• Journal of the Korean Society for Railway
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• v.10 no.5
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• pp.546-553
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• 2007

The objective of the present paper is to evaluate the effect of the evolution of contact surface profile by fretting wear on the contact stress distribution and fatigue crack initiation site of press-fitted shaft by means of an analytical method based on experimental data. A finite element analysis was performed to analyze the stress states of press-fitted shaft, considering the worn contact surface profiles of shaft. The evolutions of contact stress as wearing of contact surface were analyzed by finite element analysis and fatigue crack nucleation sites were evaluated by fretting fatigue damage parameter (FFDP) md multiaxial fatigue criteria. It is found that the stress concentration of a contact edge in press-fitted sha손 decreases rapidly at the initial stage of total fatigue life, and its location shifts from the contact edge to the inside due to fretting wear as increasing of fatigue cycles. Thus the transition of crack nucleation position in press-fitted shaft is mainly caused by stress change of a contact edge due to the evolution of contact surface profile by fretting wear. Therefore, it is suggested that the nucleation of multiple cracks on fretted surface of press fits is strongly related to the evolution of surface profile at the initial stage of total fatigue life.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.241-245
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• 2004

An analytical study was conducted to characterize the fatigue crack growth behavior of pre-cracked aluminum plates repaired with asymmetric bonded composite patch. For single-sided repairs, due to the asymmetry and the presence of out-of-plane bending, crack front shape would become skewed curvilinear started from a uniform through-crack profile, as observed from previous studies. In this study, the fatigue analysis of single-sided repairs considering crack front shape development was conducted by implementing three-dimensional successive finite element method coupled with linear elastic fracture mechanics (LEFM) concept, which enables the growing crack front to be directly traced and modeled in a step by step way. Through conducting present analysis technique, crack path of the patched plate as well as the fatigue life was evaluated with sufficient accuracy. The analytical predictions of both the crack front shape evolution and the fatigue life were in good agreement with the experimental observations.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.511-517
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• 2009

In this paper an finite element approach for the edge crack analysis of silicon-steel sheet during cold rolling is presented. Based on the damage mechanics, the proposed approach follows the analysis steps which are composed of damage initiation, damage evolution and fracture. Through those steps, we can find out the initiation instant of crack and resulting propagated length and shape of the crack. The material constants related to fracture is experimentally obtained by tension tests using standard sheet-type specimen and notched sheet-type specimen. To evaluate the prediction accuracy, we performed a pilot rolling test with a initially notched sheets. It is shown that the results obtained by the approach converged to the experimental one concerning about the direction and length of propagated crack. The capability of the proposed one is demonstrated through the application to the actual silicon-steel rolling mill.

• Korean Journal of Materials Research
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• v.28 no.7
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• pp.398-404
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• 2018

Fatigue crack growth retardation of 304 L stainless steel is studied using a neutron diffraction method. Three orthogonal strain components(crack growth, crack opening, and through-thickness direction) are measured in the vicinity of the crack tip along the crack propagation direction. The residual strain profiles (1) at the mid-thickness and (2) at the 1.5 mm away from the mid-thickness of the compact tension(CT) specimen are compared. Residual lattice strains at the 1.5 mm location are slightly higher than at the mid-thickness. The CT specimen is deformed in situ under applied loads, thereby providing evolution of the internal stress fields around the crack tip. A tensile overload results in an increased magnitude of the compressive residual stress field. In the crack growth retardation, it is found that the stresses are dispersed in the crack-wake region, where the highest compressive residual stresses are measured. Our neutron diffraction mapping results reveal that the dominant mechanism is by interrupting the transfer of stress concentration at the crack tip.

• Computers and Concrete
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• v.33 no.4
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• pp.399-407
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• 2024

This study nondestructively examined the evolution of crack density in ultra-high performance concrete (UHPC) upon cyclic loading. Uniaxial compression was repeatedly applied to the cylindrical specimens at levels corresponding to 32% and 53% of the maximum load-bearing capacity, each at a steady strain rate. At each stage, both P-wave and S-wave velocities were measured in the absence of the applied load. In particular, the continuous monitoring of P-wave velocity from the first loading prior to the second loading allowed real-time observation of the strengthening effect during loading and the recovery effect afterwards. Increasing the number of cycles resulted in the reduction of both elastic wave velocities and Young's modulus, along with a slight rise in Poisson's ratio in both tested cases. The computed crack density showed a monotonically increasing trend with repeated loading, more significant at 53% than at 32% loading. Furthermore, the spatial distribution of the crack density along the height was achieved, validating the directional dependency of microcracking development. This study demonstrated the capability of the crack density to capture the evolution of microcracks in UHPC under cyclic loading condition, as an early-stage damage indicator.

• Korean Journal of Materials Research
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• v.25 no.12
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• pp.690-693
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• 2015

Fatigue crack growth experiments were carried out on a 304 L stainless steel compact-tension(CT) specimen under load control mode. Neutron diffraction was employed to quantitatively measure the residual strains/stresses and the evolution of stress fields in the vicinity of a propagating fatigue-crack tip. Three principal stress components (i.e. crack growth, crack opening, and through-thickness direction stresses) were examined in-situ under loading as a function of distance from the crack tip along the crack-propagation path. The stress/strain fields, measured both at the mid-thickness and near the surface of the CT specimen, were compared. The results show that much higher compressive residual stress fields developed in front of the crack tip near the surface than developed at the mid-thickness area. The change of the stresses ahead of the crack tip under loading is more significant at the mid-thickness area than it is near the surface.

• Coupled systems mechanics
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• v.12 no.2
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• pp.183-197
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• 2023

Scarce research has been published on crack propagation fracture of flywheels manufactured with carbon fiber-reinforced polymers. The present work deals with a calculation method to determine the conditions for which a crack propagates in the axial direction of the flywheel. The assumptions are: flywheels made with just a single thick ply or ply clustering laminates, oriented following the hoop direction; a single crack is analyzed in the plane defined by the hoop and axial directions; the crack starts close to one of the free edges; its axial length is initially large enough so that its tip is far away from that free edge, and the crack expands the entire circumferential perimeter and keeps its concentric position. The developed method provides information for a good design of flywheels. It is concluded that a fracture-based crack propagation criterion generally occurs at a lower speed than a stress-based criterion. Also, that the evolution of failure with thickness using the fracture criterion is exponential, demonstrating that thin flywheels are relatively not sensitive to crack propagation, whereas thick ones are very prone.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.04a
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• pp.341-348
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• 2004

This paper presents a modeling technique of cracks by combined extended and superposed finite element method (XSFEM) which is a combination of the extended finite element method (XFEM) and the mesh superposition method (sversion FEM). In the proposed method, the near-tip field is modeled by a superimposed patch consisting of quarter point elements and the rest of the discontinuity is treated by the XFEM. The actual crack opening in this method is measured by the sum of the crack openings of XFEM and SFEM in transition region. This method retains the strong point of the XFEM so it can avoid remeshing in crack evolution and trace the crack growth by translation or rotation of the overlaid mesh and the update of the nodes to be enriched by step functions. Moreover, the quadrature of the Galerkin weak form becomes simpler. Numerical experiments are provided to demonstrate the effectiveness and robustness of the proposed method.

• Geomechanics and Engineering
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• v.20 no.1
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• pp.55-66
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• 2020

The damage or failure of coal rock is accompanied by energy accumulation, dissipation and release. It is crucial to study the energy evolution characteristics of coal rock for rock mechanics and mining engineering applications. In this paper, coal specimens sourced from the Xinhe mine located in the Jining mining area of China were initially subjected to uniaxial compression, and the micro-parameters of the two-dimensional particle flow code (PFC^2D) model were calibrated according to the experimental test results. Then, the PFC^2D model was used to subject the specimens to substantial uniaxial compression, and the energy evolution laws of coal specimens with various schemes were presented. Finally, the elastic energy storage ratio m was investigated for coal rock, which described the energy conversion in coal specimens with various arrangements of preformed holes. The arrangement of the preformed holes significantly influenced the characteristics of the crack initiation stress and energy in the prepeak stage, whereas the characteristics of the cumulative crack number, failure pattern and elastic strain energy during the loading process were similar. Additionally, the arrangement of the preformed holes altered the proportion of elastic strain energy U_e in the total energy in the prepeak stage, and the probability of rock bursts can be qualitatively predicted.

• Computers and Concrete
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• v.8 no.6
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• pp.735-755
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• 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.