Fatigue Life Ratio Research Articles

Evaluation on tension-compression anisotropic behavior of recycled asphalt mixture

The utilization of recycled asphalt pavement (RAP) is the effective way to improve resource conservation and reduce energy consumption. The asphalt mixture is a kind of typical anisotropic pavement materials due to its heterogeneity in composition and microstructure. This could lead to the differences of mechanical response between the tensile and compressive direction. However, there are limited researches to study the effect of RAP on the tension-compression anisotropic behavior of asphalt mixture. The strength, modulus and fatigue resistance tests are carried out and different loading modes are adopted. The results show that the tension-compression anisotropic behavior is more prominent with the increase of RAP content. The regenerant served as a kind of typical additive could alleviate this effect. In addition, the result of dynamic modulus test shows that the tension-compression anisotropic behavior has an increasing trend with the decrease of frequency and the increment of temperature. The ranking of fatigue life is opposite for the direct tensile and compressive loading mode, and the fatigue life ratio of compression to tension also show positive relation with the RAP content. Due to the difference in the stress mode, the fatigue life between the indirect tensile loading and four-point bending loading also show opposite trend, and the indirect tensile fatigue life has a larger discreteness.

Influence of friction and back stresses evolution on cyclic softening of laser powder bed fusion Ti-6Al-4V ELI alloy

Laser Powder Bed Fusion (LPBF) of Ti-6Al-4V ELI enables the fabrication of complex and individualized load-bearing patient-specific implants (PSI). These PSI are subjected to cyclic loading, which necessitates their fatigue performance evaluation. In this work, the fatigue properties of LPBF Ti-6Al-4V ELI in heat-treated conditions were characterized by studying the low cycle fatigue (LCF) behavior and underlying deformation mechanism. The fully reversed strain-controlled fatigue tests were performed at various strain amplitudes at room temperature. The ratio of fatigue life of conventional wrought alloy and LPBF Ti-6Al-4V ELI at the lowest (0.8 %) and the highest (1.8 %) strain amplitudes were found to be approximately 2.7 and 4.5, respectively. Further, the softening response during fatigue loading was correlated to the variation in the back and friction stresses. The TEM observations revealed that the dislocation pileup along α/β interfaces caused an increase in dislocation density, which drives the increase in back stress. However, the ease of slip transmission at high strain amplitude (1.8 %) reduced the heterogeneity between α and β phases, causing a decrease in the back stress. The TEM observations further suggested that the dislocation annihilation and subsequent rise in dislocation-free zones in α-phase reduced the friction stress at all strain amplitudes, which resulted in cyclic softening of LPBF Ti-6Al-4V ELI.

Effect of salt–fog spray environment on bending fatigue properties of 3D woven composites

In this study, the effect of salt–fog spray corrosion environment on bending fatigue properties of three-dimensional (3D) woven composites was investigated. Three test environmental conditions, namely a normal environment, two cycles of salt–fog spray corrosion environment, and four cycles of salt–fog spray corrosion environment, were designed. In addition, the salt–fog spray corrosion mechanism, the bending fatigue properties, damage mechanisms, and failure modes of 3D woven composites were studied. The results showed that the bending strength and bending modulus decreased by 5.5 and 9.3%, and 2.27 and 3.45% after two and four salt–fog spray cycles, respectively, compared with that of the normal environment. The bending fatigue properties of 3D woven composites were related to the applied stress and salt–fog spray cycles. The salt–fog spray environment was responsible for the degradation of the interface bonding strength. The maximum reduction ratio of bending fatigue life after salt–fog spray treatment exceeded 70%. The brittle fracture characteristics of 3D woven composite yarn were more pronounced with an increase in salt–fog spray aging cycles.

Matching relationship of low-cycle fatigue life and fatigue design method of concentrically braced frames with H-section steel

Simulations on 192 concentrically braced frames with H-section steel (Q355B) are carried out to investigate their low-cycle fatigue performance. The fatigue life of a steel-braced frame is predicted using a multiaxial fatigue damage parametric model. To depict the fatigue failure sequence and the matching relationship of the fatigue life between the two components in the braced frame, the fatigue life ratio (β) is introduced. This ratio represents the gusset plate's fatigue life to the brace's fatigue life. Simulated results are analyzed, and β is found to be positively correlated with four influencing factors, the width-to-thickness ratio of the brace flange, connection coefficient, ratio of the column length to beam length, and slenderness ratio of the gusset plate. Also, β is found to be negatively correlated with the slenderness ratio of the brace. Based on the Bayesian updating method, a probabilistic model is formulated to predict β of a steel-braced frame. Accordingly, a fatigue design method is proposed, which contributes to avoiding the in-coordination of seismic capacity caused by the significant difference between the brace’s and gusset plate’s fatigue life within the steel braced frame. The proposed fatigue design method has the potential to serve as a reference for improving design specifications.

An optimization design method of asymmetric wheel bearing with equal friction torque and equal fatigue life in two rows

Aiming at the problem of asymmetric wheel bearings with inconsistent friction torque and service life of the left and right rows, this paper proposed a different optimization design method for asymmetric wheel bearings. Firstly, the calculation model of friction torque and fatigue life of asymmetric wheel bearings is established based on the proposed quasi-statics, and the model's accuracy is verified. Furthermore, combined with the Cooperative Equilibrium Point Method, the optimization method of equal friction and equal life for the left and right rows, that is, CEPM-NSGAII, is proposed, which takes the ratio of friction torque and the ratio of fatigue life for the left and right rows as the objective function, and optimizes the structural parameters of the left and right rows such as the rolling element diameters, the pitch circle diameters, and the number of rolling elements, and so on. After optimization, the friction torque ratio and fatigue life ratio of the left and right rows tend to be close to 1, which considerably improves the performance imbalance between the left and right rows of the bearings, meanwhile prolongs the fatigue life of the bearings and reduces the friction torque of the bearings. In addition, the superiority and reliability of the CEPM-NSGAII optimization method are verified by comparison.

Experimental study on the interface fatigue between track slab and self-compacting concrete for CRTS III slab track

With the rapid development of high-speed railways, the CRTS III slab track has become one of the most important track structures. The interface between the precast track slab and cast-in-place self-compacting concrete is easily damaged under fatigue loads. However, experimental research in this field is still relatively lacking. By performing static and fatigue splitting tensile tests, the study first obtained interface failure characteristics between the track slab and self-compacting concrete. Most of the interface failures were mortar failures and mortar-aggregate bond failures, and only a few were aggregate failures. Then, the evolution law of interface strain was analyzed. The interface strain was large in the middle and small on both sides. The change of interface strain with fatigue life ratio was divided into three stages: rapid growth, stable growth, and unstable growth stages. Moreover, the S-N curve of the interface was obtained. Finally, based on the residual strain, an interface fatigue damage model was established to reveal the evolution law of damage variables with fatigue life ratio under different stress levels. This study makes up for the insufficiency of current interface damage research on CRTS III slab track and provides the reference for the subsequent numerical simulation and engineering application.

Performance characterization of asphalt mixtures under different aging levels: A fracture-based method

This paper proposes a straightforward approach to characterize the fracture properties and fatigue life of asphalt mixtures over the service time. Since the serviceability of flexible pavements varies as they age, assessing the performance of asphalt mixes under aged conditions is essential. To investigate the sensitivity of fracture-related parameters to aging, accelerated laboratory aging, which is conditioning asphalt concrete samples in a force draft oven for different aging times (0, 3, 5, 7, and 9 days), was used. The Semi-Circular Bending (SCB) test at 25 °C was carried out on neat and activated carbon-modified samples to examine the fracture responses of asphalt mixes. First, force–displacement curves at failure were plotted. Then, fracture-related parameters (e.g., peak load, fracture toughness, strain energy, and J-integral) and damage levels corresponding to each fracture criteria were measured versus aging levels. In addition, the fatigue life ratio was determined to measure the influence of aging on the long-term performance of asphalt mixtures. To incorporate the effect of aging on the overall cracking resistance of asphalt mixtures, different fracture-related parameters versus service time were studied. Experimental findings suggest that the area under the fracture property versus service time can provide a reliable index for evaluating the long-term performance of asphalt mixtures. In addition, statistical analysis was performed to assess the impact of aging on fracture-related parameters obtained from the SCB fracture test. The proposed method was able to simultaneously factor in the fracture resistance and the rate of damage development during flexible pavement service life.

Time-temperature equivalence and unified characterization of asphalt mixture fatigue properties

This work presents a new method for evaluating the time-temperature equivalence and unified characterization of the fatigue performance for asphalt mixtures. For this purpose, direct tensile strength tests and direct tensile fatigue tests were carried out on asphalt mixtures at different temperatures and loading rates. A time-temperature-dependent stress ratio was established. By exploring the correlation between stress ratio and fatigue life, a new fatigue model considering the effect of temperature and loading time was built. The time-temperature equivalent of fatigue performance was confirmed by analysis of the fatigue dates under several temperatures and loading frequencies. The results showed that the direct tensile strength of the asphalt mixture changed non-linearly with the variation of the loading rate or temperature. The stress ratio was also related to temperature and loading rate. The time-temperature stress ratio was linearly related to fatigue life in a double logarithmic coordinate system, and a new SN fatigue curve was formed. The fatigue life under several temperatures and various loading frequencies can be described in one fatigue model and the time-temperature equivalent can be explored. The master curve of fatigue life or stress ratio was built. The time-temperature superposition principle was applicable for fatigue life estimation and stress ratio calculation. The fatigue life under different loading frequencies and various temperatures of the pavement in service can be completely estimated. The relative error between the test results and the calculated values is less than 30%.

Evaluation of effect of moisture on fatigue performance of pavement designed with recycled asphalt mixtures

The moisture resistance of dense- and gap-graded bituminous mixes prepared with the replacement of virgin aggregates and fresh bitumen with reclaimed asphalt pavement (RAP) was evaluated using indirect tensile strength (ITS) and resilient modulus ( Mr). The mechanistic analysis was performed to estimate the effect of moisture resistance on the fatigue performance of thin and thick pavement sections designed with dense- and gap-graded bituminous mixes. The ITS ratio and Mr ratio results indicate that the resilient modulus ratio is more sensitive to moisture damage in bituminous mixes than the ITS ratio. In addition, the results of the fatigue life ratio indicated that the gap-graded mix prepared with different RAP content has better resistance to moisture-related cracking in thick pavement sections than the dense-graded mix. However, the effectiveness of gap-graded and dense-graded mixes prepared with different RAP content on moisture-related cracking depended on the subgrade strength for thin pavement sections.

Fatigue Behavior and Healing Properties of Aged Asphalt Binders

This study aims to investigate the fatigue behavior and healing properties of aged asphalt binders. Both 70# and SBS-modified asphalt binders were aged using a rolling thin-film oven test (RTFOT), and their physical properties were analyzed. Their fatigue behavior and healing properties were investigated using a dynamic-shear-rheometer time-sweep test. The influence of healing on fatigue behavior was evaluated in terms of the fatigue life ratio (FLR), and a new index was defined (accumulated dissipation-energy ratio, ADER) to evaluate the healing properties of aged asphalt binders. Aging reduced the penetration and ductility of both the asphalt binders, and large aging degrees increased their softening points. Small aging degrees slightly decreased the softening point of the SBS-modified asphalt binder but increased that of 70# asphalt binder. The former had a better thermal-oxidative aging resistance than the latter. Aging increased the complex shear modulus of the binders, resulting in a longer fatigue life under controlled-stress conditions. The fatigue life of aging asphalt binders obeyed a good (R2>0.90) double-logarithmic linear relationship with the stress level. Healing recovers the asphalt complex shear modulus and extends its fatigue life. Additionally, the FLR and ADER increased with a decrease in aging degree and an increase in the healing period.

Effect of stress ratios on corrosion fatigue life of high‐strength steel wires

AbstractIn order to discuss the influence of the stress ratio on the corrosion fatigue life of high‐strength steel wires, a theoretical and experimental investigation was conducted on corroded steel wires at three different stress ratios (R = 0.1, 0.3, and 0.5) under axial tensile fatigue loading. Different S‐N curves of corroded steel wires were regressed from test data. The stress method based on eight mean stress correction models, the strain energy method, and the facture mechanics method considering environmental corrosion and crack closure were proposed to estimate the fatigue life. Preliminary results show that corrosion can reduce the ultimate strength, the yield strength, and the fatigue life. There is a negative correlation between corrosion fatigue life and stress ratio. When R > 0, fatigue life predicted results by using the Morrow and Marin models in the stress method are more efficient and accurate than other models. Likewise, the Zheng model in the fracture mechanics method is in better agreement with test results. The error and scatter of the strain energy method are relatively large. Therefore, the Morrow, Marin, and Zheng models are more suitable to predict the corrosion fatigue life of high‐strength steel wires under different stress ratios.

Presentation of Predictive Models for Two-objective Optimization of Moisture and Fatigue Damages Caused by Deicers in Asphalt Mixtures

Abstract The best way to deal with the freezing of the road surfaces is to use deicers, especially in cold areas. The presence of moisture causes various stresses in the pavement and reduces the strength of mixtures. Using anti-stripping agents can decrease the moisture sensitivity of asphalt mixtures. Researchers have evaluated the impact of different deicers on the moisture sensitivity of asphalt mixtures. However, fewer studies have been conducted on the effect of these materials on fatigue failure and thermodynamic parameters of asphalt mixtures. Moreover, fewer studies have been performed to find the exact optimum amount of additives for maximizing the two objectives of tensile strength ratio (TSR) and fatigue life ratio (NFR) concurrently in moisture and fatigue damages. So in this research, the moisture sensitivity and fatigue failure of asphalt mixtures under the influence of different deicers, including calcium magnesium acetate (CMA), potassium acetate (PA), and sodium chloride (NaCl), were investigated using nanohydrated lime (NHL) as an anti-stripping agent. The surface free energy (SFE) of materials and the permeability of asphalt mixtures were examined, and a boiling water test was applied. Finally, the prediction models of multivariate regression (MVR), group method of data handling (GMDH), and genetic programming (GP) were provided to obtain optimum additive percentage with two objectives of TSR and NFR. The results showed that GP had a higher R-value than the 2 other methods such that the R-value of GP for TSR and NFR was 98.8 % and 99.8 %, respectively. The optimization results showed that 1.17 %, 1.34 %, 0.87 %, 1.21 %, and 1.06 % NHL, respectively, were the best optimum values to maximize the TSR and NFR simultaneously in all samples and samples saturated in water, CMA, NaCl, and PA solutions.

RETRACTED: Research on Fatigue Prediction Model of Asphalt Mixture with High RAP Content

Asphalt pavement hot recycling technology can improve resource utilization efficiency, reduce energy waste and CO2 emissions, and bring huge economic and social benefits, further promoting the realization of “carbon peak and carbon neutrality”. This paper uses single logarithmic regression fitting on the fatigue failure life of recycled asphalt mixture with high RAP content to characterize the influence of RAP content (R), stress ratio (C), loading frequency (H) and test temperature (T) on the fatigue life of recycled asphalt mixture. Subsequently, the relationship between fatigue life and stress ratio of recycled asphalt mixture, under the influence of different RAP content, loading frequency and test temperature was analyzed. The results showed that the fatigue life of recycled asphalt mixture decreased with an increase in RAP content, stress ratio and test temperature, and decreased as loading frequency increased. Fatigue life and stress ratio were found to be approximately logarithmic, and based on the relationship between fatigue equation parameters a, b and R, T, H, the fatigue prediction model for recycled asphalt mixtures with independent variables R, C, H, and T was established.

Effect of Loading Frequency Ratio on Multiaxial Asynchronous Fatigue Failure of 30CrMnSiA Steel.

Multiaxial asynchronous fatigue experiments were carried out on 30CrMnSiA steel to investigate the influence of frequency ratio on fatigue crack initiation and propagation. Test results show that the surface cracks initiate on the maximum shear stress amplitude planes with larger normal stress, propagate approximately tens of microns, and then propagate along the maximum normal stress planes. The frequency ratio has an obvious effect on the fatigue life. The variation of normal and shear stress amplitudes on the maximum normal stress plane induces the crack retardation, and results in that the crack growth length is longer for the constant amplitude loading than that for the asynchronous loading under the same fatigue life ratio. A few fatigue life prediction models were employed and compared. Results show that the fatigue life predicted by the model of Bannantine-Socie cycle counting method, section critical plane criterion and Palmgren-Miner’s cumulative damage rule were more applicable.

An improved manson-halford model for multi-level nonlinear fatigue life prediction

The Manson-Halford (M−H) nonlinear fatigue damage model is widely used for fatigue damage analysis. It, however, does not consider the load interaction effect. This paper presents an improved M−H model with a load interaction factor defined as the ratio of the first and second stress levels. The characteristic exponent of the M−H model is modified by multiplying the load interaction factor and fatigue life ratio. The characteristic exponent can consider the load interaction effect and the load sequence effect under multi-level loading. Experimental data from five materials under two-level and multi-level stress loadings verify the accuracy of the proposed model.

Estimating the impact of automated truck platoons on asphalt pavement’s fatigue life using artificial neural networks

ABSTRACT Automated truck platooning may cause up to 85% reduction in truck following distance compared to conventional vehicles and therefore reduces rest periods between loading cycles on pavement materials. Fatigue cracking is one of the major distresses in asphalt pavement structures, and pavement fatigue life is highly dependent on rest periods between loading cycles. In this paper, Artificial Neural Network (ANN) modeling was applied on the existing NCHRP 09-44A project’s database of extensive laboratory beam fatigue testing results on asphalt mixtures with various rest periods. The developed ANN model was used to predict number of cycles to failure as a function of rest periods and to estimate the impact of truck platooning on pavement fatigue life. In addition, a stand-alone linear multivariate regression equation of fatigue life was developed independently from the ANN model. Based on the results, an 85% reduction in the following distance of platooned trucks may lead to between 7% and 25% reduction in pavement fatigue life. The Platooning Fatigue Life Ratio (PFLR) was found to be dependent on temperature, applied strain level, and mixture parameters. Finally, the applied strain level was the most significant testing factor and binder grade was the most significant mixture parameter on PFLR.

Presentation of a New Deicer with the Least Moisture and Fatigue Failures in Asphalt Mixtures

One of the most frequently applied materials in cold weather is deicer, which is utilized to maintain winter roads. The effect of various deicers on moisture sensitivity has been explored by researchers in the asphalt industry; however, their effect on thermodynamic parameters and fatigue behavior of asphalt has rarely been studied. In this study, the effect of NaCl, potassium acetate, and calcium magnesium acetate deicers on fatigue and moisture performances of asphalt was explored using nano hydrated lime. Two prediction models of fatigue life ratio (NfR) and tensile strength ratio (TSR) were presented using genetic programming and group method of data handling to obtain optimal nano hydrated lime content. Finally, according to the results of deicer-forming minerals, two new optimal deicers were obtained, and their effect on TSR and NfR was compared with the three above-mentioned deicers. Results showed that TSR and NfR of calcium magnesium acetate saturated samples were higher than those of NaCl and potassium acetate saturated samples. Moreover, by modifying the properties of bitumen with nano hydrated lime, adhesion free energy, cohesion free energy, and debonding energy amounts increased, which indicates an increase in locking between aggregates and bitumen. By determining the minerals that make up deicers using the energy-dispersive X-ray test, two new deicer compounds were made that had better performance over NaCl and potassium acetate. By optimizing additive percentage in genetic programming method (due to higher accuracy), 1.05% nano hydrated lime was proposed as the best optimal amount for the new optimal deicer to simultaneously increase TSR and NfR.

Numerical study of fatigue behavior of the aluminum 7075-T6 cantilever beam with angular cracks in different stress ratios

The numerical simulation of fatigue behavior of the Aluminum 7075-T6 cantilever beam with an angular crack has been investigated. Cracks are located separately in three different positions of the investigated beam. To predict the fatigue behavior of the cantilever beam the crack propagation was manually simulated. Compression load is applied in different stress ratios between zero and one; then, the obtained numerical results of this research are compared with the experimental results. It is observed that increasing the stress ratio increases the percentage of the fatigue life of the sample significantly. Ascending growth of fatigue life is slow and more severe by increasing of the stress ratio for the first and the third position, respectively. By increasing the stress ratio, the rate of deviation of the crack decreases and it converges to 0° in parallel to the width of the beam. This result is also observed with an increase in the distance from the support of beam. Furthermore, it is also revealed that by the increase in the initial length of the crack, the fatigue life initially reduces with smaller ratios. However, along the larger cracks, the decreasing ratio of fatigue life increases significantly. © 2021 Growing Science Ltd. All rights reserved.

Variable Amplitude Fatigue Life Prediction of Rock Samples Under Completely Reversed Loading

Many rock structures may experience cyclic loading with variable amplitude. Therefore, considering the fatigue behavior of rocks subjected to different loading sequences is necessary. In this study, the accumulated fatigue damage for a Green onyx rock sample with two-step high to low sequences of loading levels was investigated under completely reversed loading condition. In order to apply completely reversed loading to the rock specimens, a new rotating fatigue test machine is employed. A comparison between the predicted behavior of Manson damage curve approach and experimental data was conducted. The results showed that the applicability of Manson damage curve approach depends on the fatigue life ratio of specimens subjected to high-low loading conditions. A new damage curve model was proposed based on the experimental observation and verified with a large number of laboratory tests. Also, the results manifested the higher loading level plays a significant role in the fatigue life of samples. Since the amplitude of the dynamic load conducted on the rock structures is not constant, it is necessary that variable amplitude loading to be taken into account. Otherwise, the prediction of fatigue life is overestimating.

Prediction and pareto-based multi-objective optimization of moisture and fatigue damages of asphalt mixtures modified with nano hydrated lime

Moisture sensitivity can lead to damages due to adhesion and cohesion in asphalt mixtures that cause serious damages to the pavement. Adhesion between bitumen and aggregate is a basic prerequisite for the proper performance of asphalt mixtures. The role of nano hydrated lime (NHL) as an anti-stripping agent has been extensively studied in asphalt pavements. In this study, in addition to investigating the effect of NHL as bitumen modifier on moisture and fatigue damages, and bitumen-aggregate adhesion and bitumen membrane cohesion using surface free energy (SFE) concept, the prediction model to achieve optimal additive percentage with two objectives of moisture sensitivity and fatigue failure by multivariate regression (MVR), group method of data handling (GMDH) and genetic programming (GP) were provided. By the use of the modified non-dominated sorting genetic algorithm II (NSGA-II) approach, Pareto fronts were then plotted. In addition, boiling water testing was applied to examine the sensitivity of mixtures to moisture. To simulate environmental conditions, asphalt mixtures were placed in freeze–thaw (F-T) cycles of 1, 3 and 5. 85–100 penetration grade base bitumen was modified with 0.5%, 1% and 1.5% NHL (by the weight of bitumen). The results indicated that by decreasing the number of yellow pixels in the image processing of modified mixtures with NHL, modification of bitumens decreased the moisture sensitivity of specimens. Using NHL increased the resistance of the specimens to moisture and fatigue damages. The amount of indirect tensile strength (ITS) and fatigue life of asphalt mixtures reduced by rising the number of F-T cycles. The highest increase in ITS and fatigue life was obvious in modified mixtures with 1.5% and 1% NHL, respectively. The results of calculating the surface free energy (SFE) components of the base and modified bitumens showed that using NHL enhanced the total SFE amount of bitumens. Also, using the NHL increased cohesion free energy (CFE), adhesion free energy (AFE) and debonding energy (DE) of modified bitumens and decreased the permeability of asphalt mixtures (PAMs) amount. Among the various methods, the GMDH method had the highest R2. So that the R2 value of GMDH for tensile strength ratio (TSR) and the ratio of fatigue life (NFR) was 93.9% and 86.9%, respectively. The two-objective optimization results indicated that 1.29% NHL was the best optimal amount to maximize the TSR and NFR values simultaneously.