The purpose of this study was to estimate the total fatigue life for in-service asphalt mixture fatigue with in situ accelerated pavement testing (APT) and laboratory four-point bending beam tests. ...On a selected expressway in Shanghai, China, a series of full-scale APT tests were conducted. During the APT tests, a portable seismic property analyzer was used to monitor the pavement deterioration through modulus reduction. An equivalent factor between the APT loading and equivalent single axle loads (ESALs) was estimated. Additionally, asphalt concrete slabs were cut from the APT test sections and then transferred to the laboratory for four-point bending beam fatigue tests. A new fatigue equation was proposed for the in-service asphalt mixtures. Furthermore, a shift factor between the laboratory fatigue life and field ESAL was recommended. Finally, the field total fatigue life of the in-service asphalt mixture was estimated based on all the work in this study.
In this study, experiments were conducted to study the fatigue behaviors of two full scale high strength steel built-up box T-joints. Firstly, the stress concentration factors at the joint ...intersection were measured. Secondly, fatigue tests were conducted with the crack growth monitored by the Alternating Current Potential Drop micro-gauge. It is found that the fatigue resistance of the high strength steel joints could be conservatively predicted by the existing fatigue design curves for normal strength steels. In addition, the higher residual stress present in the joints seems to produce little effects on the crack penetration rate in the thickness direction.
•The hot spot stress method can reliably predict the crack initiation position.•Crack propagation behaviors of RQT-S690 are not much different from S355J2H.•S–N curve predicted the fatigue life of high strength steel box joint conservatively.•Residual stress shows little effect on the fatigue performance for joints tested.
This paper presents a laboratory test protocol for evaluating fatigue properties of asphalt mixtures through sweep tests at multiple amplitudes and frequencies. Conventional fatigue evaluation of ...asphalt mixtures typically relies on a limited number of single fatigue tests, and each test is performed at constant test temperature. Moreover, in order to reduce laboratory effort to a minimum, testing is quite often limited to a single test temperature, which means that the dependency of asphalt fatigue on temperature is ignored. Such test procedure is in best accordance with the European Standards. However, so-derived results may provoke misleading conclusions, as exemplarily shown in this study. In order to solve this shortcoming, a sweep test protocol for fatigue evaluation of asphalt mixtures at different temperatures is proposed. Frequency-amplitude sweeps are used for complex modulus evaluation and fatigue evaluation, but without significantly extending the laboratory effort compared to conventional fatigue testing. This sweep test protocol is applicable for fatigue evaluation of any asphalt mixture.
Purpose
Fatigue damage of internal threads has gradually become the main failure mode of force sensor. To make the internal thread structure of force sensor meet the fatigue performance requirements, ...the design criteria of static strength and fatigue life are comprehensively considered in this paper.
Design/methodology/approach
The variation of static stress and fatigue life with the size of the main structure is obtained by simulation. By changing the number of thread turns, the hub height and outer diameter of the hub, the optimized design of the spoke force sensor is determined.
Findings
The experiment was carried out based on the determined optimized structure, and the results showed that the fatigue life meets the design requirements.
Originality/value
This research has certain guiding significance for the design and developments of high-cycle fatigue force sensors.
An experimental study was conducted to determine the effect of deflection waveform on four-point flexural fatigue test results for hot mix asphalt. This paper reports how the waveform affects the ...fatigue resistance of an asphalt mixture and, consequently, the fatigue models of the material. The mix was tested at different strain levels under both haversine and sinusoidal deflection-controlled modes. The findings indicate that haversine displacement control testing results in a sinusoidal strain response of half the intended amplitude. This outcome was attributed to the viscoelastic nature of asphalt mixes. In the deflection controlled haversine test, permanent deformations lead to a new equilibrium neutral position of the beam and the force output follows a sinusoidal waveform. This produces erroneous fatigue results since the test assumptions do not match the actual test conditions. It is recommended to use a sinusoidal waveform to obtain consistent results.
A buckling-restrained brace is an excellent structural member. In medium- and low-rise buildings, it is often used primarily as an earthquake-resistant brace, and in super-high-rise and high-rise ...buildings, as a seismic-response controlled brace1-3). It is particularly important to assess the fatigue performance of a buckling-restrained brace where it is used as a seismic-response controlled brace. This study summarizes the results of two studies performed on a buckling-restrained brace using steel mortar planks10,12). A fatigue test using constant strain-amplitude cyclic loading was also conducted under the following two conditions: 1) Using large plastic strain-amplitudes of axial strain exceeding 3% assumed in massive earthquakes, 2) Decreasing the value of restraining index R that affects energy dissipation performance. By combining the results of the test and past studies, the study constructed a fatigue curve in the plastic region. Based on the fatigue curve, a detailed examination was conducted on the tolerable loading cycles Nt, locations of fracture and local deformation, cumulative plastic strain energy ratio ω, compressive-to-tensile strength ratio α and restraining index R for both basic type and high-performance type specimens. Focusing on the buckling-restrained brace using steel mortar planks, a constant strain-amplitude cyclic loading test was conducted using basic type and high-performance type specimens. The following results were obtained: 1) In both types of specimen, strain-amplitude ε and tolerable loading cycles Nt in the plastic region have a linear relationship when plotted on a double logarithmic graph, from which the fatigue performance of the buckling-restrained brace can be estimated. 2) In both types of specimen, at high strain-amplitudes of axial strain exceeding 3%, the fatigue performance of the brace is determined by the fatigue performance of its core plate, hence, there is little difference in tolerable loading cycles Nt and cumulative plastic strain energy ratio ω between the two types of specimen. 3) In both types of specimen, at small strain-amplitudes of axial strain less than 3%, the fatigue performance of the brace is determined by the shape of the stress concentration location: a weld heat-affected zone in the case of the basic type specimen, and the end part (R part) where the area of the core plate plastic zone is decreased in the case of the high-performance type specimen. The high-performance type specimen is superior in both tolerable loading cycles Nt and cumulative plastic strain energy ratio ω. 4) Even for the high-performance type specimen which has a better performance than the basic type specimen, compared with the fatigue performance of the steel material, tolerable loading cycles Nt is 1 / 5.7 times with a strain-amplitude of 3.0% and 1 / 3.5 times with a strain-amplitude of 0.3%, which is a small number of times. 5) Tolerable loading cycles Nt of the basic type specimen was 5 at a strain-amplitude of 4.0%, while that of the high-performance type specimen was 2 at a strain-amplitude of 5.5%, 3 at 4.5% and 5 at 4.0%, demonstrating sufficient performance to withstand large strain-amplitudes. 6) In both types of specimen, the cumulative plastic strain energy ratio ω at a strain-amplitude of 3.0% or less greatly exceeded the values derived from the performance evaluation formula proposed in the past study11), demonstrating adequate energy dissipation performance. 7) As our past studies showed, in both types of specimen, as strain-amplitude ε increases, compressive-to-tensile strength ratio α increases.
To solve the early rutting failure of asphalt pavement, the application of rock asphalt from Sichuan, China, based on anti-rutting performance, was studied. Preparations of North Sichuan rock asphalt ...(NS RA) and NS RA-modified asphalt mixture were elaborated in detail. Using Zhonghai AH-70 asphalt, Esso AH-70 asphalt, North American rock asphalt (NA RA) and NS RA, the performances of NS RA modified asphalt were researched based on index tests, Brookfield rotary viscosity test and bending beam rheometer test. A performance verification of NS RA-modified asphalt was carried out using rutting calculation, the rutting, indirect tensile fatigue, freeze–thaw split and small beam bending tests based on five kinds of selected gradations. The results indicated that in comparison with NA RA, the NS RA has a good modification effect as well. The NS RA can obviously improve the anti-rutting ability of the asphalt binder, and it can enhance its anti-aging performance as well. For the NS RA-modified asphalt mixture, it is feasible to determine the optimum NS RA content, based on its anti-rutting performance, and its optimum NS RA content is about 8%. The dynamic stability values of NS RA-modified asphalt mixtures are at least 3-fold higher than those of the base asphalt mixtures, and they are all far greater than the summer hot area requirement (no less than 2800 times/mm). NS RA-modified asphalt mixtures used in the middle course of asphalt pavement can obviously improve the anti-rutting performance of the pavement, and to enhance the anti-rutting ability of pavements, it should be used in the middle course of the pavement. The fatigue life values of NS RA-modified asphalt mixtures are at least 14.5-fold higher than those of the base asphalt mixtures. The freeze–thaw splitting strength ratio values of NS RA-modified asphalt mixtures are improved by at least 9.5% over the base asphalt mixtures, and their freeze–thaw splitting strength ratio values are all greater than the requirement (no less than 75%). In comparison with the base asphalt, the low temperature performances of NS RA-modified asphalt and its mixtures slightly decline, but they can meet the requirements for the zones with a minimum temperature of no less than –21.5 °C too. Therefore, except for the extremely low temperature area, it is an effective method for solving the rutting problem of pavement for using NS RA-modified asphalt.
The fatigue experiment of friction stir (FS) welds in 2024-T3 aluminum alloys were performed to investigate the influence of root flaws on the fatigue strength and life of FS welds. The test results ...of welds with flaws (flawed welds) were compared with the results suggested by the International Institute of Welding (IIW) recommendations and the welds without root flaws (flaw-free) in the published research reports. It was found that there was always existed flaws at the roots of FS welds because of unsuitable welding parameters and the vertical length of the flaws is about 0.31–0.33
mm for the FS butt-welded joint of 4
mm in thickness. The fatigue life of flawed welds is 33–80 times shorter than that of flaw-free welds, and the fatigue characteristic values have decreased from 120.6
MPa for flaw-free welds to 54.7
MPa for flawed welds at 2
×
10
6 cycles.
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This research is done with the purpose of revealing an increase in the fatigue performance of carbo-nitrided powertrain shafts followed by the second tempering. The fatigue test was conducted at a ...bi-directional torsional cyclic load using an MTS torque tester. Various investigations were carried out to find out the effect of surface roughness, second tempering, inter granular oxidation, retained austenite, and residual stress. The result of this investigation shows that an increase in the carbo-nitriding processing time causes higher inter granular oxidation and a non-martensitic transformation product. The existence of the surface retained austenite has not influenced notably the enhancement in the fatigue life performance in the powertrain shaft. Existence of martensite with the removal of the non-martensitic transformation product from the shaft surface enhanced the fatigue performance significantly—up to 300% (from 12 000 to 40 000 cycles).
Asphalt binders have been modified with Crumb rubber (CR) as an effort to fulfil the demand for the development of eco-friendly and sustainable pavements. The objective of this study was to ...investigate the high temperature rheological behaviors and fatigue performance of crumb rubber modified asphalt (CRMA) binder activated using trans-polyoctenamer (TOR). Long-term and short-term aging tests were performed on samples by thin film oven test (TFOT) and pressure aging vessel (PAV). Rotational viscosity (RV), softening point, and dynamic shear rheometer (DSR) tests were conducted to characterize the rheological and physical performance. A linear amplitude sweep (LAS) test was employed to evaluate the fatigue performance. The results show that TOR-activated CRMA is more capable of hardening the matrix bitumen and improving its high-temperature viscoelastic properties after TFOT. The high temperature viscoelasticity is significantly better than styrene-butadiene-styrene block (SBS) modified asphalt (SBSMA) and CRMA. TOR-activated CRMA exhibits strong rutting resistance, but it is more likely to generate fatigue cracks under the violent advancement of complex modulus. Therefore, TOR active agent has a negative impact on the fatigue performance of CRMA. SBSMA exhibited superior fatigue resistance. The viscosity temperature index (VTS) of TOR-activated CRMA and CRMA was basically identical; the TOR did not significantly improve the temperature sensitivity of CRMA.
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