• Composites Research
• /
• 제15권2호
• /
• pp.24-31
• /
• 2002

본 논문에서는 탄소/탄소 브레이크 디스크의 시험 운용중에 키 슬롯부위의 하중지지부와 마찰재 사이에서 발생하는 크랙의 안정성에 대한 연구를 수행하였다. 이렇게 발생한 디스크 크랙의 안정성을 판별하기 위하여, 발생한 여러 가지 모양의 크랙에 대하여 충격을 고려한 반복하중실험 수행하였다. 또한 유한요소해석을 수행하여 크랙 팁(tip)의 음력집중현상과 진전가능성을 살펴보았다. 이와 같은 방법으로 디스크가 안정함을 확인하였다.

• Journal of Mechanical Science and Technology
• /
• 제18권11호
• /
• pp.1996-2008
• /
• 2004

A seamless analysis of material behavior incorporating complex geometry and crack- tip modeling is one of greatly interesting topics in engineering and computational fracture mechanics fields. However, there are still large gaps between the industrial applications and fundamental academic studies due to a time consuming detailed modeling. In order to resolve this problem, a numerical method to calculate an energy release rate by virtual crack closure technique was proposed in this paper. Both free mesh method and finite element method have been utilized and, thereafter, robust local and global elements for various geometries and boundary conditions were generated. A validity of the proposed method has been demonstrated through a series of fracture mechanics analyses without tedious crack-tip meshing.

• 대한기계학회논문집A
• /
• 제26권9호
• /
• pp.1753-1763
• /
• 2002

Stress and displacement fields for a propagating crack in a functionally gradient material (FGM) which has shear modulus as $\mu$=$\mu$$\_$0/(1＋ζX) are derived. The equations of motion in FGM which is nonhomogeneous material are different from those of homogeneous material. The stress intensity factors in stress fields have influence on odd terms of γ$\^$n/2-1/(n=1,3,5,...,) but stress at crack tip only retains term of γ$\^$-1/2/, where the γ is a radius of cylindrical coordinates centered at crack tip. When the FGM constant ζ is zero or γ→0, the fields for FGM are almost same as the those for isotropic material.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 추계학술대회논문집A
• /
• pp.9-15
• /
• 2001

In the case of a crack propagation, a portion of the work of inelastic deformation near the crack tip is dissipated as heat. In order to understand the thermal effect on fracture toughness, tensile test was carried out using thermocouples to monitor the variation of temperature with SA516 Gr70. The experimental results show that the temperature of specimen was increased $3.6^{\circ}C$ at static load condition. And the thermal effect was investigated connected with the steady-state stress in the vicinity of a crack propagation in the elastic-plastic C-T specimen theoretically. And fracture toughness, the energy to make crack surfaces, presented correctively. The fracture toughness with considering heat at the blunting of the crack tip ws lower about 19.3% than that of ignoring heat. So, it is resonable to apply the fracture toughness with considering thermal energy and it would be good explanation for constraint effect depending on the configuration in the presence of excessive plasticity.

• 한국마린엔지니어링학회:학술대회논문집
• /
• 한국마린엔지니어링학회 2006년도 전기학술대회논문집
• /
• pp.91-92
• /
• 2006

For the CT specimen of 25.4mm thickness SS400 steel, the fracture toughness and the magnitude of constraint effect, $A_2$ on the non-linear elastoplastic fracture behaviors were experimentally estimated by crack tip opening displacement. In order to estimate constraint effect, displacement measurement position near crack front should be the existed within plastic region. But it is found that the displacement measurement positions by the ${\delta}_5$ method are in elastic region at crack growth initiation. Hence the estimate of constraint effect, $A_2$ by the ${\delta}_5$ method was not reliable.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2001년도 봄 학술발표회 논문집
• /
• pp.335-342
• /
• 2001

In this paper, an improved Element-Free Galerkin (EFG) method is proposed by adding enrichment function to the standard EFG approximation and a discontinuity function is implemented in constructing the shape function across the crack surface. In this method, the singularity and the discontinuity of the crack are efficiently modeled by using initial node distribution to evaluate reliable stress intensity factor, though the standard EFG method requires placing additional nodes near the crack tip. The proposed method enables the initial node distribution to be kept without any additional nodal d.o.f. and expresses the asymptotic stress field near the crack tip successfully. Numerical example verifies the improvement and the effectiveness of the method.

• 한국안전학회지
• /
• 제16권2호
• /
• pp.1-6
• /
• 2001

In the case of a crack propagation a portion of the work of inelastic deformation near the crack tip is dissipated as heat. In order to understand the thermal effect on fracture toughness, tensile tests were carried out using thermocouples to monitor the variation of temperature. The experimental results show that the temperature of specimen was increased $5.4^{\circ}C$ at static load condition. And the thermal effect is investigated connected with the steady-state stress in the vicinity of a crack propagation in the elastic-plastic C-T specimen theoretically. And fracture toughness, the energy to make crack surfaces, presented correctively. The fracture toughness with considering heat at the blunting of the crack tip is lower about 16.9％ than that of ignoring heat. So, it is resonable to apply the fracture toughness with considering thermal energy and it would be good explanation for constraint effect depending on the configuration in the presence of excessive plasticity.

• 한국안전학회지
• /
• 제22권2호
• /
• pp.8-14
• /
• 2007

In this study, tensile and fatigue crack propagation tests machined from actual wheels were performed. FEM analysis also was performed on the crack that was assumed to be 15 mm in depth under the wheel tread surface. The stress intensity factors K I and K II at the crack tip under the stress($P_{max}=911.5MPa$) due to a rolling contact were analyzed for crack growth characteristics. As a result, the perpendicular crack was found to be more dangerous compared to the parallel one. It is found that in the wheel fatigue crack, parallel to the wheel tread surface, the crack with its length 2a = 2.4mm starts to propagate due to the fact that the effective stress intensity factor access to the threshold stress intensity factor($K_{th}=16.04MPa{\sqrt{m}}$) of the wheel.

• International Journal of Concrete Structures and Materials
• /
• 제11권2호
• /
• pp.365-375
• /
• 2017

An experimental evaluation of crack propagation and post-cracking behavior in steel fiber reinforced concrete (SFRC) beams, using full-field displacements obtained from the digital image correlation technique is presented. Surface displacements and strains during the fracture test of notched SFRC beams with volume fractions ($V_f$) of steel fibers equal to 0.5 and 0.75% are analyzed. An analysis procedure for determining the crack opening width over the depth of the beam during crack propagation in the flexure test is presented. The crack opening width is established as a function of the crack tip opening displacement and the residual flexural strength of SFRC beams. The softening in the post-peak load response is associated with the rapid surface crack propagation for small increases in crack tip opening displacement. The load recovery in the flexural response of SFRC is associated with a hinge-type behavior in the beam. For the stress gradient produced by flexure, the hinge is established before load recovery is initiated. The resistance provided by the fibers to the opening of the hinge produces the load recovery in the flexural response.

• Steel and Composite Structures
• /
• 제50권2호
• /
• pp.237-247
• /
• 2024

Research on interfacial crack formation in orthotropic bi-materials has experienced a notable increase in recent years, driven by growing concerns about structural integrity and reliability. The existence of a crack at the interface of bi-materials has a substantial impact on mechanical strength and can ultimately lead to fracture. The primary objective of this article is to introduce a comprehensive analytical model and establish stress relationships for investigating interfacial crack between two non-identical orthotropic materials with desired crack-fiber angles. In this paper, we present the application of the Interfacial Maximum Tangential Stress (IMTS) criterion, in combination with the Reinforcement Isotropic Solid (RIS) model, to investigate the behavior of interfacial cracks in orthotropic bi-materials under mixed-mode I/II loading conditions. We analytically characterize the stress state at the interfacial crack tip using both Stress Intensity Factors (SIFs) and the T-stress term. Orthotropic materials, due to their anisotropic nature, can exhibit complex crack tip stress fields, making it challenging to predict crack initiation behavior. The secondary objective of this study is to employ the IMTS criterion to predict the crack initiation angle and explore the notable impact of the T-stress term on fracture behavior. Furthermore, we validate the effectiveness of our approach in evaluating Fracture Limit Curves (FLCs) for interfacial cracks in orthotropic bi-materials by comparing our FLCs with relevant experimental data from existing literature.