Laboratory Fatigue Tests Research Articles

Mechanism-based shift factors to predict the fatigue performance of cemented pavement materials

Cemented pavement materials (CPMs) are essential components in pavement structures, yet accurately predicting their service life due to fatigue damage remains challenging. Laboratory fatigue test results are commonly employed to predict the service life of CPMs by applying a lab-to-field shift factor (SF). However, traditional approaches rely heavily on experimental data, posing challenges in ensuring the certainty of lab-to-field results. Additionally, inconsistencies in lab-to-field fatigue failure criteria further complicate SF development. To address these challenges, this study proposes a mechanism-based methodology for developing SF. This methodology comprises a rigorous two-scale fatigue model developed by the authors to characterise the fatigue performance of CPMs at the lab scale and predict their performance at the field scale, thereby facilitating the development of SFs. These SFs are established based on a consistent lab-to-field fatigue failure criterion (i.e. the modulus reduction of CPMs). By accounting for strain differences between laboratory and field scales, SFs are derived in the strain-fatigue life space. Application of this approach to typical Australian CPMs, namely siltstone and hornfels, yields mechanism-based SFs of 1.19 and 1.21, respectively.

The Relationship Between Loading Frequency and Truck Speed on Asphalt Pavements

The mechanistic-empirical road pavement design methods necessitate knowledge of the dynamic modulus master curve of asphalt mixtures. This requires the designer to accurately define both the load frequency and the temperature of the pavement structure. The parameter of load frequency is of great importance in laboratory fatigue tests. However, it presents a challenge since road structures are loaded in the time domain, not the frequency domain. This complexity has prompted researchers to develop time-frequency conversion methods to estimate the corresponding frequency from the duration of traffic-induced stress or deformation pulses. Recent findings indicate that the time-frequency equivalence factor is considerably lower than previously assumed. In this study, we introduce a new four-parameter empirical RAMBO material model, derived from the Ramberg–Osgood equation, which offers parameters to determine the time-frequency equivalence factor for asphalt mixtures. The relationship between the moving wheel load velocity and the load impulse time is analysed, primarily based on experimental data and computational methods from existing literature. A method for determining the wavelength of the load impulse is proposed. The theoretical correlation indicates that a wheel load travelling at 100 km/h results in a dynamic deformation frequency of 10 Hz. However, for a strain impulse, the same speed corresponds to a much lower frequency of 3–4 Hz. This study offers a refined understanding of the time-frequency equivalence factor, which is of crucial importance for more accurate road pavement design and fatigue testing.

Design of pavement structures consisting of paving slabs with hydraulically bound joints and bedding

To meet the needs for higher-ranked roads and traffic loads, rigid slab pavements with cement-bound bedding material and joints were analysed instead of the traditionally used unbound construction method. Since the bearing capacity and drainage of the upper base course are essential, the results of recently introduced laboratory fatigue tests for permeable concrete were considered. Additionally, fatigue tests were also conducted on concrete and natural stone slabs. The structural response of the superstructure was determined by introducing an finite-element-model that considers bound behaviour in the joints and between the slab-bedding-interface. With the derived fatigue criterions and the structural primary response of the FE Model, the deterioration under traffic load can be evaluated. The main objective of this paper is the development of a design procedure for slab pavements with cement-bound joints and bedding on a pervious concrete base course to deduce suitable standard structures in accordance with Austrian directives.

Fatigue assessment of fillet welded doubling plates using different methods

Analysis results using finite elements are compared with strain measurements and laboratory fatigue testing of doubling plates used in floating production platforms. Circular and quadratic doubling plates of thickness 10 mm with diameter and length equal to 150 mm fillet welded to a main plate of thickness 20 mm were fatigue tested. The testing was performed until crack growth through the plate thickness and the number of test cycles was compared with design standards. Finite element analyses of the doubling plates were performed using different methods for hot spot stress derivation in combination with relevant S-N curves. Analyses were performed using 8-node shell elements and 20-node solid elements. Hot spot stresses were based on calculated surfaces stresses at the weld toe. Also stresses through the thickness of the main plate were used for assessment of the hot spot stress. For purpose of analyses the main attention was made to the weld toe. However, the main reason for performing the fatigue testing was related to concern for crack growth from the weld root. This failure mode was found to be less critical than fatigue crack growth at the weld toe. The results from this work are being used for developing more reliable analysis methods to be included in design standards.

A hybrid approach for fatigue life prediction of in-service asphalt pavement.

Fatigue cracking is one of the main pavement failures, which makes accurate fatigue life prediction forthe design and maintenance of asphalt pavements crucial. The majority of traditional prediction methods are based entirely on the laboratory fatigue test, without considering the field condition and maintenance data. This paper aims to propose a hybrid approach to fill this gap. The key idea is that the damage condition isback-calculated by anartificial intelligence-based finite-element (FE) model updating using field-monitoring information (data-driven component), which is used to update the parameters in themechanistic composition-specific fatigue life prediction equation (model-driven component). The laboratory test of field cores gives the material non-destructive properties. The simulated pavement response subjected to truck loading shows good agreement with measured values, which indicates that the verified constitutive relationship could be used in the data-driven component. Furthermore, in view that the fatigue test is time- and money-consuming, this paper proposes a non-test estimation of thefatigue characteristic curve based on FE simulation of arepeated direct tension test. Three test pavement sections were employed as case studies. Results showed that the predicted fatigue life changes with the service time. At the early age, semi-rigid pavement has alarger fatigue life than flexible and inverted pavements. This article is part of the theme issue 'Artificial intelligence in failure analysis of transportation infrastructure and materials'.

Experimental evaluation of fatigue and recovery properties of a bituminous mixture during cyclic loading and rest tests

Research has shown that reversible phenomena such as non-linearity, self-heating and thixotropy occur during laboratory fatigue testing on bituminous mixes. This work aims to develop a test protocol to separate and quantify the recovery of reversible phenomena and the restoration of damage. Besides proposing some adjustments to the protocol, in the present paper, its repeatability is evaluated by comparing the results obtained for several samples of the same bituminous mixture. The test procedure is composed of two parts: short complex modulus tests (200 cycles at 10 Hz) at temperatures ranging from 8°C to 14°C with strain amplitudes ranging from 50 to 110 µm/m are used and five partial fatigue tests (at 10°C) are carried out at 100,000 cycles, 100 µm/m and 10 Hz. Each fatigue lag is followed by a 48-h rest period which consists of short complex modulus tests. The test protocol appears to show reliability and provide repeatable results.

Structural, Microstructural, Elastic, and Microplastic Properties of Aluminum Wires (from AAAC (A50) Cables) after Fatigue Tests

Single Al wires from unused AAAC (A50) cables were studied after laboratory fatigue testing, which simulated processes arising in these wires during their operation in the cables of overhead power lines (OPLs) and are valuable for predicting the lifespan of cables of OPLs. These wires, which were either fractured during testing (maximum loads—149.4–155.9 MPa; number of cycles till rupture—83,656–280,863) or remained intact, were examined by X-ray diffraction, electron backscatter diffraction, densitometry, and acoustic methods. An analysis of the structural, microstructural, and elastic-microplastic properties of the wires revealed common characteristics inherent in the samples after operation in OPLs and after fatigue tests, namely a decrease in the integral and near-surface layer (NSL) densities of the wires, a decrease in their Young’s modulus and microplastic stress, and an increase in the decrement. However, the tests did not fully reproduce the environmental influence, since in contrast to the natural conditions, no aluminum-oxide crystallites were formed in NSLs in tests and the microstructure was different. A comparison of the characteristics of the broken and unbroken wires allows us to suggest that the fastening locations of the wires are crucial for their possible failure.

Strength calculations and fatigue tests of welded bus bodywork nodes

Laboratory fatigue life tests were performed for several structural variants of welded nodes of thin-walled profiles of a bus bodywork. The laboratory fatigue tests were supported by FEM calculation and strain gauge experimental stress analysis. S-N curves were evaluated and used to predict the fatigue life of these structural nodes under random operational loading of the vehicle bodywork. Measuring systems for on-line monitoring of stresses in the vehicle bodywork have been developed and applied.

Comparison of Fracture Strengths of Three Provisional Prosthodontic CAD/CAM Materials: Laboratory Fatigue Tests

Temporary restorations play a fundamental role in oral rehabilitation. They can be used on teeth or implants for a variable period of time during the period prior to rehabilitation with definitive restorations. Temporary or provisional restorations manufactured via CAD/CAM methods are becoming increasingly used in the intermediate phase of the treatment of complex cases. The main objective of this study was to compare the fracture resistance of three materials used in the creation of provisional crowns on implants: polymethyl methacrylate (PMMA), composite resin, and polyether ether ketone (PEEK). Fracture resistance in PMMA (Zirkonzahn Temp Basic® , Gais, South Tyrol, Italy) ranged from 1216.0 N to 1461.2 N, with a mean of 1300.4 N (SD = 97.09). In the composite material (3M Lava Ultimate®, Minnesota, USA), fracture resistance varied between 1343.5 N and 1490.6 N, with a mean of 1425.9 N (SD = 49.03). Lastly, in PEEK (Tecno Med Mineral®, Zirkonzahn®, Gais, South Tyrol, Italy), fracture resistance ranged from 2294.8 N to 2451.7 N, with a mean of 2359.5 (SD = 50.01). The crowns made with the PEEK Tecno Med Mineral® (Zirkonzahn®, Tyrol, Italy) material presented the best fracture resistance, followed by the crowns made with the Lava Ultimate® (3M® ESPE, Minnesota, USA) composite resin material and, finally, those made with the PMMA Temp Basic® (Zirkonzahn®, Tyrol, Italy) material.

Effects of actual loading waveforms on the fatigue behaviours of asphalt mixtures

Fatigue cracking is one of the main distress modes of highway asphalt pavements. In laboratory fatigue tests, haversine or sinusoidal loading waves are commonly applied to characterize the fatigue performance of asphalt mixture samples. The strain wave in field asphalt layer under a moving axle load, however, is noticeably different from the haversine or sinusoidal wave. This research compared the fatigue behaviours of compacted asphalt mixture samples under actual strain waves and the commonly used haversine wave. Two types of actual strain waves induced by the single axle and tandem axle of vehicles were included for analysis. It is found that the fatigue lives of asphalt mixture samples subjected to the single-axle wave are obviously higher than those subjected to haversine wave, while the tandem–axle wave leads to the lowest fatigue life. The changing rates of stiffness, phase angle, and dissipated energy with loading cycles for the mixture samples under single-axle wave are all the lowest, while those under tandem-axle wave are all the highest. This helps explain the discrepancies in the samples’ fatigue lives under different loading waves. The above findings suggest that it is necessary to test asphalt mixture samples using loading waves that simulate the actual ones in the field (i.e., single-axle wave and tandem-axle wave) to improve the reliability of fatigue life prediction of asphalt pavements. In addition, this research reveals that three dissipated-energy-based indicators, namely initial dissipated energy, cumulative dissipated energy and plateau value, all generate a unique relationship with the sample’s fatigue life. The relationship is independent of loading wave type and strain level.

Estimating the multiaxial fatigue behaviour of C45 steel specimens by using the energy dissipation

Energy-based approaches are adopted in fatigue analysis of materials, components and structures. Several methods consider the thermal energy, which results from energy conversion of the mechanical energy expended by applying cyclic fatigue loadings. By exploiting the self-heating phenomenon, the specific heat energy can be measured during laboratory fatigue tests in a rather simple and efficient way. In previous papers, the specific heat loss has been adopted to correlate fatigue test data relevant to pure axial and pure torsional fatigue loadings. In this paper, it is adopted to correlate successfully the fatigue test data generated under in-phase and out-of-phase axial/torsional multiaxial fatigue loadings.

Joints Of Steel Sandwich Structures

Abstract Steel sandwich structures are perceived as alternatives to single-skin welded structures in the shipbuilding industry due its advantages like significant reduction of mass in relation to typical single skin structure. However, beside problems with their strength properties itself, applications in real structures requires of solving the problem of joining, both for connection sandwich to sandwich as well as sandwiches to single-shell structures. Proper design of joints is connected with some factors like lack of attempt to interior of panel, introduction of additional parts and welds with completely different stiffness. In the paper the results of laboratory fatigue tests of selected joints as well as numerical calculation of stressed for different kind of joints of sandwich structures are presented. As result of calculations optimisation of geometry for selected joints is performed.

Fatigue Performance of Double-Layered Asphalt Concrete Beams Reinforced with New Type of Geocomposites.

The reinforcement of asphalt layers with geosynthetics has been used for several decades, but proper evaluation of the influence of these materials on pavement fatigue life is still a challenging task. The presented study investigates a novel approach to the reinforcement of asphalt layers using a new type of geogrid composite, in which square or hexagonal polypropylene stiff monolithic paving grid with integral junctions is bonded to polypropylene non-woven paving fabric. The laboratory fatigue tests were performed on large asphalt concrete beams reinforced with the new type of geocomposite. Unreinforced samples were used as reference. Test results were analysed in several aspects, including the standardised approach based on stiffness reduction, but also using energy dissipation. The effect of reinforcement on pavement fatigue life was also estimated. Based on the obtained final results of fatigue life calculations, it can be concluded that the evaluated geogrid composites have an evident positive effect on pavement performance and have a significant potential to extend the overall pavement life, especially in the case of hexagonal grid.

Fatigue damage and residual life of secondary lining of high-speed railway tunnel under aerodynamic pressure wave

To investigate the fatigue behaviours of tunnel secondary lining under the aerodynamic effects produced by the running high-speed railway (HSR) trains, we proposed a dual fatigue damage accumulation model (DFDAM). In our model, a nonlinear variable load model was nested inside an equal-damage nonlinear model. The nonlinear variable load model was used to calculate the fatigue damage of a tunnel secondary lining after a single HSR train travelled through the tunnel, and the equal-damage nonlinear model was adopted to calculate the fatigue damage after multiple HSR trains travelled through the tunnel. Our proposed model was verified by comparison with laboratory fatigue testing results obtained by other researchers. The proposed model was also used to study the aerodynamic fatigue behaviours of a practical HSR tunnel project. The results show that the damage accumulation produced during the train running inside the tunnel is approximately the same as that of after an HSR train tail leaves the tunnel exit. Thus, after an HSR train leaves the tunnel exit, the influences of the aerodynamic pressure on the tunnel secondary lining cannot be ignored. The damage accumulation of a tunnel secondary lining associated with multiple HSR trains passing increases monotonically with the increase of the consumed life fraction. In contrast, the residual life of the fatigue damage decreases monotonically. This study can serve as a reference for studying the operational safety of HSR tunnels.

Residual stiffness characterization of FRP laminates under random block spectrum

The fiber reinforced polymer/plastic (FRP) laminates are often subjected to random block spectrum loading in engineering. The simplified regular load in the laboratory fatigue tests is not sufficient to describe the actual fatigue damage history of FRP laminates. In order to explore the fatigue damage evolution of FRP laminates characterized by the residual stiffness degradation under complex random loads, some random block spectra are compiled based on the real engineering fatigue loads, and the fatigue tests of two FRP laminates, the E-glass/YPX-3300 glass fiber laminate and T700/YPX-3001 carbon fiber laminate, were conducted under the random block spectra. Four kinds of differently stacked laminates were prepared for each material. The residual stiffness degradation curves are obtained from the experiments. A stiffness degradation model proposed by the authors are used to correlate the residual stiffness evolution data. The results show that the residual stiffness degradation curves of different specimens can reach satisfactory consistency after correlation, though the original experiment data show a large dispersion. The residual stiffness degradation law of FRP laminates under random block spectrum is the same as that under constant amplitude spectrum. The proposed model can well characterize the residual stiffness degradation law of RRP laminates under random block spectrum.

Concept of Similarity Method for Prediction of Fatigue Life of Pavement Structures with HiMA Binder in Asphalt Layers.

Since 2009, SBS (styrene-butadiene-styrene) polymer-modified binders (HiMA—Highly Modified Asphalt) have been tested worldwide. Highly modified binders are characterized by extraordinary properties resulting from the reversal of the binder-polymer phase. This contributes to very good test results for asphalt mixes. The use of such a modern binder poses a challenge in terms of structure design, mainly due to the lack of a recognized and calibrated method suitable for this material. The article proposes a new approach to pavement fatigue life estimation—the Similarity Method—which is based on the use of AASHTO 2004 equations and laboratory fatigue testing results of asphalt concrete mixes for asphalt base course. The article presents the method and the results of its sensitivity testing with respect to the influence of the material (type of asphalt concrete), thickness of the asphalt base course, stiffness of the subgrade and the assumed FC index (the area of bottom-up cracks). The results of fatigue life according to the Similarity Method are within the range of values obtained for AASHTO 2004 and the fatigue results according to the equations obtained in the laboratory. This approach will enable inclusion of new materials, such as HiMA asphalt mixtures, in pavement structure design.

Development of Mechanical Strengthening System for Bridge Connections Using Prestressed CFRP Rods

Stringer-to-floor beam web-to-web double-angle connections are among the most fatigue-prone elements in old riveted bridges. These connections are often designed to carry only shear loads. However, in these elements, fatigue damage occurs because of the out-of-plane deformation of the connections, which is ignored in the original design. In this study, a new retrofitting system is developed to reduce the out-of-plane deformation of the connections using prestressed carbon fiber-reinforced polymer (CFRP) rods. The proposed system consists of a mechanical wedge-barrel anchor to hold the prestressed CFRP rod and a clamping system to attach to the parent structure and to transmit forces via friction. A series of finite-element (FE) simulations was conducted to optimize the size and performance of the retrofit system. Laboratory static pull-off tests were conducted and different failure modes were studied and discussed. A novel test setup (with four supports) was designed for testing the steel connections. The effect of the geometrical imperfections during the installation of the connection was carefully investigated using the FE models and was verified through laboratory the tests. Laboratory fatigue tests were conducted on steel connections with the same dimensions as those in a railway bridge. The designed retrofit system was found to be capable of reducing the stresses at the angle connections by more than 40%. The results of the fatigue tests demonstrated that the designed system could survive more than 11 million load cycles without any fatigue damage or any indication of a loss in the CFRP prestressing level.

Fatigue behaviours of asphalt mixture at different temperatures in four-point bending and indirect tensile fatigue tests

The laboratory fatigue test for the asphalt mixture is generally conducted at the intermediate temperatures (10 °C to 20 °C). Some research findings reveal that fatigue cracking may also appear in the asphalt layer at higher temperatures. Motivated by these findings, the present research investigated and compared the fatigue behaviours of the asphalt mixture at a wide range of temperatures (15 °C to 40 °C with an interval of 5 ℃) in four-point bending (4 PB) and indirect tensile (IDT) fatigue tests. The dense-graded asphalt mixtures (AC-13) using neat asphalt binder and Styrene-butadiene-styrene (SBS) modified asphalt binder are applied for evaluation. It is found that a uniform law exists for the stiffness evolution of the asphalt mixture in the fatigue test: as the stiffness of the asphalt mixture declined to about 70% of its initial stiffness, the asphalt mixture starts to experience the stable fatigue damage accumulation stage. The temperature affects the fatigue life of the asphalt mixture oppositely in the 4 PB and IDT tests. In the 4 PB test, the rising temperature causes an increase in the fatigue life of the mixture. However, in the IDT test, the fatigue life of the mixture decreases obviously with the increase of temperature. The model Nf=a(1/F)becT is proposed and developed to describe the relationships among fatigue life (Nf), temperature (T) and stress/strain level (F) of asphalt mixture in 4 PB and IDT tests. The developed models provide reference data for evaluating the fatigue resistance of the asphalt layer under various temperature and strain/stress conditions.

Development of fatigue damage model of asphalt mixtures based on small-scale accelerated pavement test

As the primary surface type for high-grade Chinese highways, the long-term performance of asphalt pavement can affect significantly transportation efficiency. It has been confirmed that fatigue cracking is one of the major failure modes for asphalt pavement, which can cause a great reduction of asphalt pavement durability. Currently, the fatigue properties of asphalt mixtures are evaluated mainly based on traditional laboratory fatigue tests, such as bending fatigue tests and indirect tensile fatigue tests. However, none of these fatigue test methods can realistically evaluate the fatigue performance of asphalt pavement under the repeated wheel load. To resolve this issue, the model mobile load simulator (MMLS3), which is a small-scale accelerated pavement test device, was utilized to evaluate the fatigue life of six kinds of asphalt mixtures. The fatigue damage variable was defined as stiffness reduction. Based on the small-scale accelerated pavement test, a stiffness reduction model for asphalt mixtures was determined. A stiffness reduction law for asphalt mixtures during the fatigue process was proposed. The stiffness evolution process could be divided into three phases, which are the adaptation phase, the quasi-stationary phase, and the failure phase. A maximum value of the rate of stiffness reduction from the quasi-stationary phase into the failure phase was proposed as the failure threshold. Besides the fatigue life obtained from the failure criteria had a good agreement with the test results. The results from this research can be used as a theoretical reference for evaluating the fatigue life of asphalt mixtures and improving the durability of asphalt pavement.

Study on Fatigue Life of Cement Stabilized Macadam Base during Crack Expanding Phase Based on Accelerated Loading Test

The evaluation for remaining life of semi-rigid base layer has a significant effect on pavement maintenance scheduling like resurface or rehabilitation. An accurate evaluation can obviously improve the pavement maintenance, which could also utilize the original pavement structure in a rationally way, and optimize the entire maintenance plan. In this study, a series of laboratory investigation were conducted on the cement stabilized macadam materials. The fatigue life and deterioration characteristics of cement stabilized macadam materials were analyzed during the pre-cracked (fatigue cracks occurring) phase and crack expanding phase by laboratory fatigue test and full-scale accelerated loading test, respectively. Then, a fatigue life correction coefficient of the crack expanding phase was used to analyze the fatigue properties of the semi-rigid base, and a modulus degradation model of the semi-rigid base life was characterized. It proved to be convenient to evaluate the residual life of semi-rigid base according to the modulus.