• 산업기술연구
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• 제19권
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• pp.269-278
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• 1999

When a variety of repeated loads are given, most steel structures failed in much lower level of loads than static failure loads. In addition, bridge always includes the internal defects or discontinuities. from these, fatigue cracks initiates and can lead to sudden failure. Thus, in this study, tensile specimens by the cover plate shapes were used as the test specimens. The fatigue test was performed by constant amplitude fatigue loading and beach mark. From the results of this study, each specimen's fatigue section was observed. in addition, stress intensity factor at crack tip was calculated by using the Green's function which applied to discontinuous section where causing stress concentration. Therefore, the fatigue life of structural detail was investigated by adopting the theories of fracture mechanics. each specimen's crack shape is a semi-elliptical surface crack or center crack sheet, stress gradient correction factor, Fg is the most subjective of all stress intensity correction factors and fatigue life should be predicted by previous proposed function and finite element analysis.

• 대한기계학회논문집A
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• 제24권2호
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• pp.496-505
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• 2000

A semi-infinite parallel crack propagated with constant velocity in two bonded anisotropic strip under anti-plane clamped displacement is analyzed. Using Fourier integral transform a Wiener-Hopf equation is derived. By solving this equation the asymptotic stress and displacement fields near the crack tip are determined, where the results give the more general expression applicable to the extent of the anisotropic material having one plane of elastic symmetry for the parallel crack. The dynamic stress intensity factor and energy release rate are also obtained as a closed form, which are the results applicable to the problem both of dynamic and static crack under the same geometry as this study. The stress intensity factor approaches zero at the critical crack velocity which is less than the shear wave velocity, but in typical case of isotropic or orthotropic material agrees with the velocity of shear wave. Also a circular shear stress around crack tip is considered, from which the stress is shown to be approximately symmetric about the horizontal axis. Referring to the maximum stress criteria, it could be shown that a brenched crack is formed by crack growth as crack velocity increases.

• 비파괴검사학회지
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• 제8권1호
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• pp.22-29
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• 1988

The optical method of reflected and transmitted caustics has been utilized in mechanics investigations. This relatively new experimental technique has been successfully applied on various fracture analysis such as static and dynamic c rack propagation studies, some elasticity problems and contact stress, etc, In this study, the stress intensity factors in thin polycarbonate specimens, a kind of optically anisotropic material, under Mode I loading condition are estimated by the method of caustics. The values of stress intensity factors obtained from theoretical caustics shape are compared by the experiment. It is confirmed that the two stress intensity factors agree well with Srawley's solution.

• 대한기계학회논문집A
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• 제26권11호
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• pp.2277-2286
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• 2002

The application of bonded dissimilar materials to industries as automobiles, aircraft, rolling stocks, electronic devices and engineering structures is increasing gradually because these materials, compared to the homogeneous materials, have many advantages for material properties. In spite of such wide applications of bonded dissimilar materials, the evaluation method of quantitative strength considering the stress singularities for its bonded interface has not been established clearly. In this paper, the stress singularity for Bctors and the stress intensity factors were analyzed by boundary element method(BEM) for the scarf joints of Al/Epoxy with and without a crack, respectively. From static fracture experiments of the bonded scarf joints, a fracture criterion and a evaluation method of interface strength in bonded dissimilar materials were proposed and discussed.

• 한국정밀공학회지
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• 제15권6호
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• pp.159-166
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• 1998

The problem of interface crack in the bonded structures has received a great deal of attention in recent years. In this paper the aluminum bonded single lap-joint containing the interface edge crack is investigated. The tensile load and the average shear stress of the adhesive joints which have different crack length are obtained from the static tensile tests. The critical value of crack length to provoke the interface fracture is determined to a/L=0.4, where a is the interface crack length and L is the adhesive lap-length. The fracture mechanical parameters are introduced to confirm the existence of the critical crack length. The compliance and the stress intensity factors are calculated using the displacement and the stress near the interface crack tip by the boundary element method. These numerical results support the experimental results that the critical value of a/L is 0.4. It is known that the compliance and the stress intensity factors are the efficient parameters to estimate the bonded single lap-joint containing the interface edge crack.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.48-53
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• 2004

This paper suggested the method determing the stress intensity factor (SIF) for functionally gradient materials (FGMs) by photo elastic experimental method. The SIF for the center crack in a finite rectangulat plate with a linear variation of shear modulus with constant density and Poisson's ratio along the direction of the crack under mode I static loading is obtained. The exponential and linear variation of stress fields are used for obtaining the SIF. The greater crack length, the increaser the difference of the SIF between right and left side crack tip.

• 한국해양공학회지
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• 제7권2호
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• pp.57-67
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• 1993

The fracture behavior of plain woven glass/epoxy composite plates with a crack is investigated under static tensile loading. It is shown in this paper that the characteristic length associated with the point stress criterion depends on the crack length. To predict the not ched tensile strength, the point stress criterion proposed by Whitney and Nuismer are modified. An excellent agreement is found between the experimental results and the analytical prediction of the modified point stress criterion. The condition of unstable crack growth in the presence of a per-existing flaw(machined notch) is examined by means of the maximum stress intensity factor $K_max$ using maximumload P$_max$. The values of $K_max$ evaluated from energy release rate G$_max$(the compliance me thod) indicate a wide difference. Therefore in regard to anisotropy and heterogeneity of the composite materials studied, the modified shape correction factor f(a/W) is obtained. $K_max$evaluated by the compliance method a little or insignificantly depends on the initial crack length a, the specimen thickness B, the crack angle .theta. and the specimen geometry.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.655-659
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• 1997

The analysis of cracks at the interface between dissimilar materilar has received a great deal of attention in recent years. In this paper we conducted the static tensile test for the aluminum bonded single lap-joint with the interface edge crack. Comparing this results, that is ultimate load and strain value of aluminum adherend by strain gauge with the fracture mechanics parameters, compliance and stress intensity factors acquied from the boundary element analysis, we concluded that there are critical value of crack length to provoke the interface fracture.

• 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.

• 한국생산제조학회지
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• 제7권1호
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• pp.58-68
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• 1998

Advantages of adhesively bonded joints and techniques of weight reduction have led to increasing use of structural adhesives such as LSI(large scale integration) package, automobile, aircraft in the various industries. In spite of such wide applications of adhesively bonded joints, the evaluation method of bonding strength has not been established. Stress singularity occurs at the interface edges of adhesively bonded joints and it is required to analyze it. In this paper, the stress singularity using 2-dimensional elastic boundary element method (BEM) with the changes of the lap length and adhesive for single lap joint was analyzed, and experiments of strength evaluation were carried out. As the results, the evaluating method of bonding strength considering stress singularity at interface edges of adhesively bonded joints and stress intensity factor of interface crack have been proposed in static and fatigue test.