Boundary element analysis in computational fracture mechanics: TA Cruse Kluwer Academic Publishers, 1988, 162 pps ISBN: 90-247-3614-5 (original) (raw)
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Creep and creep–fatigue crack growth
International Journal of Fracture, 2015
Creep and creep-fatigue considerations are important in predicting the remaining life and safe inspection intervals as part of maintenance programs for components operating in harsh, high temperature environments. Time-dependent deformation associated with creep alters the crack tip stress fields established as part of initial loading which must be addressed in any viable theory to account for creep in the vicinity of crack tips. This paper presents a critical assessment of the current state-of-the-art of time-dependent fracture mechanics (TDFM) concepts, test techniques, and applications and describes these important developments that have occurred over the past three decades. It is concluded that while big advances have been made in TDFM, the capabilities to address some significant problems still remain unresolved. These include (a) elevated temperature crack growth in creep-brittle materials used in gas turbines but now also finding increasing use in advanced power-plant components (b) in predicting crack growth in weldments that inherently have cracks or crack-like defects in regions with microstructural gradients (c) in development of a better fundamental understanding of creep-fatigue-environment interactions, and (d) in prognostics of high temperature
Creep-Fatigue Lifetime Assessment with Phenomenological and Constitutive Material Laws
Procedia Engineering, 2013
Variations in steam temperature due to start-up a thermomechanical stresses, which can lead to fatigu heated surface. With respect to component integrit mandatory. Lifetime assessment models have bee conducted. This paper presents a comparison and phenomenological approach, based on the generaliz account creep rupture damage at stress relaxation as as is an enhanced interaction method for the influenc viscoplastic constitutive material model of the type C of the types 1CrMoNiV (1Cr), 2CrMoNiWV (2Cr), The model allows the recalculation of the material be applicability and accuracy of the models is finally uniaxial and multiaxial experiments on notched speci
Computational Methods for Lifetime Prediction of Metallic Components under High-Temperature Fatigue
Metals
The issue of service life prediction of hot metallic components subjected to cyclic loadings is addressed. Two classes of lifetime models are considered, namely, the incremental lifetime rules and the parametric models governed by the fracture mechanics concept. Examples of application to an austenitic cast iron are presented. In addition, computational techniques to accelerate the time integration of the incremental models throughout the fatigue loading history are discussed. They efficiently solve problems where a stabilized response of a component is not observed, for example due to the plastic strain which is no longer completely reversed and accumulates throughout the fatigue history. The performance of such an accelerated integration technique is demonstrated for a finite element simulation of a viscoplastic solid under repeating loading–unloading cycles.
Materials Science and Engineering: A, 2010
The accumulation of creep-fatigue damage over time is the principal damage mechanism which will eventually lead to crack initiation in critical high temperature equipment. A model has been developed that assumes on a macroscopic level that the energy dissipated in the material may be taken as a measure of the creep damage induced in the material and hence the creep damage is directly proportional to absorbed internal energy density. The model developed is derived from considerations of mechanistic cavity growth and is based on rupture elongation to failure data using true strain. The predictions of the energy density exhaustion approach are compared with the results of creep-fatigue tests on low alloy ferritic steels. The predicted results of the energy density model are found to have good correlation with the measured creep-fatigue lives.
Lifetime prediction in creep-fatigue environment
Materials Science-poland, 2008
The creep-fatigue interaction has been studied and innovative mathematical models are proposed to predict the operating life of aircraft components, specifically gas turbine blades subject to creep-fatigue at high temperatures. The historical evolution of the creep-fatigue lifetime prediction is given in order to place the present study in the context. A literature review of the life estimation under creep-fatigue environment is presented.
2018
This paper presents a novel direct method, within the Linear Matching Method (LMM) framework, for the direct evaluation of steady state cyclic behaviour of structures subjected to high temperature – creep fatigue conditions. The LMM was originally developed for the evaluation of shakedown and ratchet limits. The latest extension of the LMM makes it capable of predicting the steady state stress strain solutions of component subjected to cyclic thermal and mechanical loads with creep effects. The proposed iterative method directly calculates the creep stress and cyclically enhanced creep strain during the dwell period for the assessment of the creep damage, and also creep enhanced total strain range for the assessment of fatigue damage of each load cycle. To demonstrate the efficiency and applicability of the method to assess the creep fatigue damage, two types of weldments subjected to reverse bending moment at elevated temperature of 550C are simulated by the proposed method conside...
Model for life prediction of fatigue–creep interaction
Microelectronics Reliability, 2008
This paper discusses the development of a procedure for computing creep and stress relaxation at the critical location in a through-hole structure. A high-speed methodology was developed for calculating cyclic creep and stress relaxation at critical locations of a pile on elastic foundation subjected to cyclic thermomechanical loading. This simplified analysis was exercised for two cases involving a pile on elastic foundation problem with different thermomechanical loading. The simplified analysis exhibited no computational problems and gave a stable solution for the full dwell times. Comparisons made with experimental results for these cases gave an excellent agreement at a much faster computing time. This simplified procedure is expected to be even much faster when an entire pile on elastic foundation assembly is analyzed.