• Structural Engineering and Mechanics
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• 제20권2호
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• pp.143-160
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• 2005

Modal analysis of cracked cantilever composite beams, made of graphite-fibre reinforced polyamide, is studied. By using the finite element and component mode synthesis methods, a numeric model applicable to investigate the vibration of cracked composite beams is developed. In this new approach, from the crack section, the composite beam separated into two parts coupled by a flexibility matrix taking into account the interaction forces. These forces are derived from the fracture mechanics theory as the inverse of the compliance matrix calculated with the proper stress intensity factors and strain energy release rate expressions. Numerical results are obtained for modal analysis of composite beams with a transverse non-propagating open crack, addressing the effects of the location and depth of the crack, and the volume fraction and orientation of the fibre on the natural frequencies and mode shapes. By means of modal data, the position and dimension of the defect can be found. The results of the study confirmed that presented method is suitable for the vibration analysis of cracked cantilever composite beams. Present technique can be easily extended to composite plates and shells.

• 대한기계학회논문집
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• 제18권3호
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• pp.540-547
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• 1994

Contact and frictional locking conditions and the effect of shielding due to contact at the facet, which could be represented by the difference in energy release rate, as a function of phase angle of loading are analyzed in this study for the case of interfacial cracks by assuming single crack-kink model. The analysis of contact effects on interfacial fracture resistance shows that relative shielding increases as the shear component was increased, which indicates a qualitative agreement with the previous experimental results.

• 열처리공학회지
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• 제6권2호
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• pp.79-88
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• 1993

The static creep mechanism and behaviour of Al-Zn-Mg alloy have been investigated under condition of constant stress tension creep test in the temperature and stress range of $170-260^{\circ}C$ and 5-12.5 $kg/mm^2$ respectively. The experimental result are follows : The stress exponent value for creep was observed to about 7.3-6.43 and the activation energy for creep deformation was 44-41 kcal/mol. Larson-Miller parameter P for the crept specimens under the creep condition was obtained as P = (T + 460) (log $t_r$ + 8.6). Emperical equation for the creep rate was obtained by the computer simulation as follows. $${\varepsilon}\;=\;\exp[(-5.519{\times}10^{-4}{\sigma}+2.33{\times}10^{-2})T-6.98{\sigma}+18.295]{\times}{\sigma}^{-0.0142+10.18}\exp[\frac{(-6{\sigma}+47.8)1000}{RT}]$$ Fracture was dominated by intergranular mechanism over the experimental range.

• International Journal of Precision Engineering and Manufacturing
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• 제9권4호
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• pp.66-70
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• 2008

The propagation of a mixed-mode crack in soda-lime silica glass is modeled by movable cellular automata (MCA). In this model, a special fracture criterion is used to describe the process of crack initiation and propagation. The results obtained using the MCA criterion are compared to those obtained from other crack initiation criteria, The crack resistance curves and bifurcation angles are determined for various loading angles. The MCA results are in close agreement with results obtained using the maximum circumferential tensile stress criterion.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.306-309
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• 2009

The influence of equal-channel angular pressing (ECAP) route on dynamic deformation behavior of ultra-fine grained Al-4.4%Mg alloys was investigated in this study. The 8-pass ECAPed specimens consisted of ultra-fine grains of $0.5{\mu}m$ in size, and contained the considerable amount of second phase particles, which were fragmented and distributed homogeneously in the matrix. The result of dynamic torsional tests indicated that the maximum shear stress and fracture shear strain were lowest in the specimen deformed by ECAP via route A among the 8-pass ECAPed specimens. The formation of adiabatic shear bands was addressed by concepts of critical shear strain, deformation energy required for void initiation, and microstructural homogeneity related to ECAP routes.

• Steel and Composite Structures
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• 제18권3호
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• pp.641-657
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• 2015

Application of reduced web beam section (RWBS) as a sacrificial fuse element has become a popular research field in recent years. Weakening of beam web in these connections may cause local web buckling around the opening area which can affect cyclic behavior of connection including: maximum load carrying capacity, strength degradation rate, dissipated energy, rotation capacity, etc. In this research, effect of local web buckling on the cyclic behavior of RWBS connections is investigated using finite element modeling (FEM). For this purpose, a T-shaped moment connection which has been tested under cyclic loading by another author is used as the reference model. Fracture initiation in models is simulated using Cyclic Void Growth Model (CVGM) which is based on micro-void growth and coalescence. Included in the results are: effect of opening corner radii, opening dimensions, beam web thickness and opening reinforcement. Based on the results, local web buckling around the opening area plays a significant role on the cyclic behavior of connection and hence any parameter affecting the local web buckling will affect entire connection behavior.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.265-268
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• 2002

In this work, the blend system of epoxy and PMR-15 polyimide is investigated in terms of the cure behaviors and thermal stabilities. The cure behaviors are studied in DSC measurements and thermal stabilities are also carried out by TGA analysis. DDM (4, 4'-diamino diphenyl methane) is used as curing agent for EP and the content of PMR-15 is varied within 0, 5, 10, 35, and 20 phr to neat EP. As a result, the cure activation energy ($E_a$) is increased at 10 phr of PMR-15, compared with that of neat EP. From the TGA results of EP/PMR-15 blend system, the thermal stabilities based in the initial decomposed temperature (IDT) and integral procedural decomposition temperature (IPDT) are increased with increasing the PMR-15 content. The fracture toughness, measured in the context of critical stress intensity factor ($K_{IC}$) and critical strain energy release rate ($G_{IC}$), shows a similar behavior with $E_a$. This result is probably due to the crosslinking developed by the interactions between intermolecules in the polymer chains.

• 비파괴검사학회지
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• 제16권2호
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• pp.79-85
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• 1996

복합 재료의 single-lap 및 double-strap adhesive bonding joint 시험편에서 피로 및 인장시험시 방출되는 AE 신호의 분석에 의한 피로 수명 예측 및 파괴 과정의 감시에 대한 연구를 수행하였다. Bonding 시험편의 피로시험시 AE event의 발생양상은 피로에 의해 축적된 elastic strain energy의 방출과 관계되며, peak amplitude가 높고 event duration이 긴 event의 발생 영역과 peak amplitude가 낮고 event duration이 짧으나 많은 event가 발생되는 영역으로 나눌 수 있었다. 그리고 두 영역 사이의 경계 cycle은 피로 수명의 70-80% 근방에 존재하였으며, 이를 이용한다면 피로 수명의 예측이 가능하리라 판단된다.

• 한국자동차공학회논문집
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• 제13권1호
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• pp.153-158
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• 2005

Titanium alloy has widely been used as material for automotive parts because it has high specific strength. It is also light and harmless to human body. But, we have little design data about the creep behaviors of the alloy. Therefore, in this study, creep tests under four constant stress conditions have been conducted with low different temperature conditions. A series of creep tests had been performed to get the basic design data and life prediction of titanium products and we have gotten the fallowing results. First, the stress exponents decrease as the test temperatures increased. Secondly, the creep activation energy gradually decrease as the stresses became bigger. Thirdly, the constant of Larson-Miller parameter on this alloy was estimated as about 7.5. And for the last, the fractographs at the creep rupture showed the ductile fracture due to the intergranullar rupture.

• 소성∙가공
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• 제12권6호
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• pp.588-596
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• 2003

The relationships between evolution of microstructure and mechanical properties of porous Al-3Si-2Mg-2Cu alloy after the foaming and various heat treating were investigated. The foamed alloy having various densities were manufactured by powder compact foaming and heat treated. Then compression test was performed with deformation rate of 0.5/s. The ultimate compression strength was not changed after solution heat treatment but the flow curve after ultimate strength showed very smooth and uniform plateau region. This change of flow curve means that the deformation mechanism is altered from brittle fracture to ductile deformation and the energy absorption property of Al foam is dramatically improved. The improvement of energy absorption without any detriment of mechanical properties is due to that the very brittle precipitation like Al-Cu and Al-Mg was uniformly dissolved in Al matrix after solution heat treatment. And various mechanical properties of Al alloy porous material were improved by 40% with aging of $200^{\circ}C$ and 50min. These improvements are ascribe to the various fine precipitates like $\Omega$ and $\theta$'.