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This paper was to present how an affordable, high-temperature, interlaminar tension (ILT) strength testing method was explored and developed for ceramic matrix composites (CMCs), leading to development of a diametral-compression test methodology. The test methodology was first delved and verified at ambient temperature by employing a model, 2D-woven polymer matrix composite (PMC) with various test-specimen configurations. The test method was then applied to and confirmed with two different gas-turbine grade CMCs of 2D melt-infiltrated (MI) SiC/SiC and 2D N720/alumina oxide/oxide at both ambient and elevated temperatures. Life prediction testing was also conducted at 1316°C for the MI SiC/SiC to validate the effectiveness of test method for a long-term life prediction testing. All of the results on strength and life prediction testing indicated an applicability and feasibility as an appropriate high-temperature ILT test methodology in CMCs with provisions of simplicity, affordability, and technical soundness. [ABSTRACT FROM AUTHOR]

Highlights At present, there is limited literature available on the fatigue life estimation of glass fiber fabric‐reinforced thermoplastic polymer composites. This study performed constant amplitude fatigue testing to assess the fatigue life of twill‐woven glass fiber‐reinforced thermoplastic composites made from polypropylene (PP) and polyamide (PA) under four different stress levels (70%, 60%, 50%, and 40% of the ultimate tensile strength) with a stress ratio of 0.1. The fatigue life of the specimens was analyzed statistically using two‐parameter and three‐parameter Weibull distribution functions. Linear regression analysis results demonstrates a strong correlation between the independent and dependent variables in the two‐parameter Weibull analysis (correlation coefficient above 0.80), with an even better correlation observed in the three‐parameter analysis (correlation coefficient above 0.94). Based on the parameters derived from the Weibull distribution, the fatigue life of the laminates at varying survival rates has been evaluated. A P‐S‐N fatigue life prediction model has been developed from these results to account for different failure rates. Comparison with the tensile fatigue performance data of fiber‐reinforced polymer composites from the literature indicated that glass fiber‐reinforced thermoplastic composites exhibit excellent fatigue resistance. The fatigue of twill‐weave glass fiber reinforced PA/PP was investigated. The fatigue life was analyzed using three‐parameter Weibull distribution functions. A fatigue life prediction model was established based on the Weibull distribution function. The P‐S‐N fatigue life prediction model provides a reference for material design. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Xi'an Jiaotong University is the property of Editorial Office of Journal of Xi'an Jiaotong University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Rubber is widely used in situations involving cyclic loads, and the influence of temperature on rubber properties is particularly pronounced under cyclic loading. In this study, mechanical property tests and crack propagation tests of carbon black-filled hydrogenated nitrile butadiene rubber were conducted at four different operating temperatures. Based on the results of the crack propagation tests, the temperature-dependent characteristics of the Paris–Erdogan parameters and strain energy density were clarified. The Paris–Erdogan parameters were successfully expressed as a function of temperature. The strain energy density, on the other hand, exhibited the property of being strongly influenced by factors of strain, loading frequency, and others, while the temperature dependence was weak. On this basis, the unified fatigue crack growth kinetic model was constructed at multiple temperatures. The model results can match the experimental data well, particularly at temperatures of 60 °C and 80 °C. Finally, the fatigue life prediction model at different temperatures was constructed by combining the fatigue life test results. The results indicate a correlation between crack propagation characteristics and fatigue life predictions across different operating temperatures, with the predictions agreeing well with the measured life. The models can be used to analyze early fracture behavior or fatigue life prediction of rubber at different operating temperatures and minimize the need for extensive product testing prior to the manufacture of rubber products. [ABSTRACT FROM AUTHOR]

In order to study the frost resistance and strength regulation of desert sand concrete (DSC) subjected to sulphate freeze-thaw cycle, the freeze-thaw cycle test of DSC was carried out with three kinds of sulphate solutions (3%, 5% and 7% Na2SO4) as freezing and thawing medium. The apparent characteristics, mass loss rate, relative dynamic elastic modulus, corrosion resistance coefficient and ultrasonic velocity loss rate of DSC after exposure to sulphate freeze-thaw cycles were analyzed. A prediction model for the strength of desert sand concrete after sulphate freeze-thawing was established on the basis of GM (1, 1) model. Experimental results showed that with increasing number of freeze-thaw cycles, the mass loss rate and ultrasonic velocity loss rate increased, but the corrosion coefficient and relative dynamic modulus decreased. When desert sand replacement rate (DSRR) increased from 0 to 40%, concrete showed better frost resistance. When the DSRR was above 60%, the incorporation of excess desert sand had adversely effect on the frost resistance. Excessive larger mass fraction of sulphate solution exacerbated the failure process of DSC and reduced significantly the predicted service life of DSC. The average relative errors of the predicated results from GM (1, 1) model were less than 2% with high prediction accuracy. Research results provided references for the assessment of the predicted service life of concrete structure under the action of sulphate freeze-thawing in Northwest China. [ABSTRACT FROM AUTHOR]

In order to efficiently and accurately predict the crack propagation life of friction stir welding (FSW) welded structures, a fatigue crack propagation life prediction method for 2195 aluminum-lithium alloy FSW joints based on support vector regression (SVR) is proposed. Firstly, the Paris crack propagation model constants and the crack tip stress intensity factor dataset are obtained by the fatigue crack growth test and the finite element simulation. Then a stress intensity factor prediction model is established based on the SVR model, and the hyperparameters of the SVR model are optimized by the particle swarm optimization (PSO) algorithm. Finally, the crack propagation life is predicted based on the stress intensity factor prediction model and the Paris model. The results show that the optimized PSO-SVR model can effectively predict the crack tip stress intensity factor, and the determination coefficient R2 on the test set can reach 0.999 5, which is higher than 0.954 of the unoptimized SVR model. The prediction results of crack propagation life by the proposed method are compared with those by the finite element simulation. The maximum error is less than 5%, verifying the accuracy of the method. [ABSTRACT FROM AUTHOR]

The Ostergren model is simple in form and widely used in engineering practice, also serving as the modeling basis of both the damage differentiation and crack propagation models. However, the shortcomings of the Ostergren model are that the modeling process is affected by thermomechanical fatigue (TMF) test parameters. To establish a TMF life normalized model, a modified Ostergren model based on hysteresis energy damage and TMF data for H13 steel was proposed. The model was successfully applied to TMF life prediction for 4Cr5Mo2V steel. The band of predicted life and test life is basically within the factor of 1.5. In summary, the modified Ostergren model is suitable for the TMF life prediction of Cr-Mo-V-type die-casting die steel. [ABSTRACT FROM AUTHOR]

This study explores the application of Carbon Fiber Reinforced Plastics (CFRP) in lightweight design for wearable exoskeleton suits, crucial for success in industrial settings. We aimed to predict the lifespan of the exoskeleton in terms of temperature and time rather than merely confirming its ability to withstand loads. The material's viscoelastic behavior, establishing a master curve for long-term creep compliance, was characterized using Dynamic Mechanical Analysis (DMA). We also performed mechanical tests under various temperature conditions to measure strength in the load and fiber directions and carried out statistical analysis. From the test results, we constructed the master curves considering the probability of predicting the long-term strength variations. Subsequently, A multi-scale model assessed the exoskeleton frame's failure, revealing no failures in the current model under given load conditions, with the highest failure index of 0.7 for matrix tensile failure. Combining the predicted long-term strength results, the lifespan prediction for matrix tensile failure under a reference temperature of 50°C was approximately five years. The findings and methodology of this study can serve as a guide for predicting long-term performance and lifespan when applying CFRP to exoskeletons. [ABSTRACT FROM AUTHOR]

This study proposes a creep‐life prediction model based on a back‐propagation artificial neural network (BP‐ANN). The model predicted the minimum creep rate by optimizing microstructure characteristics, including martensite lath width, sub‐grain, precipitates (M23C6 and Laves phases), and dislocation density. The BP‐ANN‐based predicted creep life of 9%Cr heat‐resistant steel is compared with the traditional time‐temperature life prediction method and the machine learning support vector regression model. The results show that the BP‐ANN model has better accuracy and performance. The % error between the predicted and the experimental creep life is 5% to 10%, primarily distributed in the two‐factor band line (2% to 5%). The BP‐ANN model gives the lowest mean absolute error (0.9926), root mean square error (29.411), average absolute relative error (4.7%), and multiple coefficient of determination (R2 0.96693). The results show that the BP‐ANN model improved the creep fracture life prediction of 9%Cr heat‐resistant steel. [ABSTRACT FROM AUTHOR]

This paper proposes an equivalent spectrum method to predict the fatigue crack propagation (FCP) life of metallic materials subjected to random loading. To adequately account for the coupling effects between crack propagation and the random response of structures, a coupling analysis model is introduced. The stress intensity factor (SIF) can be estimated based on the power spectral density (PSD) of an equivalent displacement. Random vibration fatigue tests were conducted to evaluate the proposed model on aluminum alloy specimens. Results indicate significant variations in natural frequency with crack length. The predicted results are compared with the experimental values, demonstrating satisfactory prediction accuracy of the proposed coupling analysis model. This model enables the assessment of coupling effects between crack length and random response, facilitating more precise predictions of FCP life in metallic materials and guiding the expanded application of damage tolerance criteria in structural engineering. [ABSTRACT FROM AUTHOR]

High and very high cycle fatigue tests were performed to examine the microstructure and fracture mechanism of GH4169 superalloy in combination with techniques including electron‐backscatter diffraction (EBSD). Fractographic analysis revealed that surface failures are induced by surface flaws, whereas internal failures are caused by pores, facets, and inclusions. The three‐dimensional observation shows that fracture surfaces exhibit an irregular texture due to crystallographic mismatch of grains and plastic deformation at the crack tip. Based on EBSD analysis, Euler angles exhibited a complex geometry of grain orientation at the crack tip area, hindering crack propagation as evidenced by lower values of the Schmid factor and misorientation at the crack tip. Furthermore, the threshold values of small and long cracks decrease, whereas the transformation sizes from small to long crack growth increase from surface to internal failure. Finally, a novel microstructure defect‐based life prediction model is established, and the predicted results demonstrate a close resemblance to experimental outcomes. [ABSTRACT FROM AUTHOR]

This study utilizes the rank correlation coefficient to examine the multi‐site failure correlation of turbine discs. Drawing from the stress‐strength interference model, reliability models both with and without factoring in the multi‐site failure correlation are constructed. Furthermore, the weakest link theory (WLT) within the context of the Weibull distribution function is invoked to develop a model for predicting the fatigue life of turbine discs, taking into account the quantity of critical sections. The variability in the low cycle fatigue (LCF) of turbine discs is scrutinized, leading to the formulation of a probabilistic fatigue life prediction method for these discs. When comparing theoretical values with experimental ones, it becomes evident that factoring in the multi‐site failure correlation significantly enhances the accuracy of turbine disc life predictions. [ABSTRACT FROM AUTHOR]

To address the challenges posed by the time-consuming nature of fatigue test and the scattered nature of test data, it is evident that P-S-N curves derived from small samples with high survival rates lack sufficient accuracy, leading to unreliable predictions of fatigue life. The data fusion method based on the performance-life probability mapping principle is used to fuse small sample fatigue data of different stress levels, and the feasibility of obtaining accurate P-S-N curves by this method is analyzed and evaluated. The results demonstrated that P-S-N curves obtained post-fusion are closer to the P-S-N curve derived from larger sample datasets. This approach effectively enhances both reliability and accuracy in predicting fatigue life while simultaneously reducing the amount of required fatigue tests. A comparative evaluation is conducted on the predictive capabilities for fatigue life before and after fusion using different models; notably, it is found that the three-parameter power function model demonstrates superior predictive ability, whereas when ample fatigue data is available, the prediction capabilities among four models (Basquin S-N model, exponential S-N model, three-parameter power function S-N model (based on lognormal distribution), and three-parameter power function S-N model (based on three-parameter Weibull distribution) exhibit a considerable degree of resemblance. [ABSTRACT FROM AUTHOR]

ABSTRACT This study aims to investigate the low cycle fatigue (LCF) behavior and fatigue life prediction method of an advanced solid solution–strengthened nickel‐based superalloy at various temperatures and stress concentrations. Cylindrical specimens as well as plates with three types of holes (including straight holes and inclined holes with different orientations) were designed and machined for fatigue tests. The test results revealed fatigue life decreases with the temperature increasing. Meanwhile, the fatigue lives of the plate specimens have decreased differently and are strongly dependent on the geometry and orientation of the holes. The key damage parameter related to the fatigue life was found on the strain gradient path. A criterion based on strain gradient is defined as the boundary of the damage process zone. The results show that the prediction was in good agreement with the experimental data, for the majority of the data are within a scatter band of ±2. [ABSTRACT FROM AUTHOR]

To provide theoretical and data support for the fatigue performance test and life prediction of rejuvenated asphalt mixture, and supply parameter support for the design of rejuvenated asphalt pavement, dynamic shear rheometer (DSR) was used to conduct repeated shear tests on original asphalt, wood tar-based rejuvenated asphalt and RA-102 rejuvenated asphalt to evaluate the rationality of three parameters are defined as follows: complex modulus parameter (Nf50), dissipated energy ratio parameter (NP20), ratio of dissipated energy change parameter (Nfm) for evaluating the fatigue performance of rejuvenated asphalt, and the fatigue life prediction equation of wood tar-based rejuvenated asphalt was established considering the influence of temperature. The results show that NP20 has clear definition and accurate calculation of asphalt fatigue life, and takes into account the change of internal energy of asphalt material, which can be used as evaluation parameter of fatigue performance of wood tar-based rejuvenated asphalt. The fatigue performance of wood tar-based rejuvenated asphalt decreases with the increase of the temperature. The fitted prediction equations can accurately predict the fatigue life of wood tar-based rejuvenated asphalt. [ABSTRACT FROM AUTHOR]

In this paper, the thickness debit and stress concentration effects of a nickel‐based directionally solidified superalloy were investigated through strain‐controlled low cycle fatigue (LCF) and creep–fatigue interaction (CFI) experiments. Compared to the fatigue lives of solid specimens provided in the existing literature, the results of this paper indicate that when the wall thickness of the specimen is reduced from 5 to 1.125 mm, the fatigue life with different strain amplitudes decreases by about 45%. When film‐cooling holes (FCHs) are introduced into the hollow specimens, the fatigue life is further reduced by about 25%. Based on the observation of the scanning electron microscope (SEM), the formation mechanisms of the thickness debit and stress concentration effects under LCF and CFI loads were revealed. Subsequently, two parameters, the "wall‐thickness coefficient" and "hole coefficient," were proposed to establish a new fatigue life prediction method. Highlights: LCF and CFI tests were investigated on hollow specimens with and without holes.The deformational behaviors of hollow specimens with holes were studied.Two parameters, the "wall‐thickness coefficient" and "hole coefficient," were proposed.A method for estimating the fatigue life of hollow specimens with holes was proposed. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Xihua University (Natural Science Edition) is the property of Xihua University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Silicone Material is the property of Silicone Material Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Polyethylene (PE) pipes are widely used in urban gas transportation due to their good toughness and corrosion resistance. Currently, the designed service life of a PE pipeline is 50 years, and some urban gas PE pipelines are approaching their service life. However, research on the aging assessment of PE pipelines is not complete, and it is impossible to effectively predict their aging status in service. Once urban gas PE pipelines are damaged, serious accidents may be caused. PE80 and PE100 pipelines are commonly used for urban gas, and improved accelerated aging tests were conducted considering different conditions of pressure, pipe diameter, and temperature. According to the experimental results, an aging life prediction method for PE pipes was constructed based on the Arrhenius formula considering multiple effect factors. [ABSTRACT FROM AUTHOR]

Composite sandwich panels possess the characterizations of lightweight and high load-bearing capacity. They also face diverse failure modes，and an in-depth study of their mechanical performance and failure mechanisms is essential to ensure structural safety and applicability. In this paper，three-point bending static and fatigue tests are carried out for the sandwich panels consist of plain weave glass fiber/cyanate fabric laminate and Nomex honeycomb by using a specially designed test fixture to investigate the bending-shear load capacity and fatigue performance of the panel，and observe the fatigue damage and failure phenomena. According to the internal stress states of the sandwich panel，fatigue damage models are established for the face panels subjected to in-plane stresses and the sandwich core subjected to out-of-plane shear. Substituting the honeycomb core by an equivalent solid finite element，the bending panel is discretized by using the solid finite elements. Then the bending fatigue lives of the sandwich panel are predicted by means of finite element analysis and cumulative fatigue damage analysis. Results show that the simulated bending fatigue performance of the sandwich panel correlate well with the experimental results. The predicted fatigue lives are a little conservative and acceptable.

A large number of mechanical connection structures in aircraft face vibration fatigue problems，and the evaluation of vibration fatigue performance is the key to determine the service life，safety design and evaluation of the structure. In order to study the vibration fatigue performance of typical titanium alloy connection structures，the typical connection structures with different support shapes and rivet spacing are designed based on TC4 titanium alloy thin plates，a vibration fatigue test system is built，and the vibration fatigue performance of different connection structures under narrowband random loads is compared through experiments. The method for predicting the vibration fatigue life of connection structures based on random vibration Srms-N curves is proposed by introducing stress severity coefficients and fatigue notch factor. The results show that under similar vibration stress levels，the vibration fatigue performance of the T-shaped support connection structure is better than that of U-shaped support structure；on the premise of ensuring the strength of the connection，increasing the spacing between rivets appropriately can improve the vibration fatigue resistance of the connection structure；after introducing the stress severity factor and fatigue notch factor，the vibration fatigue life of the connection structure is significantly improved，and the difference between the predicted life and the test results is within 30%.

The axial loading high- and very-high-cycle fatigue tests with stress ratios of −1 and 0.1 were conducted to investigate the fracture mechanism, crack hindrance behavior, and life assessment of forged GH4169 nickel-based superalloy in combination with techniques including 2D and 3D microscopies, and electron-backscatter diffraction (EBSD). Fractographic observations reveal that surface failures are caused by surface flaws or slipping under both stress ratios, whereas internal failures are attributed to pores or cavities only at a stress ratio of 0.1. Based on the EBSD analysis of the crack hindrance phenomenon, it is observed that high-angle grains and annealing twins form a complex structure that impedes crack growth. This is evidenced by lower values of kernel average misorientation, geometric compatibility factor, and Schmid factors within the crack hindering zone. Under the influence of different stress ratios, the threshold values and transition sizes from small to long cracks are elucidated. Considering the effect of microstructural defects and stress concentration, a crack initiation fatigue life estimation model is developed, demonstrating a good resemblance between predicted and experimental results. Finally, a novel hypothesis is developed to analyze the relationship between loading and energy dissipation, potentially offering valuable insights for further research.

Main-shaft bearings are vital safety components in aeroengines made of bearing steels with outstanding combinational properties. The material is supposed to exhibit high surface hardness，high fracture toughness，high temperature resistance，fatigue resistance and corrosion resistance. However，under harsh operation conditions bearing steels are prone to rolling contact fatigue（RCF）that leads to bearing failure，severely endangering flight. Therefore，accurately predicting the RCF lives of bearing steels is key to the reliability of aeroengine. This manuscript reviews important results and progress in the RCF and life prediction of aeroengine bearing steels and suggests future research directions. Firstly，special stress state as a result of the Hertzian contact between rolling element and raceway is introduced，where shear stress components peak at the subsurface.This explains the origin of complexsubsurface-originated RCF mechanisms in bearing steels and indicates subsurface-originated RCF to be an important failure mode of bearing steels under ideal conditions. Meanwhile，with increasing contact pressure，the response of material evolves from elastic mode to plastic mode. Besides，due to the harsh service environment of aero-engine bearings，surface-originated also takes place and hence the competition between these two mechanisms is present. Next，three methodologies for RCF life prediction are summarized，being probabilistic models，mechanistic models and numerical models，with their advantages and limitations analyzed. Probabilistic models are well developed and widely employed by industry，but they are in nature a kind of statistical models without accounting for RCF mechanisms and are hence lacking scientificity; Deterministic models predict RCF life via describing physical processes，which are rich in science but poor in accuracy due to their simplification; numerical models balancing both engineering practice and scientific characteristic is a powerful tool to tackle the problem of RCF life prediction，although their accuracy requires further improvement. Finally，it is suggested that future research may focus on solving key scientific problems in RCF，modifying life prediction models via inserting RCF mechanisms and applying artificial intelligence in RCF life prediction.