Thermal Mechanical Fatigue Research Articles

Full-scale 3-D finite element modeling of a two-loop pressurized water reactor for heat transfer, thermal–mechanical cyclic stress analysis, and environmental fatigue life estimation

This paper discusses a system-level finite element model of a two-loop pressurized water reactor (PWR). Based on this model, system-level heat transfer analysis and subsequent sequentially coupled thermal–mechanical stress analysis were performed for typical thermal–mechanical fatigue cycles. The in-air fatigue lives of example components, such as the hot and cold legs, were estimated on the basis of stress analysis results, ASME in-air fatigue life estimation criteria, and fatigue design curves. Furthermore, environmental correction factors and associated PWR environment fatigue lives for the hot and cold legs were estimated by using estimated stress and strain histories and the approach described in US-NRC report: NUREG-6909.

On-site determination of an uncommon cracking mechanism due to composition gradients in a nickel steel weld

This article analyzes a 3.5% Ni steel cryogenic cylindrical vessel, after the detection by nondestructive inspection of cracks in a circumferential weld. Possible in-service damage mechanisms are discussed, in particular, vibration, low cycle thermal fatigue and hydrogen embrittlement. On-site experimental analysis allowed defining that cracks were due to a manufacturing problem. A final weld bead with much greater concentration of Ni generated an uncommon mechanism of thermal fatigue. In Ni alloyed steels, small variations of Ni around 36% involve variations of almost an order of magnitude in the coefficient of thermal expansion. Proposed actions for integrity assurance of the vessel and lessons learned for fabrication of future vessels are briefly discussed.

Out of phase thermal mechanical fatigue investigation of a directionally solidified superalloy DZ125

Out of phase (OP) thermal mechanical fatigue (TMF) behavior of a directionally solidified (DS) superalloy DZ125 was experimentally and numerically studied. Two different temperature conditions, which are 500–1000°C and 400–900°C, were considered in the present research. Stress and strain responses as well as fatigue life results were presented and discussed. Scanning electron microscope (SEM) and metallographic analysis were used to study the damage mechanism. An oxidation assisted crack initiation and propagation phenomenon were found to explain the shorted life under TMF cycles. In order to characterize the stress and strain deformations under TMF loadings, a modified Chaboche’s constitutive model was applied. Additionally, the TMF life of the material was modeled and predicted by Neu–Sehitoglu damage law with high accuracy.

Thermal mechanical fatigue of single crystal superalloys: Achievements and challenges

The progress on thermal mechanical fatigue (TMF) of Ni-based single crystal superalloys is summarized from an industrial perspective. The TMF behaviors of bare alloys at relatively high stress regime are well studied. However, the understanding of coated alloys is fairly limited, particularly at low stress region pertinent to application conditions. The potential influence of microstructure, chemistry, oxidation and bond coat on TMF life is discussed. Research directions for future studies are proposed.

Thermal reliability prediction and analysis for high-density electronic systems based on the Markov process

Thermal-mechanical fatigue is one of the main failure modes for electronic systems, particularly for high-density electronic systems with high-power components. Thermal reliability estimation and prediction have been an increasing concern for improving the safety and reliability of electronic systems. In this paper, we propose a stochastic process prediction model to estimate the thermal reliability of an electronic system based on Markov theory. We first divided the high-density electronic systems into four modules: the energy transformation and protection module, the electronic control module, the connection module, and the signal transmission and transformation module. By integrating failure and repair characteristics of the four modules, a stochastic model of thermal reliability analysis and prediction for a whole electronic system was built based on the Markov process. The feature parameters of thermal reliability evaluation, including thermal reliability, thermal failure probability, mean time between thermal faults, and thermal stable availability, were derived based on our comprehensive model. Finally, we applied the model to an indoor electronic system of DC frequency conversion conditioning. The thermal reliability was estimated and predicted using tested failure and debugging repair data. Effective methods for improving thermal reliability are presented and analyzed based on the comprehensive Markov model.

Damage evaluation regarding to contact zones of high-speed train wheel subjected to thermal fatigue

Repetitive high frictional forces, induced from braking, and running of a train during railway service, generate high frictional temperature increment at the contact surface, as a result, thermal fatigue damage occurs at the surface of the wheel. Microscopic deformation in the wheel surface due to repetitive fatigue damage causes an initiation and propagation of thermal crack. That is, if the microscopic deformation is accumulated beyond the tolerance of the material resistances including the hardening of material and residual stress, then the surface will be damaged and fractured. As a result, the derailment of railway vehicle may possibly happen.In the present paper, we study on the failure analyses at the tread of the thermally damaged wheel by doing the metallurgical transformation analysis, hardness analysis, and the residual stress analysis to understand the failure mechanism of thermal fatigue damaged wheel. For this purpose, the microstructure of tread surface was examined by applying non-destructive replication method, and the hardness along the tread surface was measured. Also, the change in residual stress in the tread surface of new and thermal-damaged wheels was investigated. Meanwhile, FE analyses were performed considering the heat treatment process of wheel manufacturing, and the braking process during railway service. From the analysis results, we understand that the degree of metallurgical transformation is not the same even in the same tread surface, and residual stress measured turns into tensile stress from the compressive stress in manufacturing in the magnitude of approximately 118MPa in the thermal damaged surface wheel. The finite element analysis (FEA) data of residual stress considering heat treatment process of wheel is in good agreement with the experimental results measured in the wheel tread.

Uncharacteristic Circumferential TMF Cracking in a Heavy-duty Stationary Gas Turbine Engine Burner Outlet

Abstract Burners are key components of turbomachinery with internal combustion. They allow for a particularly lean combustion in heavy-duty stationary gas turbine engines for power stations and thus contribute significantly to economical operation. Depending on their design, burners are often subject to thermomechanical stress. This failure analysis is concerned with thermal cycling cracks at the burner outlet. Circumferential cracking, parallel to the component surface, is untypical for this damage mechanism. Thermal cycling and thermal-mechanical fatigue cracks usually spread in a radial direction. Possible causes could be the special kind of centrifugal casting structure or the high thermal tension, which might have built up during burner operation.

Evaluation of thermal gradient mechanical fatigue characteristics of thermal barrier coating, considering the effects of thermally grown oxide

Gas turbines of aircraft and power generation plants operate at a high turbine inlet temperature (TIT) or combustion temperature higher than 1,000°C to obtain high thermal efficiency. The parts directly in contact with the high temperature flame are made of a nickel-base superalloy, which has strong heat resistance. In addition, the thermal barrier coating (TBC) technique is applied to increase the heat resistance. The TBC prevents direct heat transfer from the high temperature flame to the metallic substrate. Thus, the TBC technique reduces the substrate surface temperature by approximately 100~170°C. The delamination caused by the growth of thermally grown oxide (TGO) decreases the life of the TBC system. In addition, gas turbine blades experience centrifugal forces owing to high speeds of approximately 3600 rpm and they experience low cycle fatigue because of frequent startup and shutdown. Therefore, the integrity of the TBC system should be evaluated under the thermal gradient mechanical fatigue condition. In this study, finite element analysis (FEA) was performed for the TBC model considering TGO, and the effect of TGO on TBC systems was evaluated under the thermal gradient mechanical fatigue condition.

Thermal–mechanical fatigue behaviour of a new single crystal superalloy: Effects of Si and Re alloying

The thermal–mechanical fatigue (TMF) behaviour of a new single crystal superalloy suitable for power generation applications is considered. Effects of alloying with either Si or Re are elucidated. Out-of-phase TMF is emphasised, although to clarify the effects arising some static creep deformation tests are also carried out. A significant Si-effect is found: a modest addition of 0.25wt.% Si increases the TMF life by a factor of 2. A greater lower temperature yield stress and thinner slip bands traversing the γ′-phase – with a concomitant greater resistance to recrystallisation and cracking along them – contribute to the enhanced TMF performance promoted by Si alloying. Alloying with Re, whilst improving the creep behaviour more markedly than Si, does not have such a strong effect on TMF life. The results provide insights into the composition/performance relationships relevant to the TMF performance of single crystal superalloys.

Investigation on fatigue behavior of single SnAgCu/SnPb solder joint by rapid thermal cycling

Purpose – The purpose of this paper is to investigate the thermal fatigue behavior of a single Sn-3.0Ag-0.5Cu (SAC) lead-free and 63Sn-37Pb (SnPb) solder joint treated by rapidly alternating heating and cooling cycles. Design/methodology/approach – With the application of electromagnetic-induced heating, the specimen was heated and cooled, controlled with a system that uses a fuzzy logic algorithm. The microstructure and morphology of the interface between the solder ball and Cu substrate was observed using scanning electron microscopy. The intermetallic compounds and the solder bump surface were analyzed by energy-dispersive X-ray spectroscopy and X-ray diffraction, respectively. Findings – The experimental results showed that rapid thermal cycling had an evident influence on the surface and interfacial microstructure of a single solder joint. The experiment revealed that microcracks originate and propagate on the superficial oxide of the solder bump after rapid thermal cycling. Originality/value – Analysis, based on finite element modeling and metal thermal fatigue mechanism, determined that the rimous cracks can be explained by the heat deformation theory and the function of temperature distribution in materials physics.

Selective Laser Melting – Additive Manufacturing's “New Kid on the Block”; TMF Failure of a Y-shaped Pipe in a Burner Test Rig

Abstract A particular heavy-duty gas turbine burner, used in a burner rig test, featured a Y-shaped fuel gas feed pipe. The Y-pipe was made by non-conventional production, in an attempt to test the component and its specialty manufacturing process in an environment that simulates service conditions without causing collateral damage to other engine components in case of failure. The Y-pipe was produced by additive manufacturing (AM), using a process that is known as selective laser melting (SLM). This process is well suited for complex parts due to its advantageous geometrical freedom. It is known to have been used for intricate piping systems before. However, the Y-shaped pipe failed by thermal-mechanical fatigue cracking (TMF).

UCPD Model for Pb-Free Solder

A unified creep plasticity damage (UCPD) model for eutectic Sn-Pb and Pb-free solders was developed and implemented into finite element analysis codes. The new model will be described along with the relationship between the model's damage evolution equation and an empirical Coffin–Manson relationship for solder fatigue. Next, developments needed to model crack initiation and growth in solder joints will be described. Finally, experimentally observed cracks in typical solder joints subjected to thermal mechanical fatigue are compared with model predictions. Finite element based modeling is particularly suited for predicting solder joint fatigue of advanced electronics packaging, e.g. package-on-package (PoP), because it allows for evaluation of a variety of package materials and geometries.

Sn-Ag-Cuはんだ実装部の熱疲労寿命と機械疲労寿命の関連性

Sn-Ag-Cuはんだ実装部の熱疲労寿命と機械疲労寿命の関連性

Fatigue behaviour of coke drum materials under thermal-mechanical cyclic loading

Coke drums are vertical pressure vessels used in the delayed coking process in petroleum refineries. Significant temperature variation during the delayed coking process causes damage in coke drums in the form of bulging and cracking. There were some studies on the fatigue life estimation for the coke drums, but most of them were based on strain-fatigue life curves at constant temperatures, which do not consider simultaneous cyclic temperature and mechanical loading conditions. In this study, a fatigue testing system is successfully developed to allow performing thermal-mechanical fatigue (TMF) test similar to the coke drum loading condition. Two commonly used base and one clad materials of coke drums are then experimentally investigated. In addition, a comparative study between isothermal and TMF lives of these materials is conducted. The experimental findings lead to better understanding of the damage mechanisms occurring in coke drums and more accurate prediction of fatigue life of coke drum materials.

Probabilistic thermal-mechanical fatigue criterion for lost foam casting aluminium alloys based on 2D/3D porosities distribution

A thermal-mechanical fatigue criterion is proposed to assess the lifetime of aluminium alloys produced by a lost foam casting process. It is based on the observed size distribution of pores sizes which are considered as critical zones for cracks initiation and gives reliable results when both pores sizes are identified from X-ray tomography and mean stresses are taken into account. Lifetime probabilities are finally successfully compared with experimental results.

Evaluation on Thermo-Mechanical Fatigue Life of IN738LC Using Finite Element Analysis

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

Assessment of TBC Oxidation-Induced Degradation Using Compression Tests

Compression tests at room temperature are used to estimate the critical strain to spallation of EBPVD thermal barrier coating deposited on Ni based single crystals for blades used in aero-engines. The observation of fracture surfaces allows for investigating the location of delamination events leading to spallation, the eventual porosity at bond coat–alumina interface and kinetics of damage evolution. The effect of isothermal oxidation at 1,100 °C is presented for standard or low sulfur AM1 superalloy, and coating process variants. The degradation is shown to depend on the thermal–mechanical loading and varies from isothermal oxidation, cyclic oxidation and thermal–mechanical fatigue with hold time. These observations are consistent with the damage observed in blades in engine tests or in service. These tests are a useful complement to standard cyclic oxidation tests to identify engineering lifetime models.

Climate Based Performance of Carbon-Carbon Disc Brake for High Speed Aircraft Braking System

Carbon composite brake discs are lighter, economical, and have excellent high energy friction characteristics. These have twice thermal capability compared to steel, remain unaffected by thermal shocks and mechanical fatigue. These are highly useful in emergency breaking situations. Prior to this work, two dimensional (2D) reinforced carbon composite laminates were prepared through pitch impregnation process. In an effort to protect the exposed non frictional surface from high temperature service degradations, multilayered ceramic coating systems were developed on 2D composite. Oxidation studies have been carried out on these systems viz., C-SiC, C-SiC-MoSi2-Al2O3 and C-SiC-B4C. These were performed both in dynamic and static conditions up to 1200 °C in 60 per cent humid climate. The hardness, surface topography, developed phases and integrity of layers on the samples at various stages of the experiment have been characterized and analyzed. It was observed that C-SiC-B4C system performs well in the oxidizing environment. Defence Science Journal, 2013, 63(5), pp.531 -538 , DOI:http://dx.doi.org/10.14429/dsj.63.3932

In-phase thermal–mechanical fatigue investigation on hollow single crystal turbine blades

Thermal–mechanical fatigue (TMF) is the primary cause of failure of nickel-based single crystal turbine blades. TMF experiments have been performed on the critical section which is subjected to the most serious damage and determined by numerical calculation combined with service failure experience. An experimental system including the loading, heating, air cooling, water cooling, and control subsystems, is constructed to satisfy the TMF experimental requirements. This experimental system can simulate the stress field, temperature field, air cooling process, and TMF spectrum on the critical section under service conditions in a laboratory environment. A metal loading device and a new induction coil are developed to achieve the required stress and temperature distributions on the critical section, respectively. TMF experimental results have indicated that cracks initiated at the trailing edge of the suction surface on the critical section. Based on these experiments, life prediction and failure analysis of hollow single crystal turbine blades can be investigated.

Analysis of Failure Mode and Construction Improvement of Spray Tubes in Boiler Desuperheater

With macrographic examination, SEM observation and fracture quantitative analysis technology, the fracture fractography of a spray tube with both the mechanical stress and the thermal stress in a boiler desuperheater of a power plant was interpreted, and the failure mode and the cause were researched. Results showed that rupture of the spray tube was due to the fatigue, and further, the thermal mechanical fatigue. The alternating bending stress and thermal stress were main factors of the fracture failure. The shallow surface thermal fatigue cracks in tube inner wall were induced by thermal stress. When the thermal mechanical fatigue crack grew up steadily to the shallow surface cracks zone, fast growth occurred and the local fast fracture zone generated which had different fractographies with final fast fracture zone of the normal fatigue fracture.