• Nuclear Engineering and Technology
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• 제56권1호
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• pp.1-8
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• 2024

In this study, the influence of thermal aging on structural integrity is investigated for Gr. 91 steel. A commercial grade Gr. 91 steel is used for the virgin material, and service-exposed Gr. 91 steel is sampled from a steam pipe of a super critical plant. Time versus creep strain curves are obtained through creep tests with various stress levels at 600 ℃ for the virgin and service-exposed Gr. 91 steels, respectively. Based on the creep test results, the improved Omega model is characterized for describing the total creep strain curve for both Gr. 91 steels. The proposed parameters for creep deformation model are used for predicting the steady-state creep strain rate, creep rupture curve, and stress relaxation. Creep-fatigue damage is evaluated for the intermediate heat exchanger (IHX) in a large-scale sodium test facility of STELLA-2 by using creep deformation model with proposed creep parameters and creep rupture curve for both Gr. 91 steels. Based on the comparison results of creep fatigue damage for the virgin and service-exposed Gr. 91 steels, the thermal aging effect has been shown to be significant.

• 한국해양공학회지
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• 제13권3호통권33호
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• pp.29-35
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• 1999

At the design of Mark III membrane type LNG tank, an analytical and experimental approach on the fatigue strengths of membrane and its welds are very important in order to assist designers and surveyors. In this study, fatigue tests of lap weld of Mark III membrane type LNG tank were carried out and cumulative damage factor was calculated in order to estimate the fatigue life by probability density function and rule methods. It contained the following tests and reviews : 1) The fatigue tests of lap weld of stainless steel according to statistical testing method recommended by JSME, 2)Preparation of S-N curve for lap welds considering the statistical properties of the results of fatigue tests. 3) Procedure for estimating the initiation life of fatigue crack of lap welds under variable loads by the rule lf classification society and probability density function, 4) Guideline for inspection of lap welds fo membrane type LNG tank.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.60-64
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• 2001

In this paper, the tension-compression fatigue test method and the fatigue life characteristics of carbon fabric/epoxy laminate coupon are presented. To avoid the buckling during the compression, a proper design for the test coupons is essential. The critical buckling loads for the coupons are calculated by assuming the coupons as columns under two types of fixed conditions. The first is that both ends of each coupon are perfectly clamped, the second is that both ends of each coupon are simply supported. The strain-load curves are obtained by compressing the representative coupons, on each surface of which a strain gage is attached. The buckling loads obtained from the tests are all between the two calculated critical buckling loads. All the coupons are broken by the compression during the fatigue tests. It is estimated to be the reason that the fatigue load causes delamination before the eventual failure of each coupon, and sequentially the micro-buckling in the delaminated region drives each coupon into fatigue failure during the compression. The S-N curve, the fatigue life characteristics of carbon fabric/epoxy is obtained.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.711-714
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• 2002

Although recent research of metallic materials in high temperature fatigue have been much accomplished, many studies about brittle material as a die steel in high temperature fatigue does not have been reported. Especially, the study on the fatigue behavior over the transformation temperature is not studied sufficiently because of its difficult analysis and experiment. Therefore, reliable results of brittle material in high temperature fatigue behavior are needed. In this paper, stress-strain curves and stress-life curves in die STD61 steel at 700 and 900 are carefully examined, as the basic experimental data are used to predict from fatigue life over 700.

• 한국신뢰성학회지:신뢰성응용연구
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• 제7권2호
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• pp.45-55
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• 2007

In this study, two types of fatigue tests were conducted. Firs, cyclic bending tests were performed using the micro-bending tester. Second, thermal fatigue tests were conducted using a pseudo power cycling machine which was newly developed for a realistic testing condition. A three-dimensional finite element analysis model was constructed. A finite element analysis using ABAQUS was performed to extract the applied stress and strain in the solder joints. Creep deformation was dominant in thermal fatigue and plastic deformation was main parameter for bending failure. From the inelastic energy dissipation per cycle versus fatigue life curve, it can be found that the bending fatigue life is longer than the thermal fatigue life.

• 한국자동차공학회논문집
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• 제12권4호
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• pp.181-190
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• 2004

The interest of the fatigue life of rubber components such as engine mounts is increasing according to the extension of warranty period of the automotive components. Automotive engine mounts get damaged due to thermal and mechanical loadings. This paper discusses a fatigue life prediction of the 3-dimensional dumbbell specimens for natural rubber compound considering the effects of maximum strain and heat aging temperature. Displacement controlled fatigue life tests were performed using specimens with different levels of maximum strain and various hardness. The basic mechanical properties test and the fatigue test of aged rubber specimen under normal and elevated temperature were executed. A procedure to predicted the fatigue life of vulcanized natural rubber material based on the maximum strain method was proposed, and then this curve was in good agreement with fatigue test data less than 200% error range.

• 한국기계가공학회지
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• 제18권5호
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• pp.53-59
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• 2019

Continuous ship unloaders (CSUs) are used for the uninterrupted transport of material in processing industries, power plants, and harbors in accordance with the stream rate of the material. This study analyzed the structural integrity and fatigue life of a CSU structure using finite element structural analysis in ANSYS APDL software. The stress varied greatly depending on the luffing angle and the slew angle of the boom conveyor. The structural integrity of the CSU girder was evaluated by applying ASME BPVC Section VIII Division 2. The fatigue cycle at the angle with the greatest stress difference was calculated. The fatigue cycle was calculated by applying the JIS B 8821:2013 fatigue curve. It was confirmed that the fatigue cycle of the CSU satisfies the allowable fatigue of 200,000 cycles.

• 한국기계가공학회지
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• 제20권5호
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• pp.17-26
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• 2021

It is challenging to estimate the fatigue life of construction equipment consisting of a welded joint using field structure test owing to the uncertainty of the S-N curve. IIW recommends different S-N curves for various welded joint types. However, there is no way to define an appropriate curve considering complex design shape and strain gauge characteristics. This paper proposes an equivalent S-N curve method based on the relationship between IIW effective notch stress and virtual stress using finite element analysis. Moreover, a case study was conducted for the excavator fuel tank. The proposed method is expected to enhance accuracy and consistency in calculating the fatigue life for the welded structure of construction equipment.

• 대한기계학회논문집
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• 제7권4호
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• pp.425-433
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• 1983

Fatigue tests by axial loading (R=0.1) were carried out to investigate fatigue crack growth properties of small surface cracks in mild steel at room temperature, 250.deg. C and 400.deg. C, by using flat specimens with a small artificial pit. All the data of the fatigue crack growth rate obtained in the present tests are determined as a function of the stress intensity factor range, so that the applicability of liner fracture mechanics to the fatigue crack growth of surface cracks at elevated temperatures is investigated and discussed in comparison with the data of type 304 stainless steel at room temperature and elevated temperature. The obtained results are as follows: 1) Relations of both surface fatigue crack length and its depth to cycle ratio fall within a narrow scatter band in spite of different stress levels. 2) The .DELTA. .sigma. .root. .pi. a-da/dN relation of surface fatigue crack growth at room temperature is independent of the stress level and can be plotted as a straight line at log-log diagram, but the relation at 400.deg. C depends partly on the stress level. 3) Relations of the fatigue crack growth into depth d(2b)/dN and is stress intensity factor range .DELTA. $K_{I}$, accounted for the aspect ratio variation, fall within a narrow scatter band for wide range of the applied stress levels. And .DELTA. $K_{I}$E-d(2b)/dN relations of mild steel at different stress level coincide relatively well with the data of type 304 stainless steel. 4) The value of aspect ratio obtained by a beach mark method and a temper coloring method approaches about 0.9 in common with crack growth and it is independent of stress level and temperatures. 5) The equi-crack length curve is parallel to S-N$_{f}$ curve at elevated temperatures.s.s.s.

• 동력기계공학회지
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• 제11권1호
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• pp.127-133
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• 2007

SG-365 steel is an important material and used for manufacturing a pressure vessel which the gas piping. In this investigation, the elastic plastic fracture toughness of this material is evaluated by the unloading compliance method according to the ASTM E813-97 and E1152-97 method on the smooth and side groove 1CT specimens. The effect of smooth and side groove is studied on the elastic plastic fracture toughness. The side grooved specimen is very useful in estimation of the $J_{IC}$. It is much easier than the smooth specimen to the onset of the ductile tearing by the R curve method. Besides, it improves the accuracy of toughness values, decreases a phenomenon of the tunneling and shear lip by the side groove.