Thermal-mechanical Fatigue Life Research Articles

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.

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.

Evaluation of plastic deformation and prediction of thermal mechanical fatigue life of an Al–Si alloy piston for diesel engines

AbstractIn this study, a three‐step prediction method was developed to predict the thermal mechanical fatigue (TMF) life of an Al–Si alloy piston: (1) establishing a relation between the plastic deformation and fatigue life under the temperature cycle of 100–350°C via a series of TMF tests of the aluminum alloy specimens; (2) computing the dangerous plastic deformation of the piston under the thermal shock condition of interest by numerical simulation; (3) estimating the life of the piston through taking the computed plastic deformation into the established relation. The effectiveness of the proposed prediction method was verified by thermal shock tests of the piston, and the prediction error is no more than 25%. The mechanism of piston cracking can be summarized as follows: the inhomogeneous plastic deformation induced higher tensile stress around primary Si particles and protrusions at the rim and then microcracks were produced at the protrusions under the dangerous tensile stress, and finally, macrocracks occurred. The life of the piston under the thermal shock load and combustion pressure is speculated to be shorter than that under the thermal shock load. Considering the effect of stress relaxation on plastic deformation, the long full‐load operation of the engine contributes to the piston cracking in T direction, while the long idling operation reduces the piston cracking tendency in T direction and increases the piston cracking tendency in F and R directions.

Thermal-mechanical fatigue behaviour and life prediction of P92 steel, including average temperature and dwell effects

This study was devoted to an investigation of the effects of the average temperature and dwell on the thermal-mechanical fatigue (TMF) behaviour of P92 steel at elevated temperatures in the range of 350–650°C. The results revealed that increased average temperature decreased the in-phase TMF (IPTMF), out-of-phase TMF (OPTMF), and isothermal fatigue (IF) life values, and its effect was more significant in the range of 400–450°C. The effect of a short dwell time on the IPTMF life was dependent on the form of dwell, because tensile dwell decreased the IPTMF life and symmetric dwell increased the IPTMF life. Both creep stress relaxation (CSR) and dynamic strain ageing (DSA) were detected under IPTMF cycling. The application of dwell enhanced the CSR phenomenon. In contrast, the DSA effect was restrained, which was beneficial for fatigue resistance. The appearance of crack tip blunting and crack branching because of symmetric dwell indicated the retardation of crack propagation under the combined effects of enhanced CSR and the disappearance of the DSA phenomenon. In all cases, the transformation of lath structures into substructures was the dominant deformation mechanism. In addition, the equiaxial subgrain grew with increases in the strain amplitude and dwell time. Finally, the application of the current life models to P92 steel fatigue life prediction under both IF and TMF cycling were evaluated. Because of the insufficiency of the current models, a modified Coffin–Manson model is proposed by incorporating the mean stress and temperature into power law forms.

Effect of temperature range on thermal-mechanical fatigue properties of P92 steel and fatigue life prediction with a new cyclic softening model

P92 steel is a typical steel used in the main steam pipeline of an ultra-supercritical power plant. In most cases, the main load consists of the thermal-mechanical fatigue (TMF) load due to the fluctuation of temperature and pressure during operation. TMF tests at different temperature ranges and isothermal fatigue (IF) tests at different temperatures were performed in this study. The effects of different temperature ranges on the fatigue life of P92 steel were analyzed. It was found that the TMF life decreased first and then increased, as a result of an increase in the temperature range and decrease in the mean temperature. The cyclic softening of the TMF and IF was also investigated. In addition, it was found that the typical characteristics of dynamic strain aging (DSA) occurred in the TMF and IF process. This is considered to be an important reason for the decrease in the TMF life of P92 steel. A new cyclic softening model was established to describe the cyclic softening behavior of P92 steel, and the effect of the load conditions on the cyclic softening was reflected in this model.

Simulation-based design and optimization and fatigue characteristics for high-speed backplane connector

In high-speed interconnect systems, high-speed backplane connectors are widely utilized. Its mechanical reliability is related to the stability of entire application systems directly. Insertion–extraction force and fatigue characteristics are important factors that affect the reliability of high-speed backplane connectors. To enhance the reliability of high-speed backplane connectors, in this study, a single CAD/CAE parametric model of the contacts is established. Not only the dynamic analysis of the insertion and extraction process but also the electro-thermal-structure coupling of the contacts are carried out using finite element analysis. By changing the insertion position of male terminal, the length of female terminal, and the thickness of male terminal, the insertion–extraction force can be optimized. According to the simulation of the insertion–extraction force and the electric-thermal-structure coupling results, both the mechanical life of this connector and the thermal-mechanical fatigue life under electrifying condition are evaluated. The results show that the mechanical life and thermal-mechanical fatigue life were 376 cycles and 286 cycles, respectively. The design solutions can provide the reference for the structural design, optimization, and fatigue life prediction of high-speed backplane connector.

The Influence of Thermal Transient Rates on Coated Turbine Parts' Life Expectancy

During rapid engine throttling operations, turbine airfoils can experience very rapid heating and cooling, particularly at take-off conditions. These rapid transient events lead to the generation of high thermal gradients and nonuniform stress distributions through the thermal barrier coating (TBC), environmental barrier/bond coating, and substrate. This, in turn, can lead to coating delamination, overheat of the substrate materials, creep, and thermo-mechanical fatigue of the part. We present the process and computer modeling methodology for a physics-based prediction of deformation, damage, crack propagation and local failure modes in coated turbine airfoils and other parts operating at hot section turbine environment conditions as a function of engine operational regimes, with a particular emphasis on rapid transient events. The overall goal is to predict the effects and severity of the cooling and heating thermal rates on transient thermal mechanical fatigue life of coated hot parts (turbine airfoils, blade outer air seals, and combustor liners). The computational analysis incorporates time-accurate, coupled aerothermodynamics with nonlinear deformation thermal-structural finite element modeling, and fracture mechanics modeling for high-rate thermal transient events. TBC thermal failure and spallation are introduced by the use of interface fracture toughness and interface property evolution as well as dissipated energy rate. The spallation model allows estimations of the part remaining life as a function of the heating/cooling rates. Applicability of the developed model is verified using experimental coupons and calibrated against burner rig test data for high-flux thermal cycles. Our results show a decrease in TBC spall life due to high-rate transient events.

Finite element analysis and life modeling of a notched superalloy under thermal mechanical fatigue loading

Notched thermal mechanical fatigue (TMF) of a directionally solidified (DS) superalloy applied for turbine blades has been studied experimentally and numerically. The test results, failure analysis, constitutive model and life prediction method of the notched superalloy were presented. Two types of notched specimens with the theory stress concentration (Kt) of 1.5 and 2 were designed. The temperature applied to the specimens ranged from 500 to 1000 °C. With a developed constitutive model for TMF, the cyclic stress and strain responses at the notches were analyzed. The dominated damage area which was defined as 1 mm zone was identified with the basis of the scanning electron microscope (SEM) observations as well as the finite element analysis results. Finally, an averaged stress based life model corresponding to the damage process zone was proposed with good accuracy to prediction TMF lives with or without notches.

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–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.

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.

Thermal–mechanical and isothermal fatigue of 304L stainless steel under middle range temperatures

The present study investigates the crack initiation in a 304L stainless steel under thermal fatigue using volume element tests designed to assess the endurance to engineering crack initiation in real structures under middle range temperature and fairly large number of cycles. The inelastic cyclic strain is significant in most testing conditions for this alloy, even for long tests. Regarding tests, thermal–mechanical fatigue life is compared with low cycle fatigue tests under isothermal conditions. Noteworthy, throughout the different studied ranges of applied temperature cyclic behavior of the alloy has shown an initial hardening followed by a cyclic softening. In addition, no clear effect in lifetime for the high strain range has been discovered. In fact, when exposed to various increasing temperature levels, the material endurance tends to decreases for low strain range (correspond to high number of cycle). A different behavior in cyclic hardening tests is identified between the In-Phase thermal–mechanical fatigue tests and the Out-of-Phase tests at temperature levels ranges between 90 and 165 °C. In-Phase thermal–mechanical test increases lifetime with respect to the Out-of-Phase test. The fracture surfaces for all tested conditions are characterized by a fatigue striation.

Development of Thermal Mechanical Fatigue Testing Machine for Solders

This paper describes development of a thermal mechanical fatigue testing machine for solders. Several researches studying on creep, low cycle fatigue and creep-fatigue for solders at constant temperature have been reported recently, but no or small number of studies on thermal mechanical fatigue of solders have been reported. It might be resulted from that suitable thermal mechanical fatigue testing machines, which can perform the test at temperatures applicable to solders, have not been developed. In this study, the thermal mechanical fatigue testing machine which can cover the test temperatures between 233K (–40°C) and 423K (150°C) is developed. Using the developed testing machine, thermal mechanical fatigue test for Sn-3.5Ag lead-free solder was carried out and an applicability of the testing machine is investigated. This study also discusses the obtained thermal mechanical fatigue life in comparing with data in low cycle fatigue test at constant temperature.

Modelling by artificial neural network of high temperature fatigue life of oxide dispersion strengthened nickel-based superalloy PM 1000

In this study, an artificial neural network model was developed to predict the thermal-mechanical fatigue life and pure isothermal low-cycle fatigue life of oxide dispersion strengthened nickel-based superalloy PM 1000. The input parameters to the model consisted of the concentration of five inputs: mean temperature, temperature amplitude, mean total strain, total strain amplitude, and heating/cooling rate. The calculated results fit perfectly with the experimental data in both types of fatigue experiments. Furthermore, the interactions between heating/cooling rate and thermal-mechanical fatigue life were estimated based on the obtained artificial neural network model.

Modelling by artificial neural network of high temperature fatigue life of oxide dispersion strengthened nickel-based superalloy PM 1000

In this study, an artificial neural network model was developed to predict the thermal-mechanical fatigue life and pure isothermal low-cycle fatigue life of oxide dispersion strengthened nickel-based superalloy PM 1000. The input parameters to the model consisted of the concentration of five inputs: mean temperature, temperature amplitude, mean total strain, total strain amplitude, and heating/cooling rate. The calculated results fit perfectly with the experimental data in both types of fatigue experiments. Furthermore, the interactions between heating/cooling rate and thermal-mechanical fatigue life were estimated based on the obtained artificial neural network model.

Thermal–mechanical fatigue behaviour of CMSX-4 in virgin and long term aged conditions

The thermal–mechanical fatigue (TMF) behaviour of the single crystal alloy CMSX-4 has been investigated under out of phase (OP) loading in the 100–1000°C temperature range with a dwell period of 5 min. The material was tested in both virgin and aged conditions. Even though aging at 1000°C for 4000 h seems to have no significant influence on the OP TMF life, a more ductile fracture appearance was generally found for the aged material. This is also illustrated by the difference in the shape of the stabilised stress–strain hysteresis loop between virgin and aged materials, where one can see a higher degree of inelastic deformation for the aged material due to a higher degree of creep relaxation during the dwell period and more plastic deformation in the cold end of the TMF cycle. Microstructure studies showed that rafting occurred in the virgin material even during a short term TMF test with a maximum temperature of 1000°C, which may explain some of the similarities in terms of cyclic life between the two tested material conditions. The rafting was however more pronounced in the aged material where topologically close-packed phases also were found.

Lifetime of cast AlSi6Cu4 under superimposed thermal–mechanical fatigue and high-cycle fatigue loading

Out-of-phase thermal–mechanical fatigue (TMF) tests with superimposed high-cycle fatigue (HCF) loading were performed at the cylinder-head alloy AlSi6Cu4. For continuously superimposed HCF loading during TMF cycles with maximum temperatures of 250 and 300 °C a threshold of the amplitude of the superimposed HCF loading exists below which the number of TMF cycles to failure is not significantly affected. Above this threshold the TMF life shows a strong decrease with increasing HCF loading. This characteristic lifetime behaviour is also found in the case that HCF loading is only superimposed while tensile stresses are induced in the specimen during the TMF cycle. However, in the case that the HCF loading is superimposed only during the compressive phase of the TMF cycle, the number of TMF cycles to failure is not significantly affected.