• Journal of Welding and Joining
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• 제11권2호
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• pp.42-52
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• 1993

The corrosion fatigue fracture behaviour of dual phase steel was investigated in 3% NaCl solution at 302MPa and 137MPa. Fatigue test was conducted by cantilever type of self-made rotary bending fatigue testing machine. The fatigue strength increased with increasing the hardness of 2nd phase. Corrosion pit originated at the boundary of the 2nd phase. The size and number of corrosion pits were influenced by the 2nd phase hardness, and pits remained constant in size just after they were transited into cracks. The life of crack initiation was effected by stress level. The shape of relation of .DELTA. K and da/dN has smaller scattering in it in 3% NaCl solution than that in air. The higher the 2nd phase hardness is, the greater the corrosion fatigue life becomes. Corrosion fatigue fracture behaviour was primarily effected by mechanical factor in case of high stress(302MPa), but by electro-chemical reaction in a lower stress(137MPa). As stress level got lower and hardness of the 2nd phase got higher, the roughness of fracture surface increased.

• 한국안전학회지
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• 제16권2호
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• pp.44-50
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• 2001

The rotated bending fatigue test was conducted in air md in 3.5% NaCl salt solution to investigate the fatigue fracture behaviour of raw material and F.E.M dual phase steel made from raw material(SS41) by a suitable heat treatment. This study has compared the initial microcrack creation of material by tensile test with that by fatigue test. And the rotated bending test of cantilever type under the condition of 3.5% NaCl salt solution and air has investigated the corrosion fatigue fracture behaviour with the variation of stress concentration factor determined by each of notch shapes. The initial microcrack have been developed in fragile grainboundary with general corrosion occurring in raw material : in the pits built up by corrosion in F.E.M. dual phase steel because pits bring out stress concentration. It is small that the degree of decrease in corrosion fatigue life for F.E.M. dual phase steel compared with raw material because the notch sensitivity of F.E.M. dual phase steel is lower than raw material in reason of characteristics with two-phase construction.

• 한국항공운항학회지
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• 제29권2호
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• pp.67-77
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• 2021

Factors that cause fatigue, such as circadian rhythm abnormalities, have adverse effects on long-haul flights. Among many elements, the present study focused on the flight crew's expertise as a crucial factor that could influence their fatigue. The purpose of the study was to demonstrate whether long-haul flights cause fatigue and to examine whether this symptom differed between low- and high-experienced flight crews. A total of 62 Korean flight crews were informed to perform a five-minute psychomotor vigilance task twice each before and after the flight to measure objective fatigue level. Also, they were asked to indicate current flight experience to identify their expertise. Results revealed that fatigue was significantly increased after the flight compared to before the flight but this increase was significant for flight crews with low expertise not for flight crews with high expertise. Implications of our findings and limitations of the present study were discussed.

• 대한기계학회논문집A
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• 제25권8호
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• pp.1277-1286
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• 2001

Aluminum 5052/Aramid Fiber Reinforced Plastic(Al5052/AFRP) laminates are applied to the fuselage-wing intersection. The Al5052/AFRP laminates suffer from the cyclic bending moment of variable amplitude during the service. Therefore, the influence of cyclic bending moment on the delamination and the fatigue crack propagation behavior in Al5052/AFRP laminate was investigated in this study. Al5052/AFRP laminate composite consists of three thin sheets of Al5052 and two layers of unidirectional aramid fibers. The cyclic bending moment fatigue tests were performed with five different levels of bending moment. The shape and size of the delamination zone formed along the fatigue crack between Al5052 sheet and aramid fiber-adhesive layer were measured by an ultrasonic C-scan. The relationships between da/dN and ΔK, between the cyclic bending moment and the delamination zone size, and between the fiber bridging mechanism and the delamination zone were studied. Fiber failures were not observed in the delamination zone in this study. It represents that the fiber bridging modification factor should turn out to increase and that the fatigue crack growth rate should decrease. The shape of delamination zone turns out to be semi-elliptic with the contour decreased non-linearly toward the crack tip.

• 대한기계학회논문집A
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• 제24권6호
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• pp.1446-1455
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• 2000

Fatigue crack initiation and propagation behavior under cyclic biaxial loading has been investigated using thin-walled tubular specimen with a hole. Two types of biaxial loading system, i.e. cyclic tensile loading with super-imposed static torsional load and cyclic torsional loading with superimposed static tensile load, with various values of the biaxial loading ratio, $\tau$ s/ $\sigma$ max (or $\tau$ max/ $\sigma$s) were employed. Fatigue tests show that fatigue crack near the hole initiates and propagates at 900 and 450 direction to the longitudinal direction of the specimen under cyclic tensile and torsion loading with static biaxial stress, respectively, and the static biaxial stress doesn't have any great influence on fatigue crack initiation and growth direction. Stress analysis near the hole of the specimen shows that the crack around the hole initiates along the plane of maximum tangential stress range. Fatigue crack growth rates were evaluated as functions of equivalent stress intensity factor range, strain energy density factor range and crack tip opening displacement vector, respectively. It is shown that the biaxial mode fatigue crack growth rates can be relatively consistently predicted with these cyclic parameters.

• 대한간호학회지
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• 제30권4호
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• pp.857-868
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• 2000

The purpose of the present study is to identify the mediation effect of hope between fatigue and psychosocial adjustment in women with breast cancer. The framework for this study was guided by concepts and propositions derived from the theoretical and empirical literature on fatigue, hope and adjustment. The design of this study is a descriptive correlation study using a cross-sectional design. One hundred and twenty two outpatients with early breast cancer, receiving post-surgical radiation therapy or chemotherapy, were selected from three major medical centers in Seoul, Korea. A packet including PABCF (Psychosoical Adjustment to Breast Cancer Factor), revised RPFS (Revised Piper Fatigue Scale), HHI (Herth Hope Index), and self-addressed return envelope was given to the participants at seven to eight weeks post surgery. The questionnaires were to be completed at home and returned to the researcher by mail. The obtained data were analyzed using three regression equations guided by Baron and Kenny (1986); first, hope was regressed on fatigue; second, psychosocial adjustment was regressed on fatigue; and third, psychosocial adjustment was regressed on fatigue and hope, simultaneously. In the first equation, fatigue explained 4% of the variance in hope. In the second equation, fatigue explained 47% of the variance in psychosocial adjustment. In the last equation, hope and fatigue significantly explained the variance in psychosocial adjustment. Therefore, all conditions for the test of mediation effect of hope were satisfied. For the test of the mediation effect, the beta coefficients of fatigue on psychosocial adjustment on the second and third regression equations were compared. The beta coefficients were decreased from .69 (p < .001) on the second regression equation to .63 (p < .001) on the third regression equation. Thus, the hypothesis of this study was supported. As a result of this study, the negative Influence of fatigue on psychosocial adjustment is dampened through the mediator effect of hope in women with breast cancer. Therefore, when planning care for the adverse effect of fatigue on psychosocial adjustment, oncology nurses should consider hope as a mediator between fatigue and psychosocial adjustment to breast cancer.

• 한국해양공학회지
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• 제1권2호
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• pp.113-122
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• 1987

Ships and offshore strrctures are exposed to the corrosive surroundings, and the extablishment of the design criteria and the elucidation on the influence by this environment are requested to maintain the safety and to demonstrate the function of the structure. In this paper, the fatigue-crack-growth behavior on the compact tension specimens of quenched, tempered HT80 grade steels and RA36 high tensile steels having a single edge fatigue cracked notch respectively, were investigated under the repeated tensile stress with constant stroke in sea water for the welded parts by shielded metal arc welding. Main results obtained are summerized as follows; 1. The fatigue-crack-growth rates da/dN in sea water appeared to be greater behavior than those in air environment at the same stress intensisy factor range $\DeltaK$. 2. The correlation data of da/dN$\DeltaK$ of the two kinds of high tensile steels in sea water showed no great difference, however, the correlation data of da/dN$\DeltaK/\sigma_y$($\sigma_y$ stands for yield strength of the material) showed that the fatigue-crack-growth behavior of RA36 plate is affected by active path corrosion(APC) mechanism, while that of HT80 grade plate is mainly affected by hydrogen embrittlement mechanism.

• Structural Engineering and Mechanics
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• 제19권3호
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• pp.347-359
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• 2005

This paper attempts to develop the analytical model of estimating the fatigue damage using a linear elastic fracture mechanics method. The stress history on a welding member, when a truck passed over a bridge, was defined as a block loading and the crack closure theory was used. These theories explain the influence of a load on a structure. This study undertook an analysis of the stress range frequency considering both dead load stress and crack opening stress. A probability method applied to stress range frequency distribution and the probability distribution parameters of it was obtained by Maximum likelihood Method and Determinant. Monte Carlo Simulation which generates a probability variants (stress range) output failure block loadings. The probability distribution of failure block loadings was acquired by Maximum likelihood Method and Determinant. This can calculate the fatigue reliability preventing the fatigue failure of a welding member. The failure block loading divided by the average daily truck traffic is a predictive remaining life by a day. Fatigue reliability analysis was carried out for the welding member of the bottom flange of a cross beam and the vertical stiffener of a steel box bridge by the proposed model. Results showed that the primary factor effecting failure time was crack opening stress. It was important to decide the crack opening stress for using the proposed model. Also according to the 50% reliability and 90%, 99.9% failure times were indicated.

• 한국보건간호학회지
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• 제16권1호
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• pp.105-114
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• 2002

This study was to investigate the level of fatigue and its associated variables in patients with systemic lupus erythematosus(SLE) in Korea. From March to June, 2001, 100 patients, registered at one university hospital rheumatology clinic in Seoul, were accepted as subjects for this study. The sampling method was adopted a non-probability, purposive technique. The instruments used for this study were The Multidimensional Assessment Fatigue scale developed by Tack and Beck Depression Instrument develped by Beck. The collected data were analyzed by SAS program using t-test, ANOVA with Scheffe-test, Pearson correlation coefficients and stepwise multiple regression. The results were as follows: 1. Total scores of fatigue of the subjects averaged $24.46(\pm10.85)$, degree of fatigue was $5.08(\pm2.29)$, and influence of fatigue was $3.52(\pm2.12)$. 2. Regarding characteristics, more depressive(p=.0001) and more painfuI(p=.0122) patients revealed more fatigue. Also, the subjects with spouse(p=.0337) and having poor quality of sleep(p=.0445) revealed more fatigue. 3. The subjects' total fatigue score, depression, pain and age was correlated positively(r=.53; r=.48; r=.24), and total fatigue score, and exercise time, quality of sleep was correlated negatively(r=-.45; r=-.21). 4. The main influencing factors on the fatigue were depression$(52.92\%)$ and quality of sleep $(8.10\%)$. These two main variables made it possible to explain $61.02\%$ of the varience in fatigue. In conclusion, this study revealed depression and quality of sleep is an important factor that can improve quality of life in patients with SLE. It is recommended that nursing intervention for SLE patients would be focused to decrease depression and to enhance quality of sleep.

• 한국산업융합학회 논문집
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• 제6권4호
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• pp.299-305
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• 2003

This research is for the relationship with heat treatment cooling temprature and the characteristic of Mechanical properties of Boron-Addition-Steel, the main material and SM25C steel, the sub material, structure viewing fractography, hardness test, tensite test and are carried out after the manufacturing small-specimen treated with heat of $750^{\circ}C$, $850^{\circ}C$, $1050^{\circ}C$. The influence to the Mechanical properties accompanied by AISI51B20, Boron-Addition-steel shows the following result. 1. The influenc of heat treatment by the content of cabon-steel is dominant. Addition of boron result is Strengthening structure effectively by segregation and improving over all mechanical characters such as good. it results from the increase of temacity by the stability of inter granular with improvement of harden-ability. 2. Boron-Addition-Steel exist in the from of martensite structure accompanied by the ferrite precipitition centering around grain boundary, and is improved to Hv 200. 3. The height of harden-ability and fatigue stress the influence of heat results from crystal structure of martensite by difference of strength level in the structure of ferrite and doesn't have am effect on sensibility of temperature, and turns out to defend on production and growth of Matrix-structure-factor.