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Through extensive laboratory experiments on unsaturated soils, it has been discovered that particle shape and matric suction significantly influence their mechanical properties. Prior studies have typically examined these factors individually and from a macroscopic perspective. In this study, the aspect ratio is utilized as a representative parameter for particle shape. Employing the Hill constitutive model, a series of triaxial shear numerical experiments of simulations on unsaturated soil were conducted. The results indicate a non-linear relationship between peak deviator stress and aspect ratio, with peak deviator stress initially increasing, then decreasing, and reaching its maximum at an aspect ratio of 1.2. The patterns observed in friction angle, cohesion, and critical stress ratio in relation to aspect ratio mirror those seen in peak deviator stress, with the friction angle exhibiting fluctuations as the particle aspect ratio increases. At a matric suction of 0 kPa, changes in particle shape have a negligible impact on mechanical properties. However, as matric suction increases, the volumetric strain’s dilatancy turning point is advanced, and the effect of particle shape becomes progressively more pronounced. Under varying conditions of particle shape and matric suction, the alteration in bedding angle affects the peak deviator stress and stress ratio, albeit the extent of this influence is limited. [ABSTRACT FROM AUTHOR]

Weathering steel possesses good atmospheric corrosion resistance and is increasingly applied in highway and railway bridges. The fatigue performance of the weld joint is an important issue in bridge engineering. This study experimentally investigates the microstructural properties and fracture crack growth behaviors of a Q370qENH bridge weathering steel weld joint. The FCG parameters of the base steel, butt weld, and HAZs, considering the effect of different plate thicknesses and stress ratios, are analyzed. Microstructural features, microhardness, and fatigue fracture surfaces are carefully inspected. The FCG rates of different weld regions in the stable crack growth stage are obtained using integral formulas based on the Paris and Walker law. The test results indicate that the heating and cooling process during the welding of Q370qENH steel creates improved microstructures with refined grain sizes and fewer impurities, thus leading to improved FCG performances in the HAZ and weld regions. The crack growth rate of Q370qENH weld regions increases with the stress ratio, and the influencing extent increasingly ranks as the base steel, HAZ, and the weld. The thick plate has a slightly slower fatigue crack growth rate for the Q370qENH weld joints. The Q370qENH base steel presents the highest fatigue crack growth rate, followed by the heat-treated and HAZ cases, while the weld area exhibits the lowest FCG rate. The Paris law coefficients of different regions of Q370qENH welds are presented. The collected data serve as a valuable reference for future analyses of fatigue crack propagation problems of Q370qENH steel bridge joints. [ABSTRACT FROM AUTHOR]

This study presents a numerical prediction of the fatigue life of steel panels repaired by a composite patch. The effect of length cracks, the stress ratio R and properties of the patch is presented. The obtained results show that the bonded composite repair significantly reduces the stress intensity factors at the tip of repaired cracks. The results are in a good agreement with those in the literature. The Monte Carlo method is used to predict the distribution function governing crack propagation in fatigue analysis. In computing the failure probability of the structure, we consider the statistical uncertainty associated with key variables, along with the previously discussed model uncertainty. The results obtained highlight the considerable impact of variations in crack length and stress ratio on the distribution function. Notably, uncertainty in these parameters significantly amplifies the probability of structural failure in plates, thereby diminishing overall structural durability. [ABSTRACT FROM AUTHOR]

Copyright of China Rural Water & Hydropower is the property of China Rural Water & Hydropower 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.)

The accurate characterization of fatigue life affects the durability and reliability of asphalt pavement for the asphalt mixtures. This paper proposed a new fatigue test method and analysis method which, in addition to increasing the accuracy of fatigue characterization, reduces the time and cost consumed in laboratory tests of asphalt mixtures. According to the loading speed corresponding to different loading frequency and stress levels, the corresponding strength value is selected to determine the stress ratio in the fatigue equation. Therefore, the stress ratio can truly reflect the fatigue loading stress conditions and correspond to the fatigue loading speed one by one, avoiding the unscientific fatigue resistance design problem caused by the traditional S-N fatigue equation stress ratio, which takes a single strength value at a constant loading speed as the standard. Since the stress ratio takes into account the influence of loading speed under different loading frequencies and stress levels, a unified representation model of the fatigue equation of the asphalt mixture under different loading frequencies can be established; that is, the fatigue performance of the asphalt mixture under different loading frequencies can be normalized. The results showed that the loading rate in the strength test differed from the loading rate in the traditional fatigue test, which means that the fatigue curve could not be extended to point (1,1) when the fatigue equation was extended to a fatigue life N f = 1. The fatigue test related to the velocity-dependent stress ratio in multiple experimental works, and data discreteness had a remarkable influence on fatigue characterization. The fatigue curve obtained by the fatigue equation under a constant loading rate was consistent with the fatigue curve under different loading rates. This method can reduce the duration of strength tests and the impact of the strength results of discreteness on fatigue characterization. The fatigue characterization model under constant loading rates considered the viscoelasticity of asphalt mixtures and guaranteed the correspondence of test conditions among stress level t, standard strength St, and fatigue life N f . The stress levels and loading rates of the asphalt mixtures were confirmed to be equivalent. Furthermore, this paper established the relationship between strength and fatigue and obtained the fatigue life curve of the strength values. The fatigue performance of the asphalt mixtures is evaluated comprehensively. [ABSTRACT FROM AUTHOR]

Crack growth analysis is essential for probabilistic damage tolerance assessment of aeroengine life-limited parts. Traditional crack growth models directly establish the stress ratio–crack growth rate or crack opening stress relationship and focus less on changes in the crack tip stress field and its influence, so the resolution and accuracy of maneuvering flight load spectral analysis are limited. To improve the accuracy and convenience of analysis, a parameter considering the effect of unloading amount on crack propagation resistance is proposed, and the corresponding analytical model is established. The corresponding process for acquiring the model parameters through the constant amplitude test data of a Ti-6AL-4V compact tension specimen is presented. Six kinds of flight load spectra with inserted load pairs with different stress ratios and repetition times are tested to verify the accuracy of the proposed model. All the deviations between the proposed model and test life results are less than 10%, which demonstrates the superiority of the proposed model over the crack closure and Walker-based models in addressing relevant loading spectra. The proposed analytical model provides new insights for the safety of aeroengine life-limited parts. [ABSTRACT FROM AUTHOR]

The effects of stress ratio（R），loading condition，and MnS inclusion on the fatigue behavior of medium-carbon pearlitic high strength steel were investigated by the combination of rotating（frequency of 52.5 Hz，103-108）bending and ultrasonic （frequency of 20 kHz，5×104-109）axial cycling tests in high-cycle and very-high-cycle regimes. The study results show that all the S-N curves present horizontal asymptotic shapes and have clear fatigue limits. The fatigue limits（260-270 MPa）for R = −1 obtained by ultrasonic test are 140-150 MPa，which are lower than that（400-410 MPa）obtained by rotating bending，and the limit values for R = 0.3 are in the range of 195-205 MPa. For rotating bending，the fatigue fractures are originated from the surface matrix of the specimen，whereas for ultrasonic fatigue，both surface and interior crack initiation occur，and cracks are all initiated from MnS inclusions regardless of stress ratios. The influence of MnS inclusions on crack initiation and propagation is studied by finite element method. The side of elliptical MnS inclusions has higher stress concentration than the tip position，which leads to crack initiation from the side of inclusions.

To accurately evaluate the probabilistic characteristics of the fatigue properties of materials with small sample data under different stress ratios, a data fusion method for torsional fatigue life under different stress ratios is proposed based on the energy method. A finite element numerical modeling method is used to calculate the fatigue strain energy density during fatigue damage. Torsional fatigue tests under different stresses and stress ratios are carried out to obtain a database for research. Based on the test data, the W t - N f curves under a single stress ratio and different stress ratios are calculated. The reliability of the models is illustrated by the scatter band diagram. More than 85% of points are within ±2 scatter bands, indicating that the fatigue life under different stress ratios can be represented by the same W t - N f curve. Furthermore, P- W t - N f prediction models are established to consider the probability characteristics. According to the homogeneity of the W t - N f model under different stress ratios, we can fuse the fatigue life data under different stress ratios and different strain energy densities. This data fusion method can expand the small sample test data and reduce the dispersion of the test data between different stress ratios. Compared with the pre-fusion data, the standard deviations of the post-fusion data are reduced by a maximum of 21.5% for the smooth specimens and 38.5% for the notched specimens. And more accurate P- W t - N f curves can be obtained to respond to the probabilistic properties of the data. [ABSTRACT FROM AUTHOR]

The prediction of fatigue strength for metallic materials in a wide range of stress ratios is a crucial engineering challenge. To pursue a more accurate method, the dependence of fatigue strength on stress ratio for 35CrMo steel and other materials was investigated in detail. It was found that as the stress ratio increases, the damage mechanism changes, and the errors of the conventional models in predicting the fatigue strength increase. The reason is that those models fail to describe the fatigue damage evolution of metallic materials under some special conditions. Based on the variational fatigue damage, a new prediction method was proposed by introducing the damage parameter. Through the validation with fatigue strength covering a variety of metallic materials and loading conditions, the method exhibits higher universality. And then the corresponding parameter of the formula is further analyzed to elucidate the influences of various loading conditions on fatigue damage of materials. Highlights: The new method exhibits good generality and accuracy.The new method greatly improves the prediction efficiency.The optimized method can offer theoretical support to enhance fatigue properties. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing is a mainstream technology for unconventional oil and gas reservoirs development all over the world. How to use this technology to achieve high-level oil and gas resource extraction and how to form complex fracture networks as hydrocarbon transportation channels in tight reservoirs, which depends to a large extent on the interaction between hydraulic and pre-existing cracks. For hydraulic fracturing of fractured reservoirs, the impact of natural fractures, perforation direction, stress disturbances, faults and other influencing factors will produce a mixed Ⅰ&Ⅱ mode hydraulic fracture. To forecast whether hydraulic fractures cross pre-existing fractures, according to elastic mechanics and fracture mechanics, a stress state of cracks under the combination of tensile (Ⅰ) and shear (Ⅱ) is presented. A simple mixed-mode Ⅰ&Ⅱ hydraulic fracture's crossing judgment criterion is established, and the propagation of hydraulic fractures after encountering natural fractures is analyzed. The results show that for a given approaching angle there exists a certain range of stress ratio when crossing occurs. Under high approaching angle and large stress ratio, it is likely that hydraulic cracks will go directly through pre-existing cracks. The reinitiated angle is always controlled within the range of approximately 30° among the main direction of penetration.

Copyright of Journal of Aeronautical Materials is the property of Editorial Board of Journal of Aeronautical Materials 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.)

Friction Stir Welding is a process that has led to increasing usage of aluminum and its alloys in different industries, since it is an autogenous and a solid-state welding process. The work developed in this paper was focused on the analysis of the mechanical behavior of AA7075-T651 friction stir butt welded joints, of 4 mm of thickness, under different loading and temperature conditions. A selection process was applied to assure the appropriate welding parameters. The welds from which the investigated specimens were manufactured from were submitted to nondestructive testing to assess the presence of welding defects. Fatigue tests were carried out, under a constant amplitude loading regime, at stress ratios of 0.05 and 0.5 and at temperatures of 23 °C and 150 °C. The results obtained by the fatigue tests point to a higher fatigue life of the specimens when the highest stress ratio, R = 0.5, was used (for the maximum stress applied), for both loading temperatures. For the stress range, the contrary was found to be true. Room temperature was also found to result in a significantly better fatigue performance. A Scanning Electron Microscope was used to characterize the fatigue fracture surfaces. [ABSTRACT FROM AUTHOR]

This study focuses on evaluating the fatigue life performance of 3D-printed polymer composites produced through the fused deposition modelling (FDM) technique. Fatigue life assessment is essential in designing components for industries like aerospace, medical, and automotive, as it provides an estimate of the component's safe service life during operation. While there is a lack of detailed research on the fatigue behaviour of 3D-printed polymer composites, this paper aims to fill that gap. Fatigue tests were conducted on the 3D-printed polymer composites under various loading conditions, and static (tensile) tests were performed to determine their ultimate tensile strength. The fatigue testing load ranged from 80% to 98% of the total static load. The results showed that the fatigue life of the pressed samples using a platen press was significantly better than that of the non-pressed samples. Samples subjected to fatigue testing at 80% of the ultimate tensile strength (UTS) did not experience failure even after 1 million cycles, while samples tested at 90% of UTS failed after 50,000 cycles, with the failure being characterized as splitting and clamp area failure. This study also included a lap shear analysis of the 3D-printed samples, comparing those that were bonded using a two-part Araldite glue to those that were fabricated as a single piece using the Markforged Mark Two 3D printer. In summary, this study sheds light on the fatigue life performance of 3D-printed polymer composites fabricated using the FDM technique. The results suggest that the use of post-printing platen press improved the fatigue life of 3D-printed samples, and that single printed samples have better strength of about 265 MPa than adhesively bonded samples in which the strength was 56 MPa. [ABSTRACT FROM AUTHOR]

The fatigue load that a material experiences and its microstructure are important factors influencing fatigue crack propagation behavior. This study employed laser scanning microscopy and electron backscatter diffraction (EBSD) technology, along with fatigue crack propagation experiments, to investigate the fatigue crack propagation behavior of 2024 aluminum alloy under varying stress ratios (R). The results showed that the stress amplitude (σp) was the main factor controlling the fatigue crack propagation life (N). Additionally, detailed characterization of the fatigue crack propagation path was conducted using crystal models and EBSD. A fatigue crack propagation model for 2024 aluminum alloy under different R-values was established based on the grain twist angle and Schmid factor. Finally, the impact of R on the crack tip shielding (Ks) was systematically analyzed, elucidating the intrinsic mapping relationship between R, microstructure, and crack propagation characteristics.

In order to master the mechanical strength characteristics of the colluvial deposit and the influence of water content on it，a typical loose colluvial deposit of landslide in southwest China was taken as a research object. A series of large-scale direct shear tests were carried out under different water content conditions and normal stress, the macro mechanical characteristics such as stress-strain, particle breakage, volumetric strain, shear plane failure and so on in the shear process of the colluvial deposit were analyzed, and the determination method suitable for its shear strength was proposed. The research indicates that the colluvial deposit shows obvious strain hardening characteristics under different water contents, and the shear stress displacement curve has no significant peak value, but there is a certain degree of stress "jump" phenomenon. Besides, the shear process produces a relatively obvious particle crushing phenomenon, and the relative particle crushing rate increases with the decrease of water content or the increase of normal stress. Meanwhile, the tests show that the shape of shear failure surface is not an ideal plane. With the increase of water content, the shear surface gradually changes from an irregular shape of "convex up and concave down" to a flat failure surface with a certain angle with the shear joint in space. Combined with the analysis of the characteristics of the normal stress, shear stress and stress ratio on the shear plane during the shear process, a method for determining the shear strength of the accumulation based on the stress ratio is proposed, and the effectiveness of this method is verified. This method is not only simple to operate, with little human interference, but also can better reflect the essence of the shear failure of the soil rock mixture. Finally, the tests reveal that water has an obvious softening effect on the colluvial deposit. The apparent cohesion c and internal friction angle φ linearly decrease approximately with the increase of water content, and the deterioration effect of apparent cohesion is greater than that of internal friction angle. The research results can provide a reference for the determination of shear mechanical properties and strength values of deposits in the southwest mountain area.

Crack growth analysis is essential for probabilistic damage tolerance assessment of aeroengine life-limited parts. Traditional crack growth models directly establish the stress ratio–crack growth rate or crack opening stress relationship and focus less on changes in the crack tip stress field and its influence, so the resolution and accuracy of maneuvering flight load spectral analysis are limited. To improve the accuracy and convenience of analysis, a parameter considering the effect of unloading amount on crack propagation resistance is proposed, and the corresponding analytical model is established. The corresponding process for acquiring the model parameters through the constant amplitude test data of a Ti-6AL-4V compact tension specimen is presented. Six kinds of flight load spectra with inserted load pairs with different stress ratios and repetition times are tested to verify the accuracy of the proposed model. All the deviations between the proposed model and test life results are less than 10%, which demonstrates the superiority of the proposed model over the crack closure and Walker-based models in addressing relevant loading spectra. The proposed analytical model provides new insights for the safety of aeroengine life-limited parts.

The accurate characterization of fatigue life affects the durability and reliability of asphalt pavement for the asphalt mixtures. This paper proposed a new fatigue test method and analysis method which, in addition to increasing the accuracy of fatigue characterization, reduces the time and cost consumed in laboratory tests of asphalt mixtures. According to the loading speed corresponding to different loading frequency and stress levels, the corresponding strength value is selected to determine the stress ratio in the fatigue equation. Therefore, the stress ratio can truly reflect the fatigue loading stress conditions and correspond to the fatigue loading speed one by one, avoiding the unscientific fatigue resistance design problem caused by the traditional S-N fatigue equation stress ratio, which takes a single strength value at a constant loading speed as the standard. Since the stress ratio takes into account the influence of loading speed under different loading frequencies and stress levels, a unified representation model of the fatigue equation of the asphalt mixture under different loading frequencies can be established; that is, the fatigue performance of the asphalt mixture under different loading frequencies can be normalized. The results showed that the loading rate in the strength test differed from the loading rate in the traditional fatigue test, which means that the fatigue curve could not be extended to point (1,1) when the fatigue equation was extended to a fatigue life Nf = 1. The fatigue test related to the velocity-dependent stress ratio in multiple experimental works, and data discreteness had a remarkable influence on fatigue characterization. The fatigue curve obtained by the fatigue equation under a constant loading rate was consistent with the fatigue curve under different loading rates. This method can reduce the duration of strength tests and the impact of the strength results of discreteness on fatigue characterization. The fatigue characterization model under constant loading rates considered the viscoelasticity of asphalt mixtures and guaranteed the correspondence of test conditions among stress level t, standard strength St, and fatigue life Nf. The stress levels and loading rates of the asphalt mixtures were confirmed to be equivalent. Furthermore, this paper established the relationship between strength and fatigue and obtained the fatigue life curve of the strength values. The fatigue performance of the asphalt mixtures is evaluated comprehensively.

In the present study it has been endeavored to estimate the fatigue crack propagation in V-notch Charpy specimens of 2024 T351 Al-alloy. For this purpose, a new application of fatigue crack growth (FCG) is developed based on the “Gamma function.” Experimental fatigue tests are conducted for stress ratios from 0.1 to 0.5 under constant amplitude loading. The empiric model depends principally on physical parameters and materials’ properties in non-dimensional form. Deviation percentage, prediction ratio, and band error are used for validation of the performance of the fatigue life. The results determined from Gamma application are in good agreement with experimental FCG rates and those obtained from using Paris law.

Within the strain level attainable in drained triaxial tests, it is not uncommon for dense cohesionless soil to be sheared insufficiently to reach the critical state. Linear fitting of the correlative data from the maximum stress ratio or minimum dilatancy to the end of the test, and then extrapolating these fitted lines to the critical stress ratio or zero dilatancy has been frequently used to estimate the critical state void ratio. However, the linear extrapolation method is empirical and involves different choices of correlative test data, which leads to different estimates. Therefore, a series of simulations of drained tests on dense Toyoura sand are performed using a state-dependent model. Multiple data sets are generated, including void ratio e, volumetric strain εv, stress ratio η, and dilatancy D. The linear extrapolation accuracy of the e–η, e–D, and εv–D data sets is examined. It turns out that the e–η data set is best suited. The goodness of the e–η data set is examined against 18 sets of experimental data on dense sand. In addition, the selection of the start point for extrapolation is shown to influence the estimates. The latter 50% of the post-peak data is found to be reliable. [ABSTRACT FROM AUTHOR]

Loess is usually compacted as building filler in geotechnical engineering construction and the wetting-induced deformation characteristics of compacted loess are closely related to engineering safety. The influence of hydromechanical paths on compacted loess wetting-induced deformation characteristics has been rarely addressed in the literature, especially for compacted sandy loess. In this study, the scanning electron microscopy (SEM) and soil–water retention curve (SWRC) tests are performed to investigate the microstructure and water retention characteristics of compacted sandy loess. Single-oedometer triaxial wetting tests with three complex hydromechanical paths (consolidation-wetting under isotropic stress state, consolidation-loading-wetting-loading and consolidation-unloading-wetting-unloading under deviator stress) are carried out on unsaturated compacted sandy loess. Results indicate that: (1) As the dry density increases, the large inter-aggregate pores inside the compacted sandy loess turned into medium inter-aggregate pores and small inter-aggregate pores; the air entry value increases and the water retention capacity is enhanced. (2) Within a certain range of confining pressure (no more than 400 kPa), the wetting volumetric strain increases with the increase in confining pressure and dry density under isotropic stress condition; the loading paths wetting-induced deformation is greater than unloading paths wetting-induced deformation under deviator stress condition. (3) At a lower stress ratio, compacted sandy loess undergoes significant wetting-induced dilatancy; the wetting-induced deformation under the unloading path appears significant, compared with that under the loading path. [ABSTRACT FROM AUTHOR]

The structural characteristics of the soil dominate macro-mechanical behaviors. The features of loess in geological engineering contexts are related to its structural properties. Hence, quantitative studies of loess’ structural properties have been widely undertaken. In this study, a novel structural parameter—stress ratio sensitivity (Sη)—has been proposed, based on the concept of mechanical sensitivity by considering the stress ratio characteristics of undisturbed and remolded loess. The rationality of the Sη parameter was validated via the performance of triaxial shear tests on samples with different water contents. The results suggest that the value of Sη decreases first and then stabilizes as the strain increases, and here, its value converged towards, but was always larger than 1. The Sη–strain curves herein can be divided into three stages: rapidly decreasing, slowly decreasing, and stable state. A higher water content in the sample corresponds to a lower rate of decrease in Sη. Furthermore, the initial value of the structural parameter (Sηo) was obtained via the fitting of data onto the rapidly decreasing stage of the Sη–strain curves, which could be referred to evaluate the initial structural state of loess. Increasing confining pressure and water content reduced both the Sη and Sηo values significantly. Variations in loess’ structural properties have been attributed to changes in cohesion, whose difference reflected the loss in structural property due to remolding compared with the original. As the cohesion difference (∆ c ′ ) increases, the value of the Sηo increases exponentially. The Sη can reasonably describe the evolution of loess’ structural properties under different loading conditions, and provide a new idea for quantitatively illustrating the relationship between the structural characteristics and macro-mechanical behavior of loess. [ABSTRACT FROM AUTHOR]

The mechanical properties of coated fabric demonstrate significant material nonlinearity. Presently, testing methods to determine the engineering constants of coated fabric include uniaxial loading and biaxial loading. However, the engineering constants obtained through these methods often differ. This paper presents experimental investigations into the uniaxial and biaxial mechanical properties of architectural coated fabric. Initially, the elastic modulus and Poisson effect of the coated fabric under uniaxial tension are determined using non-contact measurement techniques. Subsequently, the influence of different stress ratio combinations on the engineering constants of coated fabric is explored through biaxial tensile testing. Finally, biaxial shear tests are conducted on architectural coated fabric to examine the effects of prestress and shear stress amplitude on the shear modulus. The results indicate that the orthogonal linear elastic model under the plane stress framework provides a high fitting accuracy for the biaxial tensile test data of coated fabric, with a maximum fitted RSS of 0.0843. Additionally, the calculated elastic modulus depends on the selection of the stress ratio group. The elastic modulus derived from the biaxial tensile test is smaller than that obtained from the uniaxial tensile test. Furthermore, the shear modulus of the coated fabric shows a linear positive correlation with the initial pretension value and decreases as the shear stress amplitude increases. [ABSTRACT FROM AUTHOR]

This paper discusses the theoretical and experimental correlations between fatigue and static strength statistical distributions. We use a two-parameter residual strength model that obeys the qualitative strength-life equal rank assumption (SLERA) for guidance. The modeling approach consists of recovering the model's parameters by best fitting the constant amplitude (CA) fatigue data at a given stress ratio, R, and the experimental Weibull parameters of the static strength distribution function. An extensive set of fatigue life and residual strength data for AS4 carbon/epoxy 3k/E7K8 Plain Weave Fabric with [45/−45/90/45/−45/45/−45/0/45/−45]S layups, obtained at different stress ratios, R, have been analyzed. The modeling approach consists of recovering the model's parameters from pure tension or compression fatigue data at R = 0.1 and R = 5, respectively. Once the parameters are fixed, the model's capabilities, potential, and limits are discussed by comparing its predictions with residual strength and fatigue life data obtained at stress ratios with mixed tension/compression loadings, namely R = −0,2 and R = −1. Moreover, from a preliminary analysis, the theoretical extension of the model's capabilities to variable amplitude loadings is conceptualized. The application of Miner's rule is also discussed and compared with a new damage rule to analyze the fatigue responses under variable amplitude loadings. [ABSTRACT FROM AUTHOR]

To study the effect of the variable amplitude on the carburised 17CrNi high-strength steel, very high cycle fatigue tests were performed on smooth specimens under the stress ratios of 0 and −1. After the experiment, the characteristics of the fracture surfaces were investigated by means of an optical microscope and a scanning electron microscope. Circular-formed marks were found around the inclusion inside the fisheye. Finally, based on five damage models, the fatigue life of the carburised 17CrNi high-strength steel was predicted. The comparison of the calculated lives with the experimental data shows that the modified Miner's criterion is the most accurate and it can adequately characterise the fatigue life of the 17CrNi steel. [ABSTRACT FROM AUTHOR]

The corrosion fatigue crack propagation (FCP) of the butt weld with G20Mn5QT cast steel and Q355D steel in 3.5‐wt% NaCl solution was investigated experimentally. Considering the influences of stress ratio and loading frequency, the corrosion FCP rate curve was obtained. The results indicated that the corrosion FCP rate in the corrosion environment is three times that in air. Increasing the stress ratio or decreasing the loading frequency will increase the corrosion FCP rate. The fracture morphology of the specimens in the corrosion environment had more corrosion pits and intergranular characteristics due to anodic dissolution than that in air. Anodic dissolution and hydrogen embrittlement jointly promoted the corrosion FCP of butt weld in simulated seawater. The corrosion FCP rate model was established considering the effects of stress ratio and loading frequency. Highlights: Corrosion accelerated corrosion fatigue crack propagation (FCP) significantly.The corrosion FCP rate increases with the increase of R and the decrease of f.The mathematical model of corrosion FCP rate of butt weld is proposed. [ABSTRACT FROM AUTHOR]

The integration of mesoscale modeling and macroscale experimentation has emerged as a promising approach for understanding and predicting the mechanical behavior and fatigue performance of fiber-reinforced polymer composites. In this work, the mean field homogenization technique is implemented to predict the fatigue performance of the carbon-fiber-reinforced polymer composites under cyclic loading conditions. To predict the number of fatigue cycles, Modified Gerber criteria are used with the stress-based Tsai–Hill failure indicator. Fatigue strength factor (α) and creep rupture strength factor (β) are experimentally evaluated and further implemented in a computational approach to predict fatigue life cycles of the composite. The effect of composite constituents, stress ratio, and loading direction are investigated in detail against the fatigue performance of the composite. Fatigue cycles are predicted at individual matrix and fiber levels at various stress ratios of 0.2, 0.4, 0.6, and 0.8 at different loading inclinations. The experimental results are compared with the mesoscale S–N curves. [ABSTRACT FROM AUTHOR]

Fire resistance steel maintains strength at high temperatures and its allowable temperature is higher when compared with generic steel. Thus, it is needed to analyze its fire resistance quantitatively. In this study, high temperature creep tests of fire resistance steel specimens were conducted with variables of stress ratio and temperature to analyze their mechanical properties and behavior at a fire. The creep limit temperature of the Steel New (SN) steels observed from the high temperature tests was below 538 °C. The FR (Fire Resistance) steels showed stable creep behavior until 600 °C and maintained lower level of deformation for a longer period of time when compared with what was observed from previous studies. It is deduced that the FR steels are very effective in resisting deformation at high temperatures. As stress ratio increased, strain increased almost tenfold. Since strain increased very rapidly approximately from 1%, it is required not only to compare difference in final strain but also to quantitatively analyze creep behavior when strain is 0.5–1% and build up critical deformation data. [ABSTRACT FROM AUTHOR]

To explore the application of heat-treated ribbed bar (HTRB) type HTRB630 high-strength steel bars in reinforced concrete bridges, the tensile test and high-cycle fatigue test are carried out. Then, the high-cycle fatigue properties of the specimens are analyzed and discussed from median stress-number of loading cycles (S-N) curve, P-S-N curve, comparison with 500-MPa grade steel bars, and fatigue fracture mechanism. Finally, their high-cycle fatigue properties are investigated numerically, and the influence of stress ratio on their fatigue properties is discussed. The results indicated that the probability-stress-number of loading cycles (P-S-N) curve with a confidence level γ=75% and a reliability guarantee rate P=97.7% is more accurate than the median S-N curves for the fatigue design of reinforced concrete bridges. In the P-S-N curve, the stress ranges at 2 million and 10 million cycles are 237.03 and 203.38 MPa, respectively. In the median S-N curve, the stress ranges at 2 million and 10 million cycles of fatigue life of steel bars are 262.77 and 236.08 MPa. The fatigue properties of the specimens are higher than those for the 500-MPa grade steel bars. The fatigue fracture of the specimens consists of a fatigue source zone, crack propagation zone, and transient fracture zone. Microscopically, it is a cleavage fracture in the crack propagation zone; it is micropore aggregation fractures in the instantaneous fracture zone. At a given fatigue life, the fatigue stress range decreases as the stress ratio increases. The fatigue properties of the specimens are better at a higher stress ratio with the same maximum stress. [ABSTRACT FROM AUTHOR]

The fatigue behavior of woven ply (0/90°) glass fiber reinforced plastic (GFRP) laminates filled with 2 wt.% of tungsten carbide nano‐powder at different stress ratios, 0.1 and 0.3, was investigated. Specimens were subjected to constant amplitude fatigue loading for three stress levels, 80%, 70%, and 60%, of ultimate tensile strength at each stress ratio for both neat GFRP and tungsten carbide modified GFRP (GFRP‐WC). The fatigue life was enhanced at all stress levels in neat GFRP composites with an increase in stress ratio from 0.1 to 0.3. In addition, incorporation of nanoparticles also increases fatigue life at all stress levels for both stress ratios. The addition of nanoparticles acts as a barrier to crack propagation, which leads to a significant effect on the evolution of fatigue stiffness, cyclic creep strain, and dissipated energy during cyclic loading at both stress ratios. Highlights: Effect of stress ratio (R) on fatigue behavior of woven GFRP laminate.Effect of tungsten carbide (WC) on the fatigue behavior of GFRP for R = 0.1 and 0.3.Effect of R and WC on damage, fatigue stiffness, cyclic creep, and dissipated energy.Analytical models are able to reliably predict the fatigue life of GFRP and GFRP‐WC. [ABSTRACT FROM AUTHOR]

The high‐cycle fatigue (HCF) and very‐high‐cycle fatigue (VHCF) behavior of Ti‐6Al‐4V manufactured by laser powder bed fusion (L‐PBF) was investigated to reveal the effects of surface roughness and stress ratio on fatigue performance. Fatigue tests were performed by an ultrasonic vibration machine with a frequency of 20 kHz. The fatigue strength of surface‐polished specimens is generally higher than that of as‐built specimens in HCF and VHCF regimes. Fatigue cracks initiated from the subsurface of as‐built and surface‐polished L‐PBF Ti‐6Al‐4V. The values of size and depth for the defects that acted as fatigue crack origins present large scattering for L‐PBF Ti‐6Al‐4V due to the interaction between surface roughness and subsurface defects. For surface‐polished L‐PBF Ti‐6Al‐4V, fatigue cracks have almost the same resistance to propagation at both stress ratios of R = −1 and 0.7. Highlights: Fatigue strength of surface‐polished specimens higher than as‐built L‐PBF Ti‐6Al‐4VFatigue crack initiation from lack‐of‐fusion defects in subsurface defect‐enriched layerDefect & surface roughness with greater effect on crack initiation than stress ratioCrack propagation much easier in as‐built than surface‐polished L‐PBF Ti‐6Al‐4V [ABSTRACT FROM AUTHOR]

This paper presents the development of the multiple linear regression approach based on the stress ratio and applied load that was assessed using entropy generation. The energy dissipation is associated with material degradation to determine the fatigue life with consideration to the irreversible thermodynamic framework. This relationship was developed by predicting a complete entropy generation using a statistical approach, where a constant amplitude loading was applied to evaluate the fatigue life. By conducting compact tension tests, different stress ratios were applied to the specimen. During the tests, the temperature change was observed. The lowest entropy generation was 2.536 MJm-3 K-1 when 3,000N load with a stress ratio of 0.7 was applied to the specimen. The assumptions of the models were considered through graphical residual analysis. As a result, the predicted regression model based on the applied load and stress ratio was found to agree with the results of the experiment, with only 9.3% from the actual experiment. Therefore, the entropy generation can be predicted to access the dissipated energy as an irreversible degradation of a metallic material, subjected to cyclic elastic-plastic loading. Thermodynamic entropy is shown to play an important role in the fatigue process to trace the fatigue life

A model for theoretically estimating the number of loading cycles before fatigue crack initiation at a constant applied cycle stress range and a power law equation to describe the kinetics of damage accumulation at this stage of fatigue failure are proposed. It is shown that the level of relaxation of local stress from the top of the blunt concentrator, which occurs due to local plastic deformations, depends on the value of the applied cycle stress and is nonlinear. A power law equation is proposed to estimate this local stress following the concept of critical distance, thus considering fatigue damage accumulation's kinetics. The correlation between the power-law exponents in the above equations and the equation for the growth rate of a newly initiated fatigue crack is established. In addition to the loading parameters and geometric dimensions of the concentrator, the initial data for the theoretical evaluation are the static strength characteristics (elastic modulus, Poisson's ratio, and macroscopic yield onset stress, which are determined from short-term tensile tests of standard specimens) and microstructure characteristics (grain size, Taylor's factor, Burgers vector, and grain misorientation angle, which are determined from the analysis of the microstructure of the starting material). No fitting parameters or experimentally determined data on material fatigue are used. The calculations based on the proposed model of the number of loading cycles before fatigue crack initiation in 45 steel specimens show good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Fatigue crack growth in thick‐section metals is typically controlled by an internal plane strain region where strong triaxial constraint of the crack tip occurs. However, the crack tip stress state in this region is challenging to measure. We have used neutron diffraction to study the plane strain section of fatigue crack tips in situ. A stroboscopic form of neutron diffraction using a moving frame‐of‐reference was developed to measure crack tip strains as a function of phase in the fatigue loading cycle without interrupting the cyclic load. Using point measurements of near‐tip strain in 7475‐T7351 aluminium alloy in conjunction with finite element analysis, we can estimate the extent of the crack tip plastic zone, verifying that it is small for this material and set of loading conditions. Highlights: We demonstrate stroboscopic neutron diffraction with an Eulerian frame‐of‐reference.This measures strain at the interior of a fatigue specimen without interrupting a test.Cyclic crack tip strains during fatigue of a 7xxx aluminium alloy have been observed.This near‐tip strain information can be used to validate FEA models of fatigue. [ABSTRACT FROM AUTHOR]

The behavior of microstructural short fatigue cracks (20-100 µm in length on the same scale as the grain size) in the cast aluminum alloy A07710-T6 was investigated. Two heat treatment conditions have been used, an underaged and an overaged microstructure, chosen to have very similar tensile properties, so that the effects of precipitation and hence slip distribution on fatigue behavior could be studied at the same strength level. The results of short crack propagation tests performed on smooth specimens at 25℃ and R=0.1 are compared to conventional (long) fatigue crack propagation and threshold results under the same conditions. The short crack data is also compared to long crack tests conducted at constant maximum applied load (so that the R-ratio increases to a value above 0.8 as the threshold is approached). In conventional long crack tests, better low and high threshold crack propagation resistance is associated with the underaged microstructure. This behavior is also reflected in the thresholds obtained at high R. [ABSTRACT FROM AUTHOR]

Applying fracture mechanics theory to heterogeneous welded joints might lead to an uncertain assessment of fatigue crack propagation behavior and, consequently, an inaccurate estimation of the cyclic loading capacity and fatigue life of welded structures. Combining experimental testing and analytical equations of the marine overmatched welded joints of D32 marine structural steel provided a view of the influence of strength heterogeneity on fatigue crack growth (FCG) behavior under constant cyclic loading. FCG testing was conducted using compact tension specimens under different stress ratios. The effect of residual stress on the FCG behaviors of the heat-affected zones (HAZs) and fusion zones (FZs) of the compact tension (CT) specimens was examined in the overmatched welded joints. Subsequently, the welding residual stresses were removed by post-welding heat treatment (PWHT) to focus the FCGR assessment on the microstructural effect. The results indicated that the FCG rates (FCGRs) of the FZ and HAZ materials obviously varied in as-welded and stress-relieved states. The existence of residual stress in the overmatched welded joints led to a decrease in FCG rates and prolonged the fatigue crack propagation life for the FZs and HAZs. Moreover, the FCGR increased in the base metal (BM), HAZ, and FZ with the increase in the stress ratio. The FCG curves of these materials were fitted to correct the stress ratios using the NASGRO equation. Finally, an analytical analysis of the FCGR based on the NASGRO equation revealed the relationship between different stress ratios for different materials. [ABSTRACT FROM AUTHOR]

Several types of ground improvement methods that employ fiber-reinforcement have been developed in recent years. A series of consolidated drained triaxial compression tests has been conducted here to examine the effect of short fibers on the mechanical properties of Toyoura sand. Sand with 0%, 0.2%, 0.4%, and 1% fiber contents, prepared to yield random distribution, was sheared under several confining pressures and controlled via their initial relative densities. The test results showed that the maximum and residual deviatoric stresses increased, whereas the volumetric expansion decreased with an increase in fiber content. Although the stress ratio η (=q/p′) and specific volume changed depending on the fiber content and confining pressure with shear progression, they each reached the same values for a definite fiber content at the end of shearing, independent of initial relative density. In other words, the unique critical state line can be found for a definite fiber content. Moreover, the greater the fiber content, the larger the slope of the critical state line at the end of shearing. Additionally, as the length of fibers shortened with the same percentage of fiber inclusions in sand, the deviatoric stress and the stress ratio decreased, approaching the shear-strain-volumetric response of unreinforced sand.

Purpose – This study aims to propose a semiempirical and semitheoretical cyclic compaction constitutive model of coarse-grained soil filler for the high-speed railway (HSR) subgrade under cyclic load. Design/methodology/approach – According to the basic framework of critical state soil mechanics and in view of the characteristics of the coarse-grained soil filler for the HSR subgrade to bear the train vibration load repeatedly for a long time, the hyperbolic empirical relationship between particle breakage and plastic work was derived. Considering the influence of cyclic vibration time and stress ratio, the particle breakage correction function of coarse-grained soil filler for the HSR subgrade under cyclic load was proposed. According to the classical theory of plastic mechanics, the shearing dilatation equation of the coarse-grained soil filler for the HSR subgrade considering particle breakage was modified and obtained. A semiempirical and semitheoretical cyclic compaction constitutive model of coarse-grained soil filler for the HSR subgrade under cyclic load was further established. The backward Euler method was used to discretize the constitutive equation, build a numerical algorithm of “elastic prediction and plastic modification” and make a secondary development of the program to solve the cyclic compaction model. Findings – Through the comparison with the result of laboratory triaxial test under the cyclic loading of coarse-grained soil filler for the HSR subgrade, the accuracy and applicability of the cyclic compaction model were verified. Results show that the model can accurately predict the cumulative deformation characteristics of coarse-grained soil filler for the HSR subgrade under the train vibration loading repeatedly for a long time. It considers the effects of particle breakage and stress ratio, which can be used to calculate and analyze the stress and deformation evolution law of the subgrade structure for HSR. Originality/value – The research can provide a simple and practical method for calculating deformation of railway under cyclic loading.