• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.4
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• pp.82-89
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• 2012

In order to clarify the effect of overload on crack growth behaviors, fatigue tests for overload were carried out for round plain specimens of SM45C steel. In the experiment, typical semi-elliptical crack shape was found and further crack growth behaviors were tested. Using three types of single overload fatigue tests, Crack growth retardation phenomenon were examined. The growth rate of surface crack(da/dN) during retardation period was analyzed in terms of ${\Delta}K$ and ${\Delta}K_{eff}$. On the growth rate of surface crack analyzed by ${\Delta}K$, the dependence of overload stress levels appears. However, on the growth rate by ${\Delta}K_{eff}$ obtained by Willenborg analysis, there is a liner relationship between da/dN and ${\Delta}K_{eff}$ with narrow scatter band.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.5
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• pp.13-20
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• 2012

In order to clarify the effect of overload on crack growth behaviors, fatigue tests for overload were carried out for round plain specimens of SM45C steel. In the experiment, typical semi-elliptical crack shape was found and further crack growth behaviors were tested. Using three types of single overload fatigue tests, Crack growth retardation phenomenon were examined. The growth rate of surface crack(da/dN) during retardation period was analyzed in terms of ${\Delta}K$ and ${\Delta}K_{eff}$. On the growth rate of surface crack analyzed by ${\Delta}K$, the dependence of overload stress levels appears. However, on the growth rate by ${\Delta}K_{eff}$ obtained by Willenborg analysis, there is a non-liner relationship between da/dN and ${\Delta}K_{eff}$ with narrow scatter band.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.9
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• pp.1605-1614
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• 1992

The effects of % overload (% O.L), baseline stress intensity factor range (.DELTA. $K_{b}$) and dimension-less crack depth (a/W) are examined for the retardation behaviors after a single overload and high-low block loads in 7075-T73 aluminum alloy. And wheeler model, which is one of the fatigue life prediction models, is modified to predict retardation life using these test results. The retardation cycles( $N_{d}$) increased with a decrease in a/W and an increase in % O.L. and (.DELTA. $K_{b}$) These effects are more severe after high-low block loads than single overload. In the case of single overload, the main mechanisms of the retardation are the crack closure and the relaxation of K due to crack branching. But in the case of high-low block loads, that of the main mechanism is the crack closure caused by the accumulated compressive residual stree at the crack tip, which is related with the contact of fracture surfaces. Test results were multiple regression analyzed and got regressed shaping correction factors, (n)$_{REG}$, as function of %O.L., a/W and (.DELTA. $K_{b}$) Wheeler model is modified by using these (n)$_{REG}$. The number of delay cycles calculated by modified Wheeler model were in good agreement with the test results of this study.y.udy.y.y.y.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.5
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• pp.42-49
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• 2013

In this study, in order to analyze the crack retardation behaviors, effective plastic zone concept was proposed. By use of the proposed concept, crack retardation period, compressive residual stress and variation of effective plastic zone shapes were obtained. The results were compared with those of Willenborg model. Retardation period, compressive residual stress and effective plastic zone size obtained by using effective plastic zone concept were larger then the results obtained by using Willenborg analysis. Effective stress intensity factors obtained by using effective plastic zone concept were smaller then the results obtained by using Willenborg analysis.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.481-485
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• 1997

6063-T5 alloys are tested in laboratory air, water and 3% NaCl solution to investigate the effects of corrosive environment on the retardation behavior through single overload fatigue test. Also, the fatigue crack propagation and the crack closure behavior are studied. The results obtained in this experimental study are summarized as follows: 1) Behaviors of fatigue crack growth retardation are observed in water and 3% NaCl solution as they do in air. The number of delay cycles and the size of affected region by single overload decrease greatly in water and 3% NaCl compared with those in air. 2) In fractographic results, the overload marking by single overload appear remarkably in air, but indistinctly in water and 3% NaCl solution. 3) The effect of crack closure on crack propagation is most remarkable in the beginning of crack propagation. With crack propagation, the crack closure level and its effect decrease greatly.

• Journal of the Korean Society of Safety
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• v.12 no.3
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• pp.38-44
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• 1997

6063-T5 alloys are tested in laboratory air, water and 3% NaCl solution to investigate the effects of corrosive environment on the retardation behavior through single overload fatigue test. Also, the fatigue crack propagation and the crack closure behavior are studied. The results obtained in this experimental study are summarized as follows. 1) Behaviors of fatigue crack growth retardation are observed in water and 3% NaCl solution as they do in air. The number of delay cycles and the size of affected region by single overload decrease greatly in water and 3% NaCl compared with those in air. 2) In fractographic results, the overload marking by single overload appear remarkably in air, but indistinctly in water and 3% NaCl solution. 3) The effect of crack closure on crack propagation is most remarkable in the beginning of crack propagation. With crack propagation, the crack closure level and its effect decrease greatly.

• Journal of the Korean Academy of Child and Adolescent Psychiatry
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• v.7 no.2
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• pp.258-266
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• 1996

Self-injurious behaviors are commoly founded in the case of the developmentally impaired, such as mental retardation and autistic disorder. These behaviors are primary serious sources of distress for both child and their parents, another obstacle to overcome within the family and society. The author has a case that a child, had never before shown self-injurious behaviors. He abruptly started to injury his face and heel. The beginnings of these harmful behaviors are associated with symptoms of physical illness, such as fever, chills and general aches. The self-injured wounds were very severe. After the patient was treated with haloperidol and improved his physical conditions, self-injurious behaviors disappeared. The author reports the child's clinical process, characteristics of self-injurious behaviors, and discuss the treatment factors, along with a literature review.

• Journal of the Korean Society of Safety
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• v.7 no.2
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• pp.47-56
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• 1992

The retardation effect of fatigue crack propagation after cyclic overloading seems to be affected by strain hardening exponent. Namely, for the material with high values of n, the delay effect is found to be severe. We proposed a modified crack retardation equation which may apply the retardation of fatigue crack growth after a cyclic overloading, as (da/dN)'$_{cyc}$=($\mu$n＋λ)B $\Delta$ $K^{q}$ /[(1－ $R_{eff}$) $K_{cf}$ －$\Delta$K]. where, $R_{eff}$ is effective stress ratio [＝( $K_{min}$－K, os)/( $K_{max}$－ $K_{res}$)] The constants $\mu$＝－0.5 and λ＝0.6, and the values are found to be identical for materials such as aluminum (A 1060), steel (SS 34), brass ( $B_{s}$ SIB) and stainless steel (SUS 304) used in this investigation. (SUS 304) used in this investigation.ation.n.n.

• Journal of Powder Materials
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• v.19 no.2
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• pp.127-133
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• 2012

The sintering behaviors and process parameters of some compounds (carbides, oxides, sulfides, borides) were investigated experimentally. These compounds were successfully consolidated and showed high densities. Some unique phenomena such as retardation of grain growth, suppression of thermal decomposition and maintenance of initial non-equilibrium phases, were observed by the proper control of process in spark sintering.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.4
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• pp.103-113
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• 1987

Fatigue tests using a single-peak loading and a two-step loading were carried out to examine the fatigue crack growth behaviar and to find the appropriate analysis method. C-T specimens were made using structural steel SWS58 for the tests. From this, just after a single-peak loading acceleration effect was occured and after some times retardation effect was found. And eminent retardation effect was found after High-Low two-step loading. The transition effect of crack growth due to this variable loading was occured owing to the residual stress and the plastic zone size at the crack tip. And the behaviors of these are well explained by Elber's Crack Closure Model. Also I could find that the Wheeler's Retardation Model is a simple and appropriate theory among analysis methods of fatigue crack growth under the variable loading.