• Title/Summary/Keyword: crack prediction

Search Result 557, Processing Time 0.025 seconds

Stress Intensity Factor Analysis for Surface Crack in Inhomogeneous Materials (비균질재료의 표면균열에 대한 응력확대계수 해석)

  • 김준수;이준성
    • Proceedings of the Korean Society of Precision Engineering Conference
    • /
    • 2002.10a
    • /
    • pp.816-819
    • /
    • 2002
  • Accurate stress intensity factor analyses and crack growth rate of surface-cracked components in inhomogeneous materials are needed for reliable prediction of their fatigue lift and fracture strengths. This paper describes an automated system for analyzing the stress intensity factors of three-dimensional (3D) cracks in inhomogeneous materials. 3D finite element method (FEM) was used to obtain the stress intensity factor for subsurface cracks and surface cracks existing in inhomogeneous materials. To examine accuracy and efficiency of the present system, the stress intensity factor for a semi-elliptical surface crack in a plate subjected to uniform tension is calculated, and compared with Raju-Newman's solutions. Then the system is applied to analyze cladding effect of subsurface cracks in inhomogeneous materials. The results were compared with those surface cracks in homogeneous materials. It is clearly demonstrated from these analyses that the stress intensity factors for subsurface cracks are less than those of surface cracks.

  • PDF

Effect of Residual Stress on Fatigue Characteristics at the Welds of Stainless Steel (스테인리스강 용접부의 잔류응력이 피로특성에 미치는 영향)

  • 권종완;양현태
    • Transactions of the Korean Society of Machine Tool Engineers
    • /
    • v.10 no.5
    • /
    • pp.110-117
    • /
    • 2001
  • In the weldments, the crack propagation rate is changed due to the residual stress. The crack propagation rate is high in the region with the residual stress. However it shows the same behavior with the base metal in the region that does not include the residual stress. The fatigue crack growth rate for the material with residual stresses can be predicted more precisely by using the effective stress ratio. The difference between experimental results and prediction results seems to be due to the redistribution of the residual stresses and microstructural change.

  • PDF

Creep Crack Growth Properties of Low Pressure Turbine Rotor Steel under Constant Load and Ct

  • Jeong, Soon-Uk
    • International Journal of Precision Engineering and Manufacturing
    • /
    • v.3 no.2
    • /
    • pp.95-101
    • /
    • 2002
  • The propagation rate(da/dt) prediction parameter and the microstructure properties of creep crack in domestic 3.3NiCrMov steel were investigated at 550$\^{C}$ by using 0.5" CT specimen under constant load(4090N) and constant Ct(300∼4000N/mhr) condition that was maintained during crack growth of 1mm distance. C* usually increased with crack length though load was reduced in order to maintain constant Ct value as crack growth and considerably showed the scatter band, but Ct depended on load line displacement rate and represented a good relation with da/dt. At constant toad and Ct region, crack growth slope was 0.900 and 0.844 each, in the other hand C* slope was 0.480. Fully coalesced area(FCA) ahead of crack tip was increased as Ct value increase to the critical value, and after that value FCA decreased. The average diameter ditribution of cavity in FCA showed the greatest value about 1.5 ㎛ when Ct=2000N/mhr. The increasing of Ct in FCA view point enlarged the size of damage area and the size reached to maximum 800 ㎛ when Ct=2000N/mhr.

Numerical analysis of the Influence of the presence of disbond region in adhesive layer on the stress intensity factors (SIF) and crack opening displacement (COD) in plates repaired with a composite patch

  • Benchiha, Aicha;Madani, Kouider;Touzain, Sebastien;Feaugas, Xavier;Ratwani, Mohan
    • Steel and Composite Structures
    • /
    • v.20 no.4
    • /
    • pp.951-962
    • /
    • 2016
  • The determination of the stress intensity factor at the crack tip is one of the most widely used methods to predict the fatigue life of aircraft structures. This prediction is more complicated for repaired cracks with bonded composite patch. This study is used to compute the stress intensity factor (SIF) and crack opening displacement (COD) for cracks repaired with single and double-sided composite patches. The effect of the presence of disbond region in adhesive at the crack was taken into consideration. The results show that there is a considerable reduction in the asymptotic value of the stress-intensity factors and the crack opening displacement at the crack tip. The use of a double-sided patch suppresses the bending effect due to the eccentricity of the patch on one side only.

Crack constitutive model for the prediction of punching failure modes of fiber reinforced concrete laminar structures

  • Ventura-Gouveia, A.;Barros, Joaquim A.O.;Azevedo, Alvaro F.M.
    • Computers and Concrete
    • /
    • v.8 no.6
    • /
    • pp.735-755
    • /
    • 2011
  • The capability of a multi-directional fixed smeared crack constitutive model to simulate the flexural/punching failure modes of fiber reinforced concrete (FRC) laminar structures is discussed. The constitutive model is implemented in a computer program based on the finite element method, where the FRC laminar structures were simulated according to the Reissner-Mindlin shell theory. The shell is discretized into layers for the simulation of the membrane, bending and out-of-plane shear nonlinear behavior. A stress-strain softening diagram is proposed to reproduce, after crack initiation, the evolution of the normal crack component. The in-plane shear crack component is obtained using the concept of shear retention factor, defined by a crack-strain dependent law. To capture the punching failure mode, a softening diagram is proposed to simulate the decrease of the out-of-plane shear stress components with the increase of the corresponding shear strain components, after crack initiation. With this relatively simple approach, accurate predictions of the behavior of FRC structures failing in bending and in shear can be obtained. To assess the predictive performance of the model, a punching experimental test of a module of a façade panel fabricated with steel fiber reinforced self-compacting concrete is numerically simulated. The influence of some parameters defining the softening diagrams is discussed.

Prediction of chloride diffusion coefficient of concrete under flexural cyclic load

  • Tran, Van Mien;Stitmannaithum, Boonchai;Nawa, Toyoharu
    • Computers and Concrete
    • /
    • v.8 no.3
    • /
    • pp.343-355
    • /
    • 2011
  • This paper presented the model to predict the chloride diffusion coefficient in tension zone of plain concrete under flexural cyclic load. The fictitious crack based analytical model was used together with the stress degradation law in cracked zone to predict crack growth of plain concrete beams under flexural cyclic load. Then, under cyclic load, the chloride diffusion, in the steady state and one dimensional regime, through the tension zone of the plain concrete beam, in which microcracks were formed by a large number of cycles, was simulated with assumptions of continuously straight crack and uniform-size crack. The numerical analysis in terms of the chloride diffusion coefficient, $D_{tot}$, normalized $D_{tot}$, crack width and crack length was issued as a function of the load cycle, N, and load level, SR. The nonlinear model as regarding with the chloride diffusion coefficient in tension zone and the load level was proposed. According to this model, the chloride diffusion increases with increasing load level. The predictions using model fit well with experimental data when we adopted suitable crack density and tortuosity parameter.

Fatigue Crack Initiation and Propagation From Two Micro Hole Defects (두개의 미소원공결함에서의 피로크랙발생과 전파에 관한 연구)

  • Song, Sam-Hong;Bae, Joon-Soo
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.21 no.5
    • /
    • pp.842-849
    • /
    • 1997
  • The aim of this study is an investigation of the interaction of two micro hole defects affecting fatigue crack initation life and propagation behavior. The locatio of two micro hole defects was considered as an angle of alignment and the distance between the centers of two micro hole defects. The fatigue cracking behavior is experimented under bending. When micro defects are located close to each other, the fatigue crack initiation lives are varied with their relative locations. In the experiments, the area of local plastic strain strongly played a role in the fatigue crack initiation lives. Therefore we introduce a parameter which contains the plastic deformation area at stress concentrations and propose a fatigue crack initiation life prediction curve. In addition, the directions and propagation rates of fatigue cracks initiated at two micro hole defects are studied experimentally.

A Stochastic Analysis for Crack Growth Retardation Behavior and Prediction of Retardation Cycle Under Single Overload (단일과대하중하에서 피로균열진전지연거동 및 지연수명의 확률론적 해석)

  • Shim, Dong-Suk;Kim, Jung-Kyu
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.23 no.7 s.166
    • /
    • pp.1164-1172
    • /
    • 1999
  • In this study, to investigate the fatigue crack retardation behavior and the variability of retardation cycles, fatigue crack growth tests were conducted on 7075-T6 aluminum alloy under single tensile overload. A retardation coefficient, D was introduced to describe fatigue crack retardation behavior and a random variable, Z to describe the variability of fatigue crack growth. The retardation coefficient was separately formulated according to retardation behavior which is composed of delayed retardation part and retardation part. The random variable, Z was evaluated from experimental data which was obtained from fatigue crack growth tests under constant amplitude load. Using these variables, a probabilistic model was developed on the basis of the modified Forman's equation, and retardation behavior and cycles were predicted under certain overload condition. The predicted retardation curve well agrees with the trend of experimental crack retardation behavior. And this model well predicts the scatter of experimental retardation cycles.

Fatigue Life Prediction for High Strength AI-alloy under Variable Amplitude Loading (변동하중하에서 고강도 알루미늄 합금의 피로수명 예측)

  • Sim, Dong-Seok;Kim, Gang-Beom;Kim, Jeong-Gyu
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.24 no.8 s.179
    • /
    • pp.2074-2082
    • /
    • 2000
  • In this study, to investigate and to predict the crack growth behavior under variable amplitude loading, crack growth tests are conducted on 7075-T6 aluminum alloy. The loading wave forms are generated by normal random number generator. All wave forms have same average and RMS(root mean square) value, but different standard deviation, which is to vary the maximum load in each wave. The modified Forman's equation is used as crack growth equation. Using the retardation coefficient D defined in previous study, the load interaction effect is considered. The variability in crack growth process is described by the random variable Z which was obtained from crack growth tests under constant amplitude loading in previous work. From these, a statistical model is developed. The curves predicted by the proposed model well describe the crack growth behavior under variable amplitude loading and agree with experimental data. In addition, this model well predicts the variability in crack growth process under variable amplitude loading.