Cyclic Fatigue Loading Research Articles

Fatigue crack growth in CNT-reinforced polymer composite

Carbon nanotubes (CNT)-reinforced polymer composite has many engineering applications due to attractive properties, like high strength to weight ratio. These materials are subjected to cyclic fatigue loading during their service life. This work proposed a dual scale modeling approach to predict fatigue crack growth behavior of CNT-reinforced polymer composite under the thermo-mechanical loading environment. The effective orthotropic property of CNT-reinforced polymer composite is estimated using the mean-field homogenization technique in meso-scale modeling. Further, the equivalent composite property is used for macro-scale fatigue crack growth study using higher-order extended finite element method. To present the efficiency of the proposed modeling approach, various combinations of polymer composite (by volume fraction of reinforcement at 7.5%, 10%, 12.5%, 15%, 17.5%, and 20%) are taken for analysis. At macro-scale modeling, XFEM with higher-order enrichment terms is employed to improve the solution accuracy at the crack tip region. The proposed computational approach has been employed with the in-house developed MATLAB code and DIGIMAT software. Several numerical examples are considered with geometrical discontinuities like multiple holes and cracks.

Advanced characterisation of flexural fatigue performance of foamed bitumen stabilised pavement materials

This study investigates the flexural fatigue behaviour of FBS mixtures at different temperatures (11℃, 22℃ and 31℃) bitumen contents (2%, 3% and 4%), secondary binders (cement at 2% and hydrated lime at 2% and 4%), densities (2.14 kg/m3, 2.20 kg/m3 and 2.26 kg/m3) and moisture contents (dry and 90% saturation) with a view to developing a rigorous design approach for FBS pavements. The experimental results showed that the flexural fatigue life of the FBS beams increases with increasing density and bitumen content while it decreases with increasing temperature and moisture content. Further, no noticeable difference was seen in the flexural fatigue life of FBS specimens with 2% and 4% hydrated lime contents while the FBS mixtures with 2% cement showed significantly higher fatigue life than those prepared with 2% hydrated lime. The flexural fatigue life of 3% bitumen and 2% lime FBS mixture under strain-controlled mode was found to be around 21 times higher than that under stress-controlled mode for a given initial flexural strain. The normalised modulus degradation master curve in stress-controlled mode appears to demonstrate a characteristic behaviour of FBS materials under cyclic fatigue loading. Using this new concept and the experimental results, suitable analytical models were developed for the prediction of the flexural fatigue life of FBS mixtures under both stress-controlled and strain-controlled modes taking into account the variations in temperature, bitumen content, moisture content and density of the FBS mixtures.

Finite Element Analysis of Crack Propagation in Precise Separation Process of Tubing Eccentric Loading Fatigue Fracture

Aiming at the difficulties of efficient and precise separation of metal tubes. For tubing fatigue fracture precision separation, this paper proposes a tubing precision separation process under eccentric wheel rotational bending fatigue loading. Mechanical properties experiments for 304 stainless steel tubing are carried out. On this basis, the J-C constitutive model of 304 stainless steel tubing fatigue fracture is established. In addition, the tubing stress at different rotation angles of the eccentric wheel and the axial stress at four positions of the tubing V-groove section are analyzed, and the process of the tubing precision separation is simulated. According to the results, the axial stress of the tubing V-groove section changes basically symmetrically, and the stress is the largest at the smallest distance from the eccentric wheel excircle axis. During fatigue loading cycles from 0 to 500, the crack growth rate of tubing outer ring is greater than that of the inner ring. With the increase in loading cycles, the crack surface gradually changes from smooth to undulating. Finally, an obvious final fracture region appears, which is consistent with the experimental results.

Strengthening pre-damaged RC square columns with fabric-reinforced cementitious matrix (FRCM): Experimental investigation

This study investigates the effectiveness of using fabric-reinforced cementitious matrix (FRCM) systems in repairing pre-damaged reinforced concrete (RC) square columns. Two groups of columns were fabricated and tested under concentric loading up to failure. Columns of each group had different spacing between their transverse reinforcement to investigate the effectiveness of FRCM reinforcement in confining the columns. The columns were subjected to two pre-damaging criteria prior to strengthening. Four columns were loaded up to their yielding capacity and then unloaded while the other two columns were subjected to three cycles of fatigue loading that ranged between 2% and 75% of the unstrengthened column’s capacity. The pre-damaged columns were then strengthened with either two or four layers of polyparaphenylene-benzobisoxazole (PBO)–FRCM system. Test results showed that confining the pre-damaged columns with PBO–FRCM systems resulted in 7–42% enhancement in their load–carrying capacity and 47–272% improvement in their ductility. The predicted columns’ capacity calculated as per ACI 549 guidelines showed a good agreement with the experimental results. The experimental–to–predicted capacity ratio ranged between 0.82 and 1.03 for columns with tie spacing of 180 mm and between 0.92 and 1.09 for columns with tie spacing of 90 mm.

Evaluation of the Fatigue Behaviour and Failure Mechanisms of 52100 Steel Coated with WIP-C1 (Ni/CrC) by Cold Spray

Cold spray technique has been major improved in the last decades, for studying new properties for metals and alloys of aluminum, copper, nickel, and titanium, as well as steels, stainless steel and other types of alloys. Cold sprayed Ni/CrC coatings have the potential to provide a barrier as well as improved protection to steels. Fatigue characteristics of 52100 steel coated with Ni/Chrome-Carbide (Ni/CrC) powder mixture by using cold gas dynamic spray are investigated. Fatigue samples were subjected to symmetrically alternating, axially applied cyclic fatigue loading until failure. The test was stopped if a sample survived more than 5 × 106 cycles at the applied stress. Fracture surfaces for each sample were examined to investigate the behaviour of the coating both at high stress levels and at a high number of stress cycles. Scanning electron microscopy was used to assess the damage in the interface of the two materials. Good fatigue behaviour of the coating material was observed, especially at low stresses and a high number of cycles. Details of the crack initiation region, the stable crack propagation region and the sudden crack expansion region are identified for each sample. In most of the samples, the initiation of the crack occurred on the surface of the base material and propagated into the coating material. The possible effects of coatings on the initial deterioration of the base material and the reduction of the lifespan of the coated system were also investigated. The aim of the paper was to study the interface between the base material and the coating material at the fatigue analysis for different stresses, highlighting the appearance of cracks and the number of breaking cycles required for each sample.

Behavior of Postcracked steel fiber‐reinforced concrete in fatigue and development of a damage prediction model

AbstractThis paper reports the results of 27 tests on determinant round panels undertaken to determine the postcracking resistance to repeated cycling (fatigue) loading of steel fiber reinforced concrete (SFRC) of low fiber dosages. The experiments were conducted for both precracked and uncracked panels to examine the contribution of postcracking tensile strength, and the effectiveness of steel fibers in providing resistance to fatigue damage. The results quantify the improvements of fibers to fatigue life of SFRC and, particularly, to the important second stage of crack growth during cyclic loading. From the outcomes of the testing program, a damage prediction model is proposed for forecasting postcracking fatigue damage during repeated cyclic loading. The model is shown to accurately predict the overall load‐stiffness response, capture the development crack openings with increasing cycles, as well as quantify the stiffness development and number of load cycles to failure.

The study on the overloading effect on fatigue crack growth considering residual stress relaxation in Al 5456-H38

A numerical and experimental study was conducted on fatigue crack growth (FCG) of metallic components to investigate the effect of redistribution of mechanical residual stresses induced by overloading in notched specimens. The compact tension (CT) specimens of an aluminum alloy were used, and mechanical residual stresses were introduced in them by applying tensile overload (OL). Then, the specimens were subjected to fatigue loading. In the calculations of finite element method (FEM), the modified cyclic J-integral was used as the crack growth parameter. Good agreement was observed between the numerical and experimental results. The FEM results demonstrated a clear redistribution of residual stresses during FCG process. It was observed that after a few cycles, the residual stress field reached a lower magnitude value confining in a small zone around the around the crack tip. Furthermore, the effects of stress ratio, load amplitude, and OL ratio (OLR) on the redistribution of residual stresses are studied in this research. It was observed that the residual stresses are considerably released during the initial cycles of fatigue loading.

The influence of cyclic ageing on the fatigue performance of bonded joints

Although the cyclical environment can significantly influence the fatigue performance of the bonded joints, however, the interactions of cyclic ageing and fatigue loading on the mechanical performance of bonded joints have not been studied yet. Accordingly, the aim of the current study is to investigate the influence of cyclic ageing on the fatigue behaviour of epoxy adhesive joints using Arcan samples. Accordingly, different ageing frequencies, different ageing and drying cycles, and different loading conditions are analysed. As a result, performing a single ageing analysis overestimates the life of adhesive joints if they are exposed to cyclic environments. Results also showed that the life cycle decreases with the ageing frequency.

A Multihull Boat’s Fatigue Analysis at Early Design Phase

Fatigue analysis and life cycle prediction of a naval craft or a commercial ship are one of the most critical phases of structural integrity calculations. Many structural failures have occurred due to insufficient structural design, production methods, and inappropriate operational environmental conditions. As a result of the deterioration of the structural integrity, the occurrence of both vital and economic losses becomes inevitable. This paper emphasises the importance of fatigue and life cycle analyses at the early design phase since the fatigue phenomena are generally considered in the late design stages. In this study, fatigue calculations and life predictions were carried out by the Palmgren–Miner method. The wave rosette, also called long-term wave directionality, was used as the wave spectrum approach. Based on wave loads and accelerations, an FE analysis was carried out using the Maestro Marine Altair Partner Alliance (APA) software. The undamaged life prediction of the vessel was calculated based on different sea states and vessel speeds. A specific scenario, which was prepared based on the International Code of Safety for High-Speed Craft, was also analysed to compare the fatigue life of the vessel with regards to safe operating conditions for passengers and crew. In this study, the effect of sea states, environmental conditions, and materials used on the fatigue behaviour of the vessel are discussed and analysed. As a result of this study, the shortest and the longest undamaged life spans based on the loading scenarios are put forth clearly. Analyses and calculations prove that loading scenario 5 is the most effective scenario in terms of the undamaged life span of the boat. On the contrary, loading scenario 1 gives the shortest service life. The main reason behind this phenomenon is the relation between the fatigue endurance limit and load cycles.

Crack Closure in Cycles with Dwell Times at High Temperature

The growth of short cracks in round bar specimens with a circumferential notch has been investigated by an extensive experimental study. This specific specimen geometry has been applied to determine notch support based on a reduced crack growth rate due to the induced stress gradient compared to situations without a notch. At the same time, this investigation of crack growth in low cycle creep-fatigue conditions reveals a significant influence of dwell times on crack closure, which is discussed in detail in this paper. Therefore, a fracture mechanical approach based on an elastic-(visco)plastic crack growth simulation is used to compute the cyclic effective fatigue and creep crack tip loading. The crack growth rates are then determined by a Paris and Nikbin–Smith–Webster model. All investigations are based on strain controlled conditions at different loading levels. The shape of the applied cycles is trapezoidal, having a dwell time of three minutes at maximum and minimum load, and is symmetric in tension and compression. It turns out that a separate consideration of crack opening and closure reveals an important difference in effective crack tip loading range and therefore has a significant impact on fatigue crack growth. Moreover, this paper shows that the effect of dwell times is linked to the influence on plasticity induced crack closure and to the stress relaxation during the dwell time in compression, yielding less crack closure.

Damage-failure transition under consecutive dynamic and very high cycle fatigue loads

The Foreign Object Damage problem is considered as the damage tolerance statement for consecutive loading tests, which include the shock-wave loading (by explosive generator) of massive planar targets (aluminum alloy AlMg6) to provide a billet for the specimen machining with controlled damage that is the analogous material of the fan blades subjected to high-speed collision with solid particles. These samples were used to perform high cycle fatigue and very high cycle fatigue tests with the ultrasonic testing machine, which allows fatigue loading for 108–1010 cycles with an amplitude of up to several tens of micrometers and a frequency of 20 kHz. It is shown that the fatigue strength of AlMg6 alloy specimens pre-loaded by shock in the 109 cycle regime reduces by 24%. The fatigue damage-failure transition and crack initiation were studied by the amplitude–frequency analysis of higher harmonics associated with the influence of defects on the effective elastic properties. The structural study of the fracture surface for the specimens after consecutive loading was conducted using the profilometry data to identify the roughness scale invariants induced by defects for corresponding areas responsible for the staging of fatigue damage-failure transition. The scale invariants and corresponding lengths were used for the formulation of the generalized Paris law for the crack advance in the damaged material.

Strength deterioration and crack dilation behavior of BFRC under dynamic fatigue loading

To simulate the dynamic traffic loads imposed on the concrete during service, a piece of self-designed dynamic loading equipment was used to study the strength deterioration pattern of basalt fiber reinforced concrete (BFRC) under fatigue loading at 0.5 and 0.7 stress levels. Subsequently, crack images of the fracture surface and interior were obtained with a high-pixel camera and SEM, respectively, from which the fractal dimension of the cracks was finally obtained by processing and calculating with MATLAB, Image-Pro Plus, and Fractalfox software. The results showed that, at 0.5 and 0.7 stress levels, the flexural strengths of both BFRC and the reference concrete gradually decreased with increasing number of load actions, but the higher stress caused a faster decrease. Significantly, the flexural strength of BFRC consistently dropped more slowly than that of the reference concrete. The reduction rate of flexural strength of basalt fiber reinforced concrete was reduced by 2.26% and 5.28% compared with the reference group after 200,000 times at 0.5 and 0.7 stress levels, respectively. The maximum crack length, average crack width and crack area density of fiber concrete decreased by 8.81%, 10.69% and 42.29%, respectively, after 200,000 cycles of dynamic fatigue loading at low-stress level compared to the reference concrete. Fatigue loading with high-stress level accelerates the rate of structural deterioration within the concrete, but basalt fibers improve the fatigue performance of concrete by synergistically stressing it with concrete, changing the direction of crack development and extending the crack expansion path. The flexural strength at low-stress level is significantly negatively correlated with the average crack width, while the flexural strength at high-stress level is significantly correlated with the fractal dimension of cracks, crack area density and average crack width.

Composite-Wedge Anchorage for Fiber-Reinforced Polymer Tendons

A novel composite-wedge anchorage is proposed here for prestressing fiber-reinforced polymer (FRP) tendons. The composite wedge was designed and optimized in terms of the length and elastic modulus of the wedge segments via finite-element analysis. The manufacturing technologies for the composite wedge involving a molding process, are presented in detail. Static, creep, and fatigue tests on basalt FRP (BFRP) tendons with the proposed anchorages were conducted. The tensile capacity, long-term deformation, and fatigue life of the tendon–anchor assemblies were analyzed. The experimental results show that the proposed anchorage exhibits an anchor efficiency factor of up to 91%; the corresponding value for a conventional steel–wedge anchorage is only 80%. The tendon–anchor assembly displays a creep behavior similar to that of BFRP tendons. Furthermore, the system survives 200 million cycles of fatigue load at a maximum fatigue load of 0.5 Fu (Fu is the tensile capacity of the tendon–anchor assembly) and a load range of 0.05 Fu. Wedge–sleeve and tendon–wedge sliding under a sustained load or cyclic load cannot cause considerable prestress loss in practical engineering. The results validate the effectiveness of the proposed anchorage under service loads and demonstrate the application prospects of this anchorage.

Evaluation and comparison of control and heat treated L-shape furniture joints produced from Scotch pine and ash wood under static bending and cyclic fatigue bending loadings

This study investigated how the mechanical properties of L-shape joints produced from heat treated Scotch pine or ash wood behaved under cyclic fatigue loading and compared this with the mechanical properties of non-heat treated wood materials. Additionally, static bending performances of the L-shape of joints were investigated and compared to fatigue bending performance of same type of joints. Results indicated that increasing number of staple from 6 to 8 and density generally increased static bending of L-shape joints. Static bending resistance of L-shape joints produced from control Ash wood significantly higher than those of L-shape joints produced from heat treated Ash wood while no significant difference were observed between static bending resistance L-shape joints produced from control Scotch pine and L-shape joints produced from heat treated Scotch pine wood. The fatigue bending resistances of L-shape joints produced from heat treated samples generally passed and failed the same loading steps with those produced from control samples which means both L-shape joints could be used in same service area. L-shape joints under static and fatigue loadings mostly indicated staple leg shear mode. The one under fatigue loading was more than the one under static loading. Additionally, some joints under fatigue loading indicated staple rupture. The overall ratio of static bending loading to cyclic fatigue bending loading for L-shape joints was obtained as 2.85.

Research on Fatigue Characteristics of Bonding interface of Solid Rocket Motor Propellant

Abstract With the continuous expansion of the combat mission of the Chinese Navy, the solid rocket motor will be on duty at sea for a long time. During the service period of solid rocket motor, the bonding interface will bear a large number of cyclic fatigue loads. According to the design test, the influence of the strain amplitude and frequency of loading on the bonding interface was studied. The results show that the cyclic loading frequency made no difference on the cyclic damage number in the high frequency. The natural logarithm of the cyclic loading times and cyclic loading accord with linear fitting equation.

Efekty oddziaływań zmęczeniowych na drogowe obiekty inżynierskie w Pakistanie na podstawie danych ze stacji ważenia pojazdów w ruchu

Bridges are considered to be the essential structures and represent a vital part of a transportation network. Their safe operation with minimal maintenance closures is paramount for their efficient operation. The continuous increase in volume and weight of truck traffic directly translates into a higher number of accumulated fatigue load cycles. This study utilizes truck traffic data from a Weigh-in-Motion (WIM) station located on Pakistan’s busiest and longest National Highway. An algorithm was developed to simulate vehicle passages over simple analytical bridge models of various span lengths to compute fatigue cycles at critical locations. This was followed by a case study on a reinforced concrete T-beam bridge located under the influence of the selected WIM station to obtain a fatigue stress spectrum for its critical details. This information provides an identification tool for bridges within a stock that are more susceptible to fatigue problems and could form part of a full-bridge management framework.

Strain localization and crack initiation behavior of a PM Ni‐based superalloy: SEM‐DIC characterization and crystal plasticity simulation

AbstractThe strain localization and crack initiation behavior of a powder metallurgy (PM) nickel‐based superalloy FGH4098 under low cycle fatigue (LCF) loads at room temperature is investigated by combining scanning electron microscope (SEM)‐digital image correlation (DIC) characterization with crystal plasticity simulation. The elastic anisotropy near annealing twin boundaries contributes to strain localization and results in high propensity of LCF failure. The effect of local microstructure on the fatigue crack initiation at {111} slip bands and tortuous crack propagation is revealed. Meanwhile, local crystal plasticity finite element cyclic deformation simulation is carried out based on explicit microstructure reconstructed from electron backscatter diffraction (EBSD) characterization. Four metrics of accumulated shear strain, effective plastic strain, shear strain energy dissipation density, and Fatemi–Socie parameter are selected as fatigue indicator parameters to predict crack initiation site. Fatemi–Socie parameter is proved to be a promising metric for crack initiation prediction.

On the correlation of temperature harmonic content with energy dissipation in C45 steel samples under fatigue loading

Fatigue damage onset involves a transformation of mechanical energy. This is in part spent into work of plastic deformation and fracture and in part transformed into heat. Therefore, different thermomechanical heat sources are activated during a fatigue loading cycle, resulting in a temperature modulation that can be characterized by its frequency content. Several studies have monitored the temperature on samples undergoing high-cycle fatigue, measuring specific thermomechanical metrics which could serve as indicators of damage evolution. The present work evaluates the harmonic content of temperature, to investigate its correlation with the material dissipation. The harmonic terms investigated are the amplitude and phase of temperature at the loading frequency (First Harmonic) and at twice the loading frequency (Second Harmonic). The paper reviews the mechanisms linking the evolution of heat dissipation to changes in these four parameters. The theoretical analysis is supported by an experimental campaign carried out on C45 steel tensile specimen subject to R=−1 and R=0.1 loading ratios. The harmonic metrics are evaluated analyzing both their spatially averaged value and their spatial dispersion, to check for the formation of localized heat dissipation zones in early fatigue life. The study shows that the phase of the Second Harmonic signal has a peculiar bimodal distribution that can be correlated to either a thermoelastic or dissipative prevailing effect. This behavior evolves towards a unimodal dissipative behavior when the load amplitude is increased, thus proposing the Second Harmonic phase parameter as an effective indicator for monitoring internal intrinsic dissipation in the material.

Damage Evolution Modeling for Steel Structures Subjected to Combined High Cycle Fatigue and High-Intensity Dynamic Loadings

This paper presents a method for modeling the initiation and propagation of the damage in steel structures under combined fatigue loading. An existing model in the literature is used as the main key to the development of the new formulation herein proposed, where a significant computational improvement for the cracking incubation phase under high cycle fatigue (HCF) is achieved. The results show a satisfactory comparison with experimental data available in the literature and the carried parametric simulations demonstrate the effectiveness of the model once strength reduction could be estimated after 0, 20, 40, and 60 years of HCF. The reduction of the structural capacity was evaluated by the consideration of the final damage due to a high-intensity dynamic loading at the end of the HCF phase.

Conformity assessment model for mechanical coupling devices and anchors for reinforcing steel for use in concrete structure

The use of mechanical coupling devices and anchors for reinforcing steel for use in concrete structures can simplify the design and construction of reinforced concrete and reduce the amount of reinforcement required. Technical Approvals of these products by suitably qualified organisations are acceptable under Building Regulations and by major specifiers as the appropriate way of assessing non-standard or new and innovative products. Specifiers, manufacturers, traders, and customers increasingly demand certainty in the quality management of mechanical coupling devices and anchors entering the supply chain. The supply chain is extremely complex. The weak traceability systems and pressure on the supply chain to reduce cost have created the environment where risks increase. This unique and comprehensive model describes the technical and assessment requirements for the conformity of mechanical coupling devices and anchors. It covers all stages in the supply chain from the production, assembly, product performance and evaluation of mechanical properties including tensile strength, ductility, permanent elongation (slip), cyclic loading performance and fatigue performance. The essential elements of the quality management system combined with additional requirements on process control, product testing and robust installation methodology are essential and agreed by all relevant sectors of industry.