Papers by Keyword: Thermo-Mechanical Fatigue (TMF)

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Authors: Keum Oh Lee, Seong Gu Hong, Soon Bok Lee
Abstract: Isothermal cyclic stress-strain deformation and thermomechanical deformation (TMD) of 429EM stainless steel were analyzed using a rheological model employing a bi-linear model. The proposed model was composed of three parameters: elastic modulus, yield stress and flow stress. Monotonic stress-strain curves at various temperatures were used to construct the model. The yield stress in the model was nearly same as 0.2% offset yield stress. Hardening relation factor, m, was proposed to relate cyclic hardening to kinematic hardening. Isothermal cyclic stress-strain deformation could be described well by the proposed model. The model was extended to describe TMD. The results revealed that the bi-linear thermomechanical model overestimates the experimental data under both in-phase and out-of-phase conditions in the temperature range of 350-500oC and it was due to the enhanced dynamic recovery effect.
Authors: Dong Keun Lee, Jeong Min Lee, Jae Mean Koo, Chang Sung Seok, Jae Won Kim
Abstract: A gas turbine blade operates under severe conditions including high temperature, high speed rotation, and frequent starts and shutdowns. Under such operating conditions, a blade is exposed to a thermo mechanical fatigue environment. These conditions shorten the life of the turbine parts and reduce the reliability of the gas turbine. Therefore, research on the characteristics of blade material is necessary. In this study, thermo-mechanical fatigue (TMF) tests were conducted for IN738LC, which is base a material for turbine blades. Tests were conducted under both the IP (in-phase) and OP (out of-phase) conditions, and tests results were compared in terms of fatigue life. After obtaining the ε-N curves, additional TMF tests were conducted according to variations in fatigue life. The purpose of the TMF test is to observe the change in mechanical properties of materials damaged during TMF and how these relate to fatigue life. For this purpose, an indentation test was conducted and the relationship between hardness and fatigue life were obtained.
Authors: Wei Na Hao, Guo Zhong Chai, J. Zhou
Abstract: A viscoplastic constitutive model with void damage is developed to analyze the macroscopic mechanical response and damage mechanism of lead-free solder alloy in CBGA packaging under cyclic thermal loading. The constitutive model is implemented into ABAQUS through its user defined material subroutine. Two-dimensional nonlinear finite element analysis of a ceramic ball grid array(CBGA) package is conducted to simulate the viscoplastic deformation and damage failure process of the lead-free solder joint under cyclic thermal loading. The damage model is helpful for optimization and reliability of electronic package.
Authors: Lu Cui, Peng Wang
Abstract: Description of crack initiation behavior under thermo-mechanical fatigue (TMF) of modern high chromium steel is prerequisite for design optimization of steam turbine components. In this paper a phenomenological method which envelopes the synthesis of stress-strain hysteresis loops according to cycle counting methods and the individual assessment of creep fatigue damage is extended to TMF with superimposed creep. Recalculation of such service-type experiments on specimen of rotor steel 10CrMoWVNbN shows acceptable results for deformation description and lifetime estimation.
Authors: Adwait U. Telang, Thomas R. Bieler
Abstract: To investigate the effect of external loads arising from differential thermal expansion between a substrate and a surface mount component, specimens with a simulated surface mount component (nickel) on a copper substrate having a 1 mm2 joint area and solder thickness of about 100 µm were prepared to induce extrinsic shear in joints undergoing thermomechanical fatigue (TMF) cycling. The specimens were fabricated stress free and later clamped to a copper block to cause a significant reversal in sign of the shear imposed on the solder joint during TMF cycling for 20 minutes at 150°C and 3.5 hr at -15°C. The evolution of surface damage and microstructure was examined using SEM and Orientation Imaging Microscopy (OIM). The joints were almost single crystals. However, the orientations of the tin in each joint is different, leading to different resolved stresses on a given slip system. The joint with the largest resolved shear aligned with the crystal caxis showed the most damage. Low angle tilt boundaries developed, and sliding was observed on boundaries near 7 and 14° that have a coincident site lattice. Schmid factor analysis was carried out in regions that showed ledges or grain boundary sliding. Slip on (110) planes correlated well with some of the ledges.
Authors: Z.W. Huang, Zhong Guang Wang, Shi Jie Zhu, F.H. Yuan, F.G. Wang
Abstract: A cast nickel based superalloy M963 was coated by high-velocity oxy-fuel (HVOF) spraying process. The effect of HVOF MCrAlY coating on thermo-mechanical fatigue (TMF) and isothermal fatigue (IF) in M963 was studied to understand fatigue life and failure mechanisms in coated and uncoated M963 alloy. Two types of TMF tests, i.e. in-phase (IP) and out-of-phase (OP), were performed in temperature range of 450~900°C, and IF tests were conducted at 900°C. It was found that the coating had a detrimental effect on fatigue life under OP TMF, while a beneficial effect of the coating existed under IP TMF and IF. Crack initiation time in the coated specimen was shorter than that in the uncoated specimen and the former’s crack density was higher than the latter’s one under OP TMF. The relationship of deformation and fracture response with fatigue life was discussed based on microscopic analysis.
Authors: Motoki Sakaguchi, Masakazu Okazaki
Abstract: Behavior of thermo-mechanical fatigue (TMF) failure of a single crystal Ni-base superalloy, CMSX-4, was studied and, compared with isothermal low-cycle fatigue (ILCF) of it. Strain-controlled TMF and ILCF tests of CMSX-4 were carried out under various test conditions, where the experimental variables were strain rates, strain ratio, test temperature and the range, and strain/temperature phase angle. At first it was shown from the experiments that the TMF and LCF failures associated with some noteworthy characteristics were rarely seen in the traditional pollycrystalline heat-resistant alloys. These phenomena could be explained inadequately, on the basis of the macroscopic parameters and the historical failure criteria; e.g., Manson-Coffin law and Ostergren approach. A new micromechanics model is proposed to predict the TMF and LCF lives, based on the Eshelby's theory.
Authors: Jeong Min Lee, Dong Keun Lee, Jae Mean Koo, Chang Sung Seok
Abstract: In this paper, thermo-mechanical fatigue tests were performed for the nickel-based super alloy IN738LC, after which the thermo-mechanical fatigue life was evaluated using finite element analysis. Nickel-based super alloy is used as the main material of turbine blades, which are important equipment in thermal power generation plants. In general, such materials receive three types of damage under thermo-mechanical fatigue loading. In the case of low-cycle fatigue behavior in which large plastic deformation mainly occurs, the lifetime can be decided by its relationship with the plastic strain amplitude. In order to obtain the plastic strain amplitude from the measured strain amplitude, a hysteresis loop should be derived. However, low-cycle fatigue tests are difficult. Moreover, precise experimental techniques are required to obtain the hysteresis loops. In this study, after thermo-mechanical fatigue tests were performed, thermal mechanical fatigue tests on IN738LC were simulated using finite element analysis. The results of analysis were verified by comparing with the hysteresis loops of an experiment
Authors: Reinhard Bardenheier, Graham Rogers
Abstract: Fatigue damage plays an increasingly important role in the design of various safety critical components that are exposed simultaneously to thermal and mechanical loads. Non-isothermal conditions, as these are to be found in turbine components, rocket engines, but also in high-speed machining tools makes the understanding even more complex. As the nature of those loading histories is mostly multiaxial, design engineers are interested in material models, which take into account the complexity of stress state and temperature history as well. The experimental validations of those models require specially designed test set-ups. The basic concepts of experimental techniques to perform non-isothermal, uniaxial fatigue tests will be described in general. Test systems, capable to simulate non-isothermal multiaxial stress states are presented. A new miniaturised electrothermalmechanical test rig, which allows testing of small specimens under complex thermomechanical loading conditions, will be discussed.
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