Creep Conditions Research Articles

Physics-informed machine learning with high-throughput design module for evaluating rupture life and guiding design of oxide/oxide ceramic matrix composites

In this paper, a unified physics-informed machine learning (PIML) model is proposed for the accurate prediction of the creep rupture life of oxide/oxide ceramic matrix composites (CMCs) by incorporating prior physical information and microstructure features. The collected dataset undergoes missing value imputation and standardization methods for processing. Key feature parameters that influence rupture life are identified through global sensitivity analysis. Furthermore, a high-throughput design module is developed to explore optimal composition under specific creep conditions, providing design guidelines for new materials in oxide/oxide CMCs. This study demonstrates that the predicted results consistently fall within the ±3 error bands. Improved life expectancy is attained with fiber modulus (220–290 GPa) and matrix modulus (>310 GPa). The transformation from expensive creep testing to low-cost exploration of modulus and proportional limit is achieved, offering theoretical support and analytical methods for the design of CMC components and the development of new materials for high-temperature applications.

Environment-Induced Crack Initiation and Early Stages of Crack Growth in Aluminum Alloys, Part 2

A second group of ‘state-of-the-art’ contributions [1-4] by invited researchers on the ‘Environment-Induced Crack Initiation and Early Stages of Crack Growth in Aluminum Alloys’ appear in this issue, complementing the papers published in the January 2023 issue of Corrosion [5-8]. The second section, presented herein, includes an overview of the experimental study of the initiation of environment-induced cracking (EIC) in aluminum alloys conducted since the 1950’s [1], showing crack initiation typically dominates the total life experienced during both service-life for structural applications and for smooth tensile test specimens subjected to conventional standard EIC testing. The review also reveals, although research conducted over the last 30 years almost exclusively focus on EIC propagation, there are notable exceptions worthy of re-evaluation and further study using modern in-situ advanced experimental techniques, paying particular attention to the roles of creep, crack-arrest and surface conditions during EIC initiation, paying particular attention the immediate sub-surface layers. The three additional papers in this collection are experimental studies. One investigates the significant differences in EIC initiation observed from fatigue pre-cracks and corrosion-induced fissures under controlled electrochemical conditions in a sensitized AA5456-H116 fracture mechanics test specimen exposed to a marine environment [2]. The final two papers involve testing conducted on high Zn-content Al-Zn-Mg-Cu 7xxx series alloys [3, 4]: one involves two commercial thick pate commercial high Zn content new-generation alloys [3], AA7449 and AA7085 in the T7651 temper and provides a detailed description of EIC initiation and its transition to long-crack growth during exposure to water vapor at 70 °C. Information gleaned from in-situ time-lapse, optical imaging over large areas has enabled the exact initiation sites to be identified and investigated with high-resolution fractographic studies. In the final paper [4] based on the deformation and fracture behavior of a high Zn-content Al-Zn-Mg-Cu 7xxx alloy observed in situ using synchrotron radiation X-ray tomography, it is proposed the dispersion of Mn-based second-phase particles may offer a novel approach for preventing hydrogen embrittlement in 7xxx series aluminum alloys.

Creep behavior analysis on ruptured welds of heat-resistant steels with two different failure modes

The crept welded joints of heat-resistant steel 12Cr10Co3W2MoNIVNbNB under different creep conditions, 898–948 K and 105–250 MPa, were researched, and the fracture surface reveals two modes, ductile rupture in parent material for high level stress and intergranular type Ⅳ failure in fine grain heat affected zone for low stresses. Creep data are analyzed with Monkman-Grant relation and Larson-Miller parameter method. The extrapolating creep rupture stresses for 100,000 h satisfy the industry requirements. The calculated normalized creep life growth rate values indicate that mediate stress range (150–195 MPa) yields greater influence on creep life compared with high or low stresses. Micro-voids along with precipitates near the fracture surface are observed and analyzed, and creep cavities in fine grain heat affected zone grow and coalesce together and form cracks during creep with precipitates serving as the preferential cavity nucleation sites, leading into the eventual type Ⅳ fracture. Nanoindentation results in different welding zones demonstrate that local physical-mechanical properties do not maintain a decrease trend when creep time increases.

Calculation of fatigue damage under cyclic complex loading considering the effect of the strain rate

A method has been proposed for calculating fatigue damage under cyclic loading, in which the loading in half-cycles is not simple, i.e., the stress components in a half-cycle do not change proportionally to one parameter. In addition, the proposed method takes into account the situation when the strain rate in a half-cycle affects the degree of damage to the material (for example, in the case of material deformation under conditions of creep or exposure to a corrosive environment) and this rate can change in different loading half-cycles.

Creep behavior and characterization analysis of Mg-1.8Zn-0.3Ca alloy:a molecular dynamics analysis

The addition of Zinc (Zn) and Calcium (Ca) on the Magnesium (Mg) has invoked better biocompatibility in various orthopedic applications. But this addition (Zn and Ca) leads to inducing greater modifications in the creep characteristics. In this current study, a study on the creep characterization of Mg-1.8Zn-0.3Ca alloy has been examined using molecular dynamics analysis. The creep analysis has been focused on numerous grain sizes and creep environments such as temperature and pressure to analyze its effect on the creep performance and its features. Further, the creep performance, radial distribution function, dislocation length, and structural and microstructural transformation under various grain size and deformation time has been confirmed by the modifications in the deformation mechanism and its features under various grain size and creep conditions.

Investigation of Damage and Creep for Bedding's Carbonaceous Slate with Chemical Erosion Effect.

Tunnel projects in the southwestern mountainous area of China are in full swing. According to the tunnel burial depth, structural characteristics, and chemical erosion environments of the Lixiang railway tunnel, carbonaceous slate specimens obtained in the field were taken to experimentally investigate the physical, mechanical, and creep characteristics of the bedding's slate specimens after chemical erosion. The results of scanning electron microscopy (SEM) indicate that chemical erosion leads to internal damage in the carbonaceous slate specimens, and the internal damages are increasing with the increase of erosion days. Moreover, the specimens' ultrasonic test (UT) results prove that specimens with smaller bedding angles suffer a more serious erosion and induce more internal cracks. Under conventional triaxial compression conditions with 40 MPa of confining pressures, the conventional triaxial compressive strength (σs) decreases with the decrease of the bedding angle and the increase of erosion days, and the failure modes of the specimens are mainly controlled by oblique shear fractures and accompanied by the occurrence of slip dislocation fractures between the bedding inclination. Under creep conditions with 40 MPa of confining pressures, the final deformations of specimens are increasing with the increase of erosion days, which means the longer the erosion days, the greater the deformations. The failure modes of the specimens under creep conditions are controlled by shear fractures, and for the specimen with a 60° bedding angle and long-term erosion, there are block separations and many cavities along the shear planes. Therefore, more attention should be paid to prevent serious failure of the surrounding rock if the surrounding rock has a bedding angle of 60° or suffers long-term erosion.

Machine-learning investigation on the creep-rupture time of heat-resistant steels

Currently, the reliable prediction of creep-rupture times of heat-resistant alloys is a major research area with regard to structural materials. Numerous efforts to predict creep rupture times have been made using phenomenological parameter methods; however, these approaches have only been able to achieve a limited prediction accuracy. Furthermore, the applicability of machine learning to improve the prediction accuracy of creep-rupture time has been investigated. In both studies, nevertheless, approaches have been used where explicit analytical formulas are not available. Because creep rupture is a safety issue, it is essential to use an analytical equation for predicting rupture time. Therefore, in this study, a machine learning method was applied to the analysis of creep-rupture time of heat-resistant steel to obtain an explainable prediction formula. An accurate regression model was obtained using the linear independent descriptor generation (LIDG) regression method of adding independent higher-order terms that were generated from operations between variables. By utilizing LIDG regression, we show that various creep-rupture times could be well-reproduced by different heats using explanatory variables such as creep conditions, chemical compositions, and Vickers hardness. The heat-to-heat variation in creep-rupture time could not be accounted for at all in the evaluation using the conventional parameter method. On the other hand, the LIDG regression could naturally explain the difference in the creep rupture time of various heats. Furthermore, the excellent extrapolation of the LIDG regression model was confirmed, showing its potential for long-time creep-rupture time prediction updating the conventional parametric method.

EXPERIMENTAL AND THEORETICAL INVESTIGATIONS OF HIGH-TEMPERATURE CREEP OF ENAW 5251 (AMg2) ALUMINUM ALLOY UNDER STEP LOADING

In conditions of high-temperature creep, the evolution of the damage of metallic materials is observed. To describe this effect, the damage conception of the Kachanov-Rabotnov is used. The damage parameter is defined as the relative changes of the material density, which is an integral characteristic of the damage. Taking into account this parameter and the law of conservation of mass, interrelated kinetic equations for creep deformation and damage parameter are formulated. Analytical solutions of these equations are obtained for the case of two-stage loading. Experimental studies of uniaxial stress state under conditions of high-temperature creep under two-stage loading of aluminum alloy ENAW 5251 (AMg2) at a temperature of 250°C were conducted. A good agreement of the obtained theoretical curves with the experimental results is observed.

STABILITY OF RODS WITH INITIAL IMPERFECTIONS IN THE FORM OF ECCENTRICITY OF LOAD APPLICATION UNDER LINEAR AND NON-LINEAR CREEP CONDITIONS

Stability of a compressed rod having initial imperfections in the form of eccentricity of applied load under conditions of linear and nonlinear creep is considered. It is noted that all real elements have some initial imperfections in the form of technological deflections, eccentricities of applied loads, etc., so they begin to bulge from the very beginning of loading. Another important factor in stability theory is the consideration of material creep. In this regard, the loading process is divided into two phases: the instantaneous loading process and the creep phase under constant external load. Moreover, creep can be time-limited or unrestricted. In the paper formulas for determination of critical forces of stability loss of the rod having initial imperfections, under short-term and long-term action of load are obtained. The equation allowing to determine time of the first crack appearance is derived. Derived are equations the roots of which are loads at action of which the first cracks appear at initial moment of time and at arbitrarily long period of load action. Analysis of acting force determining the character of rod deformation is executed. From the constructed stability equation it is possible to determine the critical force corresponding to the critical length of the section with cracks. For similar problems in nonlinear formulation formulas for determining critical force and critical displacement corresponding to maximum load are obtained. For the case of long duration load the equation which establishes relationship between load and displacement is obtained. Equation for determination of critical force under prolonged action of load has been derived. It has been established that critical displacement is the same under short- and continuous action of load. It is shown that at any intermediate moment critical displacement can be achieved under load lying in certain interval. Keywords: stability, rod, initial imperfection, eccentricity, linear creep, non-linear creep, critical force, crack, critical displacement.

Creep Monitoring of Submersible Observation Windows Using Mueller Matrix Imaging.

Safety of the observation window is one of the core concerns for manned submersibles. When subjected to underwater static pressure, extrusion and creep deformation always occur in the observation window, which can pose a threat to both safety and optical performance. To assess the deformation, real-time and non-contact monitoring methods are necessary. In this study, a conceptual setup based on the waveplate rotation and dual-DoFP (division of focal-plane polarimeter) polarization camera is built for the observation window's creep monitoring by measuring the Mueller matrix images of the samples under different pressures and durations. Then, a series of characteristic parameters, such as t1, R, r, R', are extracted from the Muller matrix images by Mueller matrix transformation (MMT), Mueller matrix polar decomposition (MMPD), correlation analysis and phase unwrapping method. The results demonstrate that these parameters can effectively describe the observation window's creep at different pressure levels which are simulated by finite element analysis. Additionally, more characterization parameters, such as ψ, A and D, are given from the Mueller matrix images and discussed to illustrate the method's potential for further applications and investigations. Ultimately, future devices based on this method could serve as a valuable tool for real-time and non-contact creep monitoring of the submersible observation windows.

Development of creep resistant high yttria 18Cr ferritic ODS steel through hot powder forging route

The present work reports the creep behaviour of a high yttria Fe-18Cr-2W-0.57Ti-1Y2O3 (all compositions in wt.%) ferritic oxide dispersion strengthened (ODS) steel produced by powder forging. The creep tests were carried out in a temperature range of 873 K to1023K and a stress range of 150 MPa to 425 MPa. Creep data is analysed using the power law creep equation. A large value of stress exponents (n ∼ 10 at 873 K, ∼ 18 at 923 K and 8.5 at 973 K) and a high activation energy (Q ∼581 kJ/mol) are obtained. These high values are attributed to threshold stress (σth) generated due to attractive interaction between dislocation and oxide particles. Threshold stress for different creep conditions was determined. True stress exponent values of 4 to 5 were obtained after accounting for the threshold stress. Electron back scattered diffraction (EBSD) revealed an equiaxed strain free grain structure in the powder forged ODS steel. Transmission electron microscopy (TEM) of creep tested samples indicates that microstructure remains stable after creep with no significant coarsening of nano size oxide particles. Dislocation pinning by the oxide particles was observed in creep tested samples. The observed values of true stress exponent suggest dislocation climb over the nano oxide particles to be the creep mechanism operating in the ODS steel. Samples sections close to creep fracture surfaces were investigated by EBSD. Void formation at triple junctions followed by crack propagation normal to the loading direction was observed. All the samples exhibited mixed mode (cleavage + ductile dimple) failure. Conventional ODS steel compositions contain up to 0.35% yttria. A significant improvement in creep life as well as an increase in activation energy for creep was observed because of high (1%) yttria content used in the ODS steel studied.

Microstructure and creep properties of cast hypereutectic Al-11Ce alloy with Si addition

This study systematically investigated the as-cast microstructure, heat and creep- resistance of Al-11Ce-xSi (x = 0, 0.9, 1.7 wt%) alloys. A tetragonal AlCeSi intermetallic compound was formed by adding Si. With the increase of Si content, the Chinese-script Al11Ce3/α-Al eutectics changed to rod-like structure and were gradually replaced by broad flaky AlCeSi/α-Al eutectics. The Al-11Ce alloy containing 0.9 wt% Si possessed the optimal tensile properties with an ultimate tensile strength of 129.2 MPa and an elongation of 4.3%, which were 8.4% and 65.4% higher than that of the based alloy, respectively. After aging at 400 ℃ for 1008 h, the microhardness of Si-containing alloys remained unchanged, indicating excellent coarsening resistance of the strengthening AlCeSi phases. Under tensile creep conditions at 300 ℃, the creep deformation of three alloys was the dislocation creep mechanism. Nevertheless, with the addition of 1.7 wt% Si, the steady-state strain rate of Al-11Ce alloy was decreased to 1/3 of its original value. The enhanced creep resistance was mainly attributed to the relatively high volume fraction of intermetallic phase, the reduced volume fraction of coarse primary phase, and the presence of AlCeSi precipitates that effectively hinder dislocations motion.

A Two-Layer Beam under Conditions of Creep and Damage Growth with Three-Point Loading

A Two-Layer Beam under Conditions of Creep and Damage Growth with Three-Point Loading

Inverse Problem of Pure Bending of a Beam under Creep Conditions

Inverse Problem of Pure Bending of a Beam under Creep Conditions

Повзучість малопластичних жароміцних матеріалів при вигині…

Express method of testing the initial creep stagiess of low-plastic heat-resistant materials that work in extreme conditions using the bending scheme proposed and developed. The features of stress and deformation calculation are analyzed. The limitations of using the elastic approximation are outlined: the degree of plastic deformation of the sample should not exceed 1—1,5%. The deflection should not exceed 10% of the distance between the supports, the height should not be greater than 1/10 of the distance between the supports. Under these conditions, the first and second stages are well distinguished on the creep curves. This makes it possible to analyze the influence of phase and structural changes on the mechanisms of creep at each stage, and the conditions for the transition to stationary creep. The results of model experiments performed on TNM titanium aluminide alloys and Fe3Al powder alloy samples indicate the expediency of using the three-point bending scheme for researching the initial stagiess of creep of heat-resistant materials. Experimentally determined values of the deformation rate vary in the range έ ~ 10-5—10-8, which is the most characteristic for the creep of heat-resistant materials. For low-plastic intermetallics, the influence of temperature and loading force on creep curves was studied. The dependences deformation rate vs time on the first and second stages of creep were obtained from bending tests. Thermal activation parameters are defined for the stage of permanent creep. The proposed method allows to study the speed sensitivity and to determine the thermal activation parameters of creep. In extreme conditions of operation of low-plastic heat-resistant materials, the proposed method allows to take into account and analyze the contribution to the creep of cracking and slow destruction processes. Keywords: three-point bending test, rate of deformation, initial stages of creep,high temperature materials, thermal activation parameters.

A non-isothermal creep fracture prediction method of DS superalloy considering microstructural damage

Nonisothermal service conditions are one of the main abnormal failure modes of aero-engines. The creep tests of a Ni-based directionally solidified superalloy under nonisothermal creep conditions (Tover = 980 °C, 1000 °C and 1020 °C) and constant load (σ = 227 MPa) were analyzed by SEM. According to the creep tests, we calculate the key creep parameters. By studying tests interrupted at different stages of creep, the microstructure evolution law is obtained. Based on the above research, an improved constitutive model is proposed. The creep behavior under different Tover is simulated and calculated. The simulation results are in good agreement with the experimental results.

Creep strain recovery of an in situ spinel-forming refractory castable under loading/unloading compressive creep conditions

Creep strain recovery after unloading has been well studied for metals and certain ceramic composites; however, it has not yet been investigated for ordinary ceramic refractories applied in industrial furnaces. The present study explores the question whether creep strain recovery can be observed in ordinary ceramic refractories to justify its consideration in the design of such refractories and refractory linings. To this end, the dependence of creep strain recovery on different loading conditions was investigated for a high-alumina in situ spinel-forming castable, commonly used as refractory lining of steel ladles in secondary steel metallurgy. Several loading/unloading compressive creep tests were performed at 1300 °C for different loading histories. Creep strain recovery was observed to occur and it was significantly affected by the holding time and degree of unloading. A longer holding time for the loading period was found to increase the internal stress, which is the driving force for creep strain recovery. In addition, the findings indicate that a higher excess of internal stress over external stress after unloading induces higher strain recovery.

Experimental Investigation on the Influence of Crack Width of Asphalt Concrete on the Repair Effect of Microbially Induced Calcite Precipitation.

The appearance of cracks is one of the reasons that affect the performance of asphalt pavement, and traditional repair methods have the potential problem of causing adverse effects on the environment. In this paper, an environmentally friendly method for asphalt concrete crack repair was investigated using microbially induced calcite precipitation (MICP) for asphalt concrete cracks of different widths (0.5 mm, 1.0 mm, 1.5 mm, and 3 mm), and the effectiveness of repair was evaluated using nondestructive and destructive experiments. A varied ultrasonic pulse velocity was used to evaluate the healing process, and it was found that the samples with an initial crack width of 0.5 mm showed the most significant increase in wave velocity of 18.06% after repair. The results also showed that the uniaxial compressive strength and indirect tensile strength of the MICP-repaired samples recovered up to 47.02% and 34.68%. Static creep test results showed that MICP-repaired samples with smaller width cracks had greater resistance to permanent deformation. The results of uniaxial compressive strength tests on larger width (3 mm) cracks repaired by MICP combined with fibers showed that the strength of the samples was significantly increased by the addition of fibers. In addition, the SEM/EDS results showed that the MICP products were spherical calcite particles with a particle size distribution from 0 to 10 μm. This study shows that MICP has some potential for repairing cracks in asphalt concrete of different widths within the range investigated.

Rate and State Simulation of Two Experiments With Pore Fluid Injection Under Creep Conditions

AbstractThis study uses a spring‐block model and rate and state friction to simulate experiments conducted in a double direct‐shear apparatus on carbonate fault gouge (Scuderi et al., 2017, https://doi.org/10.1016/j.epsl.2017.08.009) and on shale bearing rock (Scuderi & Collettini, 2018, https://doi.org/10.1029/2018jb016084). Both sets of experiments used the same loading protocol and injected pore fluid under creep conditions. When velocity strengthening rate and state friction is used to simulate the experiments on the carbonate fault gouge the results agree well with the observed onset of tertiary creep in the experiment. Thus, the simulation reinforces the observation that pore fluid injection can induce rapid slip even when the friction relation is velocity strengthening. The rate and state framework provides an interpretation alternative to the standard one of the Mohr's circle moving to the left as pressure increases. In the rate and state framework, the friction coefficient must increase with pore pressure increase. The shale has a low nominal friction coefficient (0.28) and is much more velocity strengthening than the carbonate. The simulation agrees with the observations that increases in pore pressure induce an increase in slip velocity but the magnitudes reach only about 100 microns/s by the end of the experiment. The simulation for the shale also agrees well with the magnitude of the observed displacement at the end of the experiment but observed displacement is increasing much more rapidly the calculated. Although the calculations agree well with features of the observations near failure, the overall curves of displacement and velocity are significantly different.

Rate-dependent ratcheting characteristics of high density polyethylene subjected to cyclic pulsating compression

Monotonic and pulsating cyclic compression tests were performed systematically based on high density polyethylene (HDPE). The compressive creep behaviors were further implemented to compare with the ratcheting deformation under the same peak stress level. Monotonic compression experiments reveal that HDPE shows obvious four-stage characteristics which are sensitive to temperature, but independent of the stress rate when the temperature is greater than 80 °C. Interestingly, the strain range during the stage III always starts at 7.4% and ends at 62.6% under various temperatures and stress rates. Moreover, the compressive ratcheting behavior of HDPE significantly depends on temperature T, peak stress σp, stress rate σ˙, stress amplitude Δσ and stress ratio R, especially when T ≥ 80 °C, σp ≥15 MPa, σ˙ ≤0.1 MPa/s and R ≥ 0.8. Additionally, decreasing the stress rate or increasing the temperature will decrease the compressive modulus of HDPE. An approximate linear relationship between the creep strain rate and the ratcheting strain rate under different temperatures and stress ratios was observed. The compressive deformation characteristics of HDPE were compared with that of some other gasket materials, a universal phenomenon is found that the compressive ratcheting evolution with time can be characterized by creep approximately under the same loading peak stress, stress rate and temperature for various gasket materials when the stress ratio is greater than zero, which indicates that the ratcheting deformation for gaskets under cyclic loads may be estimated by the corresponding static creep strain in practical engineering.