Creep-fatigue Failure Research Articles

Thermomechanical analysis of tungsten-copper joints for fusion applications using digital image correlation

The European DEMOnstration Fusion Power Plant DEMO represents a significant milestone in the progression towards sustainable fusion energy and a critical phase between ITER and commercial fusion reactors, aiming to demonstrate sustained net positive electricity production. Thanks to its properties, tungsten is a promising material for divertor armor. Coupled with copper alloys as heatsinks, they offer robust thermal management properties to deal with intense thermomechanical loads and irradiation damage. Understanding the thermomechanical behaviour of tungsten-copper joints during their application is then necessary for divertor design.This study presents experimental analysis on tungsten-copper brazed materials subjected to thermomechanical solicitations to simulate mono-block conditions with heat fluxes expected to reach 20 MW/m2 and so to face potential creep-fatigue failure. The experimental tests were coupled with Digital Image Correlation up to 400 °C to analyse the thermomechanical behaviour of these joints, providing insights into their thermal behaviour, structural integrity, damage accumulation, joint failure and identification of strains required for creep-fatigue assessment using design codes.

Creep–fatigue life prediction of a titanium alloy deep-sea submersible using a continuum damage mechanics-informed BP neural network model

Deep-sea submersibles are subjected to trapezoidal wave loading during operation, which can cause creep–fatigue failure of pressure hull structures. To ensure structural safety, it is necessary to develop accurate and efficient creep–fatigue life prediction methods. This paper proposes a continuum damage mechanics-informed BPNN approach for predicting the creep–fatigue life of titanium alloy submersibles. To obtain a reliable sample set, the creep–fatigue life is calculated based on the titanium alloy room-temperature creep–fatigue damage model and numerical analysis methods proposed by the authors. The operating duration, operating pressure, axial stress, and circumferential stress were selected as the input variables, whereas the number of cycles and actual operating duration were chosen as the output variables. The proposed model fills the current gap of a lack of research on the creep‒fatigue life prediction of titanium alloy deep-sea submersibles via machine learning methods. The research results show that the neural network model established in this paper can quickly and accurately predict the creep–fatigue life of titanium alloy deep-sea submersibles. A sensitivity analysis of the input parameters revealed that the creep–fatigue life is more sensitive to the operational pressure than to the dwell time.

Multiaxial creep–fatigue failure mechanism and life prediction of a turbine blade based on a unified numerical solution approach

AbstractExposure of turbine blades to cyclic torsional loading at high temperature, stemming from pre‐torque installation and the aerodynamic forces during operation, has the potential to induce substantial creep–fatigue damage, thereby contributing to the likelihood of premature failure. Investigating the deformation mechanisms and proposing a reliable life prediction method aiming at torsional loading is critical to ensure the structural integrity of turbine blades. This study conducted strain‐controlled fatigue and creep–fatigue tests on Inconel 718 superalloy, employing a multiaxial servo‐hydraulic testing machine. Electron backscattering diffraction elucidated deformation and damage mechanisms, forming a basis for subsequent constitutive modeling and life prediction. The lack of creep–fatigue mechanical behavior and microscopic failure mechanism when stress triaxiality equal to 0 is filled, which provides the theoretical basis and data support for the life design and damage assessment of this material under extreme service conditions. The unified viscoplasticity constitutive model effectively characterized macroscopic deformation under torsional loading. Prediction of creep–fatigue life under torsional loading, utilizing the multiaxial ductility factor‐modified strain energy density exhaustion model, demonstrated excellent alignment with experimental findings. Finally, parametric analyses of stress distribution and damage assessment under different conditions were carried out for the example of a turbine blade with relatively rarely considered aerodynamic loading as a variable. It is expected to be popularized and applied in life design and damage assessment of high‐temperature structures under multiaxial loading in engineering.

Neural network-assisted probabilistic creep-fatigue assessment of hydrogenation reactor with physics-based surrogate model

In order to obtain better hydrogenation reaction efficiency, the prospective hydrogenation reactor faces harsh working conditions, including the high-stress level, high-temperature environment, long creep dwell period and degradation of material resistance, leading to significant creep-fatigue interaction at the structural critical locations. The uncertainty widely existing in such design conditions further aggravates the creep-fatigue failure risk of the hydrogenation reactor structure, and makes the damage evolution and lifetime difficult to capture and predict. According to the latest appendix A15 of the R5 Procedure, a series of probabilistic analysis practices are delivered based on Volume 2/3 regarding creep-fatigue crack initiation. In this study, the probabilistic analysis for the hydrogenation reactor is implemented by the neural network-assisted creep-fatigue surrogate model under the probabilistic Linear Matching Method Framework (pLMM), with the superior balance between the computational efficiency and prediction accuracy fully achieved. The statistical distribution of structural creep-fatigue lifetime is investigated with the physics-based modelling technology, and the reliability-centred evaluation diagram and safety factors of the hydrogenation reactor are proposed for different reliability levels, which is dedicated to facilitating the risk management of crucial components in the hydrogen industry.

Crystal plasticity constitutive model and thermodynamics informed creep-fatigue life prediction model for Ni-based single crystal superalloy

Ni-based single crystal superalloys are the main constituent materials for aeroengine turbine blades. They are subjected to extensive in-service plastic deformation and creep-fatigue interaction, which can cause damage and failure and hence limit the turbine blade durability. In this study, a novel crystal plasticity-based constitutive model is proposed to predict the cyclic inelastic deformation of Ni-based single crystal superalloy under creep-fatigue loads, and the key aspects examined include cyclic strain hardening, ratcheting and stress relaxation behavior. The novelty of the model lies in the introduction of a dislocation density parameter in the kinematic hardening rule to describe the evolutionary characteristics of hysteresis loops. The constitutive model is implemented via the crystal plasticity finite element method and the predictions are in good agreement with experimental results. Furthermore, thermodynamic entropy generation is innovatively adopted as an indicator parameter for analysis of Ni-based single crystal creep-fatigue failure, and the corresponding creep and fatigue damage models are developed to evaluate the degree of damage. The half-life concept associated with the steady-state hysteresis loop is employed in the failure model to predict the creep-fatigue life without being limited by the computational efficiency of the crystal plasticity finite element method. The proposed model can well capture the characteristics of Ni-based single crystal creep-fatigue life, and the prediction falls within a scatter band of factor 2.0 compared to experimental results. The proposed creep-fatigue life prediction model is underpinned by deformation and failure mechanisms, which would provide a basis for accurate analysis and robust assessment of Ni-based single crystal superalloy performance and life.

Uncovering the high-temperature microstructural evolution and creep-fatigue damage mechanism of CMSX-4 brazed joints

Brazing is a promising joining technique for nickel-based single-crystal superalloy (Ni-SXs) intended for turbine blades, which endure the creep-fatigue conditions. In this work, the high-temperature microstructural stability and creep-fatigue damage mechanism of brazed joint are studied. The microstructural evolution of brazed joint, especially Zone I, where the creep-fatigue failure occurs, is influenced by the aging duration. The governed creep-fatigue damage mechanism is correlated with the strain amplitude and microstructural evolution in the brazed joints. The results obtained will be beneficial to improve the joining quality of Ni-SX brazed joints used for turbine blades.

Retraction Note: High-G drop effect on the creep-fatigue failure of SAC solder joints in BGA packages

Retraction Note: High-G drop effect on the creep-fatigue failure of SAC solder joints in BGA packages

Physics-based probabilistic assessment of creep-fatigue failure for pressurized components

To achieve a high-reliability design of high-temperature structures with a feasible balance between accuracy and efficiency, the physics-based probabilistic assessment for creep-fatigue failure is proposed under the probabilistic Linear Matching Method (pLMM) framework. At the physical level, the structural failure mechanism is reflected in the prepared training database, which is generated by the direct method procedures. And to efficiently express the relationship between design parameters and structural responses implicitly, the direct method-driven artificial neural network is built with the superior fitting quality of damage and lifetime. With the benchmarks provided, the applicability of the proposed probabilistic analysis approach for risk management of critical infrastructures is demonstrated, where the reliability-based creep-fatigue evaluation diagram is established according to different requirements. Furthermore, a novel data classification scheme is proposed to deal with the randomness in creep damage-dominated probabilistic assessment.

Creation of a Life Prediction Model for Combined High-Cycle Fatigue and Creep

Abstract While industrial gas turbine blades are commonly designed to resist creep and high-cycle fatigue (HCF) failure, the combination of these two loading conditions is seldom considered. The effect of creep damage elicited prior or concurrent to HCF loading is not well established and can significantly reduce the HCF lifetime of these critical components. A comprehensive life prediction model capable of capturing these superimposed effects is needed to ensure current reliability standards are maintained when designing aggressively loaded, next-generation industrial gas turbine blades. The consequence of combined HCF and creep loading to the lifetime a Ni-base superalloy is characterized and modeled in this study. Composition and calibration of the model are carried out using data from HCF tests conducted on virgin and pre-crept specimens at 750 °C and 850 °C. The experimental data encompass a wide range of stress ratios and pre-creep strains to mimic to the expansive set of potential turbine blade loading conditions. The proposed microstructurally informed model is based on existing principles and relies on test data and information gathered from a comprehensive failure analysis of the tested samples.

Creep-fatigue damage behavior of a titanium alloy at room temperature: Experiments and modeling

In this paper, the creep-fatigue failure mechanism and damage behavior of a Ti-6Al-3Nb-2Zr-1Mo titanium alloy at room temperature were quantitatively investigated with a series of fatigue and creep-fatigue tests. Based on experimental data and continuum damage mechanics theory, a phenomenological creep-fatigue damage model applicable to Ti-6Al-3Nb-2Zr-1Mo titanium alloy at room temperature is proposed that can describe the stress dependence of the interaction between fatigue damage and creep damage. The proposed model can consider the mutual effects of fatigue damage and creep damage at room temperature. Remarkably, the previous damage models proposed based on creep-fatigue experiments at high temperatures cannot accurately characterize the creep-fatigue damage behavior of titanium alloys at room temperature. Creep damage accumulates at a fast rate and dominates the damage evolution in the initial stage, and fatigue damage predominates in the late stages. The fatigue life is significantly reduced by creep damage at room temperature. Moreover, fatigue and creep damage promote each other.

Designing Cladded Components for High Temperature Nuclear Service: Part I—Analysis Methods

AbstractUse of corrosion-resistant cladding can greatly extend the design life of structural components in many advanced reactor systems. However, there are currently no ASME design rules for cladded components to guard against creep-fatigue failure and ratcheting strain accumulation in elevated temperature nuclear service. This paper, presented in two parts, addresses this gap by proposing a design strategy for cladded components that do not require long-term testing of clad materials. The proposed approach relies on approximate design analysis methods for two types of clad materials—a soft clad that creeps much faster than and has lower yield stress than the class A base material and a hard clad that creeps much slower than and has higher yield stress than the class A base material. Part I discusses the approximate analysis strategies for the clad materials—treat a soft clad as perfectly compliant and a hard clad as linear elastic—and Part II develops a complete set of design rules for each of the two types of cladded components. Finite element analyses of representative high temperature reactor components show that the proposed design analysis methods can bound the design quantities in soft cladded components and approximate the design quantities in hard cladded components.

Creep-fatigue lifetime estimation of efficient photovoltaic module ribbon interconnections

As the solar PV harvesting energy system are becoming more important sector of renewable energy day to day, improving the efficiency of the solar PV module and reducing the cost of modules are receiving more attentions of PV module manufacturers. Design of the PV module interconnection ribbons is one of the main focus for developing the efficiency of the PV modules and improving the reliability of the modules. In the last decade, new designs for the PV module interconnection ribbon have been introduced, however, there is still a need to optimize their configuration and geometry to achieve higher reliability without dropping the efficiency of the PV modules. Indeed, solely using the wider interconnection ribbons (to provide more joint length) may increase the reliability of the module, but it directly reduces the efficiency of module due to more shading effect. This study provides the results for determining the optimal design for long-term reliability of PV module interconnections. Three main PV module ribbon interconnection designs including Conventional Ribbon (CR), Light-Capturing Ribbon (LCR), and Multi-Busbar (MBB) interconnections are compared in terms of number of cycles to creep-fatigue failure. This study uses the FEM simulation and creep-fatigue reliability formulations to find the effect of the main geometrical parameters on the failure of different PV module ribbon interconnection designs. The finding showed that the MBB interconnections has up to 15 % higher creep-fatigue lifetime compared to the LCR and the CR interconnections.

Study on thermodynamic behaviour of natural gas and thermo-mechanical response of salt caverns for underground gas storage

Using salt caverns for underground gas storage (UGS) is an important energy storage solution. A coupled aero-thermo-mechanical (ATM) model with an integrated wellbore–3D realistic cavern geometry was established to investigate the thermodynamic behaviour of natural gas and the thermo-mechanical response of rock salt for UGS caverns. Unlike classical thermo-gas-mechanical (TGM) models that assume the cavern gas is an ideal gas and in an isotropic thermodynamic state, the ATM model solved thermodynamic properties for the real gas, and revealed the tempo-spatial varying gas state and its mechanism. Predictions of gas temperature, pressure and flux by ATM modelling well captured the in-situ measurements obtained by the distributed optical cable monitoring system during a one-month field testing at Jintan UGS site. Effects of the tempo-spatial varying gas state on the mechanical response were unveiled by ATM modelling. Predictions of mechanical response by TGM modelling shared similar patterns as that by ATM modelling, however, the TGM model tended to underestimate the risk of creep failure, tensile failure, fatigue failure and plastic damage due to the isotropic gas state. The proposed model could be used to improve the thermodynamic and mechanical predictions that are pertinent to the optimal design and the stability of caverns.

A Nested Weighted Tchebycheff Multi-Objective Bayesian Optimization Approach for Flexibility of Unknown Utopia Estimation in Expensive Black-Box Design Problems

Abstract We propose a nested weighted Tchebycheff Multi-objective Bayesian optimization (WTB MOBO) framework where we built a regression model selection procedure from the ensemble of models, toward better estimation of the uncertain parameters (utopia) of the weighted Tchebycheff expensive black-box multi-objective function. In our previous work, a weighted Tchebycheff MOBO approach has been demonstrated which attempts to estimate the model parameters (utopia) in formulating the acquisition function of the weighted Tchebycheff multi-objective black-box functions, through calibration using an a priori selected regression model. However, the existing MOBO model lacks flexibility in selecting the appropriate regression models given the guided sampled data and, therefore, can under-fit or over-fit as the iterations of the MOBO progress. This ultimately can reduce the overall MOBO performance. As, in general, it is too complex to a priori guarantee a best model, this motivates us to consider a portfolio of different families (simple-to-complex) of predictive models that have been fitted with current training data guided by the WTB MOBO, and the best model is selected following a user-defined prediction root-mean-square error-based approach. The proposed approach is implemented in optimizing a thin tube design under constant loading of temperature and pressure, minimizing the risk of creep-fatigue failure and design cost. Finally, the nested WTB MOBO model performance is compared with different MOBO frameworks with respect to accuracy in parameter estimation, Pareto-optimal solutions, and function evaluation cost. This approach is generalized enough to consider different families of predictive models in the portfolio for best model selection, where the overall design architecture allows for solving any high-dimensional (multiple functions) complex black-box problems and can be extended to any other global criterion multi-objective optimization methods where prior knowledge of utopia is required.

Improved Kriging-based hierarchical collaborative approach for multi-failure dependent reliability assessment

Reliability assessment considering multi-failure dependency brings in highly complex computing tasks, which is impracticable for some complex structures like turbine cooling blades. To efficiently investigate the failure dependency between multiple frail sites and multiple failure modes, an improved Kriging (IK) model is first established by optimizing model parameters with dynamic hybrid ant colony optimal algorithm, and the IK-based hierarchical collaborative (IK-HC) method is further developed by absorbing the advantages of IK model into HC strategy. Based on the multidimensional Copula function with dependency capture power and the IK-HC method with high-fidelity computing power, the multi-failure dependent reliability framework is first built. The computing efficiency and accuracy of the proposed IK-HC method are pre-verified by several numerical cases, and the method is applied to the multi-site (i.e., blade root, front edge) multi-mode (i.e., low-cycle fatigue, creep fatigue) failure dependent reliability assessment of a high-pressure turbine cooling blades. Method comparisons reveal that the proposed method can perform the multi-failure dependent reliability assessment with high accuracy and efficiency.

Creep-fatigue interaction and damage behavior in 9-12%Cr steel under stress-controlled cycling at elevated temperature: Effects of holding time and loading rate

Considering that most creep-fatigue tests were conducted under strain-controlled mode in previous works, creep-fatigue behavior of 9–12%Cr steel under stress-controlled cycling at elevated temperature was investigated in this work. Particular attention was paid to the effects of holding time and loading rate on the deformation and damage behavior. Results indicated that a remarkable creep ratcheting is generally observed in the creep-fatigue tests with the stress ratio of −1. Ratcheting strain and creep damage progress faster as the holding time becomes larger or the loading rate becomes smaller, resulting in the decrease of the number of cycles to creep-fatigue failure.

Creep–Fatigue Interaction Effects on Pressure-Reducing Valve Under Cyclic Thermomechanical Loadings Using Direct Cyclic Method

Abstract Supercritical boiler system has been widely used to increase efficiency of electricity generation in power plant industries. However, the supercritical operating condition can seriously affect structural integrity of power plant components due to high temperature that causes degradation of material properties. Pressure reducing valve is an important component being employed within a main steam line of the supercritical boiler, which occasionally thermal-fatigue failure being reported. This research has investigated creep-cyclic plastic behavior of the pressure reducing valve under combined thermomechanical loading using a direct numerical method known as extended direct steady cycle analysis of the linear matching method framework (LMM eDSCA). Finite element model of the pressure-reducing valve is created based on a practical valve dimension and temperature-dependent material properties are applied for the numerical analysis. The simulation results demonstrate a critical loading component that attributes creep-fatigue failure of the valve. Parametric studies confirm the effects of magnitude of the critical loading component on creep deformation and total deformation per loading cycle. With these comprehensive numerical results, this research provides engineer with an insight into possible failure mechanisms of the pressure-reducing valve at high temperature.

The Multiaxial Creep–Fatigue Failure Mechanism of Mod. 9Cr-1Mo Steel Under Non-proportional Loading: Effect of Strain Energy on Failure Lives

The Multiaxial Creep–Fatigue Failure Mechanism of Mod. 9Cr-1Mo Steel Under Non-proportional Loading: Effect of Strain Energy on Failure Lives

A Multi-Objective Bayesian Optimization Approach Using the Weighted Tchebycheff Method

Abstract Bayesian optimization (BO) is a low-cost global optimization tool for expensive black-box objective functions, where we learn from prior evaluated designs, update a posterior surrogate Gaussian process model, and select new designs for future evaluation using an acquisition function. This research focuses upon developing a BO model with multiple black-box objective functions. In the standard multi-objective (MO) optimization problem, the weighted Tchebycheff method is efficiently used to find both convex and non-convex Pareto frontiers. This approach requires knowledge of utopia values before we start optimization. However, in the BO framework, since the functions are expensive to evaluate, it is very expensive to obtain the utopia values as a prior knowledge. Therefore, in this paper, we develop a MO-BO framework where we calibrate with multiple linear regression (MLR) models to estimate the utopia value for each objective as a function of design input variables; the models are updated iteratively with sampled training data from the proposed MO-BO. These iteratively estimated mean utopia values are used to formulate the weighted Tchebycheff MO acquisition function. The proposed approach is implemented in two numerical test examples and one engineering design problem of optimizing thin tube geometries under constant loading of temperature and pressure, with minimizing the risk of creep-fatigue failure and design cost, along with risk-based and manufacturing constraints. Finally, the model accuracy with frequentist, Bayesian and without MLR-based calibration are compared to true Pareto solutions.

Economic and thermo-mechanical design of tubular sCO2 central-receivers

Supercritical CO2 central-receivers must withstand high temperatures and pressures combined with cyclic operation, which makes the solar receiver susceptible to creep-fatigue failure. In this work, a creep-fatigue analysis of a sCO2 Inconel 740H tubular receiver of a 2 MWe solar tower plant has been accomplished to study the influence of the tube size on the receiver and solar field design. A 2D numerical model of the tubular receiver that accounts for the thermal conduction in both radial and circumferential directions was developed to determine the sCO2 and wall temperature profile, which is crucial for the creep-fatigue calculations. The receiver flux distribution, which is an input to the model, was obtained with SolarPILOT, while a conventional recompression model was used to calculate the cycle efficiency and inlet temperature to the receiver. Comparison of the results of the 2D model with those of a 1D model showed that the 1D model overestimates the creep fatigue rupture time by two orders of magnitude. Furthermore, the efficiency and costs of the heliostat field and receiver were calculated for different receiver tube sizes. Smaller tubes allowed a higher maximum heat flux leading to smaller receiver and heliostat field designs, which resulted in higher overall efficiency of the power plant and lower material costs. For a design ensuring 25 year receiver lifetime the minimum sCO2 solar receiver cost, 345 €/kWth, was obtained for the smallest pipe diameter.