Stress-controlled Mode Research Articles

Analysis of short-term self-healing performance of asphalt mixture under a three-point bending fatigue test

To evaluate the self-healing performance of asphalt mixture under repeated loads, indoor three-point bending fatigue tests and self-healing tests were conducted on asphalt mixture AC-13. The stress control mode was selected to test the fatigue resistance of the mixture, and the dissipated energy recovery value and visco-elastic ratio were proposed to evaluate the self-healing performance of the mixture. The experimental results show that there is a good linear relationship between fatigue life and fatigue stress, and the damage degree to the mixture is exponentially related to the load times. The numerical dispersion of flexural tensile modulus is large, which is not suitable for evaluating the self-healing performance of the mixture. As the number of loading cycles increases, the hysteresis dissipated energy of the mixture gradually decreases and tends to stabilize. After the loading interval, due to the self-healing effect, the visco-elastic performance of the asphalt material is partially restored. The initial dissipated energy before and after interval can be used as an evaluation index for self-healing behavior, and there is a good linear relationship between the initial dissipated energy and the damage degree. Due to the deformation migration of the mixture during the initial loading stage before and after interval, the visco-elastic ratio has changed, and this change becomes more pronounced with the damage degree of the mixture, indicating that the self-healing ability of the mixture has also been improved.

Using the indirect tensile fatigue test to evaluate fatigue characterisation of asphalt mixtures

Fatigue cracking is a principal structural failure mode in asphalt pavement layers, resulting from repeatedtraffic-induced loading stresses. Therefore, understanding fatigue deterioration behaviour is crucial for ensuring effective pavement design. In recent years, the indirect tensile fatigue test has become one of the mostcommonly used methods for evaluating the fatigue behaviour of asphalt mixtures, owing to its simplicity andsuitability for cylindrical specimens either produced in the laboratory or cored from pavement constructionsites. In this research paper, the indirect tensile fatigue test was employed to assess the stiffness modulus andfatigue behaviour of one unmodified asphalt mixture (DBM50) and two polymer-modified mixtures (EME2and SMA) in stress-controlled mode across various temperatures. The results indicated that the indirect tensile fatigue test worked well and it can be considered to characterise effectively fatigue behaviour of differentasphalt mixtures in Vietnam. In addition, the test results revealed that the SMA mixtures exhibited the bestperformance at both 20 °C and 10 °C compared to other mixtures. Specially, the fatigue lines for DBM50 andSMA at 20 °C were positioned above those at 10 °C, while the fatigue lines for EME2 lines remained quitesimilar across both temperature levels.

Comparation of non-proportional hardening behavior and microscopic mechanism for CP-Ti under strain-controlled and stress-controlled multiaxial low cycle fatigue

Proportional and non-proportional multiaxial low cycle fatigue tests were performed on commercial pure titanium (CP-Ti), employing both strain-controlled and stress-controlled modes. CP-Ti exhibits a four-stage characteristic under higher applied strain amplitude. For other cases and under stress-controlled mode, the initial hardening dissipated, giving way to a typical three-stage cyclic softening characteristics. Two failure modes, fatigue failure and ratcheting failure, occur depending on the applied stress amplitude. CP-Ti exhibits obvious asymmetric strain response under symmetric stress-controlled mode depending on the loading level. CP-Ti demonstrates non-proportional hardening under both strain-controlled mode and stress-controlled mode with different microscopic mechanisms. The additional hardening due to non-proportional loading results in an increase in the axial response stress with increasing multiaxial strain ratio. Interactions between dislocations with different slip systems hinder the development of stable dislocation structures, leading to pronounced non-proportional hardening of CP-Ti under strain-controlled mode. As for stress-controlled mode, the significant growth of twin content improves the grain boundary strength, leading to the non-proportional hardening of CP-Ti.

Cyclic deformation response of annealed low-carbon steel: Insights from ratcheting and LCF experiments

Low cycle fatigue (LCF) and ratcheting experiments were carried out on annealed low-carbon steel at room temperature within a laboratory environment, utilising stress and strain control modes. The annealed low-carbon steel consistently demonstrates a cyclic softening response over its LCF lifespan, across all tested strain amplitudes. Notably, it was observed that ratcheting strain rises while ratcheting life declines with both rising mean stress and stress amplitude. Annealed low-carbon steel, being entirely ferritic and lacking precipitation or substitutional solid solution strengthening or hard phase strengthening, exhibits a restricted ability to withstand or alleviate the accumulation of ratcheting strain, particularly under very low mean stress conditions. In both LCF and ratcheting, significant substructure formation was detected. Nevertheless, there was no discernible difference in substructure formation between LCF and ratcheting when employing electron channelling contrast imaging techniques. The existing mean stress-based fatigue life prediction model has successfully forecasted ratcheting and LCF life within the 102–105 cycles range. A novel approach utilising modulus is introduced to characterise the cyclic hardening/softening behaviour of alloys in stress and strain-controlled experiments. The cyclic hardening model based on modulus effectively captures the responses observed in cyclic hardening/softening during LCF and ratcheting experiments.

Cyclic behavior and damage mechanism of 304 austenitic stainless steel under different control modes

In this work, low cycle fatigue experiments under both strain and stress control modes with different loading levels were conducted on 304 austenitic stainless steel at ambient temperature to discuss the influence of loading mode and level on the cyclic response and physical mechanism. The results demonstrated that the cyclic response generally exhibited three stages: primary cyclic hardening, subsequent cyclic softening, and the secondary hardening finally. The degree of each hardening and softening stage was depended on not only the loading modes but also the strain/stress level. Accelerated cyclic softening and retarded secondary hardening occurred under the stress mode, which made a higher low-cycle fatigue life during stress cyclic loading than that for the strain control mode, especially at relatively high strain/stress level. The secondary hardening stage, occupying the main portion of the lifetime, was proved to be associated with the development of martensitic phase and the extension and intersecting of stacking faults or micro-twin.

The effect of precipitates on low-cycle fatigue behavior of WE54 magnesium alloys under stress-controlled mode

The precipitates have a significant influence on fatigue behavior in magnesium (Mg) alloy. In this work, the effects of precipitates on deformation mode, cracking mode and mechanical behavior during low-cycle fatigue under stress-controlled mode in WE54 Mg alloy at room temperature (RT) was analyzed quantitively and statistically via quasi-in-situ electron backscattered diffraction (EBSD), slip trace analysis, coupled with transmission electron microscopy (TEM). The results reveal that precipitates promoted the activation of pyramidal < c + a > dislocation slip and suppressed the activation of tension twinning in the T6 alloy. In the T4 alloy, persistent slip band (PSB) induced cracking together with intergranular cracking dominated fatigue damage, while intergranular cracking was the primary cracking mode in the T6 alloy. The obvious cyclic hardening behavior of the T4 alloy was attributed to dynamic precipitation, whereas suppressed dynamic precipitation, restrained multiplication of dislocations, together with the appearance of PFZ generated the marginal cyclic hardening behavior in the T6 alloy. Both the T4 and T6 alloys exhibited ratcheting behavior, and precipitates suppressed ratcheting deformation in the T6 alloy. Moreover, the underlying mechanism for the higher fatigue resistance in the T6 alloy was also discussed.

Mechanical Resistance of Hot-Mix Asphalt Using Phosphorite as Filler

Phosphorites (PF) have small particle sizes and interesting chemical compositions to be used as filler in asphalt mixtures. The present study assessed the performance that a hot-mix asphalt (HMA) displays when the natural filler (NF) is completely replaced by PF. X-ray diffractometry (XRD), X-ray fluorescence (XRF), and scanning electron microscope (SEM) tests were carried out on NF and PF particles. Asphalt mastic was manufactured using a weight ratio of filler (NF and PF) to asphalt binder of 1∶1.2. Penetration, softening point, viscosity, and linear amplitude sweep test were performed on the asphalt mastic. The following tests were carried out on mixes manufactured with NF (control) and PF (HMA-PF): Marshall, indirect tensile strength, Cantabro, resilient modulus, permanent deformation, and fatigue under stress-controlled mode. Additionally, moisture damage resistance was assessed through the tensile strength ratio (TSR) parameter. The HMA-PF mix displayed a better performance in all the evaluated properties, without increasing the optimum asphalt binder content. PF as fillers could be an interesting alternative in the manufacture of HMA mixtures subjected to high temperature climates.

Asymmetrical multiaxial low-cycle fatigue behavior and life prediction of CP-Ti under non-proportional stress-controlled mode

Asymmetrical multiaxial fatigue tests were performed. A new quantification parameter is proposed to represent the difference in velocity during ratcheting accumulation. Although the stress–strain response under asymmetric loading is similar to that under symmetric loading, substantial deteriorations of life are observed. The threshold value for ratcheting strain accumulation of axial stress amplitude is closer to 287 MPa. The brand-new stress parameters-based KBM-PH model with mean stress correction is the best overall among a series of models based on strain and stress parameters with or without mean strain and stress corrections with the best accuracy and ease of use.

Liquefaction proneness of stratified sand-silt layers based on cyclic triaxial tests

Most studies on liquefaction have addressed homogeneous soil strata using sand or sand with fine content without considering soil stratification. In this study, cyclic triaxial tests were conducted on the stratified sand specimens embedded with the silt layers to investigate the liquefaction failures and void-redistribution at confining stress of 100 kPa under stress-controlled mode. The loosening of underlying sand mass and hindrance to pore-water flow caused localized bulging at the sand-silt interface. It is observed that at a silt thickness of 0.2 H ( H is the height of the specimen), nearly 187 load cycles were required to attain liquefaction, which was the highest among all the silt thicknesses with a single silt layer. Therefore, 0.2 H is assumed as the optimum silt thickness ( t opt ). The silt was placed at the top, middle and bottom of the specimen to understand the effect of silt layer location. Due to the increase in depth of the silt layer from the top position (capped soil state) to the bottom, the cycles to reach liquefaction ( N cyc,L ) increased 2.18 times. Also, when the number of silt layers increased from single to triple, there was an increase of about 880% in N cyc,L . The micro-characterization analysis of the soil specimens indicated silty materials transported in upper sections of the specimen due to the dissipated pore pressure. The main parameters, including thickness ( t ), location ( z ), cyclic stress ratio (CSR), number of silt layers ( n ) and modified relative density ( D r,m ), performed significantly in governing the liquefaction resistance. For this, a multilinear regression model is developed based on critical parameters for prediction of N cyc,L . Furthermore, the developed constitutive model has been validated using the data from the present study and earlier findings. ©2022 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ).

Modeling the Effects of Particle Shape on Damping Ratio of Dry Sand by Simple Shear Testing and Artificial Intelligence

This study investigates the effects of sand particle shape, in terms of roundness, sphericity and regularity, on the damping ratio of a dry sand material. Twelve different cyclic simple shear testing scenarios were considered and applied using vertical stresses of 50, 150 and 250 kPa and cyclic stress ratios (CSR) of 0.2, 0.3, 0.4 and 0.5 in both constant- and controlled-stress modes. Each testing scenario involved five tests, using the same sand that was reconstructed from its previous cyclic test. On completion of the cyclic tests, corresponding hysteresis loops were established to determine the damping ratio. The results indicated that the minimum and maximum damping ratios for this sand material were 6.9 and 25.5, respectively. It was observed that the shape of the sand particles changed during cyclic loading, becoming progressively more rounded and spherical with an increasing number of loading cycles, thereby resulting in an increase in the damping ratio. The second part of this investigation involved the development of artificial intelligence models, namely an artificial neural network (ANN) and a support vector machine (SVM), to predict the effects of sand particle shape on the damping ratio. The proposed ANN and SVM models were found to be effective in predicting the damping ratio as a function of the particle shape descriptors (i.e., roundness, sphericity and regularity), vertical stress, CSR and number of loading cycles. Finally, a sensitivity analysis was conducted to identify the importance of the input variables; the vertical stress and regularity were, respectively, ranked as first and second in terms of importance, while the CSR was found to be the least important parameter.

Dual frequency domain characteristics of ratcheting behavior of AZ31B alloy under asymmetrically stress-controlled loading mode

Dual frequency domain characteristics of ratcheting behavior of AZ31B alloy under asymmetrically stress-controlled loading mode

"Ladetes"-A novel device to test deformation behaviors of hydrate-bearing sediments.

Natural gas hydrate (NGH) exploitation is severely restricted by geotechnical problems. Deformation behaviors of the hydrate-bearing strata (HBS) control the occurrence and evolution of geotechnical problems during extracting natural gas from HBS. In this paper, a novel approach named Ladetes is introduced to evaluate the lateral deformation behaviors of the near-wellbore and fracture-filling regions of the HBS. The pressuremeter test and the flat dilatometer test are designed to simulate the inner boundaries of an NGH-producing well and an artificial stimulation fracture for the first time. The device can realize the in situ hydrate formation prior to the experiment and axial loading application throughout the experiment. Both the strain control mode and the stress control mode can be achieved to estimate the deformation characteristics of HBS under different downhole conditions. Prime experiments proved their adaptability and reliability. The Ladetes provides an effective and alternative way of obtaining geotechnical parameters for HBS.

Fatigue Properties and Damage Characteristics of Polyurethane Mixtures under a Stress Control Mode

A polyurethane mixture (PUM) is an energy-saving and emission-reducing pavement material with excellent temperature stability; however, the fatigue properties and fatigue damage models of PUM still require further research. Therefore, four-point bending static load tests, fatigue tests, and digital speckle correlation method (DSCM) tests with different load levels of PUM and styrene butadiene styrene (SBS)-modified asphalt mixture (SMA) were carried out. The fatigue life, stiffness, midspan deflection, and maximum tensile strain were obtained and compared. The fatigue damage factor calculation method of PUM based on stiffness degradation was proposed, and the fatigue damage function of PUM at different load levels was fitted. The results show that the fatigue life of PUM was much larger than that of SMA, and the static loading failure and fatigue failure modes of PUM were both brittle. The fatigue damage of PUM exhibits an obvious three-stage damage law: the rapid development stage (accounting for about 10–20% of the fatigue life), the deformation stability expansion stage (accounting for about 70–80% of the fatigue life), and the instability development stage (accounting for about 10–20% of the fatigue life). The fatigue damage factors (DB) were calculated based on stiffness, according to DB=EI0−EInrEI0−EINr, and the fatigue damage functions of PUM were fitted based on the stiffness degradation, according to fnN=1−1−(n/N)a(1−n/N)b. The fatigue damage fitting curves have good correlation with the calculation results of the damage factor based on test data, which can predict the stiffness degradation of PUM at different load levels. The results can help further the understanding of the fatigue characteristics and damage mechanism of PUM, which will provide theoretical support for the application of PUM in pavement structures.

The role of prior creep duration on the acoustic emission characteristics of rock salt under cyclic loading

This study aimed to investigate the acoustic emission (AE) behavior of rock salt under combined creep and fatigue. The loading path was in a stress-controlled mode and contained a constant stress load with different durations, followed by cyclic loading. The AE counts, peak frequency, amplitude, b-value, and RA (rise time/amplitude)-AF (average frequency) distribution were systematically analyzed. The results show that the AE counts gradually increased during loading and existed sporadically within the prior creep stage and frequently in the subsequent cyclic loading phase. The peak frequency exhibited a zonal distribution and was divided into low, medium, and high parts. A longer prior creep duration induced a wider frequency distribution range, a higher average amplitude, and a reduction in b-value. According to the RA-AF distribution, the tensile cracks constituted more than 90% of the total cracks, and the prior creep duration decreased the shear crack propagation compared with the cases without prior creep. The results indicate that prior creep increases the crack dimensions and damage severity and makes the salt sample prone to fracture in the subsequent cyclic loading.

Rheological modeling and simulation of semi-solid slurry based on experimental study

The rheological behavior of semi-solid slurry is systematically studied via three different testing modes under either shear stress or shear rate control mode. Then the non-Newtonian constitutive parameters, consistency coefficient k and power-law index n, are determined by using Power-Law (PL) and Herschel-Bulkley (HB) models. Results indicate that the viscosity curve from the shear stress control test is more suitable for the PL model fitting and numerical simulation. This investigation not only provides important insights into the rheological characteristics of slurry during semi-solid die casting but also offers a new modeling strategy for non-Newtonian fluid flow.

Differentiation of thixotropy from damage for accurately characterizing fatigue resistance of asphalt binder

Accurate characterization of the fatigue resistance of asphalt binder is of great significance to the prediction of asphalt pavement performance. Traditionally, apparent changes in viscoelastic parameters, including dynamic shear modulus and phase angle, with the number of loading cycles are used to define the fatigue performance of the asphalt binder. However, thixotropy also leads to changes in these viscoelastic parameters, and its contribution is not yet well understood. This study develops a method to quantify the effects of damage and thixotropy on the changes of viscoelastic parameters under the cyclic stress-controlled loading mode. The new method includes the four key steps: (1) determining the thixotropy influence-dominated phase; (2) establishing a thixotropy model to characterize the influence of thixotropy on the effective dynamic shear modulus; (3) calculating damage density from the apparent and effective dynamic shear moduli; and (4) characterizing thixotropy behavior based on Black space diagram. The effectiveness of the newly developed method is verified by the time sweep test, which is conducted on two types of asphalt binder under varying stress levels.with a loading frequency of 10 Hz and a test temperature of 25 °C. The results show that: (1) the change of dynamic shear modulus is resulted from the damage and thixotropy, while that of phase angle is only caused by the thixotropy; (2) thixotropy leads to the decrease of dynamic shear modulus and increase of phase angle; and its influence on viscoelastic parameters increases with the loading time and stress level increased; (3) under the influence of thixotropy, the dynamic shear modulus is linearly related to the phase angle, which is independent of the stress level applied and the damage accumulated in the asphalt binder.

Advanced characterisation of flexural fatigue performance of foamed bitumen stabilised pavement materials

This study investigates the flexural fatigue behaviour of FBS mixtures at different temperatures (11℃, 22℃ and 31℃) bitumen contents (2%, 3% and 4%), secondary binders (cement at 2% and hydrated lime at 2% and 4%), densities (2.14 kg/m3, 2.20 kg/m3 and 2.26 kg/m3) and moisture contents (dry and 90% saturation) with a view to developing a rigorous design approach for FBS pavements. The experimental results showed that the flexural fatigue life of the FBS beams increases with increasing density and bitumen content while it decreases with increasing temperature and moisture content. Further, no noticeable difference was seen in the flexural fatigue life of FBS specimens with 2% and 4% hydrated lime contents while the FBS mixtures with 2% cement showed significantly higher fatigue life than those prepared with 2% hydrated lime. The flexural fatigue life of 3% bitumen and 2% lime FBS mixture under strain-controlled mode was found to be around 21 times higher than that under stress-controlled mode for a given initial flexural strain. The normalised modulus degradation master curve in stress-controlled mode appears to demonstrate a characteristic behaviour of FBS materials under cyclic fatigue loading. Using this new concept and the experimental results, suitable analytical models were developed for the prediction of the flexural fatigue life of FBS mixtures under both stress-controlled and strain-controlled modes taking into account the variations in temperature, bitumen content, moisture content and density of the FBS mixtures.

Dual Frequency Domain Characteristics of Ratcheting Behavior of Az31b Alloy Under Asymmetrically Stress-Controlled Loading Mode

Dual Frequency Domain Characteristics of Ratcheting Behavior of Az31b Alloy Under Asymmetrically Stress-Controlled Loading Mode

In situ neutron diffraction study of fatigue behavior of CrFeCoNiMo0.2 high entropy alloy

In situ neutron diffraction measurement was applied to study the low-cycle fatigue behavior of CrFeCoNiMo0.2 high entropy alloy. A two-step stress-controlled fatigue test with a stress range of 100–460 and 20–500 MPa was employed. The as-cast sample was cycled 129,000 and 61,000 times, respectively, before fracture. The evolution of the lattice strain and peak intensity demonstrates that the main deformation mechanism is dislocation slip, while no evidence of stacking fault was found. A three-stage ratcheting was clearly observed. Under the stress-controlled mode, the experimentally determined dislocation density increases linearly with the ratcheting strain. The increase of the dislocation density results in a decay of the ratcheting strain rate, which stabilizes the structure and is beneficial for fatigue resistance.

Effect of Graphene Nanoplatelets (GNPs) on Fatigue Properties of Asphalt Mastics.

To investigate the effect of graphene on the fatigue properties of base asphalt mastics, graphene nanoplatelets (GNPs)-modified asphalt mastics and base asphalt mastics were prepared. A dynamic shear rheometer (DSR) was used to conduct the tests in the stress-controlled mode of a time-sweep test. The results showed that GNPs can improve the fatigue life of asphalt mastic. Under a stress of 0.15 MPa, the average fatigue life growth rate () was 17.7% at a filler-asphalt ratio of 0.8, 35.4% at 1.0, and 45.2% at 1.2; under a stress of 0.2 MPa, the average fatigue life growth rate () was 17.9% at a filler-asphalt ratio of 0.8, 25.6% at 1.0, and 38.2% at 1.2. The growth value (ΔT) of fatigue life of GNPs-modified asphalt mastics increased correspondingly with the increase of filler–asphalt ratio, the correlation coefficient R2 was greater than 0.95, and the growth amount showed a good linear relationship with the filler–asphalt ratio. In the range of 0.8~1.2 filler–asphalt ratio, the increase of mineral powder can improve the fatigue life of asphalt mastics, and there is a good linear correlation between filler–asphalt ratio and fatigue life. The anti-fatigue mechanism of GNPs lies in the interaction between GNPs and asphalt, as well as its own lubricity and thermal conductivity.