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1.
Orlando J. A. Gonalves Filho 《International Journal of Mechanical Sciences》2004,46(4):527-539
A lower bound to the creep rupture time of internally pressurised thick cylinders is derived. Material behaviour is described by a phenomenological creep rupture theory that accounts for all phases of creep, and for the full coupling between the deformation and damage processes. To obtain the desirable lower bound, the effective stress and the equivalent rupture stress, which represent the effects of multiaxial stress states on the creep strain and damage rates, respectively, were approximated by the maximum shear stress in the constitutive equations. By comparing the lower bound estimations for a wide range of cylinder dimensions and different engineering materials with the rupture times determined from accurate finite element calculations, it is shown that the lower bound estimations provide quite conservative lifetime predictions. 相似文献
2.
Ho-Kyung Kim Duk-Kyu Chun Sung-Hoon Kim 《Journal of Mechanical Science and Technology》2005,19(7):1432-1440
High-temperature rupture behavior of 5083-A1 alloy was tested for failure at 548K under multiaxial stress conditions : uniaxial
tension using smooth bar specimens, biaxial shearing using double shear bar specimens, and triaxial tension using notched
bar specimens. Rupture times were compared for uniaxial, biaxial, and triaxial stress conditions with respect to the maximum
principal stress, the von Mises effective stress, and the principal facet stress. The results indicate that the von Mises
effective and principal facet stresses give good correlation for the material investigated, and these parameters can predict
creep life data under the multiaxial stress states with the rupture data obtained from specimens under the uniaxial stress.
The results suggest that the creep rupture of this alloy under the testing condition is controlled by cavitation coupled with
highly localized deformation process, such as grain boundary sliding. It is also conceivable that strain softening controls
the highly localized deformation modes which result in cavitation damage in controlling rupture time of this alloy. 相似文献
3.
This paper describes a numerical model developed for the computation of creep damages in a thick-walled sphere subjected to
an internal pressure and a thermal gradient. The model predicts the creep damage histories during the life of the sphere,
owing to variations in stresses with time and through-thickness variations. The creep damage fraction is based on the Robinson’s
linear life fraction damage rule, which has been incorporated in a nonlinear time-dependent stress analysis. Following the
stress histories, the effective stress histories are obtained and the creep damages are calculated and summed during the life
of the sphere. The material long-term creep properties up to the rupture and creep rupture data are defined by the Θ projection
concept [1]. The damage histories up to 38 years are calculated and the results show that the maximum damages are always located
at the inner surface of the sphere, while the outer surface of the vessel sustains minimum damages. 相似文献
4.
D.R. Hayhurst 《International Journal of Mechanical Sciences》1976,18(2):75-80
Constitutive relationships are discussed for materials which undergo creep rupture due to cyclic loading. Relationships are proposed which describe the strain rates in terms of the current stress and a single state variable. An approximate method is derived which enables a lower bound on the rupture life to be obtained for kinematically determinate structures subjected to cyclic load and isothermal conditions. The bound on the rupture life is expressed in terms of the energy dissipation rates within the structure corresponding to stationary-state creep. The effect of multi-axial stress creep-rupture upon the structural performance is examined and bounds are derived for materials which obey maximum tension and octahedral shear stress criteria. For both multi-axial stress rupture laws and structures subjected to cyclic and reverse load conditions formulae are derived which express the lower bound rupture life in terms of the behaviour of a steady-load uni-axial creep rupture test. Results of experiments which have been carried out on copper and aluminium beams are presented for cyclic and reverse load conditions. For both rupture laws the experimental rupture times are closely predicted by the representative rupture stresses and uni-axial data. 相似文献
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6.
考虑应力松弛的涡轮盘蠕变持久寿命可靠性分析方法 总被引:1,自引:0,他引:1
提出考虑应力松弛的轮盘蠕变持久寿命可靠性分析方法。该方法基于概率Miner累积损伤理论,考虑载荷和材料参数的分散性以及应力松弛效应,通过对若干计算点有限元蠕变分析结果响应面回归,获得损伤临界函数的近似表达式。进而采用Monte-Carlo法获得轮盘蠕变持久寿命可靠度或给定可靠度的蠕变持久寿命。并分析了应力松弛和各随机变量对蠕变持久寿命的影响。 相似文献
7.
Lars Brthe 《International Journal of Mechanical Sciences》1978,20(9):617-624
A simple method for extrapolation of isothermal constant load creep rupture test data is presented and discussed. It is shown that the method has support from the Kachanov theory of brittle creep rupture. As a consequence, the material parameters of the Kachanov creep damage rate law can be quickly estimated from short time tests. Five sets of experimental data are used to illustrate the method and its limitations. 相似文献
8.
An analysis of the environmental effect on creep and creep rupture of metals is presented. It is pointed that the investigation of the diffusion processes leads to significant computational difficulties. These difficulties arise on representing the solution of the diffusion equation with variable boundaries in the form convenient for analysis.The process of damage accumulation is modelled for a material, which is subjected to the combined action of mechanical loads and the aggressive environment. The Rabotnov kinetic theory is applied in which two parameters are taken into account: the damage of the material and the concentration of chemical elements reducing the resistance of the material to mechanical loads. An approximate solution of the diffusion equation is suggested for rod or shell subjected to axial tension. This solution is based on dividing the cross-section of rod or shell into the disturbed and undisturbed parts and determining the motion of the boundary between these parts. The system of constitutive equations which describe the interaction between the diffusion and rupture fronts during the creep process until failure is obtained. A good quantitative agreement between experimental and theoretical results has been received. 相似文献
9.
A. R. Ragab 《International Journal of Mechanical Sciences》2002,44(3):601-620
A phenomenological formulation based on a theory of plasticity for voided solids, and power-law creep, to estimate the rupture times and strains for pressurized tubes is presented. Realistic values of the damage parameters involved are selected by satisfying the creep rupture uniaxial data for the same materials. Void growth and coalescence and hence the loss of load-carrying capacity of the tube is taken as a failure criterion. Computed values of rupture times for thin- and thick-walled tubes are shown to be mostly in close agreement with the experimental data found in the literature. Only fair agreement among predicted and experimental fracture strains is observed. 相似文献
10.
Failure prediction for multi-material creep test specimens using a steady-state creep rupture stress
The steady-state stress distributions in single- and multi-material notched and waisted specimens were investigated for practical creep test specimens using material properties obtained for materials from a service-aged CrMoV pipe weldment. The tri-axial stress conditions existing in notched and waisted specimens machined from welded pipes were identified. By using a steady-state effective failure stress, it has been shown that an approximate method, based on steady-state stress, for the prediction of rupture life and failure position can produce reasonably accurate results. The applicability of the approximate method was confirmed by comparing the results obtained using it with those obtained from corresponding creep continuum damage modelling. These results indicate that use of steady-state stress analysis, as an approximate technique, may be useful for assessing creep failure behaviour, for determining the effect of specimen size and for generating material properties for welded components. 相似文献
11.
A simplified, two parameter creep curve model is developed, which represents primary-secondary-tertiary creep behaviour. The two parameters are related via the secondary strain respectively to: the sum of secondary and primary strains; and, the sum of secondary and tertiary strains. Techniques are described for fitting the model to laboratory data; and, for the determination of the parameters which characterize primary-secondary and secondary-tertiary creep. The single state variable theory used to describe tertiary creep is compared with mechanisms based models and shown to closely predict the effect of stress-state on rupture strain. A two bar plane strain model component subjected to steady load is studied and used to determine the effect on the component lifetime of primary creep; and, of the multi-axial creep rupture criterion. The representative rupture stress is found to be weakly dependent on primary creep and strongly dependent on the multi-axial rupture criterion of the material. 相似文献
12.
I. W. Goodall R. D. H. Cockroft E. J. Chubb 《International Journal of Mechanical Sciences》1975,17(5):351-360
The economic design of high temperature structures requires an accurate estimation of the creep rupture life. Earlier work by the authors has shown that it is possible to bound the life of a structure subject to fixed loading. The bounds, however, are well separated and it is important to establish where the actual lives lie relative to the two bounds. In this paper, detailed finite element calculations and experimental work on plate structures are reported. These results, together with the concept of local kinematic determinacy, lead to a correction factor on the upper bound life prediction. This enables a good measure of the load-carrying capacity of any ductile structure to be obtained from knowledge of the limit load, the elastic stress concentration factor and material stress rupture data. 相似文献
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14.
A method is given for the calculation of creep rupture strength of parts containing stress concentrations. The creep theory takes account of the damage and anisotropy of materials. which arise during deformation. For the example of a plane specimen with a notch, results of calculations are compared with experimental data. The results of an investigation into the creep strength of the fir-tree root of a turbine blade at non-stationary loading is given. 相似文献
15.
Woo-Gon Kim Jae-Young Park Seon-Jin Kim Eung-Seon Kim Jinsung Jang 《Journal of Mechanical Science and Technology》2018,32(9):4165-4172
This study aims to improve the long-term creep life extrapolation of Grade 91 (Gr. 91) steel using a new master curve of a hyperbolic sine (“sinh”) form. In the master curve for extrapolating creep rupture life, a controversial point of a polynomial form, which has usually been used in time–temperature parametric methods, was preliminarily indicated. The validity of the new master curve was verified. A large body of creep rupture data for Gr. 91 steel was prepared from different sources of available worldwide data at 500 °C to 700 °C for Gr. 91 steel. The material constants of the Larson–Miller, Orr–Sherby–Dorn, and Manson–Harferd parameters were obtained using the polynomial and sinh forms on the basis of the rupture data. Long-term creep rupture life was extrapolated for up to 60 years using the two forms that defined the master curves. Results of long-term creep life extrapolation showed that the master curve of the polynomial form exhibited overestimation due to the divergent curves in the low stress ranges, whereas the master curve of the sinh form revealed goodness in the low stress ranges beyond the experimental data. The proposed sinh form was superior to the polynomial form. The sinh form could be applied to extrapolate the long-term creep rupture life of other heat-resistant steels. The creep rupture stresses predicted by the sinh function were comparable to those of RCC-MRx code. 相似文献
16.
Kwang-Il Ho 《Journal of Mechanical Science and Technology》1990,4(1):92-97
The purpose of this study is the development of an anisotropic creep damage theory within the continuum damage mechanics,
applicable to creep-dominated cyclic loading histories. A damage distribution is expressd in rate form as a symmetric tensor
of rank necessary to match physically measured damage. A theoretical model which expresses general anisotropic creep damage
phenomena with power law cavity growth is proposed. The coupling of damage with a bounding surface cyclic viscoplasticity
theory is also accomplished. Comparison with experimental results are made for weakly anisotropically damaging materials,
type 304 stainless steel at 593°C. Good correlation of rupture time, secondary creep, and tertiary creep has been obtained
for proportional and nonproportional, isothermal, constant isochronous nominal stress loading histories. A modification of
the isochronous stress (the set of stress state which have a same rupture time) for compressive hydrostatic stress state has
been offered. 相似文献
17.
A. R. S. Ponter 《International Journal of Mechanical Sciences》1977,19(2):79-92
Upper bounds on the rupture life and time to initial rupture of a body obeying the Katchanov creep rupture equations are derived for cyclic load and temperature. The bounds are derived from the creep rupture equation without reference to the deformation properties. The relationship to previously derived bounds of this type are discussed, and the circumstances when the bounds can be both very good and very poor are demonstrated through simple examples. 相似文献
18.
针对法兰连接系统长时间在高温下工作会导致泄漏失效的问题,对法兰连接系统的3个主要部件的失效机理进行了分析,其中从蠕变、预紧力、脆性断裂及疲劳等方面分析了螺栓的失效机理;从蠕变松弛失效、高温回弹性失效和高温强度失效等方面分析了垫片的失效机理;从高温蠕变松弛失效和高温下的界面泄漏失效等方面分析了法兰的失效机理。本文为更快地找出高温下法兰连接系统的失效原因提供了参考依据。 相似文献
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20.
Omega蠕变寿命评估方法及应用 总被引:1,自引:0,他引:1
传统高温过热蒸汽管及过热炉管蠕变寿命评估多采用等温外推、Larson-Miller参数和θ参数等寿命评估方法,此类寿命评估方法常通过开展多组高应力蠕变测试进行短时外推,不仅耗时长、取样破坏性大、寿命评估存在分散性,而且此方法没有考虑材料的老化与损伤,长时外推结果置信度下降。1986年,美国材料学会(MPC)发起了用于评估工作在蠕变范围内部件剩余寿命的O-mega工程,目前该评估方法已被编入API 579 Fitness-For-Service标准中。通过介绍Omega寿命评估方法,并对1Cr0.5MoV和1.25Cr0.5MoSi两种材料开展Omega蠕变分析,再将Omega方法预测的材料蠕变断裂时间与实际断裂时间进行对比,发现Omega方法在评定蠕变寿命评估方面更具优越性。 相似文献