탄성계수, 응력-변형률 관계 및 구조 부재 거동 등에 대한 연구가 필수적이다. 본 논문에서는 50MPa급 알칼리 활성 슬래그 콘크리트를 사용한 철근콘크리트 보시험체 6개를 제작한 후, 전단실험을 수행하였다. 실험과 해석에 의해 얻은 공칭전단강도는 전단철근이 배치되어 있는 시험체에서는 최대 18% 정도의 차이를 보이나, 전단철근이 없는 시험체에서는 최대 31% 정도의 차이를 보였으며 또한 알칼리 활성 슬래그 콘크리트의 설계전단강도에 비하여 전단강도 실험값이 22~57% 정도 크게 나타나 전단설계식이 상당히 안전측임을 알 수 있다.

• Composites Research
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• 제36권4호
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• pp.259-263
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• 2023

This study investigated the open hole tensile (OHT) properties of carbon fiber/epoxy composites and compared them to bolt joint tensile (BJT) properties. The net nominal modulus and strength (1376 MPa) were found to be higher than the gross nominal strength (1041 MPa), likely due to increasing hole size. The OHT and BJT specimens exhibited similar stiffness, as expected without bolt rotation causing secondary bending. OHT specimens experienced a sharp drop in stress indicating unstable crack propagation, delamination, and catastrophic failure. BJT specimens failed through shear out on the bolt side and bearing failure on the nut side, involving fiber kinking, matrix splitting, and delamination, resulting in lower strength compared to OHT specimens. The strength retention of carbon fiber/epoxy composites with open holes was 66%. Delamination initiation at the hole's edge caused a reduction in the stress concentration factor. Filling the hole with a bolt suppressed this relieving mechanism, leading to lower strength in BJT specimens compared to OHT specimens. Bolt joint efficiency was calculated as 15%. The reduction in strength in bolted joints was attributed to fiber-matrix splitting and delamination, aligning with Hart Smith's bolted joint efficiency diagram. These findings contribute to materials selection and structural reliability estimation for carbon fiber/epoxy composites. They highlight the behavior of open hole and bolt joint configurations under tensile loading, providing valuable insights for engineering applications.

• 한국강구조학회 논문집
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• 제10권3호통권36호
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• pp.355-367
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• 1998

볼트 구멍의 크기가 고장력 볼트 이음부의 역학적 거동 및 내부 압축응력 분포에 미치는 영향을 살펴보기 위하여 과대공 및 표준공을 갖는 고장력 볼트 이음부에 대한 실험 및 해석적 연구를 실시하였다. 실험적 연구에서는 정적 인장시험과 피로시험을 실시하여 미끄러짐 특성, 피로강도 및 피로파단 양상을 평가하였으며, 해석적 연구에서는 유한요소해석을 통하여 내부 압축응력의 분포영역을 밝히고, 내부 압축응력의 분포가 역학적 거동에 미치는 영향을 평가하였다. 실험결과, 과대공을 갖는 고장력 볼트 이음부의 미끄러짐 계수와 피로강도는 표준공을 갖는 이음부와 비교하여 큰 차이는 없으나 다소 감소하는 경향이 나타났다. 이러한 원인은 과대공 시험편의 경우 볼트 구멍의 크기가 표준공 시험편과 비교하여 상대적으로 크기 때문에 축력의 작용폭이 좁아져 마찰영역으로 작용하는 내부 압축응력의 분포영역이 작아지기 때문으로 판단되며, 이는 유한요소해석 결과로도 확인할 수 있었다. 또한, 피로시험 결과 과대공 시험편의 피로균열의 발생점이 표준공 시험편 보다 볼트 구멍 내벽에 가까운 것을 알 수 있어, 피로균열의 발생위치는 고장력 볼트의 도입축력에 의해 모재와 이음판에 형성되는 내부 압축응력의 분포영역과 밀접한 관계가 있음을 알 수 있었다.