The objective of the presented study was to evaluate the fatigue performance of reinforced concrete (RC) beams strengthened with basalt fiber-reinforced polymer (BFRP) grids. A total of eight RC ...beams (dimensions of 300 × 150 × 2240 mm) were constructed and tested. Out of these, three beams served as the control specimens, and the remaining five beams were strengthened. The variable parameters included the load ranges, presence of prestress, and number of prestress release. The experimental results indicated that the BFRP grids can be used to significantly extend the fatigue life of the beams. Moreover, when employing prestressed BFRP grids for strengthening, the fatigue life of the beams can be further prolonged. Nevertheless, the strengthening effectiveness of prestressed BFRP grids exhibited notable sensitivity to the number of prestress release. For all the strengthened beams, exceptional bonding performance between the BFRP grids and the concrete interface was evident under cyclic loading, and no interface debonding was observed prior to the fatigue failure of the strengthened beams. Based on the relevant experimental data, this study established a fatigue life prediction model for BFRP grid strengthened beams.
•A pre–tensioning system suitable for applying prestress to BFRP grids has been developed.•A method of multiple prestress releases has been proposed, which can extend the fatigue life of the strengthened beams.•A fatigue life prediction model for BFRP grid–strengthened RC beams has been established.
•Submerged micro-abrasive waterjet peening is proposed to improve the metal surface integrity and fatigue performance.•The surface integrity state of TA19 titanium alloy after the SMA-WJP is ...systematically analyzed.•The high-cycle fatigue life of TA19 titanium alloy treated by SMA-WJP is increased by a maximum of 2.72 times.•The improved fatigue life is attributed to the plastic deformation layer and large CRS induced by SMA-WJP.
Waterjet peening has become a critical surface treatment technology due to its great potential for improving the surface integrity and fatigue performance of metallic materials. The present study aims to investigate the influence of submerged micro-abrasive waterjet peening (SMA-WJP) on the surface integrity and fatigue properties of TA19 titanium alloy. First, the SMA-WJP with different water pressure (P = 70, 100, and 130 MPa) was conducted on the TA19 specimen. The surface integrity of the specimen before and after SMA-WJP treatment was studied, including the microstructure, surface roughness, microscopic morphology, microhardness, and residual stress. Results showed that the SMA-WJP treated specimen with different water pressure formed a plastic deformation layer with a depth of 24–44 μm, the minimum surface roughness of Ra = 0.363 μm and Sa = 0.95 μm. The depth of the work-hardened layer and compressive residual stress (CRS) layer was approximately 100–150 μm and 160–290 μm. The microstructure evolution on the top surface and sub-surface of the as-received and SMA-WJP treated specimens were characterized by transmission electron microscopy (TEM), which showed that nanocrystals with an average size of 12 nm and high density of dislocations formed on the top surface of the SMA-WJP treated specimen. Finally, stress-controlled high-cycle fatigue (HCF) tests were carried out to study the fatigue behavior of the TA19 titanium alloy before and after SMA-WJP treatment. The HCF life of the specimen is increased by a maximum of 2.72 times. The fatigue fracture surface was examined with scanning electron microscopy (SEM), which revealed that the existence of the plastic deformation layer and large CRS induced by SMA-WJP could effectively inhibit the initiation and propagation of cracks. This work enriches the waterjet peening process by investigating submerged abrasive waterjet peening and brings a new solution for improving the surface integrity and fatigue performance of TA19 titanium alloy.
•FlexPAVE™ is able to model the effects of climate and traffic loading on long-term pavement performance.•Preliminary transfer functions are developed herein for fatigue cracking and rutting.•The ...fatigue transfer function converts predicted %Damage to surface %Cracking.•The distresses predicted by FlexPAVETM agree well with the field measurements.
Mechanistic-empirical design and performance-related specifications are state-of-the-art tools for designing pavements and determining incentives/disincentives for paving contracts. These methods require the reliable prediction of pavement performance throughout the pavement’s design life. One such prediction program is FlexPAVE™, which applies three-dimensional viscoelastic finite element analysis with moving loads to calculate the pavement’s mechanical responses under traffic loading and given climate data. The simplified viscoelastic continuum damage model and shift model are used to calculate the fatigue damage in the pavement’s cross-section and the rut depths, respectively. With regard to fatigue damage, a fatigue transfer function is needed to convert the computed cross-sectional damaged area (i.e., the damage level) to the cracked area on the pavement surface. With regard to rut depth, a rutting transfer function is needed to calibrate the predicted rut depths. In this study, preliminary transfer functions for the predicted fatigue damage and rut depths were developed using four sets of field measurement data obtained from test sections in the United States, Canada, and South Korea that include interstate highways and an accelerated testing facility. Good agreement between the predicted performance and field observations was found after calibration of FlexPAVE™.
The most common primary damage form of rubber asphalt pavements is fatigue cracking. At present, the indirect tension, direct tension, bending, and unconfined compression tests are the main ...considered fatigue parameters to design the structure of rubber asphalt pavement. However, the fatigue test results analyzed by various test methods have a quite significant divergence, which represents a lack of accuracy to access the durability of rubber asphalt mixture objectively. Thus, in the structural resistance design of rubber asphalt pavement, there exists a problem of artificial randomness of fatigue parameters. Hence, the primary objective of this study is to improve the procedure for determining the structural resistance of rubber asphalt pavement. To this end, the direct tensile, unconfined compressive, and indirect tensile strength tests of rubber asphalt mixture were performed under various loading rates to reveal the velocity-dependent of the strength of rubber asphalt mixture. The model of direct tensile strength, unconfined compressive strength, and indirect tensile strength increasing with loading rate are SD = 7.772v0.205, SC = 1.748v0.204, and ST = 1.077v0.207, respectively. The stress ratio related to both the traditional S–N fatigue equation and the loading rate was defined as the standard stress ratio and the velocity-dependent stress ratio, respectively. The fatigue test of rubber asphalt mixture was conducted. The results from those experiments were analyzed. A fatigue equation (Nf = tv−5.129R2 = 0.853) related to the loading rate was established. The results indicated that the viscoelastic characteristics of rubber asphalt mixture are not taken into consideration in the traditional S–N fatigue equation, which contributed to the non-uniqueness and uncertainty of fatigue test results. The viscoelastic characteristics of rubber asphalt mixture are considered by the fatigue equation related to the velocity-dependent stress ratio. Thus, a new method (Kv = Nf0.0958) considering the influence of the loading rate for calculating the strength structure coefficient of the rubber asphalt mixture was proposed. The effectiveness and completeness of the mechanical behavior of pavement structure characterized by material parameters were improved. Thus, the utilization rate of waste rubber for pavement construction can be significantly increased and the life cycle cost of asphalt pavement is reduced.
•The velocity-dependent of rubber asphalt mixture strength was revealed under various loading modes.•A unified characterization model of fatigue performance was established under various loading modes.•A new method for calculating the strength structure coefficient was proposed.
Although there are many kinds of fracture tests to choose from in evaluating the crack resistance of asphalt mixture, the semi-circular bending (SCB) test has attracted a lot of attention in the ...academic road engineering community because of its simplicity, stability, and flexibility in testing and evaluation. The SCB test has become a common method to study the cracking resistance of asphalt mixture in recent years. This paper mainly summarizes the overview of the SCB test, summarizes some research results and common characterization parameters of the SCB test method in monotone test and fatigue test in recent years, and predicts and suggests the research direction of the SCB test in the future. It is found that the research on the monotonic SCB test is more comprehensive, and the research on the SCB fatigue test needs to be further improved in the aspects of loading mode, characterization parameter selection, and so on. Researchers can flexibly adjust the geometric dimensions and the test parameters of semi-cylindrical specimens, and conduct comprehensive analysis combined with the results of numerical simulation. The crack resistance of asphalt mixture can be comprehensively evaluated by fracture energy, fracture toughness, stiffness, flexibility index and other fracture indicators, combined with the crack propagation of the specimen. The analysis of numerical simulation can confirm the test results. In order to standardize the setting of fatigue parameters for future application, it is necessary to standardize the setting of bending performance.
•The similarities and differences of several existing semi-circular bending test standards are compared.•Various research ideas developed by researchers on the basis of semi-circular bending test are summarized.•Evaluation index parameters of semi-circular bending test commonly used by researchers are summarized.
An ultrasonic surface rolling process (USRP) is a novel mechanical surface treatment technique for enhancing the fatigue performance of metallic materials. In this work, USRP with different repeated ...processing numbers was employed for enhancing the fatigue performance of a Ti-6Al-4V alloy. The effect of USRP on their surface integrity (including microstructure, surface quality, microhardness, and residual stress) were investigated, which were characterized by means of scanning electron microscope, transmission electron microscope, confocal laser scanning microscope, microhardness tester, and X-ray diffraction residual stress tester. Especially, a refined microstructure (grain size: ~100–400 nm) was formed on the topmost surface of twelve-repeat USRP specimen. Subsequently, the fatigue behavior of the specimens was investigated via rotating-bending fatigue tests, and the results suggested that USRP could effectively enhance the fatigue performance of the Ti-6Al-4V alloy. The USRP-induced enhancement mechanism of the fatigue performance can be ascribed to the synergistic effect of the compressive residual stress, microstructure, work hardening, and improved surface quality. The best synergistic effect and, correspondingly, the greatest improvement in the fatigue performance were realized for the one-repeat USRP specimen.
Display omitted
•Fatigue limits are markedly improved via USRP with different processing numbers.•Fatigue enhancement degree decreases gradually with increasing processing number.•Moderate work hardening is more conducive to improving the fatigue performance.•The more degree of grain refinement does not mean the better fatigue performance.
Combining both Fibre-reinforced polymer (FRP) and sea sand concrete (SSC), the new composite structure of FRP bar-reinforced SSC can not only solve the issue related to reinforcement corrosion but ...also alleviate the problem of river sand shortage. Here, four-point bending tests were performed to investigate the fatigue performance of basalt FRP (BFRP) bar-reinforced SSC slabs. Results revealed that fatigue life decreased significantly with the increasing load levels. The average reduction of fatigue life was about 28% when the load levels increased by 0.05. The main fatigue failure mode of BFRP bar-reinforced SSC slabs was the BFRP bar rupture, which occurred at the mid-span or loading point. The load levels had no evident effect on the attenuation rate of bending rigidity. The critical value for the fatigue deflection growth rate could be set at 35%. An equation for the mid-span deflection at upper loads was established. Herein, considering the growth rate of fatigue deflection, insights to detect the deflection of BFRP bar-reinforced SCC slabs were presented. Meanwhile, based on the S–N curve, Miner rule, and axle load frequency spectrum, a fatigue life prediction method was proposed.
The effect of slide burnishing (SB) on the high‐cycle fatigue (HCF) performance of 2024‐T3 high‐strength aluminium alloy has been studied. After SB with optimum basic process parameters under ...‘minimum roughness’ criterion, the 107 cycle fatigue strength increases with 25% – from 180 to 225 MPa, fatigue life is increased more than 50 times, and the roughness obtained reaches up to Ra = 0.05 μm. Further, various combinations of burnishing force and deforming element radius have been applied to reach maximum HCF performance despite roughness obtained. It has been established that with the optimum combination under ‘maximum HCF performance’ criterion, 107 cycle fatigue strength increases with 44% – from 180 to 260 MPa as the roughness obtained is Ra = 0.25 μm. This significant enhancement in the HCF performance is due to introduced beneficial residual compressive stresses. They shift the fatigue crack initiation site from surface to subsurface layers and, as a result, the nucleation and propagation of the first‐mode fatigue cracks are retarded. In order to establish the fatigue limit (based on 2 × 108 cycles), a combined approach, based on limited Wöhler's curve and Locati's method, has been applied. The fatigue limit of 2024‐T3 high‐strength aluminium alloy can be increased up to 250 MPa using SB with optimal basic parameters under ‘maximum HCF performance’ criterion.
•Silica modified asphalt binders have more resistance against thermal aging.•SuperPave Volumetric Mix Design is undertaken.•Rutting performance of Silica 0.3% modified asphalt binder is ...improved.•Fatigue performance of Silica 0.3% modified asphalt binder is improved.•Energy saving is improved by modification.•Optimum binder contents are decreased by Silica 0.1% and 0.5% modification.•Performance of HMA mixtures modified with silica are improved.•Silica 0.3% modified HMA mixture is resistive to moisture.
The aim of the study is to evaluate the performance of Hot Mix Asphalt (HMA) and bitumen by modifying bitumen with nano materials according to Superpave™ mix design procedure. In this study, bitumen is modified by silica nanopowder (SiO2NP). Nano powders are mixed with base bitumen at contents of 0.1, 0.3 and 0.5% by weight. Rutting and fatigue performance of bitumens are determined. HMA is prepared with nano modified bitumens at optimum binder content (OBC). Moisture susceptibility of modified HMA is evaluated according to Modified Lottman test procedure. Nano modified bitumens are also evaluated by scanning electron microscopy (SEM) whether the modification is uniform or not. As a result, better performance is obtained by SiO2NP at a content of 0.3% modification. Performance Grades (PG) of all modified bitumens are determined as PG 64-22. OBCs are decreased by modification. HMA sample modified by SiO2NP at a content of 0.3% is determined 26.25% higher resistive to moisture compared to reference sample. Homogenous mixture is obtained according to SEM results. It is found that the agglomeration of nano materials is mostly lower than 4μm in the mixtures. As a result, SiO2NP 0.3% shows satisfying results.
