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Fracture, fatigue, and creep of metals
Published in Gregory N. Haidemenopoulos, Physical Metallurgy, 2018
Several types of fatigue are encountered in engineering. Mechanical fatigue is associated with a material subjected to a cyclic stress or strain. When at the same time the material is exposed at high temperatures, then the behavior is characterized as creep-fatigue. When the material is subjected, concurrently, to both cyclic loading and cyclic heating or cooling, the behavior is characterized as thermo-mechanical fatigue. When cyclic loading takes place in a corrosive environment, then it is characterized as corrosion fatigue. Cyclic loading with simultaneous sliding or rolling between two metallic surfaces results in sliding contact fatigue or rolling contact fatigue respectively. Finally cyclic loading with simultaneous relative oscillatory sliding friction between two metallic surfaces causes fretting fatigue. The present chapter deals primarily with mechanical fatigue. For the other types of fatigue the interested reader is advised to consult the suggested reading list at the end of this chapter.
Fatigue Design Philosophy of an Aero Engine Combustor Casing
Published in Sashi Kanta Panigrahi, Niranjan Sarangi, Aero Engine Combustor Casing, 2017
Sashi Kanta Panigrahi, Niranjan Sarangi
Gas turbine components experience severe cyclic thermal-mechanical loading in the high-pressure compressor, turbine modules, and the combustion chamber. Therefore, it is a requirement of the gas turbine designer to study the fatigue behavior of the materials used for these modules in detail. The oldest and still most commonly used method for estimating the fatigue life of metallic components is the S-N curve, even though the drawbacks are well known. One of them is that the fatigue life of notched specimens differs considerably from those observed for smooth specimens. The local strain method has been assumed to overcome this problem. In this method, it is suggested that the same strain amplitude always leads to the same fatigue life, regardless of the specimen shape. Evan et al. [45] developed a test procedure to test Inconel specimens to establish the thermo-mechanical fatigue characteristics of a material. The experiment was conducted on cylindrical specimens. The procedure highlighted the overview of the test procedure. Since the combustor casing is made of Inconel alloy in sheet form, an attempt is made to extract the mechanical properties from the specimens in sheet form as an input to the numerical analysis work carried out as a part of this book.
Creep and Fatigue of Metals
Published in Yichun Zhou, Li Yang, Yongli Huang, Micro- and MacroMechanical Properties of Materials, 2013
Yichun Zhou, Li Yang, Yongli Huang
Fatigue failure of an engineering component is mainly influenced by the type and magnitude of externally applied loads, the frequency and the number of cycles of cyclic loading, the service temperature, and the environmental medium. Fatigue failure can be classified according to the following factors: At the microscopic level, the initiation of fatigue cracking is related to the local microscopic plastic deformation. However, at the macroscopic level, when the magnitude of cyclic loading is relatively low, elastic strain dominates fatigue. Fatigue life is relatively long, and is called stress fatigue or high-cycle fatigue Nf>105, where Nf denotes the number of cycles when fatigue failure occurs).When the magnitude of cyclic stress is relatively high, plastic strain dominates. Fatigue life is relatively short, and is called strain fatigue or low-cycle fatigue Nf<105.Mechanical fatigue is fatigue failure that occurs solely under applied cyclic stress or strain.Creep-fatigue is fatigue failure under the synthetic action of cyclic loading and high temperature.Thermo-mechanical fatigue is fatigue under the synthetic effect of cyclic loading and cyclic temperature.Corrosion fatigue is fatigue under cyclic loading in a corrosive chemical medium or in an embrittled medium.Sliding contact fatigue and rolling contact fatigue is fatigue under the synthetic action of cyclic loading and sliding contact, or rolling contact between materials.Fretting fatigue is fatigue caused by the synthetic action of cyclic stress and the minute relative motion and friction sliding at contact surfaces.
Thermo-mechanical fatigue progressive analysis of delamination in composite laminates
Published in Mechanics of Advanced Materials and Structures, 2023
In the damaged composite laminates, the delaminations usually appear at many interfaces. The fatigue delaminations at different interfaces should be described simultaneously in an accurate analysis approach, together with their interactions of fatigue growth. However, the fatigue growth of multiple delaminations is not studied in the existing research works, considering the thermo-mechanical fatigue loading. In this work, based on the XLWM and TM-CZM, the thermo-mechanical fatigue progressive analysis is carried out for the delamination in composite laminates. A modified Peerlings damage law was introduced into TM-CZM, and its fatigue parameters are obtained by a large number of numerical results. The rest of the article is organized as follows: In Section 2, the TM-CZM across a partially open interface crack is presented briefly. The mathematical formulations of proposed XLWM are deduced in Section 3, including the displacement fields, virtual displacement principle, constitutive equations, and governing equations. In Section 4, some example problems are elaborated to demonstrate the merits of the proposed formulations. Finally, some conclusions are presented in Section 5.
Prediction of forging dies wear with the modified Takagi–Sugeno fuzzy identification method
Published in Materials and Manufacturing Processes, 2020
Andrzej Macioł, Piotr Macioł, Barbara Mrzygłód
For all research goals mentioned above, it was assumed that the problem will be treated as a classification task. The nature of the Takagi–Sugeno method (using a function describing conclusions) could lead to treating the problem of estimating the probability of wear occurrence and the degree of wear as a typical prediction task. It is obvious, however, that we can only estimate the probable values of these variables, and therefore it is rational to treat the conclusion as a certain set of disjoint classes and not continuous values (Tables 4 and 5). In the case of the characteristics of wear mechanisms in the cited studies, a percent share of each mechanism was determined (thermo-mechanical fatigue, abrasive wear, plastic deformation, and mechanical fatigue) depending on conditions of the forging process. For our research, we have found it desirable to create simplified models describing the structure of individual phenomena, as shown in Table 6.
A Computational Analysis of the Aerodynamic and Aeromechanical Behavior of a Thermo-Well for Steam Temperature Measurement in a Steam Turbine
Published in Heat Transfer Engineering, 2023
Mariusz Banaszkiewicz, Janusz Badur, Sebastian Kornet, Daniel Sławiński, Bartosz Kraszewski, Paweł Ziółkowski, Anna Rehmus-Forc, Grzegorz Bzymek
Thermal and deformational analyses of elements working at high-pressure were presented in [17–21]. Other studies [22, 23] have modeled and predicted the stress rupture of alloys and the residual life of the most critical components while considering the effects of creep, thermo-mechanical fatigue, corrosion, and oxidation. A new design thermometer and an innovative technique for measuring the fluid temperature with the purpose of monitoring transient thermal stresses in pressure thick-walled components and pipelines was presented in [24–26]. Allowable rates of fluid temperature variations are used for thermal stress monitoring and startup control of supercritical boilers [27] and steam turbines [28].