• Journal of the Korean Society for Precision Engineering
• /
• v.6 no.3
• /
• pp.78-89
• /
• 1989

Applicability of tearing modulus based on J-integral proposed by Paris et al is investigated using compact tension specimens of strutural alloy steel (SCM4). Both general fracture test and instability fracture test are performed. The applied tearing modulus, ( $T_{j}$)app estimated from the real load vs. crack growth curve measured from experiments are compared with that estimated from the limit load vs. crack growth curve. The results are : (1) the $T_{j}$parameter could be applied to predict crack growth instability : (2) The use of ( $T_{j}$)app estimated from the load vs. crack growth curve, proposed in this study could be well predicted crack growth instability instead of that estimated form the limit load vs. crack growth curve.e.

• Journal of the Korea Concrete Institute
• /
• v.14 no.3
• /
• pp.357-364
• /
• 2002

The resistance curves (R-curves) for 381 m crack extension of CLWL-DCB specimens had been determined. The average velocities of the crack extension measured with strain gages were 0.70 and 55 ㎜/sec. The measured rotation angle of the notch faces showed the existence of the singularity at least before 171 and 93 mm crack extensions for the 0.70 and 55 ㎜/sec crack velocities, respectively. The maximum slopes of the R-curves occurred between 25 and 89 ㎜ crack extensions for 0.70 ㎜/sec crack velocity and between 51 and 127 ㎜ crack extensions for 55 ㎜/sec crack velocity During the maximum slopes of the R-curves, the micro-crack localization can be expected, and faster crack velocity may form longer micro-cracking and micro-crack localizing zones. The fracture resistance of 0.70 ㎜/sec crack velocity reached a roughly constant maximum value of 143 N/m at 152 ㎜ crack extension, while that of 55 ㎜/sec crack velocity increased continuously to 245 N/m at 254 ㎜ crack extension and then decreased to the value of 0.70 ㎜/sec crack velocity. The R-curve of 55 ㎜/sec crack velocity was similar to that of the small size three-point bend test, and it showed that small size specimen or fast crack velocity could cause more brittle behavior.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.3
• /
• pp.497-505
• /
• 1992

본 연구에서는 최근에 개발된 직물 탄소섬유강화 복합재료의 파괴인성치를 정 량적으로 결정하고 파괴거동을 조사하고자 한다. 본 연구의 목적은 이 재료에 선형 탄성파괴역학의 적용여부를 알아보고, R곡선을 이용하여 균열의 생성점 및 불안정 파 괴점의 파괴인성치를 정확히 구하며, 주사형 전자현미경을 통해 파단면 및 균열 성장 시점을 관찰하여 파괴거동을 조사하는데 있다.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.12 no.1
• /
• pp.53-63
• /
• 1988

Using COD-R curves, instability of crack growth in ductile material is studied here. Tearing modulus $T_{\delta}$, based on the COA concept is defined and the instability criterion $T_{{\delta}{\app}}$> $T_{{\delta}{\mat}}$ is compared with experiments. Variations of the COD-R curve and the location of rotation center are experimentally investigated as the initial crack ratio varies. Three-point bend specimens of alloy steel SCM4 are used here and two clip-on gauges are installed in order to obtain the COD-R curve. The results show that the tearing modulus $T_{\delta}$ is a good measure to characterize the instability of crack growth. Also it is found that the location of rotation center is almost constant regardless of the initial crack ratio and the amount of the crack growth.

• The Journal of Engineering Geology
• /
• v.21 no.4
• /
• pp.295-304
• /
• 2011

The first step in improving our understanding of uncertainties suclt as rock mass strength parameters and deformation modulus in rock masses around high-level radioactive waste disposal repositories, for improved safety, is to study the process of crack development in intact rock. Therefore, in this study, the fracture process and crack development were examined in samples of KURT granite taken from the KAERI Underground Research Tunnel (KURT), based on acoustic emission (AE) and moment tensor analysis. The results show that crack initiation, coalescence, and unstable crack occurred at rock uniaxial compressive strengths of 0.45, 0.73, and 0.84, respectively. In addition, moment tensor analysis indicated that during the early stage of loading, tensile cracks were predominant. With increasing applied stress, the number of shear cracks gradually increased. When the applied stress exceeded the stress level required for crack damage, unstable shear cracks which directly result in failure of the rock were generated along the failure plane.

• Journal of Ocean Engineering and Technology
• /
• v.12 no.3 s.29
• /
• pp.60-67
• /
• 1998

In this study, the J-Resistance Curve and material tearing modulus of SA508-C3 steel, which is one of the used nuclear pressure vessel steel, are measured ar room temperature, $200^{circ}C$ and $300^{circ}C$ according to load ratio analysis and ASTM E813, ASTM E1152, respectively. It is observed that J-R curve and Tmat value decrease as the temperature level increase. Applicability of $T_j$ proposed by Paris et al as instability parameter for ductile material is investigated. It is concluded that results are the $T_j$ parameter may be used as a crack instability parameter.

• Composites Research
• /
• v.16 no.4
• /
• pp.44-50
• /
• 2003

The damage zone around a crack tip occurring before the fracture is a significant domain. which affects the toughening mechanism of materials. In this study. the growth process of damage zone in the vicinity of crack tip for rubber-modified epoxy resin is investigated using an acoustic emission(AE) analysis. The weight fractions of rubber(CTBN 1300$\times$B) in rubber-modified epoxy resin are 5 wt% and 15 wt%. The fracture toughness($K_{IC}$) and the fracture energy($G_{IC}$) were measured using 3 point bending single-edge notched specimens. The damage zone and rubber particles distributed around the crack tip were observed by a polarized optical microscope and an atomic force microscope(AFM). The damage zone around crack tip of rubber-modified epoxy resin was formed at 13 % loading and developed until 57 % loading of the fracture load. The crack initiated at 57 % loading grew repeatedly in the stick-slip propagation behavior. Based on time-frequency analysis, it was confirmed that AE signals with frequency bands of 0.15~0.20 MHz and 0.20~0.30 MHz were generated from cavitation and stable/unstable cracking inside the damage zone.

• Journal of the Society of Naval Architects of Korea
• /
• v.33 no.4
• /
• pp.75-86
• /
• 1996

A fatigue life prediction program for multiple planar surface cracks in finite plates and T-fillet joints, based on linear elastic fracture mechanics was developed. This prediction technique include the crack coalescence, mutual interation and the stress intensity concentration effect in welded joints. Total of 44 cases were compared with lida's and Vosikovsky's experimental results and it was found that the present method was a reasonable tool for the predictioin of fatigue life.

• Composites Research
• /
• v.34 no.5
• /
• pp.323-329
• /
• 2021

In this paper, the characteristics of fracture in mode I loading were analyzed for adhesively bonded joints with non-uniform adhesion. The Double Cantilever Beam test was performed and mode I fracture toughness was obtained. In the case of non-uniform adhesively bonded joints, the stable crack growth sections and unstable crack growth section were shown. The fracture characteristics of each section were observed through the load-displacement curve of the DCB test and the fracture surface of the specimen. Finite Element Analysis was performed at the section based on segmented section by crack length measured through the test and using the mode I fracture toughness of each section. Through DCB test results and finite element analysis results, it was confirmed that the fracture behavior of specimens with non-uniform adhesion can be simulated.

• Tunnel and Underground Space
• /
• v.14 no.3
• /
• pp.167-174
• /
• 2004

This paper is to introduce an article published in Rock Mechanics and Rock Engineering, 2003. In this research, a fracture mechanics model is developed to illustrate the importance of time-dependence far brittle fractured rock. In particular a model is developed fer the time-dependent degradation of rock joint cohesion. Degradation of joint cohesion is modeled as the time-dependent breaking of intact patches or rock bridges along the joint surface. A fracture mechanics model is developed utilizing subcritical crack growth, which results in a closed-form solution for joint cohesion as a function of time. As an example, a rock block containing rock bridges subjected to plane sliding is analyzed. The cohesion is found to continually decrease, at first slowly and then more rapidly. At a particular value of time the cohesion reduces to value that results in slope instability. A second example is given where variations in some of the material parameters are assumed. A probabilistic slope analysis is conducted, and the probability of failure as a function of time is predicted. The probability of failure is found to increase with time, from an initial value of 5% to a value at 100 years of over 40%. These examples show the importance of being able to predict the time-dependent behavior of a rock mass containing discontinuities, even for relatively short-term rock structures.