Thermal Mechanical Fatigue Research Articles

Quantifying the tangential oscillation of thermal stratification by using principal component analysis

Tangential oscillation of thermal stratification is a new finding in previous investigations on thermal-mixing process at pipeline T-junctions. This phenomenon can create regular temperature changes on the pipeline inner surface and lead to material damage caused by the degradation mechanism of thermal fatigue, which has been frequently reported as a reason for incidents in piping systems of nuclear power plants. Previous investigations cannot provide a quantitative description of this phenomenon, making it difficult to understand or evaluate the fatigue potential due to this phenomenon. In this study, a new method namely principal component analysis has been employed for quantitatively estimating the angular shift of the thermal stratification in pipe tangential direction. Time-dependent angular shift is extracted from the temperature data of the transient simulations of the pipe flow and confirms the initiation of the tangential oscillation of thermal stratification. Moreover, a characteristic frequency of approximately 2.3 Hz has been identified from the frequency spectrum of the time-dependent angular shift. It indicates a potential risk in the piping material due to thermal fatigue. Furthermore, results of this study show a high efficiency and accuracy of the principal component analysis method in quantifying tangential oscillation. It can be applied in further investigations of similar phenomena of thermal stratification.

Thermal fatigue mechanisms in laser cladding at varying elevation angles for metallurgical bearing seats

Thermal fatigue mechanisms in laser cladding at varying elevation angles for metallurgical bearing seats

Thermal mechanical fatigue cracking of a bladed disk in a turbo engine

After 1221 h of bench testing, linear fluorescent displays were observed on the transition arcs between the blade and the edge plate. Macroscopic and microscopic inspections revealed fatigue cracks originating from cracked grain boundaries on the surface. Metallographic examinations indicated severe oxidation of the crack flank and blunting tip. Finite element thermal stress analysis aligns with the crack distribution. The nature of the cracking is identified as thermal mechanical fatigue, and the elevated temperature gradient induced by the exhaust gas purification device is the main promoter for cracking. Comparative analysis suggests that the root cause lies in the low thermal impact resistance of the material, ultimately resulting in reduced thermal mechanical fatigue resistance. Corresponding remedial methods are proposed to enhance service life and safety.

A modified constitutive model for whole-life thermal-mechanical fatigue incorporating dynamic strain aging in 316LN stainless steel

A comprehensive analysis of experimental data is presented for 316LN stainless steel subjected to isothermal and thermal-mechanical fatigue loading conditions within the temperature range of 350–600 °C. The study aims to provide a thorough understanding of the cyclic behavior through meticulous data integration, supplementation, and the use of stress decomposition methods combined with a classical damage evolution definition. The modeling approach employed in this study is based on the classical AF-OW-Kang model, with the incorporation of the Arrhenius term in the plastic flow rate equation. Furthermore, to consider the effect of dynamic strain aging at varying temperatures, temperature-dependent terms are introduced into the equations that govern the evolution of isotropic stress and backstress, resulting in enhanced accuracy in describing cyclic hardening behavior. Additionally, a modified damage evolution equation is utilized, along with equations for isotropic stress and backstress evolution, to address cyclic softening. Simulation results confirm the effectiveness of the modified model in capturing the cyclic hardening/softening behavior of 316LN stainless steel throughout the whole-life time, under both isothermal and thermal-mechanical fatigue loading conditions.

Prediction of engine combustion chamber outlet temperature field based on deep Learning: Application in aero-engine life extension control

One of the current research hotspots is the prediction of combustion chamber flow field based on deep learning methods, but how to effectively utilize these prediction results is a key issue that needs to be addressed urgently. This paper further proposes a study on the predictive control method for engine life extension considering the dangerous point temperature of turbine guide vane based on the prediction of combustion chamber outlet temperature field. Firstly, a combustion chamber outlet temperature distribution prediction model is established through Computational Fluid Dynamics (CFD) numerical simulation and inception deconvolution network, and integrated into the variable cycle engine component level model to achieve real-time prediction of combustion chamber outlet temperature distribution. Furthermore, based on this, the dangerous point temperature of the high-pressure turbine (HT) guide vanes is introduced as a constraint into the prediction optimization, and a predictive control method for engine life extension considering the thermal mechanical fatigue life (TMFL) of the guide vanes is proposed. The simulation results show that compared to the traditional LEC control method, the temperature at the critical point of the blade is reduced by 12.28 K, and the TMFL of the blade is increased by 29.23 %. The research results of this article provide a good application example for predicting the temperature distribution at the outlet of the combustion chamber, expanding the application scenarios for predicting the flow field parameters inside the engine.

Simulation-Based Thermal Fatigue Validation Test Development for Exhaust Manifold

Abstract Exhaust manifolds in diesel engines undergo continuous thermal cycle loading of varying thermal cycles with different mean, amplitude, and rate of temperature change created by application duty cycles. This makes analysis and testing of the exhaust manifold to meet the thermal mechanical fatigue life expectation of different applications challenging. In this paper, a simulation-based product development approach, which uses application duty cycles, simulation models of different capabilities, including three-dimensional Finite element simulation model, one-dimensional (1D) physis-based damage model to develop an abusive thermal cycle engine test for validating exhaust manifold, is presented.

Failure-mode dependence on the formation of deformation twinning in the fourth-generation single crystal Ni-based superalloy at high temperatures

In this work, the twinning-related deformation mechanisms under different failure modes of a fourth-generation single crystal (SX) superalloy at high temperatures were investigated. Notably, the twinnability of alloy increased in the sequence as follows: pure tension, in-phase (IP) thermal mechanical fatigue (TMF), isothermal low cycle fatigue (LCF), hot compression, out-of-phase (OP) TMF. High-temperature compressive loading which facilitated the successive operation of {111}〈1 1 2〉 viscous slipping, was indispensable for the nucleation of micro-twins. However, this stimulative effect could be markedly offset by the co-existence of high-temperature tensile loading. Moreover, the activation of different {111}〈1 1 2〉 slipping systems as well as potential interactions between stacking faults played a significant role in the formation and thickening processes of deformation twins. In the experimental alloy system, the presence of deformation twins was attested to impair the fatigue resistance of the specimen. These findings provided new insights for ensuring the safe service of the fourth-generation SX superalloys.

Thermal fatigue failure mechanism in the joint of nano Cu/Ti–Si3N4 ceramic substrates after thermal fatigue test

Thermal stress fatigue failure caused by mismatch in the coefficients of thermal expansion (CTE) between the metal layer and ceramic sheet during a high and low temperature cycle is considered as the big issue of high-power ceramic substrates. The aim of this study is to explore the thermal fatigue mechanism of nano Cu/Ti–Si3N4 ceramic substrates after thermal fatigue test. Thermal fatigue test has been performed by thermal cycles experiment from −30 °C to 150 °C. After thermal cycles, the microstructure of the interface is observed by SEM and TEM. The results show after 400 thermal cycles, the nano-Cu metal layer oxidizes severely. Various oxides are found in the corrosion zone, such as CuO, CuAlO2 and CuAl2O4. Higher dislocation density and nanoscale-twins are observed in Cu or Cu2O, which indicate that Cu and Cu2O alleviates thermal stress. As the number of thermal cycles increases, CuO CuAlO2, CuAl2O4 as a corrosion layer in the corrosion zone were formed. The corrosion layer is difficult to alleviate interfacial thermal stress, and easy to form cracks in the joint zone.

Simulation-based microstructural analysis of thermal–mechanical fatigue behavior in SiCp/A356 composites for brake disc applications

Simulation-based microstructural analysis of thermal–mechanical fatigue behavior in SiCp/A356 composites for brake disc applications

Dependence of deformation mechanisms on micro-pores in the fourth-generation single crystal superalloy during out-of-phase thermal-mechanical fatigue

The high-temperature and long-term solution heat treatments of fourth-generation single crystal (SX) superalloys have sparked an increasing number of homogenization pores in the alloy. Out-of-phase (OP) thermal–mechanical fatigue (TMF) experiments were conducted to elucidate the effect of pores on the fatigue behaviors and deformation mechanisms. The results showed that the plastic deformation was mainly concentrated upon γ matrix in regions away from pores, more specifically, intrinsic stacking fault (ISF) and extrinsic stacking fault (ESF) as well as dislocation cross-slipping were detected. In areas near micro-pores, however, the γ/γ′-structure was subjected to severe twinning shearing. High-resolution observation illustrated that the amount of ESF and a/6 〈112〉 twinning dislocations had remarkably increased. Besides, the partial dislocations were more prone to move in different slipping systems at these regions with considerable stress concentration. These factors collectively enabled the formation of deformation twins from the edge of micro-pores. Moreover, the twinning nucleation could occur near both H-pores and S-pores, while the increasing pore size would enhance the nucleation and propagation of pore-induced twins by a large margin. These findings reported have provided important guidance for the future application of the fourth-generation SX superalloys.

Investigation into the failure of a superheater tube in a power generation plant utilizing waste material combustion in a furnace

This study presents an investigation into the failure of a superheater tube. To pinpoint the primary cause of failure, a range of destructive and non-destructive analyses were conducted at various points on both the failed and non-failed sides of the tube. Visual inspection unveiled longitudinal fissures indicative of the initiation of a fish-mouth opening, along with minor bulging, a slight diameter increase, and a marginal thickness reduction at the failure zone. Through chemical composition analysis, mechanical testing, and hardness measurements, it was determined that the material satisfies the specification for low-alloyed steel as per P265GH standard. The microscopic examination revealed the non-fireside (not failed) of the tube consisted of ferrite and pearlite structure, whilst the fireside (failed) showed spheroidization of the pearlite colonies without any evidence of recrystallized grain structure. A more in-depth examination using scanning electron microscopy on the failed section indicated that the tube rupture on the fireside was triggered by an interactive mechanism involving sulfidation corrosion and thermal fatigue. The propagation of cracks occurred through an environmentally assisted thermal-fatigue process. Suggestions for corrective actions have also been proposed to prevent this type of failure.

Reliability Analysis of PAUT Based on the Round-Robin Test for Pipe Welds with Thermal Fatigue Cracks.

Thermal fatigue cracks occurring in pipes in nuclear power plants pose a high degree of risk. Thermal fatigue cracks are generated when the thermal fatigue load caused by local temperature gradients is repeatedly applied. The flaws are mainly found in welds, owing to the effects of stress concentration caused by the material properties and geometric shapes of welds. Thermal fatigue pipes are classified as targets of risk-informed in-service inspection, for which ultrasonic testing, a volumetric non-destructive testing method, is applied. With the advancement of ultrasonic testing techniques, various studies have been conducted recently to apply the phased array ultrasonic testing (PAUT) method to the inspection of thermal fatigue cracks occurring on pipes. A quantitative reliability analysis of the PAUT method must be performed to apply the PAUT method to on-site thermal fatigue crack inspection. In this study, to evaluate the quantitative reliability of the PAUT method for thermal fatigue cracks, we fabricated crack specimens with the thermal fatigue mechanism applied to the pipe welds. We performed a round-robin test to collect PAUT data and determine the validity of the detection performance (probability of detection; POD) and the error in the sizing accuracy (root-mean-square error; RMSE) evaluation. The analysis results of the POD and sizing performance of the length and depth of thermal fatigue cracks were comparatively evaluated with the acceptance criteria of the American Society of Mechanical Engineers Code to confirm the effectiveness of applying the PAUT method.

Comprehensive damage and deformation mechanisms during out-of-phase thermal mechanical fatigue of the fourth-generation single crystal superalloy

To shed light on the stability and reliability of the fourth-generation single crystal (SX) superalloy during in-service operation, out-of-phase (OP)- thermal mechanical fatigue (TMF) experiments were systematically carried out. The TMF behavior, deformation and damage mechanisms were thoroughly investigated. The results showed that at comparatively low strain ranges (0.5% and 0.6%), the dislocation movements were basically concentrated in γ matrix and the TMF life was basically governed by high-temperature oxidation. More locally, the fatigue cracks initiated from the spalling of surface oxides, while the discontinuous Al2O3 layer could only provide limited protective resistance to crack propagation. Additionally, deformation twins could nucleate in the vicinity of micropores or crack tips, which further induced more complex defects and accelerated the fatigue fracture of the alloy. Nevertheless, as the strain range reached 0.8% and 0.9%, the nucleation and extension of micro-twins were independent on the defects, the mechanisms of twinning-shearing and anti-phase boundary (APB)-shearing were observed throughout the specimen. Under these conditions, the fatigue cracks basically initiated from the severe plastic deformation, which resulted in the much-reduced TMF life of the specimen. Ultimately, salutary guidance for the further application of fourth-generation SX superalloys was rationally summarized.

Thermal-Mechanical Fatigue Behavior and Life Assessment of Single Crystal Nickel-Based Superalloy

Thermal-mechanical fatigue (TMF) tests and isothermal fatigue (IF) tests were conducted using thin-walled tubular specimens under strain-controlled conditions. The results of TMF tests showed a strong correlation between mechanical behavior and temperature cycling. Under different phases of temperature and mechanical loading, the hysteresis loop and mean stress of the single crystal superalloy showed noticeable variations between the stress-controlled and strain-controlled conditions. In the strain-controlled TMF test, temperature cycling led to stress asymmetry and additional damage, resulting in a significantly lower TMF life compared to IF life at the maximum temperature. Moreover, the OP TMF life is generally lower than that of the IP TMF at the same strain amplitude. The Walker viscoplastic constitutive model based on slip systems was used to analyze the TMF mechanical behavior of the single crystal superalloy, and the change trends of the maximum Schmid stress, the maximum slip shear strain rate, and the slip shear strain range were analyzed, and their relationship with the TMF life was investigated. Finally, a TMF life prediction model independent of the loading mode and phase was constructed based on meso-mechanical damage parameters. The predicted TMF lives for different load control modes and phases fell within the twofold dispersion band.

Microstructural Evolution and Tensile Properties of a Corrosion-Resistant Ni-Based Superalloys Used for Industrial Gas Turbines

As an important mechanical property, tensile behavior has been regarded as an indicator for the creep and thermal mechanical fatigue properties of Ni-based superalloys. The tensile property of Ni-based superalloys is closely related to the amount, size, and distribution of γ'-phase and carbides. To further clarify the tensile deformation mechanism of the CM247LC alloy, this study investigated its solidification characteristics and directionally-solidified and heat-treated microstructure. The dependence of tensile properties on the varied temperature ranging between 650 and 950 ℃ is discussed in detail. It was found that the deformation mechanism at 650 ℃ is dominated by the shearing of dislocations into the γ'-precipitates to form the superlattice stacking faults. At 800 ℃, the K-W lock leads to the anomalous yield effects. At 950 ℃, the deformation mechanism is dominated by the dislocations bypassing the γ'-precipiates. The results provide a comprehensive understanding of the CM247LC alloy and are beneficial for the development of corrosion-resistant Ni-based superalloys.

EVALUATION OF RESOURCE CHARACTERISTICS OF POWER EQUIPMENT PARTS UNDER THERMAL CYCLIC LOADING

The problem of assessing the strength and resource of critical engineering facilities, the operational properties of which are characterized by multiparametric non-stationary thermo-mechanical effects, is discussed. The main degradation mechanisms of structural materials (metals and their alloys) characteristic of such objects are considered. The basic requirements for mathematical models of these processes are formulated. A mathematical model describing the processes of thermoplastic deformation and accumulation of fatigue damage during degradation of the material by the mechanism of thermal fatigue has been developed from the position of mechanics of the damaged medium (MPS). The IPU model consists of three interrelated parts: relations that determine the cyclic thermoplastic behavior of the material, taking into account the dependence on the destruction process; equations describing the kinetics of fatigue damage accumulation; strength criteria of the damaged material. The variant of the defining relations of thermoplasticity is based on the idea of the yield surface and the principle of gradiency of the velocity vector of plastic deformations to the yield surface at the loading point. This version of the equations of state reflects the main effects of the process of cyclic thermoplastic deformation of the material for arbitrary complex trajectories of combined thermomechanical loading. The variant of kinetic equations of fatigue damage accumulation is based on the introduction of a scalar damage parameter, is based on energy principles and takes into account the main effects of formation, growth and fusion of microdefects under arbitrary complex loading conditions. As a criterion of the strength of the damaged material, the condition of reaching the critical value of the damage value is used. To assess the degree of reliability and determine the limits of applicability of the developed defining ratios of MPS, calculations of the processes of thermoplastic deformation and accumulation of fatigue damage were carried out and the numerical results obtained were compared with the data of field experiments on the example of a specific applied problem. A numerical analysis of the characteristic features of the thermal fatigue durability of a compact sample with stress concentrators simulating the operation of parts in the nozzle box of a steam turbine of a nuclear power plant (NPP) is carried out. The results of calculations of fatigue damage accumulation processes during thermal pulsations are compared with experimental data. It is shown that the developed MPS model qualitatively and with the accuracy necessary for engineering calculations quantitatively describes experimental data and can be effectively used to assess the thermocyclic fatigue durability of structures with multiaxial disproportionate paths of combined thermomechanical loading.

Unveiling the damage evolution of SAC305 during fatigue by entropy generation

Low-cycle thermal-mechanical fatigue loadings induce progressive and permanent degradation of mechanical properties of lead-free solder materials, and thus reduce the fatigue life of electronic devices. In this study, damage evolution and accumulation of Sn-3.0Ag-0.5Cu (SAC305), the most successfully commercialized lead-free solder material, was investigated by performing strain-controlled fatigue tests at different temperatures (288–373 K) and strain rates (0.001–0.004 s−1). Unlike existing empirical models, a fatigue damage model was proposed based on entropy generation related to the thermodynamic nature of fatigue damage. To be intrinsic to entropy generation, the proposed model was calibrated with the peak stress degradation at different temperatures and strain rates. Our findings showed that the damage parameter is closely related to temperature and strain rate and monotonically increases from 0 to 1 during the low-cycle fatigue loading, which unveiled the fact regarding the irreversibility of the internal entropy generation. For the first time, the damage evolution is found to be more associated with the applied strain rate than the temperature. By observations using an optical microscopy, the physical damage mechanism is elucidated for SAC305 solder by correlating microstructures and damage evolutions. The evolving dendritic β-Sn phase and the surrounding Sn-Ag-Cu ternary eutectic network also explained the effects of temperature and strain rate based on the energy dissipation. Our proposed damage model reconciled the damage accumulation of SAC305 solder subjected to the low-cycle fatigue loading, which is readily adopted to predict the fatigue life of the electronic packaging structures.

Research on the Creep and Fatigue Evaluation Method of the Double-Layered Annulus Metal Hydride Bed Combined with Numerical Modeling and ASME Code

Applied to a hydrogen absorption-desorption cycle, the hydrogen storage bed will experience higher exchange temperatures and variety of mechanical load. Due to the complex structure of the double-layered annulus metal hydride bed and the importance of thermal stress on the failure of a metal hydride bed, the numerical modeling of its hot spot stress was carefully carried out. Moreover, in this paper, an analysis method considering the limit failure mode condition is proposed to deal with the stress analysis in the process of hydrogen absorption and desorption. According to the proposed analysis method, the maximum stress of thermal-structural coupling in the process of hydrogen absorption occurs at about 1/3 along the diameter direction and at the geometric mutation of the connection between the cooling pipe and the main body of the hydrogen storage bed in the process of hydrogen desorption. Apart from that, the hydrogen storage bed is also subjected to thermal-mechanical fatigue by the iterative process of absorption and desorption, and its operating temperature range is in the thermal creep temperature region. Based on the distribution of the stress and temperature, evaluation hot sites were selected and the ASME-NB and ASME-NH codes were used to evaluate fatigue and fatigue creep, respectively. The evaluation showed that the fatigue damage generated during its service life is small, while the creep damage is relatively large and the total damage generated during the service life of the hydrogen storage bed is within the safe range. Aiming at the structure and complex process of a double-layer hydrogen storage bed, creep and fatigue evaluation methods are proposed, various failure modes of hydrogen storage bed are highlighted, and the relationship between process parameters and life is established.

Unified viscoplasticity model for type 316 stainless steel subjected to isothermal and anisothermal-mechanical loading

316FR-type low carbon stainless steel is usually used for many advanced gas cooled reactor (AGR) power plants which are subjected to operating temperatures in the range of 500–650 °C under thermo-mechanical loading, which may lead to isothermal low cycle fatigue (LCF) and thermal mechanical fatigue (TMF) damage. The strain controlled thermo-mechanical fatigue test with and without holding time was carried out for 316FR-type stainless steel under the temperature cycling between 500 °C and 650 °C, and the strain ranges are Δε = ± 0.4%, ±0.8%, ±1.0% and ±1.2%, respectively. Within the framework of Abdel Karim and Ohno model, an improved unified viscoplastic constitutive model (UVM) is proposed to simulate the cyclic plastic behavior of 316FR stainless steel. The improved UVM includes strain rate sensitivity, temperature rate dependence, static recovery, average stress evolution and strain range dependence of cyclic hardening. And then based on the radial return mapping and backward Euler integration methods, the implicit stress integration algorithm and the new expressions of the consistent tangent modulus are derived respectively, the improved UVM is implemented by a User Material Subroutine into ABAQUS software again. The good correlation between simulation results and experimental data is obtained.

Analysis of temperature gradients in thin-walled structures under thermomechanical fatigue loading conditions

In recent thermal gradient mechanical fatigue (TGMF) investigations, it is verified that the material fatigue lives are significantly affected by the temperature gradients. Determination of temperature gradients of thin-walled structures is always a difficult task. In the present work, tubular specimens were experimentally and computationally investigated under different conditions. The inverse heat conduction (IHCP) method was improved to predict the inner boundary from external measurements. Two models were finally developed, based on direct IHCP or modified Nusselt number estimation. The models are qualified to acquire temperature gradients in TGMF experiments with reasonable accuracy and versatility.