• 대한기계학회논문집
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• 제18권7호
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• pp.1722-1729
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• 1994

At early stage of creep-fatigue crack growth tests, initial transient behavior which implies high crack growth rate has been generally observed by some researchers. Since the influence of the initial transient crack growth behavior on the remaining life of components is significant, cause of it should be further studied. In this study, characteristics of the initial transient behavior of 1Cr-1Mo-0.25V steel is studied experimentally by performing creep-fatigue crack growth tests at $538^{\circ}C$ in air under trapezoidal waveshapes. It is verified that the cause of the initial transient behavior is not high ${(C_t)}_{avg}$ values due to the small scale creep condition at the early stage of test, but oxidation-dominated crack growth mechanism during the transient period which is different from the creep-dominated crack growth mechanism in steady crack growth period.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 춘계학술대회 논문집
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• pp.167-174
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• 1994

The creep behavior and creep fracture of alumina at high temperature were investigated under four point flexural test. The steady-state creep behavior was observed at low bending stress and the primary creep until fracture was observed at high bending stress. The loading history of bending stress did not affect on the steady-stated creep rate. Intergranular fracture was dominant for fracture of alumina at room and high temperature. However, transgranular fracture was dominant on creep fracture of alumina under high temperature by nuclueation and growth of microcracks due to residual flaws or cavities in the material.

• 한국세라믹학회지
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• 제31권5호
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• pp.543-551
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• 1994

The creep behavior and creep fracture of sintered alumina at high temperature were investigated under four point flexural test. Steady-state creep behavior was observed at low bending stress and primary creep until fracture was observed at hish bending stress. The loading history of bending stress did not affect on steady-state creep rate. Intergranular fracture was dominant for fracture of alumina at room and high temperature. However, transgranular fracture was dominant on creep of alumina under high temperature by nucleation and growth of microcracks due to residual flaws or cavities in the material.

• Nuclear Engineering and Technology
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• 제52권4호
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• pp.802-810
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• 2020

Three-dimensional finite element simulations are implemented for the in-pile thermo-mechanical behavior in U-Mo/Al monolithic fuel plates with different thermal creep rates of cladding involved. The numerical results indicate that the thickness increment of fuel foil rises with the thermal creep coefficient of cladding. The maximum Mises stress of cladding is reduced by ~85% from 344 MPa on the 98.0^th day when the creep coefficient of cladding increases from 0.01 to 10.0, due to its equivalent thermal creep strain enlarged by 3.5 times. When the thermal creep coefficient of Aluminum cladding increases from 0 to 1.0, the maximum mesoscale stress of fuel foil varies slightly. At the same time, the peak mesoscale normal stress of fuel foil can reach 51 MPa on the 98.0^th day for the thermal creep coefficient of 10, which increases by 60.3% of that with the thermal creep un-occurred in the cladding. The maximum through-thickness creep strain components of fuel foil differ slightly for different thermal creep coefficients of cladding. The dangerous region of fuel foil becomes much closer to the heavily irradiated side when the creep coefficient of cladding becomes 10.0. The creep performance of Aluminum cladding should be optimized for the integrity of monolithic fuel plates.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.320-323
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• 2004

In general, polymer concrete has more excellent mechanical properties and durability than Portland cement concrete, but very sensitive to heat and has large deformations. In this study, the long-term creep behaviors was predicted by the short-term creep test, and then the characteristic of creep of recycled-PET polymer concrete was defined by material and experimental variables. The error in the predicted long-term creep values is less than 5 percent for all polymer concrete systems. The filler carry out an important role to restrict the creep strains of recycled PET polymer concrete. The creep strain and specific on using the CaCO3 were less than using fly-ash. the creep increases with an increase in the applied stress, but not proportional the rate of stress increase ratio. The creep behavior of polymer concrete using recycled polyester resin is not a linear viscoelastic behavior.

• 콘크리트학회논문집
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• 제11권4호
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• pp.3-11
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• 1999

The creep characteristics of concrete under tensile stress has been usually assumed to have the same characteristics as that under compressive stress in the time-dependent analysis of concrete structures. However, it appears from the recent experimental studies that tensile creep behavior is much different from compressive one. In particular, high sustaining tensile stress may cause time-dependent cracking and thus lead to tensile failure. It is, therefore, necessary to model the tensile creep behavior accurately for realistic time-dependent analysis of concrete structures. The present paper to have been focused to suggested more realistic model for the tensile creep behavior of concrete. The models are compared with tensile creep test data available in the literature. The proposed model may allow more refined analysis of concrete structures under time-dependent loading.

• Journal of Mechanical Science and Technology
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• 제20권12호
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• pp.2136-2146
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• 2006

A study on a creep-fatigue crack growth behavior has been carried out for a cylindrical structure with weldments by using a structural test and an evaluation according to the assessment procedures. The creep-fatigue crack growth behavior following the creep-fatigue crack initiation has been assessed by using the French A16 procedure and the conservatism for the present structural test has been examined. The structural specimen is a welded cylindrical shell made of 316 L stainless steel (SS) for one half of the cylinder and 304 SS for the other half. In the creep-fatigue test, the hold time under a tensile load which produces the primary nominal stress of 45 MPa was one hour at $600^{\circ}C$ and creep-fatigue loads of 600 cycles were applied. The evaluation results for the creep-fatigue crack propagation were compared with those of the observed images from the structural test. The assessment results for the creep-fatigue crack behavior according to the French Al6 procedure showed that the Al6 is overly conservative for the creep-fatigue crack propagation in the present case with a short hold time of one hour.

• 터널과지하공간
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• 제28권1호
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• pp.25-37
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• 2018

미고결 암석에 대한 Creep 특성을 분석하고자 Burger 모델을 이용하였다. Burger 모델은 자료쌍 D(u,t)으로부터 4개의 역학적 매개변수를 결정 하여야 한다. 본 연구에서는 수학적 개념 해를 적용하여 매개변수를 결정 하였다. 미고결 암석에 대한 Burger 모델의 결정된 매개변수를 이용하여 Creep을 3년간 가속시켰다. 그 결과 Creep 거동은 수렴이 되지 않고 지속적인 변형거동을 보였다. 따라서 본 광산에서는 Roofbolt 보다 U-Beam 적용이 안정성 측면에서 더 적합 할 것으로 분석 되었다.

• Fibers and Polymers
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• 제7권2호
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• pp.123-128
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• 2006

The present study aims at characterizing and modeling the anisotropic creep behavior of coated textile membrane, a class of flexible textile composites that are used for moderate span enclosures (roofs and air-halls). The objective is to develop a creep model for predicting the lifetime of coated textile membrane. Uniaxial creep tests were conducted on three off-axis coupon specimens to obtain the directional creep compliance. A potential with three parameters is shown to be adequate for modeling the anisotropic creep behavior of coated textile membrane. Furthermore, a possibility of predicting the creep deformation of coated textile membrane in a multi-axial stress state is discussed using the three-parameter potential.

• Nuclear Engineering and Technology
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• 제53권2호
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• pp.572-582
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• 2021

This study investigated the creep and creep crack growth (CCG) behavior of the base metal (BM), weld metal (WM), and heat affected zone (HAZ) in a Gr. 91 weldment, which was made by a shield metal arc weld process. A series of tensile, creep, and CCG tests were performed for the BM, WM, and HAZ at 550 ℃. Creep behavior of the BM, WM, and HAZ was analyzed in terms of various creep laws; Norton's power-law, Monkman-Grant relation and damage tolerance factor (λ), and their constants were determined. In addition, each CCGR law for the BM, WM, and HAZ was proposed and compared in terms of a C^*-fracture parameter. The WM and HAZ revealed faster creep rate, lower rupture ductility, and faster CCGRs than the BM, but they showed a similar behavior in the creep and CCG. The CCGRs obtained in the present study exhibited a marginal difference when compared with those of RCC-MRx of currently elevated design code in France. A creep crack path in the HAZ plane progressed towards a weak fine-grained HAZ adjacent to the BM.