• Journal of Welding and Joining
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• v.35 no.1
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• pp.61-67
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• 2017

Recent studies on the fatigue assessment of high strength steel weld based on the fracture mechanics have frequently raised the problems related to the conservatism in the fatigue crack growth rate specified in the relevant design code. The purpose of this study is to evaluate the effect of the fatigue crack growth parameter on the fatigue life for the low carbon steel weld. In order to do it, the fatigue tests with the constant stress ratio were performed to evaluate the fatigue crack growth rate in the butt weld of SM490. And the fatigue crack growth parameters of the weld were evaluated in accordance with ASTM E647. From the comparative fatigue assessment results, it was found that the fatigue crack growth rate specified in the relevant design code was too conservative to estimate the residual fatigue life of welded structure. So, in order to get the more reliable results, it was recommended that the fatigue life estimation based on the fracture mechanics be performed with the fatigue crack growth parameter specified by test.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.15-22
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• 2003

The fatigue crack growth model is derived and the retardation model is proposed. The fatigue crack growth model considers the residual plastic stretch on the crack surface which results from the plastic deformation at the tip of fatigue crack. The fatigue crack growth rate is calculated by using the cumulative fatigue damage and plastic strain energy in the material elements at the crack tip. This model gives the crack growth rate in reasonable agreement with test data for aluminum alloy AL6061-T651 and 17-4PH casting steel. The fatigue crack growth retardation model is based on the residual plastic stretch produced from a tensile overload which reduced the plastic strain range of the following load cycles. A strip-yield model of a crack tip plasticity is used for the calculation of a plastic zone size. The proposed retardation model characterized the observed features and delayed retardation of the fatigue crack growth under tensile overload.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1998.03a
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• pp.251-257
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• 1998

The distribution of fatigue crack growth rate is subjected to the measuring interval and calculated method of growth rate. In this paper, in order to establish the method of determining the distribution of fatigue crack growth rate, which ignores those influences, a series of fatigue crack growth experiments and measuring intervals of crack length calculated reasonable are presented. The main conclusions obtained are summarized as follows: 1) As a result of the ΔP constant test and ΔK constant test, it is thought that an approximate measuring interval of 0.3~0.7mm is reasonable, which allows for few errors and is little subjected to the calculated method of crack growth rate.

• Journal of Welding and Joining
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• v.13 no.4
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• pp.155-162
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• 1995

Redistribution of residual stress and its effects during fatigue crack propagates from tensile residual stress region in weldment are investigated. Tests are performed by using welded CCT specimens of structual rolling steel (SS400) and it makes fatigue crack propagate from tensile residual stress region. For this study tension-tension loading type is selected by external loading condition and magnetizing stress indicator is used correctly to measure redistribution of residual stress according to fatigue crack growth and number of loading cycles. From this result, it is proved that redistribution of residual stress is mainly consist of residual stress released by fatigue crack growth. When fatigue crack propagates from tensile residual stress region residual stress are redistributed and it makes fatigue crack growth rate largely increase. Fatigue crack growth rate is low in case of redistributed residual stress compare with initial distributed residual stress.

• Journal of the Korean Society of Mechanical Technology
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• v.13 no.2
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• pp.31-37
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• 2011

Sheet aluminum alloys have been used in manufacturing of machine structures. In fatigue crack propagation behavior of thin sheet aluminum alloys, it is important that fatigue crack growth rate is affected by crack closure phenomenon. In this work, we analyzed the characteristics of fatigue crack propagation behavior in experiment of constant stress condition for thin sheet Al 2024-T3 alloys, and identified the retardation behavior of crack growth by comparing experimental results of thin and thick plate specimen. We attempt to operate the fatigue life estimating process using the fatigue related material constants from referred fatigue crack propagation analysis. And we analyzed the experimental and prediction results of fatigue life of thin sheet aluminum alloy in order to identify the relation between retardation behavior of fatigue crack growth and crack closure phenomenon.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05c
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• pp.92-97
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• 1996

The fatigue crack propagation behavior in SA106 Gr.C main steam pipe weld joint was investigated in air environment. Crack growth rate tests were conducted on base metal and weld metal at load ratio of 0.1 and 0.3 and at frequency of 10Hz. The fatigue crack growth rates of the base metal and the weld metal were above the ASME reference line and the fatigue crack propagation rate of the weld metal was higher than those of the base metal. Fatigue crack growth rate increased with increasing the load ratio and the effect of the load ratio was more significant in the weld metal. The post weld heat treatment increased the fatigue crack growth rates of the base metal by reducing compressive residual stress and decreased those of the weld metal by reducing weld defects.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.2
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• pp.252-256
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• 1989

In the low cycle fatigue fracture testing with KS(or JIS) SS41, crack growth rate, AE count rate and J-integral range are measured to get empirical relations between crack growth rate and J-integral range, AE count rate and J-integral range as well as AE count rate and crack growth rate. All the relations are shown to be linear on the log-log graphs. It is also shown that the linear relations can be formulated by using Dunegan's assumption and elastic-plastic fracture mechanics along with the well-known relation of crack growth rate and J-integral range. It is concluded that the differences between experimental and theoretical values are due to Dunegan's assumption.

• Journal of Korean Society of Steel Construction
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• v.22 no.6
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• pp.589-597
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• 2010

Steel structures have a higher probability of being damaged by fatigue than by other causes of deterioration. As such, their maintenance to prevent fatigue damage is essential to sustain their safety and performance during their service period. In their maintenance, the current state of their fatigue cracks must be assessed to determine appropriate reinforcement methods and the suitable time intervals of periodic inspections when fatigue cracks are detected. Determining the crack growth rate is a successful method of predicting fractures, but it requires technical knowledge on fracture mechanics and experience in numerical methods and software for finite element analysis. In this study, a fatigue crack growth test on through-thickness cracked steel plates was conducted to assess the crack growth rate without superior technical knowledge and experience. The relationship between the Crack Opening Displacement (COD) and the crack growth rate was found in relatively long fatigue cracks.

• Journal of Ocean Engineering and Technology
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• v.10 no.1
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• pp.53-64
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• 1996

In this paper, rotating bending fatigue tests have been carried out to investigate the growth behabiors of surface fatigue crack initiated from a small artificial surface defect, that might exist in real structures, on 2024-T3 and 6:4 brass. The test results are analysed in the viewpoints of both strength of materials and fracture mechanics, it can be concluded as follows. The effect of a small artificial surface defect upon the fatigue strength is very large. The sensitivity of 2024-T3 on the defect is higher than that of 6:4 brass. The growth behavior of the surface fatigue crack of 2024-T3 is different from that of 6:4 brass. The growth rate of the surface fatigue crack of 2024-T3 is considerably rapid in the early stage of the fatigue life and apt to decrease in the later stage. It was impossible to establish a unifying approach in the analysis of crack growth begabior of 2024-T3 and 6:4 brass using the maximum stress intensity factor because of their dependence on stress level. But if the elastic strain and cyclic total strain intensity factor range were applied to obtain the growth rate of surface fatigue cracks of the materials, the data were found to be nearly coincided.

• Journal of Ocean Engineering and Technology
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• v.9 no.2
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• pp.98-111
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• 1995

High temperature low cycle fatigue shows that cycle-dependent crack growth owing to cyclic plastic deformation occurred simultaneosly with time-dependent crack growth owing to intergranular deformation. Consequently, to estimate crack growth rate uniquely, many to investigators have proposed various kinds of parameters and theories but these could not produce satisfactory results. Therefore the goal of this study is focused on prediction of crack growth rate using predominant damage rule, linear cumulative damage rule and transitional parameter ${\Delta}J_c/{\Delta}J_f$. On the basis of these sinusoidal loading waveform at 600$^{\circ}C$ and 700$^{\circ}C$.