• 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.

• Structural Engineering and Mechanics
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• 제6권4호
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• pp.467-471
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• 1998

A mathematical model is developed to predict the fatigue notch factor of butt welds subject to number of parameters such as weld geometry, residual stresses under dynamic combined loading conditions (tensile and bending). Linear elastic fracture mechanics, finite element analysis, dimensional analysis and superposition approaches are used for the modelling. The predicted results are in good agreement with the available experimental data. As a result, scatters of the fatigue data can be significantly reduced by plotting S-N curve as ($S{\cdot}K_f$) vs. N.

• 한국해양공학회지
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• 제2권2호
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• pp.61-70
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• 1988

In order to consider the concept of the fitness for purpose'in fatigue design of offshore structure, fracture mechanics is applied to evaluate initial or weld defects. Generally, linear elastic fracture mechanics has been applied to tstimate initial fatigue crack propagation rate as well as long fatigue crack propagation rate. But, initial fatigue crack propagation rate in elasto-plastic notch field may not be characterized by application of stress intensity factor range .DELTA. K, because plastic effect due to stress concentration of notch may contribute to initial crack propagation. Therefore, to introduce the plastic effect into fatigue crack driving force, in this studty, the evaluating method of J-integral range .DELTA. J, was developed by willson was modified for application to notch field. In calculation of .DELTA. J obtained from the modified J-integral, stress gradient and crack closure behavior in the notch field were considered. The initial crack propagation rates in the notch fields of mild steels and high tensile strength steels were correlated to .DELTA. J. As the result, it was cleared that the present .DELTA. J is applicable to charachterize the fatigue crack propagation rates in both the elastic and elasto-plastic notch fields.

• Coupled systems mechanics
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• 제11권3호
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• pp.217-231
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• 2022

The present paper is concerned with a delamination analysis of a multilayered frame structure that exhibits non-linear creep behavior. A solution to the strain energy release rate is obtained by considering the time-dependent complementary strain energy in the frame. The mechanical behavior of the frame is treated by using a non-linear stress-strain-time relationship. The time-dependent solution to the strain energy release rate obtained in the present paper holds for a multilayered frame made of arbitrary number of adhesively bonded layers of different thicknesses and material properties. Besides, the dealamination is located arbitrary along the thickness. The solution to the strain energy release rate is verifiedby applying the J-integral approach. A parametric study of the strain energy release rate is carried-out. Two three-layered frame configurations are analyzed in order to evaluate the influence of the delamination crack location along the thickness on the strain energy release rate. The strain energy release is analyzed also for the case when a notch is cut-out in the inner delamination crack arm. The results obtained are compared with these for a frame without a notch.

• 기계저널
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• 제35권3호
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• pp.242-251
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• 1995

균열(crack)을 갖는 부재의 강도를 평가할 때에 있어서 응력확대계수를 이용하는 데에 대한 합 리성은 현재까지 의심할 여지없는 사실로서 받아들여지고 있다. 그 근거는 소규모 항복의 조건이 만족되고 있을 때에는 균열의 치수가 틀리더라도 균열선단부근의 역학적 상태는 응력확대계수 만에 의해 지배된다는 사실에 있다. 한편, 노치(notch)를 갖는 부재의 강도를 평가할 때에 최대 응력만을 고려하는 것은 불충분하다. 예를 들면, 그것은 노치반경 .rho.가 10 mm 정도의 노치와 .rho.가 0에 상당하는 균열과는 최대응력 .sigma.$_{max}$를 같게 하더라도 역학적 상태의 가 혹함(severity)이 동일하게 되지 않는다는 사실로부터도 명백하다. 그렇다면, .rho.가 0과 10 mm의 중간값, 예를 들면 1 mm 혹은 0.1 mm일 때와 같은 역학적 상태의 가혹함이 생기기 위해서는 .sigma.$_{max}$가 얼마이면 될까\ulcorner 또는, 만약 .rho.가 틀릴 때, 동일한 현상(same phenomenon)이 생기지 않는다고 한다면 그것은 어떠한 물리적 배경에 근거한 것일까\ulcorner 이글에 서는 이러한 질문에 대한 해답과 함께 선형파괴역학과 선형노치역학이 생겨나게 된 간략한 역사적 배경과 선형노치역학의 개념에 대해 언급하기로 한다.

• 콘크리트학회지
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• 제2권2호
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• pp.81-92
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• 1990

콘크리트는 혼합물로서 비균질성, 이방성 및 비선형성 재료이기 때문에 그의 파괴해석에 있어서 재래의 강도 개념보다 파괴역학 개념을 적용하여 콘크리트의 파괴인성을 도입하여 평가하는 것이 보다 합리적이라 할 수 있다. 지금까지 콘크리트에 적용되어 온 파괴역학 개념은 두가지로 대별될 수 있는데 하나는 선형탄성파괴역학 개념이고 다른 하나는 비선형파괴역학 개념이다. 그러너 전자를 콘크리트에 적용하는데는 문제점과 불합리성이 지적되어 왔다. 본 연구에서는 비선형파괴역학에서 많이 이용되어온 J-적분법과 COD법을 도입하여 굵은골재의 최대치수와 노치깊이의 변화가 콘크리트의 파괴거동, 파괴에너지 및 균열성장에 미치는 영향, 균열개구변위와 파괴에너지의 관계 등을 고찰하기 위하여 콘크리트 작사각형 보를 제작하여 3점 휨 파괴실험을 수행하였다. 그 결과 굵은골재의 최대치수와 노치깊이가 증가할수록 하중-치 짐거동의 비선형성이 더욱 두드러졌고, 굵은골재 최대치수의 증가는 콘크리트의 연성을 증가시켜 보다 안정된 파괴를 유도하였으며, 균열전파경로는 굵은골재의 최대치수가 증가할수록 점점 더 직선에서 벗어나 불규칙적이었으나 노치깊이의 변화에는 거의 영향을 받지 않았다. 또한 파괴에너지는 굵은골재의 최대치수가 증가하고 노치깊이가 감소할수록 증가하였으나, 균열개구변위는 노치깊이가 증가할수록 감소하였으며 굵은골재의 최대치수의 변화에는 거의 영향을 받지 않았다.

• 한국해양공학회지
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• 제12권1호
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• pp.23-31
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• 1998

Kind 1 propeller shaft in ships is the shaft which is provided with effective measures against corrosion by sea water, or the shaft which is made of approved corrosion resistance materials. The propeller shaft other than specified above is Kind 2. Thus, this study is mainly concerned with the resistance to fatigue damage in sea water against stress concentrations due to the notches. The results obtained can be summarized as follows; (1) The stress increases with curing time, however, when the curing time reaches at 96 hours the stress becomes a constant value. The elongation decreases with curing time, however, when the curing time reaches at 48 hours the elongation becomes a constant value. Thus, in case of FRP coating on propeller shaft, it is necessary to cure for 48 hours at least. (2) The relation of $\sigma$$_n$-K$_t$ is to be classified into two parts, which is a part where fracture nominal stress, $\sigma$$_n$, decreases with increasing $K_t$, and a part where $\sigma$$_n$ is nearly constant independent of $K_t$. (3) According to a linear notch mechanics, the measure of severity controlling the fracture in notched FRP body is the notch root radius, $\rho$. The notched static strength of an arbitrary specimen will be estimated from $\sigma$$_{max}$ -1/$\rho$ curve. (4) Through the observation of cross section after fatigue test, the part of interface was kept good condition irrespective of loading conditions.

• Journal of Advanced Marine Engineering and Technology
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• 제18권2호
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• pp.41-53
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• 1994

In this paper, rotating-bending fatigue tests of the SiC-whisker- reinforced 6061-T6 aluminum alloy and 6061-T6 alumiunm alloy made by power metallurgy were carried out to investigate the fatigue characteristics of plain and notched specimens at room temperature. The fatigue mechnisms in both materials were clarified through successive surface observations using the plastic replica method. In the case of the SiC-whisker-reinforced composites, there are whisker rich and poor zones and the fatigue crack is nucleated from the end of whiskers near the boundary. On the other hand, in the case of the 6061-T6 aluminum alloy, the fatigue crack is nucleated from defects and propagates by shear. Moreover, the results were discussed based on linear notch mechanics.

• International Journal of Precision Engineering and Manufacturing
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• 제8권3호
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• pp.60-63
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• 2007

Weight functions in fracture mechanics represent the stress intensity factors as weighted averages of the externally impressed boundary tractions and body forces. We extended the weight function theory for cracked linear elastic materials to calculate the notch stress intensity factor of a notched structure with anti-plane deformation. The well-known method of deriving weight functions by differentiation cannot be used for notched structures. By combining an appropriate singular field with a regular field, we derived weight functions for the notch stress intensity factor. Closed expressions of weight functions for notched cylindrical bodies are given as examples.

• 한국압력기기공학회 논문집
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• 제11권1호
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• pp.69-73
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• 2015

The study investigated effects of residual stresses and Charpy impact energy on brittle fractures of the butt weld between the valve and the piping, and of the valve body in nuclear power plants via a linear elastic fracture mechanics approach in the ASME B&PV Code, Sec.XI and finite element analysis. Weld residual stress in a butt weld between close check valve and piping, and residual stress in the valve due to casting process were assumed to be proportional to yield strength of base metal. Operating stresses in the butt weld and the valve body were calculated using approximate engineering formulae and finite element analysis, respectively. Applied stress intensity factors were calculated by assuming postulated cracks with specific sizes and then by substituting the residual stresses and the operating stresses into engineering formulae presented in the ASME B&PV Code, Sec.III. Plane strain fracture toughness was derived by using a correlation between Charpy V-notch impact energy and fracture toughness. Structural integrity of the weld and the body against brittle fracture was assessed by using the applied stress intensity factors, plane strain fracture toughness and the linear elastic fracture mechanics approach. As a result, it was identified that the structural integrity was maintained with decreasing the residual stress levels and increasing the Charpy V-notch impact energy.