A novel continuum damage coupled unified viscoplastic model is used for simulating the stress–strain responses of SiMo 4.06 cast iron under Low-Cycle Fatigue (LCF), fatigue-creep and creep loading ...for temperatures up to 650 °C. The advanced constitutive model that is developed within the framework of the Chaboche model allows the simulation of various effects including strain rate sensitivity, cyclic hardening and softening, static recovery and strain range dependency. The hyperbolic sine flow rule and the static recovery of kinematic hardening rule are proposed in order to effectively simulate both stress relaxation and creep strains. The isotropic damage variable is introduced into the constitutive equations to represent the effects of material degradation. Three main damage mechanisms are considered: fatigue, creep and ductile damage. In addition, the model is further modified to take into account the progressive microdefects closure effect. Finally, the prediction capability of the proposed model is illustrated for the experimental data obtained from the various uniaxial material tests. A good correlation was achieved between the simulated and the experimental results.
•A multi-mechanism damage coupled viscoplastic model for ductile cast irons is proposed.•The creep damage, fatigue damage and ductile damage contribute to the total damage.•Creep strains are modelled primarily via the static recovery of kinematic hardening.•Microdefects closure effect allows for various damage accumulation rules.•The damage mechanisms under various loading conditions are investigated.
•A constitutive model for combustor liner material Haynes 230 is developed.•A broad set of isothermal low-cycle fatigue and fatigue-creep responses are simulated.•Static recovery feature simulated ...stress relaxation in rate-independent regime.•Simulation of mean stress evolution needs additional modeling feature.•Strain range modeling features are essential to simulate hysteresis loop shapes.
A robust cyclic viscoplasticity model is developed for simulating a broad set of isothermal, low-cycle fatigue and fatigue-creep responses of Haynes 230 (HA 230) under uniaxial loading. High temperature components experiencing thermo-mechanical fatigue failures can be designed considering their failure responses such that their fatigue life is predictable. Hence, design of high temperature components in aerospace, automobile, nuclear power, and chemical industries should be based on viscoplastic nonlinear analysis using a robust constitutive model. A unified viscoplasticity model based on the nonlinear kinematic hardening rule of Chaboche with several added features for strain-range dependence, rate-dependence, static recovery, and mean stress evolution is developed and evaluated against a broad set of HA 230 responses. Robustness of the constitutive model is demonstrated against predicting fatigue and dwell period stress relaxation responses under uniaxial strain-controlled loading for a broad temperature range of 25–982°C and strain rate range of 1.1×10−2 to 2.6×10−5/s. Parameter determination of such an advanced model is discussed showing the importance of a well thought out experimental database and thereby providing physical meaning to model parameters.
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•A low-computation cost procedure is proposed to assess the solar receiver lifetime.•The lifetime of a solar receiver similar to Gemasolar power plant is investigated.•The stress ...relaxation effect has a strong impact on the receiver lifetime.•The receiver operation based on UTS/3 stress limit leads to a huge economic penalty.
One of the major uncertainties in the design of molten-salt solar receivers is the estimation of the lifetime because solar receivers have to withstand high temperature, thermal stress and corrosive-media in addition to daily star-up and shutdown. The first step to estimate the receiver damage and therefore, to monitor and manage the receiver life cycle, is to obtain properly the tube stresses under daily operating conditions. Whit this aim, we propose a straightforward low-computational cost procedure to determine the stresses under elastic-plastic regime. In addition, the stress relaxation due to visco-elastic behavior of the material, is also calculated. The analytical thermo-elastic, elastic-plastic and relaxation stress models for the high-nickel alloy Haynes 230 were verified against finite element simulations showing a good accuracy with a low-computational cost.
For exemplification purposes, a reference operation day of a molten-salt solar receiver like Gemasolar is investigated. A receiver creep-fatigue damage assessment was developed for a flat aiming strategy. The results showed that the fatigue damage is 0.03% of the total damage. The average-field-receiver efficiency was 42.18% with a predicted lifetime higher than the expected. On the contrary, the receiver lifetime increases unnecessarily and the field-receiver efficiency drops to 26.25% when the receiver is operated limiting the stress as one third of the ultimate tensile strength (UTS/3). This limit results in a loss of revenues of around 250,000€ per month. Hence, the excessive level of conservatism produced by stress limit methods are not suitable for solar receivers due to the resulting economic penalties.
Interaction of fatigue and creep behavior is the dominant failure mode for high cycle or very high cycle fatigue under high mean stress at high temperature. As for large rotating component working as ...high-speed at high temperature, such interaction drives the need to update strength assessment and design method. In this work, a constant life diagram incorporating dual-criterion for evaluating the interaction behavior between high cycle/very high cycle fatigue and creep at high temperature was proposed, and then verified using six types of materials data. This dual-criterion method was proved to be more precise for assessing the serious fatigue-creep interaction behavior in long-life regime, that was promising for design and safety assessment of high-temperature rotating components.
•Interaction of creep with high cycle or very high cycle fatigue is a dominant failure mode for high-temperature rotating components.•The dual-criterion assessment method considering HCF/VHCF and creep interaction was established and widely verified.•The dual-criterion assessment result is more precise with accuracy improvement for up to as high as 70 %.
This study proposes a method for calculating the fatigue–creep of a supercritical carbon dioxide (sCO2) solar receiver based on the linear damage accumulation (LDA) theory. The effects of temperature ...and stress on creep and fatigue were considered through the Manson–Coffin formula and Mendelson–Roberts–Manson (M–R–M) correlation, and the interaction between creep and fatigue was reflected by adopting the damage allowable region (DAR). Based on the DAR, a comprehensive damage coefficient K was proposed to assess the damage and safety margin of the receiver. Furthermore, this study used this method to analyze the impact of critical design parameters, namely the flow rate, tube wall thickness, and tube radius on the fatigue–creep damage of a single tube of an sCO2 solar receiver. The results demonstrated that increasing the design flow rate or decreasing the tube radius could reduce the fatigue–creep damage of the receiver, and the effect of wall thickness on creep was related to the heat flux at the location of the receiver. For the same design parameters, the creep damage was evidently greater than the fatigue damage and thus, the influence of creep on the receiver should be given priority in the design process.
•Comprehensive fatigue-creep damage evaluation of tubular sCO2 tower solar receivers.•The fatigue-creep damage of receiver is analyzed by LDA theory.•Increasing flow rate or decreasing radius resulted in a fatigue-creep damage decrease.•The effect of wall thickness on creep damage was related to the heat flux level.
•Cyclic stress softening occurred in P92 with fully inverse loading waveforms and related to dwells.•A modified kinetic and isotropic rule was proposed coupled with damage model.•Modified model well ...predicted full loop stress-strain behaviors and failure life.•Modified model well demonstrated dependence of stress relaxation on cycle number.
The low cycle fatigue and low cycle fatigue-creep behaviours of P92 steel with strain-control mode and fully inverse loading waveforms at the temperature of 630 °C were investigated. A typical cyclic softening behaviour of P92 steel was observed. As the hold time was introduced at the tensile peak and compressive valley strains, the failure cycle was reduced and the stress reduction became more obvious with the increasing hold time because of the improvement in creep deformation. Moreover, a modified combined kinematic and isotropic hardening model by introducing a non-linear interaction damage accumulation constitutive model was proposed to capture the loop stress-strain behaviour until fracture and predict the failure life as the applied strain amplitudes and duration periods changed. The validation results showed that the accelerated cyclic softening and the greatly reduced failure cycle as the duration periods prolonged under the low cycle fatigue-creep interaction conditions were well described by the modified model.
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The mechanical responses of rock-backfill composite structure (RBCS) material under fatigue-creep interaction loading is critical to the stability of mine stopes. Although many investigations have ...been attempted to reveal the failure evolution of RBCS, almost all the studies are under static loading conditions. The fracture and instability of RBCS subjected to fatigue-creep loading is poorly understood. In the present study, laboratory tests were performed to investigate the influence of a mixed ratio (MR) of cement and tailings on the stress strain responses, deformation, damage evolution, stiffness deterioration, and mesoscopic failure pattern. The strain-time curves for RBCS under fatigue-creep interaction loads present S-shaped evolution. The steady strain rate at the fatigue loading stage (CLS) shows first a decrease and then an increasing trend. It is the largest for a specimen with the smallest stiffness. The cumulative cyclic damage and time-dependent damage in RBCS promote each other, which results in a notable positive interaction between them. A novel damage evolution model is proposed using the irreversible radial strain, the model matches well with the testing data and can accurately describe damage evolution for RBCS with different cement-tailing ratios. Mesoscopic failure pattern analysis confirms the internal influence of MR on RBCS fracture and instability—it seems that the typical failure pattern tends to transmit from tension-splitting to shear failure with the decrease of CTB stiffness.
•Fatigue-creep interaction tests reveal the influences of c/t on RBCS volumetric deformation.•Deformation development at the FLS is larger than at the CLS, a notable positive interaction between them.•A novel damage evolution model is proposed by on the irreversible radial strain.•Failure of RBCS transmits from axial splitting to shear mode with decreasing CTB stiffness.
•Red sandstone containing pre-existing crack was tested under fatigue-creep tests.•Combined AE, SEM and DIC techniques for combined measurement analysis.•A macro and meso multi-scale analysis of the ...rock fracture mode was carried out.•A damage evolution model was established based on the LURR theory.•The improved Harris distribution was used to establish the damage model.
To study the effect of creep loading on the fracture mode and damage evolution process of jointed rock masses during fatigue loading, a series of multilevel cyclic loading and unloading tests (MCT) and fatigue-creep tests (FCT) were carried out on jointed sandstone samples. First, a combined detection platform was built using acoustic emission (AE), scanning electron microscopy (SEM) and digital image-related (DIC) technologies. Then, the fracture mode of the sample is analyzed at the macro- and mesoscale. Finally, based on the loading and unloading response ratio (LURR) theory, assuming that the internal damage of the sample obeys the improved Harris distribution, a damage evolution model of the sandstone sample was established, and the applicability and validity of the model were verified. The test results show that applying creep load during the fatigue loading process can increase the axial strength, reduce the axial deformation, weaken the energy dissipation, and exhibit the phenomenon of early hardening. In terms of fracture mode, applying creep load can change the type of cracks that dominate the failure of the sample, improve the shear resistance, and increase the brittleness when the sample is broken. At the same time, the dislocation movement between the grains, pressure solution and splitting phenomenon will be enhanced, and the types of micro-defects will increase. In terms of the damage evolution process, a short-term low-stress level creep load can reduce the rate of damage growth, thereby increasing the fatigue life of the rock mass.
A unified viscoplastic constitutive model with wide temperature adaptability is developed based on the basic framework of the Chaboche type model to capture the intricate cyclic viscoplastic ...behaviors of Haynes 230 subjected to isothermal low-cycle fatigue and fatigue-creep loads. By introducing effective aging time into drag stress in the hyperbolic sine viscosity function, the critical value of back stress and the additional hardening model, a rate-dependent model based on the dimensionless concentration of solute atoms or precipitates is further improved to realize simulation of dynamic strain aging effects. A multistage evolutionary approach to determining asymptotic value of back stress influenced by strain range and cumulative plastic strain is proposed to respond to cyclic hardening or softening evolved differently with the variation of temperature. For the fatigue-creep interaction, a rate or time dependent directional hardening cumulative model combined with the existing mean stress model is established. After the multi-step material parameter determination method is given, the capabilities of the proposed model are fully validated to accurately depict the mechanical behaviors of Haynes 230 for five representative temperatures.
•A systematically modified viscoplastic constitutive model with wide temperature adaptability has been developed.•A rate-dependent model to fully reflect the effect of dynamic strain aging is given.•The idea of the multistage asymptotic value evolution of back stress is proposed to respond to cyclic hardening and softening.•A rate-dependent directional hardening accumulation model is proposed for fatigue-creep interaction.•The capabilities of the proposed model are fully validated to accurately depict the mechanical behaviors of Haynes.
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