Transverse Fatigue Crack Research Articles

Unbonded Concrete Overlay Critical Stress Prediction for Conventional and Short Width Lanes

Accurate critical stress prediction is a key element for a mechanistic–empirical design of pavement structures. For unbonded concrete overlays (UBOL), the critical stress prediction procedure used by the current Mechanistic–Empirical Pavement Design Guide (MEPDG) has several shortcomings. The current MEPDG UBOL model only predicts top or bottom-critical longitudinal stresses, so transverse fatigue cracking is considered whereas longitudinal cracking, which has been observed in several in-service overlays, is ignored. The MEPDG critical stress prediction models assume that the UBOL and the existing pavement have the same deflection profiles, ignoring the separation between the overlay and the existing pavement. Various interlayer properties influencing critical overlay stress are also overlooked. In addition, the model only considers conventional lane width UBOLs and is unable to analyze short slab overlays. The latter has been gaining popularity as an attractive geometry for UBOLs. This paper documents the development of an improved procedure for computing UBOL critical stresses for conventional and short width slabs geometry. The procedure is able to predict critical transverse and longitudinal stresses at various locations taking into account interlayer stiffness and the presence of voids in the interlayer. Rapid solutions using neural networks were developed to enable computationally efficient UBOL critical stress prediction.

Dynamic Strain Response of Hot-Recycled Asphalt Pavement under Dual-Axle Accelerated Loading Conditions

Accelerated pavement testing (APT) is an effective method to study the long-term performance of pavement. Therefore, the dynamic strain behavior analysis of asphalt pavement has important guiding significance in the study of pavement failure modes. To explore the dynamic response of a high-content plant-mixed hot-reclaimed asphalt mixture under a dynamic load of vehicles, a full-scale test road was paved, and ALT biaxial accelerated loading test equipment was used to simulate the dynamic loads of vehicles. Based on parameters such as axle load, temperature, speed, and loading times, the development law for the bottom strain of the three pavement structures was analyzed. The test results show that the most unfavorable position of the asphalt pavement load is located just below the centerline of the wheel track on one side, and the damage effect of a single double-axle wheel load is far greater than that of two single-axle wheel loads. Then, the longitudinal tensile strain of the pavement bottom always maintains the alternating state of compression-tension and compression. The longitudinal tensile strain of the pavement bottom is larger than the transverse tensile strain, and transverse fatigue cracks appear first. Under normal temperature conditions, the bottom tensile strains of the three composite pavement structures under different axial loads are close, and the pavement performance of the hot-recycled asphalt pavement of structure A and structure B can meet the specification requirements. The relationship between the bottom strain and axle load is nonlinear and is directly related to the tire ground pressure, and the difference in the tensile and compressive strain values of the bottom of the three composite pavement structures is small. Under high temperature conditions, the bottom layer temperature of structure A and structure B is lower than that of structure C, and the thermal heat transfer efficiency of hot-recycled asphalt pavement is lower than that of ordinary asphalt pavement. Additionally, the longitudinal tensile strain is about 1–1.5 times that of the transverse tensile strain. Based on the Boltzmann function, the accumulative tensile strain prediction model was established to reflect the relationship between the cumulative strain at the bottom and the number of loads.

Numerical and experimental study on quantitative assessment of multiple fault parameters in a warped internally damped rotor with a transverse fatigue crack integrated with an active magnetic bearing

This work aims to apply experimental data in the multi-fault identification algorithm developed for an internally damped warped cracked rotor system integrated with an auxiliary active magnetic bearing (AMB).A quantitative assessment of additive stiffness due to crack, unbalance, and residual bow with their orientations, multiplicative fault due to residual bow and crack, external and internal (rotating) damping, and AMB parameters that affect the dynamics of the system is done. The rotor experiences multiple harmonics in rotation due to the effect of crack and multiplicative bow-crack fault. To overcome the drawback of removal of residual bow at only 1X harmonic in signal processing, the present work addresses the simultaneous estimation of crack, bow, and multiplicative faults. Measurements of vibrational signalsof shaftand control current from PID controller are taken from the rotordynamic test bench. The multi-harmonic full spectrum amplitudes and phases of forward and backward whirl extracted from the measured test data are fed to theidentification algorithm which estimates fault and system uncertain parameters of fatigue cracked rotor system.This technique can effectively identify simultaneous rotor faults with prior knowledge of some characteristics of the rotor system. The novelty of this work is the identification of shaft residual bow with additive stiffness of crack where the additive crack stiffness is the direct indicator of crack and the magnitude of residual bow is of the permanent bend in rotor defining their severity.

Анализ разрушения перлитной рельсовой стали с внутренней макротрещиной

One of the most dangerous defects leading to transverse fractures of rails is internal transverse cracks in the rail head. In this work, a fractographic analysis of the cross-sectional surface of a rail with a transverse fatigue crack is carried out. The rail sample was taken out of work after many years of service. Microstructural analysis of the crack surface and the surrounding material shows a significant degradation of the physical and mechanical properties of the rail steel.

Assessing surface fatigue crack growth in railway wheelset axle

Purpose: The aim of the proposed research is to create a calculation model of surface fatigue crack growth at the axle of railway wheelset working under operational loads. Design/methodology/approach: The energy approach of the fracture mechanics was used to formulate the calculation model of fatigue crack propagation at the wheelset axle surface. The method of least squares was used to determine the investigated material mechanical constants that the kinetic equations of the calculation model contain. The system of differential equations of crack growth kinetics was solved numerically using the Runge-Kutta method. Findings: On the basis of the energy approach of the fracture mechanics the calculation model of fatigue macrocrack growth in three-dimensional elastic-plastic body in case of a mixed-mode I+II+III macromechanism of fracture has been built. On the basis of the created calculation model, the kinetics of the growth of fatigue cracks was investigated both in the middle part of the wheelset axle and in the axle journal. Research limitations/implications: The results obtained on laboratory specimens should be tested during a real railway wheelset axle investigation. Practical implications: The created calculation model can be used in practice to formulate method of residual lifetime estimation of railway wheelset axle. Originality/value: It was shown, that surface crack kinetics depends not only on the crack initial area but also significantly depends on the crack edge geometry and comparatively small crack-like defects at the wheelset axle surface can reach critical sizes in comparatively short run. It has been found that mechanical shear stresses caused by the weight of the loaded railway wagon in the cross section of the wheelset axle journal can significantly accelerate the growth of the transverse fatigue crack at the axle surface, reducing the period of crack subcritical growth by about 20%.

Detection and localization of fatigue-induced transverse crack in a rotor shaft using principal component analysis

Rotor shafts subjected to severe operating stresses are prone to develop transverse fatigue cracks at the localized stress raisers. Therefore, the ability to identify and locate the incipient fatigue crack is imperative in order to avoid catastrophic failure. The literature on rotor crack detection discussed the importance of monitoring the steady-state 1X, 2X and 3X harmonic response components of rotors. However, the other rotor faults such as misalignment and unbalance, exhibit similar symptoms. Thus, the main aim is to develop new independent fault-related features which measure the driving principle governing the behaviour of various rotor faults. In this article, the application of principal component analysis–based statistical pattern analysis, as a tool for early detection and localization of fatigue-induced transverse crack in a rotor shaft is investigated. To perform this study, accelerated fatigue experiments are conducted on a customized setup. This developed test rig is novel and unique by itself that facilitates generating a fatigue crack in a shaft, under conditions that mimic a real in-service loading environment of industrial rotors. Unlike conventional methods, noise in the acquired vibration and strain data is denoised via classical principal component analysis method. Time- and frequency-domain statistical features extracted from different vibration and strain sensor signals are used for this study. Damage indices such as Hotelling’s T2-statistic and Q-index are used to detect the presence of the crack. It is observed that irrespective of the sensor location, damage index such as Q-statistic of all the sensors is very effective to detect the presence and time of incipient crack. Partial decomposition contributions method is found to be very effective in identifying the location of the crack. This article provides the most significant vibration-based statistical features, which are sensitive to shaft transverse cracks, for different sensor types and their mounting location. Finally, a new fused health indicator which is highly sensitive to the presence of rotor shaft crack is defined and is found successful when applied to a new experimental data.

Experimental study of the performance of a stress-absorbing waterproof layer for use in asphalt pavements on bridge decks

The presence of negative bending moments at the top of a continuous beam bridge can facilitate the sawing of false seams. The concrete bridge deck and its asphalt pavement will therefore develop transverse fatigue cracks under long-term cyclic traffic loads. This paper aims at preventing reflective cracks from forming in such asphalt pavements. The structure and materials used in crack prevention based on a composite stress-absorbing layer (CSAL) consisting of a geotextile and an asphalt gravel seal coat were investigated. The properties of polypropylene (PP) geotextiles were evaluated by means of differential scanning calorimetry, thermogravimetric analysis, thermal shock tests, etc. Adhesion, shear, and tensile tests were used to study the influences of factors such as the type, amount of asphalt materials, and construction temperature on the bonding performance of the pavement interface. Texas overlay tests were also carried out to explore the anti-reflective cracking and anti-fatigue performance of different pavement structures including an asphalt rubber stress-absorbing membrane interlayer (ARSAMI) and a CSAL. The results show that the PP geotextile has a melting point of about 166 ℃, a glass-transition temperature in the range of –20 to –10 ℃, and a thermal decomposition temperature of about 400 ℃. In addition, it retains good strength and deformability when subjected to thermal shock at 180 ℃, and it has high thermal stability. The modified asphalt has the highest adhesion strength to concrete slabs, followed by ordinary asphalt and then emulsified asphalt. The temperature state of the bonding layer is not sensitive to the bond strength of the bridge deck paving structure. The asphalt mixture waterproofs the surface after paving. The adhesive stress-absorbing layer imparts a secondary heating effect, thereby ensuring interface adhesion. Using a pavement structure with a CSAL can enhance resistance to reflective cracking at a low temperature by more than 5 times compared to the case not taking preventative measures. Its resistance to reflective cracking under a deformation amplitude of 2 mm at the room temperature (20 ℃) is also slightly better than that of the ARSAMI. Hence, CSALs have promising prospects for use in crack prevention.

Experimental Identification of Internal and External Damping in a Rotor System with a Fatigue-Crack Using Full Spectrum

Demand of higher speeds in rotor systems has elevated the possibility of numerous instabilities. Internal damping is one of the key parameters for instability in such machinery. Its studies are generally conducted for a possible range of chosen internal damping values. Hence, experimental estimation of internal damping along with external damping is very vital for an accurate prediction of rotor stability, which is scarcely addressed in the literature. To fill this gap, current paper presents an experimental identification methodology for estimation of the internal and external damping in a cracked rotor system. Other crucial unknown fault parameters of rotor system, like additive crack stiffness and unbalance, have also been identified. In present work, internal damping due to rub between transverse fatigue crack faces has been envisioned for the first time. Hence, internal damping has been considered due to combined effect of material hysteretic, i.e. the rub between transverse fatigue crack faces, and the rub between disc and shaft during shaft rotation. Measurements much below critical speeds ensures the main contribution of crack in internal damping due to weight dominance effect as compared to shaft material damping. In experimental setup, a hairline fatigue crack was artificially developed by three-point bending procedure in a shaft at a notch location. The opening and closure behavior of crack faces during rotation of the shaft leads to the forward and backward whirls of the rotor at multiple frequencies, which are apparent in the full spectrum. Mathematical modeling of the rotor system for development of identification algorithm is based on these behaviors of cracked rotor system. Experimentally measured responses have been converted into the full spectrum (both amplitude and phase) based on regression analysis and fast Fourier transform (FFT). Earlier, amplitudes of full spectrum have been used for qualitative indication of crack. But in the present work, corresponding phase has also been considered in quantitative estimation of crack parameter along with other system fault parameters. With the help of a multi-frequency reference signal, phase anomalies have been removed during processing of full spectrum. The bow effect of shaft has been removed from full spectrum responses with the help of a slow roll measurement. Estimated parameters are consistent for different sets of rotor speeds and for different frequency ranges of excitation forces due to fatigue crack. Validations of identified parameters have been done by comparing experimental responses with numerically generated system responses. The latter was generated using experimentally identified parameters in the mathematical model of cracked rotor system.

Determination of the Fatigue Crack Growth Rate and Time in Rails Using Fatigue Macrolines

The kinetic of propagation of the transverse fatigue crack nucleated in the rail head at a depth of 4 mm from the roll surface and caused the fracture of the rail is studied. Fatigue macrolines are shown to be used to determine the transverse fatigue crack growth rate and time in the head of the rail in a one-track railway line, where the train motion direction is periodically changed at known times.

Analysis and identification of the additive and multiplicative fault parameters in a cracked-bowed-unbalanced rotor system integrated with an auxiliary active magnetic bearing

The present work brings out a novel model based analysis and identification of the additive and multiplicative fault parameters in an active magnetic bearing (AMB) controlled rotor system. In mathematical modeling, the unbalance is considered as an additive fault, whereas the effect of shaft residual bow on crack are considered as multiplicative faults. In equations of motion (EOMs), the multiplicative fault parameters appear in a product form, which is much more challenging to handle as well of the practical importance for its analysis and identification. EOMs have been developed considering the influences of the external as well as internal (rotating) damping, and the gyroscopic effect due to axially offset disc on the rotor-AMB system. The shaft has a transverse fatigue crack (breathing model) and an initial shaft bow. The proposed rotor-AMB model uses a PID (proportional-integral-derivative) controller to regulate the supply currents to the AMB to actively control the vibration of the system due to inherent faults. In the response analysis, the effects of rotor faults on the rotor displacements and AMB control currents are shown in full spectrum. Furthermore, an identification methodology has been developed from complex frequency domain EOMs to facilitate the estimation of the additive and multiplicative fault parameters in a cracked bowed rotor system. To comply with the practical aspects, different measurement noises and modeling errors have been added to test the robustness of the proposed algorithm.

Self-healing of fatigue damage in cross-ply glass/epoxy laminates

Self-healing of fatigue damage is reported in laminated composites fabricated from unidirectional glass/epoxy prepreg with embedded microcapsules. Microcapsules (ca. 2.5 μm) containing a mixture of ethyl phenylacetate (EPA) solvent and diglycidyl ether of bisphenol A (DGEBA) epoxy are seamlessly incorporated into cross-ply [(0/903)4/0]T laminated composites. Specimens subjected to tension-tension fatigue testing followed by a 24 h rest period at ambient conditions recover 52% of the initial Young's modulus as a result of self-healing. Fluorescent labeling of microcapsules and matrix resin combined with confocal fluorescent imaging reveals that the healing agents wick into transverse fatigue cracks, ultimately rebonding the crack faces after self-healing. Furthermore, self-healing composite laminates exhibit a higher resistance to crack growth as a result of the presence of the embedded microcapsules. The fatigue behavior of laminated self-healing composites demonstrates the potential for extended fatigue life of fiber-reinforced polymer composites for structural applications.

Effect of Deoxidation Process on Inclusion and Fatigue Performance of Spring Steel for Automobile Suspension

55SiCrA spring steel was smelted in a vacuum induction levitation furnace. The liquid steel was treated by Si deoxidation, Al modification with Ca treatment and Al modification, and the steel samples were obtained with deformable Al2O3-SiO2-CaO-MgO inclusions closely contacted with steel matrix, Al2O3-CaO-CaS-SiO2-MgO inclusions surrounded by small voids or Al2O3(> 80 pct)-SiO2-CaO-MgO inclusions surrounded by big voids, respectively. Effect of three types of inclusions on steel fatigue cracks was studied. The perpendicular and transverse fatigue cracks around the three types of inclusions leading to fracture were found to vary in behavior. Under the applied stress amplitude of 775 MPa, the fatigue lives of the three spring steels decreased from 4.0 × 107 to 3.8 × 107, and to 3.1 × 107 cycles. For the applied stress amplitude of 750 MPa, the fatigue lives of the three spring steels decreased from 5.2 × 107 to 4.1 × 107, and to 3.4 × 107 cycles. Based on the voids around inclusions, the equivalent size of initial fatigue crack has been newly defined as $$ \sqrt {\frac{{{\text{area}}_{\text{inclusion}} }}{{(1 - {\text{CC}})}}} $$ , where the contraction coefficient CC of inclusion was introduced. A reliable forecast model of the critical size of inclusion leading to fracture was established by the incorporation of actual width binclusion or diameter dinclusion of internal inclusion; the model prediction was found to be in agreement with experimental results.

New crack breathing mechanism under the influence of unbalance force

In this paper, a new analytical model (unbalanced one), which considers the coupling effects of unbalance force, rotor weight, and rotor physical and dimensional properties, is developed to study the actual breathing mechanisms of the transverse fatigue crack in a cracked rotor system. The results are also compared with those of the existing balanced model, where only rotor weight is considered. It has been identified that a crack in the unbalanced model breathes differently from the one in the balanced model. A crack’s breathing mechanism in the unbalanced model depends strongly on its location along shaft length. At some special locations, a crack in the unbalanced model may remain fully closed or open during the shaft rotation, which will never occur in a balanced model. It may also behave completely like the one in the balanced shaft. Depending on the crack location, unbalance force magnitude and orientation, the unbalanced shaft may be stiffer or more flexible than the balanced counterpart. It is also demonstrated that the unbalanced model will progressively approach balanced one as unbalance force decreases. Further, different crack breathing mechanisms between two models lead to a large difference along shaft length in the second area moment of inertia, which forms the elements of local stiffness matrix at crack location. It is expected that more accurate prediction of the vibration response of a cracked rotor can be achieved when the effect of unbalance force and rotor properties on the crack breathing has been taken into account.

Rotordynamic Crack Diagnosis: Distinguishing Crack Depth and Location

The goal of this work is to establish simple condition monitoring principles for diagnosing the depth and location of transverse fatigue cracks in a rotordynamic system. The success of an on-line crack diagnosis regimen hinges on the accuracy of the crack model, which should account for the crack's depth and location. Two gaping crack models are presented; the first emulates a finite-width notch typically manufactured for experimental purposes, while the second models a gaping fatigue crack. The rotordynamic model used herein is based upon an available overhung rotordynamic test rig that was originally constructed to monitor the dynamics of a mechanical face seal. Four degree-of-freedom, linear equations of motion for both crack models are presented and discussed. Free and forced response analyses are presented, emphasizing results applicable to condition monitoring and, particularly, to diagnosing the crack parameters. The results demonstrate that two identifiers are required to diagnose the crack parameters: the 2X resonance shaft speed and the magnitude of the angular 2X subharmonic resonance. First, a contour plot of the 2X resonance shaft speed versus crack depth and location is generated. The magnitude of the 2X resonance along the desired 2X frequency contour is then obtained, narrowing the possible pairs of crack location and depth to either one or two possibilities. Practical aspects of the suggested diagnostic procedure are discussed, as well as qualitative observations concerning crack detection.

An Experimental Investigation on Wear of Rail in Different Curve Radius

Among the rail defects, the transverse fatigue crack, which has been the most dangerous damage, is developed near the rail running face and grows perpendicular to the rail surface. Finally, the transverse fatigue crack would result in the failure of railway rail. In this paper, the rolling tests were performed using a JD-1 wheel/rail simulation facility without any lubricant. The tester is composed of a small wheel served as rail and a larger wheel served as wheel. The fatigue behavior of rail rollers with different materials and curve radius were investigated in detail by examining wear volume and wear scar using optical microscopy (OM) and scanning electronic microscopy (SEM). The results indicate that with curve radius decreasing, the wear volume of rail roller increases rapidly and the fatigue damage becomes severe. Furthermore, the cracking propagation angle increases obviously with curve radius decreasing and fatigue wear is dominating during the wear process. There appears distinct plastic deformation on the section of rail roller under small curve radius condition. For the same curve radius, the wear volume of PD3 rail is more than that of PG4 rail and the plastic deformation is more obvious. Moreover, the cracking propagation angle of PD3 rail material is smaller than that of PG4 rail. In conclusion, PG4 rail material is not suitable for the high-speed railway.

Crack Detection in a Rotor Dynamic System by Vibration Monitoring—Part II: Extended Analysis and Experimental Results

Abstract An increase in the power-to-weight ratio demand on rotordynamic systems causes increased susceptibility to transverse fatigue cracking of the shaft. The ability to detect cracks at an early stage of progression is imperative for minimizing off-line repair time and cost. The vibration monitoring system initially proposed in Part I is employed herein, using the 2X harmonic response component of the rotor tilt as a signature indicating a transverse shaft crack. In addition, the analytic work presented in Part I is expanded to include a new notch crack model to better approximate experimental results. To effectively capture the 2X response, the crack model must include the local nature of the crack, the depth of the crack, and the stiffness asymmetry inducing the gravity-forced 2X harmonic response. The transfer matrix technique is well suited to incorporate these crack attributes due to its modular nature. Two transfer matrix models are proposed to predict the 2X harmonic response. The first model applies local crack flexibility coefficients determined using the strain energy release rate, while the second incorporates the crack as a rectangular notch to emulate a manufactured crack used in the experiments. Analytic results are compared to experimental measurement of the rotor tilt gleaned from an overhung rotor test rig originally designed to monitor seal face dynamics. The test rig is discussed, and experimental angular response orbits and 2X harmonic amplitudes of the rotor tilt are provided for shafts containing manufactured cracks of depths between 0% and 40%. Feasibility of simultaneous multiple-fault detection of transverse shaft cracks and seal face contact is discussed.

On some causes of damage to the water-wall tubes of hot-water boilers

The main causes of damage to the water-wall tubes of hot-water boilers are discussed. The quality of the system water, design factors, and furnace conditions contribute to the damage. Transverse fatigue and corrosion-fatigue cracks on the outer and inner surfaces of water-wall tubes are described. The results of standard and special high-cycle fatigue tests on damaged metal are analyzed. The most important recommendations on the prevention of damage to the water-wall tubes of hot-water boilers are formulated.

Coupled bending-torsional vibration analysis of rotor with rub and crack

Rotor–stator rub and fatigue crack of the shafts are two important rotor faults. They have detrimental effects on health and reliability of the rotating machinery. In this paper, modelling and vibration signature analysis of rotor with rotor–stator rub, transverse fatigue crack and unbalance is attempted. The rotor–stator interaction effects on the response of a rotor are investigated in the presence/absence of a transverse crack. The torsional vibrations are investigated for their sensitivity to rubbing using finite element model that also accounts for cross coupling of stiffness introduced due to crack. Due to the presence of both rotor–stator rub and transverse crack in a horizontal rotor, the system becomes highly nonlinear. The time localised rub excitations and nonlinear stiffness variation due to breathing of the crack influence the rotor response in both lateral and torsional modes and are explored extensively using Hilbert–Huang transform with the objective of unravelling some unique features of these faults that may be useful for fault identification.

Transverse Cracking of Layered Structures: Evaluation of Fatigue Crack Propagation

The objective of this paper is to investigate the transverse fatigue cracking of layered structures. To this end a fatigue crack propagation rate for a crack growing perpendicularly through the interfaces between individual layers of the structure is estimated. The suggested procedure takes into account the influence of different material properties of the layers on the stress field around the fatigue crack and the change of the stress singularity exponent in the special case of a crack touching the material interface. The assumptions of linear elastic fracture mechanics and elastic behaviour of the composite are considered. It is shown that the existence of the interfaces can have a negative influence on the residual fatigue life of layered structures.

Investigation of service failures of steel music wire

An investigation of a number of service failures of the hard steel strings of plucked musical instruments is reported. All the failed strings were found to contain transverse fatigue cracks, mostly located near the end of the vibrating length (e.g. at the “bridge” of the instrument) and extending to about one third of the section thickness. One wire had corroded severely before failing in fatigue. Final failure occurred by ductile fracture. An analysis of the service stresses showed that the strings are subjected to high mean tensile stresses resulting principally from elastoplastic bending opposite the failure location. It is shown that a small cyclic axial tension arises from repeated plucking during playing and this can lead to fatigue initiation and propagation over a large proportion of the wire cross section. Neither surface nor bulk defects, wear nor contact stresses were found to be factors of importance in the cases examined, contrary to some speculation.