• Journal of Industrial Technology
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• v.13
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• pp.49-57
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• 1993

Bending fatigue tests were carried out on the specimenes with two different strength levels in order to investigate small crack growth rate. The main results obtained are as follows : (1) Small crack growth law, $da/dn=C{\sigma}_a{^n}a$ is useful several materials, but is not the rule applicable to all cases generally. (2) When da/dn in several specimens are equal, COD near the crack tip are also nearly equal. (3) Crack tip opening displacement(CTOD) is the main factor to control the small crack growth rate, and da/dn ${\propto}$ CTOD comes into being between the two. Accordingly, $da/dn=C({\sigma}_a{^2}/{\sigma}_s){^n}a^n$ shows the small crack growth rate being reflected crack closure phenomenon.

• Journal of the korean Society of Automotive Engineers
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• v.12 no.2
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• pp.43-50
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• 1990

The fatigue growth behavior of surface cracks cannot be adequately predicted solely by stress intensity factor analysis. This is caused by different plastic deformation due to variations in the stress field triaxiality along the crack tip. Therefore, a new model which accounts for the crack closure phenomenon is proposed in this paper to predict the fatigue crack growth patterns for surface cracks. Fatigue tests were performed to develop the new model for the prediction and to assess the accuracy of the analysis. The predicted crack growth behavior for PMMA and Aluminum alloy 7075-T6 materials agreed well with the experimental data.

• Journal of the Korean Society of Safety
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• v.9 no.3
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• pp.13-21
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• 1994

Effects of tensile and compression residual stresses in the welded SS41 and A17075-76 on fatigue crack propagation behavior are investigated when a crack propagates from residual stresses region. We propose the fatigue crack growth equation on tensile and compression residual stresses in welded metal. The results obtained in this experimental study are summarized as follows . 1 ) A fatigue crack growth equation which applied fatigue fracture behavior of the welded metal is proposed. (equation omitted) where, $\alpha$, $\beta$, ${\gamma}$ and $\delta$ are constants, and R$_{eff}$ is effective stress ratio [R$_{eff}$=(Kmin+Kres)/(Kmax+Kres)], Kcf is critical fatigue stress intensity factor. The constants are obtained from nonlinear least square method. The relation between crack length and number of cycles obtained by integrating the fatigue crack growth rate equation is in agreement with the experimental data. 2) The experimental results confirmed that the cause of crack extension and retardation by residual stresses has relation to the phenomenon of crack closure. 3) The relaxing trend of residual stresses by the crack propagation was greater In case of compressive residual stress than that of tensile residual stress in the welded metal.tal.

• Transactions of the Korean Society of Mechanical Engineers
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• v.2 no.1
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• pp.10-18
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• 1978

Kikukawa's compliance method using the conventional crack mouth clip-on gauge was proposed as a desired measurement technique to monitor the notched specimen fatigue behavior. The measurement technique makes it possible to continuously monitor the initiation and growth of incipient small part-through crack originated at the notch root and the phenomenon of crack closure. The variarion of natural flaw geometry with fatigue cycling was investigated. The test results on 7075-T6 aluminium alloy suggest the dependence of effective stress intensity factor range ratio .upsilon. on the maximum stress intensity factor .KAPPA.max.

• Geomechanics and Engineering
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• v.35 no.4
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• pp.333-366
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• 2023

Rock as a mass generally exhibits discontinuities, commonly witnessed in rock slopes and underground structures like tunnels, rock pillars etc. When these discontinuities experiences loading, a new crack emerges from them which later propagates to a macro scale level of failure. The failure pattern is often influenced by the nature of discontinuity, geometry and loading conditions. The study of crack growth in rocks, namely its initiation and propagation, plays an important role in defining the true strength of rock and corresponding failure patterns. Many researchers have considered the length of the discontinuity to be fully persistent on rock or rock-like specimens by both experimental and numerical methods. However, only during recent decades, there has been a substantial growth in research interest with non-persistent discontinuities where the crack growth and its propagation phenomenon were found to be much more complex than persistent ones. The non-persistence fractures surface is generally considered to be open and closed. Compared to open flaws, there is a difference in crack growth behaviour in closed or narrow flaws due to the effect of surface closure between them. The present paper reviews the literature that has contributed towards studying the crack growth behaviour and its failure characteristics on both open and narrow flaws subjected to uniaxial and biaxial compression loading conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1361-1368
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• 2011

Fatigue crack propagation behavior and the fatigue life in-high performance steel were investigated by means of fatigue crack propagation tests under constant loading conditions of 'R=0.1 and f=0.1 Hz', 'R=0.3 and f=0.3 Hz', and 'R=0.5 and f=0.5 Hz' for the load ratio and frequency, respectively. A modified Forman model was developed to describe the fatigue crack propagation behavior for the conditions. The modified Forman model is applicable to all fatigue crack propagation regions I, II, and III by implementing the threshold stress intensity factor range and the effective stress intensity factor range caused by crack closure. The results show that predicted fatigue lives of Forman and modified Forman models were 8,814 and 12,292 cycles, respectively when the crack propagated approximately 5.0 mm and the load ratio and frequency were both 0.1. Comparison of the test results indicates that the modified Forman model showed much more effective fatigue crack propagation behavior in high-performance steel.