Laboratory Fatigue Research Articles

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

AbstractCemented 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.

Laboratory Fatigue Characterization of Foamed Bitumen Stabilized Granular Base and Recycled Blends for Pavements

ABSTRACT Foamed bitumen stabilization offers a sustainable solution for the construction of new pavements or rehabilitation treatments while also improving the performance of pavement structures. This technique allows up to 100 % of the existing pavements to be used, which will lead to lower use of quarry resources and reduced material transportation cost. In recent years, there have been advances in the use of foamed bitumen stabilized (FBS) pavements. However, prior to the research in this paper, no specific Australian performance relationship had been developed for FBS materials. Also, there was a lack of test procedures specifically developed to manufacture and evaluate the fatigue cracking resistance of FBS conventional and recycled pavement materials. This paper presents the laboratory characterization and development of a fatigue relationship to predict performance of FBS materials. For this purpose, laboratory experiments were undertaken including flexural fatigue, modulus, and strength tests using a four-point bending beam system. Five different host materials were selected for laboratory investigations, including three crushed rocks and two recycled blends incorporating 50 % reclaimed asphalt pavement and 80 % recycled cement–treated crushed rock. A total of eight FBS mixes were tested with varying host materials, foamed bitumen content from 2 to 4 %, and hydrated lime content of 1 or 2 %. A testing procedure to measure and analyze the fatigue performance of FBS granular base and recycled blends was produced. Using the laboratory test results, a specific laboratory fatigue relationship for FBS materials, including recycled blends, is developed. The flexural modulus, flexural strength-to-modulus ratio, and volume of bitumen were found to be major parameters affecting the fatigue life of FBS materials and were consequently employed to develop the predictive model. This research will assist with the subsequent development of a performance-based in-service fatigue model for thickness design of FBS flexible pavements.

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'.

Summarizing the Effect of Mixture Variables and Test Parameters on Fatigue Performance of Asphalt Mixtures

Abstract Fatigue cracking performance of asphalt mixtures is significantly affected by mixture variables and environmental and loading conditions in the field. Thus, there is a need to understand the effect of critical factors on the fatigue cracking resistance of asphalt mixtures through an extensive study. For this purpose, the present research is focused on characterizing fatigue cracking resistance of asphalt mixtures by considering different factors such as aggregate gradations (two dense and two gap gradations), binder types (two unmodified and three modified binder types), binder content (optimum binder content and optimum binder content ±0.5 %), test temperatures (15°C, 25°C, and 35°C), and three stress levels for different asphalt layer thicknesses (40, 80, 120, 160, 200, and 240 mm). An indirect tensile fatigue test was performed to characterize fatigue cracking resistance of asphalt mixtures, and a Kaplan–Meier survival analysis was carried out to examine whether the factors that were considered significantly affected the fatigue performance. Pavement sections with varying thicknesses of asphalt layers were analyzed using IITPAVE, a pavement analysis software, to compare the mixtures’ fatigue performance. All of the variables taken into consideration in this study were shown to have a statistically significant effect (p value < 0.05). However, the binder type had a stronger influence than the other variables on the resistance to fatigue cracking. Finally, a fatigue life equation (adjusted R2 = 0.77) was developed considering all the mixture combinations, which can be used for determining the laboratory fatigue life of asphalt mixtures.

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.

Data-driven fault detection of a 10 MW floating offshore wind turbine benchmark using kernel canonical variate analysis

Floating offshore wind turbines (FOWTs) can harvest more wind energy in deep water. However, due to their complex mechanical structure and harsh working conditions, various sensors, actuators, and components of FOWTs can malfunction and fail. To avoid serious accidents and reduce operation and maintenance costs, fault detection plays a critical role in wind-energy engineering, particularly for offshore wind energy. Because of complex characteristics, such as dynamics and nonlinearity, an accurate mathematical model cannot be easily obtained from first principles for FOWTs. In this paper, a new data-driven fault-detection method based on kernel canonical variable analysis (KCVA) is proposed for FOWTs. In the proposed method, the collected measurements are first augmented into time-lagged variables to capture the dynamics of FOWTs. The time-lagged variables are then mapped to a high-dimensional feature space to extract nonlinear features. Specifically, canonical variable analysis (CVA) is carried out to explore the correlations in high-dimensional feature space. For fault detection, two monitoring indexes including T 2 and squared prediction error () statistics are established. To verify the performance of the proposed KCVA-based fault-detection method, experiments on a high-fidelity FOWT benchmark, which was created from the National Renewable Energy Laboratory Fatigue, Aerodynamics, Structures, and Turbulence v8.0 simulator, were carried out. The results show the capability and efficiency of the proposed KCVA-based fault-detection method in comparison with other related methods.

Improving asphalt mix design by predicting alligator cracking and longitudinal cracking based on machine learning and dimensionality reduction techniques

• Reasonable asphalt mixture design can mitigate the cracking problems. • Alligator cracking (AC) and longitudinal (LC) cracking are predicted from asphalt mixture properties. • The effect of three different dimension reduction methods on the performance of ML models is analyzed. • ML algorithms includes Support vector regression, Artificial Neural Networks, Kernel ridge regression, Gradient boosting, Extra-trees, eXtreme Gradient Boosting. • The paper improves the current asphalt mix design by adding the criteria of AC and LC and ML models. The asphalt mix design based on traditional laboratory fatigue cracking tests of asphalt mixture is not reasonable due to the difficulty of simulating the circumstance where asphalt mixture experiences in the pavement structure and under realistic climate and traffic conditions. The study aims to mitigate the cracking problems during the pavement design life, by improving the asphalt mix design process by introducing machine learning (ML) models, which are used to predict alligator cracking (AC) and longitudinal cracking (LC), and their criteria (required ranges). The data containing AC and LC were extracted from the NCHRP 1-37A report and the long-term pavement performance (LTPP) program. A total of 33 input features about climate condition, traffic, pavement structure, and materials properties of each pavement layer were selected. Support Vector Regression (SVR), Artificial Neural Networks (ANN), Kernel ridge regression (KRR), Gradient boosting (GB), Extra-trees, and eXtreme Gradient Boosting (XGBoost) were used. Meanwhile, three dimensionality reduction approaches, including Auto-Encoder (AE), Principal Component Analysis (PCA), and Recursive feature elimination with Random Forest, were combined with the six ML algorithms (18 hybrid models produced) in order to decrease the computation complexity and search for the optimum model. The 24 models (6 basic ML models plus 18 hybrid models) were trained, and their hyperparameters were tuned using Bayesian optimization. Different evaluation criteria R 2 , RMSE, MAE, SMAPE, and SI are calculated to evaluate the performance of these models. The results of the study showed that except for ANN and SVR, the basic ML models can get better for predicting AC and LC when they are combined with PCA or AE. Based on the performance indices, the optimum among these developed models proved to be PCA-ANN for predicting AC (R 2 = 0.84) and LC (R 2 = 0.83). Compared to other pavement layers, the asphalt surface course is the highest contributor to AC and LC. The improved mix design process was implemented to determine the mix proportion for the asphalt surface course of a construction project and Mix-2 with 5.1 % asphalt content was recommended.

Interlaminar stability analysis and evaluation of the asphalt pavement with heating cables based on shear fatigue test

The asphalt pavement with heating cables (APHC) was widely used for snow/ice-melting. However, the adverse effects of heating cables on the interlaminar stability of APHC was neglected. Therefore, an evaluation method was developed to evaluate the interlaminar stability of APHC. Firstly, the shear fatigue life equations for APHC with different cable types were obtained through shear fatigue test results. Through the fatigue life equations, the damage model was established to describe the nonlinear shear damage characteristics of APHC, andthe safety range of cumulative strain (ϵN ) was obtained as an evaluation index. Secondly, the actual shear fatigue life (NAf ) was proposed by axial-load conversion and the number of laboratory fatigue loading. Finally, an evaluation method was developed, which has a good agreement with the field validation data. The mentioned method evaluate the interlaminar stability of AHPC from two aspects. One is ϵN should be controlled within the safe range. Another is NAf meets the number of standard axial load in transverse shear. .

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.

Laboratory fatigue performance of the cement-stabilised loess fabricated using different compaction methods

Herein, the fatigue performance of cement-stabilised loess (CSL) designed using two compaction methods were investigated. The reliability of the vertical vibration testing method (VVTM) was verified by comparing the physical properties of the laboratory samples prepared using the VVTM and the proctor compaction test (PCT) and the mechanical properties of the core samples obtained using these methods and from the construction site. Further, the CSL samples fabricated using the two compaction methods were subjected to indirect tensile fatigue tests to establish a fatigue equation. Finally, the influence of the compaction method, compaction degree and cement content on the fatigue performance of CSL was analysed based on the fatigue equation of CSL. Results showed that the correlation between the mechanical strength of the CSL sample prepared using VVTM and the core sample obtained from the construction site is more than 90%. The fatigue equation based on the Weibull distribution can effectively evaluate the fatigue life of CSL. Furthermore, the fatigue performance of VVTM sample is better than PCT sample. The equivalent fatigue life of VVTM sample with 4% cement dosage can be increased by at least 33% compared with PCT sample under the same condition. With the increase of compaction degree or cement content, the fatigue performance is gradually enhanced.

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.

Fatigue Resistance and Cracking Mechanism of Semi-Flexible Pavement Mixture.

Semi-flexible pavement (SFP) is widely used in recent years because of its good rutting resistance, but it is easy to crack under traffic loads. A large number of studies are aimed at improving its crack resistance. However, the understanding of its fatigue resistance and fatigue-cracking mechanism is limited. Therefore, the semi-circular bending (SCB) fatigue test is used to evaluate the fatigue resistance of the SFP mixture. SCB fatigue tests under different temperature values and stress ratio were used to characterize the fatigue life of the SFP mixture, and its laboratory fatigue prediction model was established. The distribution of various phases of the SFP mixture in the fracture surface was analyzed by digital image processing technology, and its fatigue cracking mechanism was analyzed. The results show that the SFP mixture has better fatigue resistance under low temperature and low stress ratio, while its fatigue resistance under other environmental and load conditions is worse than that of asphalt mixture. The main reason for the poor fatigue resistance of the SFP mixture is the poor deformation capacity and low strength of grouting materials. Furthermore, the performance difference between grouting material and the asphalt binder is large, which leads to the difference of fatigue cracking mechanism of the SFP mixture under different conditions. Under the fatigue load, the weak position of the SFP mixture at a low temperature is asphalt binder and its interface with other materials, while at medium and high temperatures, the weak position of the SFP mixture is inside the grouting material. The research provides a basis for the calculation of the service life of the SFP structure, provides a reference for the improvement direction of the SFP mixture composition and internal structure.

Modelling the stiffness development in asphalt concrete to obtain fatigue failure criteria

The study of fatigue is critical to good usability and durability of asphalt pavements. Inaccurate calculation of the fatigue failure criteria can cause incorrect evaluation of the fatigue performance, leading to inaccurate prediction of the pavement performance and poor maintenance planning. This paper develops a stiffness change tendency method (SCTM) that can be used to model the stiffness evolution in asphalt concrete and determine critical laboratory fatigue failure points to characterise different fatigue damage stages. A logistic model was selected to represent the relationship between the log of the stiffness (E) and the log of the number of cycles (N) obtained from two-point bending (2PB) fatigue tests. The measured stiffness reduction versus loading curves were determined for a range of asphalt mixtures in unaged, aged and moisture damaged conditions by testing at various temperatures and strains. By analysing the derivatives of the logistic model, it is possible to identify three transition points associated with fatigue progression. There is good agreement between the laboratory data and the logistic model proposed, confirming that the logistic model is a good approximation to the stiffness reduction curves. The number of loading cycles associated with the first two transition points in the SCTM (NP1 and NP2) were compared to the value of N1 and Nfm obtained from the energy ratio (ER) method and the ratio of dissipated energy change (RDEC) method, respectively. There are no statistically-significant differences between the SCTM and two energy-based methods, proving that P1 can be viewed as the number of cycles to micro-crack initiation and propagation, and P2 can be defined as the macro-crack generation point (the true failure point). Three different mixtures are subjected to four-point bending (4PB) fatigue tests to demonstrate the applicability of the SCTM with different bitumen types, mixture grades and test methods. The SCTM provides a method to model stiffness development, obtain different fatigue failure criteria and characterise different fatigue damage stages, which could be useful in a simulation of pavement deterioration.

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.