Fatigue Damage Analysis Research Articles

Mesoscale Analysis of Fatigue Damage through Aggregate–Mortar Bond Cracks in Cementitious Composites

AbstractA micromechanics-based model is developed to study the fatigue response of cementitious composites. Microcrack growth, which is the predominant mechanism responsible for fatigue damage, is ...

Real time cable force identification by short time sparse time domain algorithm with half wave

In the fatigue damage analysis of cables, it is very important to understand the cable force history. However, most current cable force identification methods are based on the average cable force assumption. To overcome this issue, this paper proposes the short time sparse time domain algorithm combined with the simplified half wave method (STSTD + SHW). This method only requires one acceleration sensor and is thus simple, economical, convenient, and fast. Its reliability and accuracy were verified by two experiments and one engineering application. According to the results, this method does not only reduce the influence of the boundary conditions on cable force identification but can also quickly identify the dynamic cable force. Moreover, only one accelerometer is required to avoid the problem of sensor placement and optimization, which is conducive to practical engineering applications.

Microstructure and fatigue performance of high strength concrete under compression after exposure to elevated temperatures

The fatigue tests of high-strength concrete after exposure to elevated temperatures of 200 °C, 500 °C, and 800 °C under low cyclic compression at different stress levels were carried out by an electro-hydraulic servo fatigue tester. The microstructure of high-strength concrete specimens during fatigue was studied with the aid of five comprehensive microscopic research methods—scanning electron microscopy, X-ray diffraction, ultrasonic, microhardness testing, and mercury intrusion porosimetry. By measuring the microscopic parameters such as ultrasonic velocity, microhardness, and the most probable aperture, the variation of microstructure during the fatigue process was analysed. It was found that with the increase of fatigue cycles, the variation speed of microscopic parameters follows a three-phase trend. The relationship between microscopic parameters and residual strain or elastic modulus ratio was established, and the fatigue damage models based on the microscopic parameters were obtained. A simplified mean damage variable was proposed and the residual life of concrete was predicted. The research results can provide reference for non-destructive testing, fatigue damage analysis and structural evaluation of high-strength concrete structures subjected to elevated temperature processes.

Analysis of fatigue strain, fatigue modulus and fatigue damage for the model formulation of concrete based on strain life approach

Analysis of fatigue strain, fatigue modulus and fatigue damage for the model formulation of concrete based on strain life approach

Progressive fatigue damage analysis of composite bolted joint using equivalent stress model.

Composite bolted joints are quite necessary for composite structures connection, which has become the main limit for the use of composites in main load-bearing structures. In this article, a fatigue model of composite bolted joint based on equivalent stress is established by programming in ABAQUS USDFLD subroutine to simulate the progressive failure of composite bolted joints. By introducing three-dimensional Tsai-Hill static failure criterion, equivalent stress is calculated for investigating effects of multiaxial stress on fatigue life. In the subroutine of progressive failure for fatigue model, fatigue life of composite bolted joint and damage state of elements that are meshed in the process of modelling are connected by defining field variable. Different fatigue modes are predicted here by changing stress amplitude and ratio loading, in which simulation results agree well with that obtained in corresponding experiments.

Fatigue damage analysis of reinforced concrete column considering low‐cycle behavior of HRB400 steel

SummaryIn this study, a damage model‐based fatigue behavior is proposed. To consider the fatigue behavior of steel in the damage model, the experimental research on reinforcing steel bar grades HRB400 was presented. The monotonic tension test and low‐cycle fatigue test were carried out. The plastic strain amplitude–fatigue cycle (εp–2Nf) curve and plastic strain amplitude–strength loss factor (εp–ϕSR) curve were obtained. The fatigue parameters (Cf, Cd, and α) were proposed by nonlinear fitting. The specimens were simulated using the “Reinforcing Steel” material in “OpenSees” program. These fatigue parameters were proved to accurately describe the fatigue behavior of HRB400 rebar. Moreover, to verify the application of fatigue damage model in RC column, fiber‐based element models were established based on the quasi‐static cyclic test on RC columns. The calculated results agreed well with those of the tests. The damage degree of RC column was calculated by the recorded stress–strain curves of material. The proposed fatigue parameters could be referred in damage model based on material fatigue behavior.

High-temperature fatigue behavior of a steam turbine rotor under flexible operating conditions with variable loading amplitudes

This study investigated the high-temperature fatigue behavior of a steam turbine rotor under long-term operation with multiple startup types including one cold, three warm and 16 hot-startups at intervals of 45 days. To better describe the mechanical behavior of the rotor material, a unified viscoplastic constitutive model was experimentally validated then implemented with a user-defined material. Analysis initially focused on the inlet region, where thermal loads dominated. Next, the stress and damage at three selected positions with differences in temperature and load were compared and analyzed in detail. The effect of different startup types on the fatigue damage was statistically assessed. The equivalent hot startup (EHS) ratio was calculated to compare the risk level of each position under each startup type in flexible operation mode. Investigation of the inlet region showed that the warm startup conditions adopted here were more damaging than cold startup due to the higher warmup rate. The analysis of fatigue damage showed a temperature-dependent characteristic of the thermo-mechanical load-dominated positions. The EHS ratio of Groove-1 was larger than that of Groove-4, indicating a higher risk level in Groove-1 under flexible operating conditions. For the inlet region, the accumulation of viscoplastic strain made this region a fatigue-damageable position.

Fatigue damage investigation and optimization of a viscoelastically damped system with uncertainties

The need for larger and more efficient structures has led to the development of numerical models to approach real-world complex behaviors. Normally, engineering systems consider deterministic parameters, while in real-world situations, they are subjected to parametric uncertainties, resulting in differences between the calculated responses. This work is devoted to performing numerical and computational studies of fatigue damage analyses of viscoelastically damped systems in the frequency domain subjected to parametric uncertainties. Here, the discretization of the random field is performed using the finite element method combined with the Karhunen–Loeve expansion and the fatigue damage index is estimated by applying the so-called Sines’ global criterion. Optimization techniques were applied in order to obtain the optimal design of surface viscoelastic treatments in terms of fatigue. Therefore, the main contribution intended for the present study is to show the importance of considering optimal–robust parameters to estimate the failure probability of engineering structures with constrained viscoelastic layers. After presenting the underlying foundations, the numerical results are presented and the main features of the proposed methodology are highlighted.

Dynamic finite element modeling and fatigue damage analysis of thermite welds

AbstractRailway track comprises of continuous welded rail mounted with rail clips on sleepers integrated to a ballast track form system. Modeling the rail structure with thermite weld subjected to the complex dynamic loadings is a challenging problem. Fatigue failures at the head‐to‐web, web‐to‐foot, and foot regions of weld collar are investigated. In this paper, a combined method of multibody system dynamic analysis and dynamic finite element analysis was used. A train roll‐in experiment was conducted at a train depot test track to validate modeling results predicted at the strain gauge location. Three critical plane‐based multiaxial fatigue criterions incorporated with a smallest enclosing circle algorithm were implemented in Python code to study the fatigue behavior at weld collar. Parametric studies were also conducted to investigate the effects of track component materials, track curvature, and train velocity. This approach provides a method for predicting the failures of thermite welded joints in railway tracks.

Fatigue damage analysis of a riveted steel overhead crane support truss

A method is proposed to evaluate the residual life of existing steel structures in terms of fatigue damage. The proposed method is demonstrated on the assessment of selected elements in a nearly 100-year old exterior riveted crane support truss. The Monte Carlo method is used to generate a time-dependent load based on the operation of the overhead crane, and detailed numerical modelling based on rainflow counting and the Palmgren-Miner rule to assess their fatigue resistance and estimate their residual life is evaluated and discussed. This study provides a novel approach to the reliability assessment of riveted joints stressed by cyclic loading and stochastic modelling of the load history of existing structures.

Nonlinear fatigue damage accumulation: Isodamage curve-based model and life prediction aspects

Cumulative fatigue damage analysis and life prediction of engineering structures/components is vital for ensuring their structural integrity and operational reliability under variable amplitude loadings. In this regard, a new nonlinear fatigue damage accumulation model is proposed by introducing a damage function related to the isodamage curves and remaining life aspects. Specifically, its damage exponent is refined by considering effects of loading history. Experimental data from tests available in literature are utilized for model validation and comparison. Compared with four existing models, the proposed model shows higher precision for cumulative damage modelling and fatigue life prediction than others. Moreover, it improves the deficiencies inherent in other rules under the promise of maintaining its simplicity in practice.

Ratchetting–multiaxial fatigue damage analysis in gear rolling contact considering tooth surface roughness

Under the combined effect of the tooth surface roughness and heavy load condition, gear materials might experience both the fatigue damage and the ratchetting damage. An elastic-plastic finite element contact fatigue model is proposed considering the optically measured tooth surface roughness and the gear contact geometry. The kinematic hardening constitutive equation and the Jiang and Sehitoglu ratchetting-multiaxial fatigue model are applied, and the contribution of the ratchetting-fatigue damage in the mechanism of gear contact fatigue problems is discussed. Results reveal that the surface roughness can promote the emergence of ratchetting behavior within a very shallow area near surface. Furthermore, the effect of the normal load condition on the ratchetting-fatigue damage is also discussed.

Fatigue life prediction for butt‐welded joints considering weld‐induced residual stresses and initial damage, relaxation of residual stress, and elasto‐plastic fatigue damage

AbstractFatigue damage of butt‐welded joints is investigated by a damage mechanics method. First, the weld‐induced residual stresses are determined by using a sequentially coupled thermo‐mechanical finite element analysis. The plastic damage of material is then calculated with the use of Lemaitre's plastic damage model. Second, during the subsequent fatigue damage analysis, the residual stresses are superimposed on the fatigue loading, and the weld‐induced plastic damage is considered as the initial damage via an elasto‐plastic fatigue damage model. Finally, the fatigue damage evolution, the relaxation of residual stress, and the fatigue lives of the joints are evaluated using a numerical implementation. The predicted results agree well with the experimental data.

Fatigue damage analysis of 2D braided C/SiC composite plate

Fatigue damage analysis of 2D braided C/SiC composite plate

Fatigue damage analysis of steel components subjected to earthquake loadings

PurposeExamination of steel moment resisting frames after the 1994 Northridge earthquake showed fatigue cracks presented in the beam–column connections of the frames. These observations indicate that fatigue failure may occur in the steel components of building structures in an earthquake event. To apply the fatigue design approach using the Palmgren–Miner’s rule for steel components of the moment resisting frames requires the knowledge regarding the damage index value at fatigue failure. The purpose of this paper is to perform fatigue tests to give the first damage values of steel components subjected to real earthquake-induced loadings.Design/methodology/approachThe added-damping-and-stiffness steel plates which are used in building structures for earthquake mitigation were fabricated and tested by constant amplitude, SAC block and earthquake-induced loadings to failure. The earthquake loadings were obtained from the dynamic analysis of a steel frame with the mentioned plates. The load cycles of the SAC block and the calculated earthquake loadings were counted using the rainflow-counting method, and the damage index value of each specimen were calculated using the Palmgren–Miner’s rule.FindingsReverse stiffness obtained from cyclic load-displacement loops is a robust and consistent parameter that can be used for determining fatigue failure of tested components. The Palmgren–Miner’s damage values at failure, caused by earthquake loadings, are smaller than 1, and in addition, are also smaller than those obtained from the tests of the SAC block loading. The large-amplitude cycles in the earthquake loading produce large damage on the specimens, and intermediate range cycles also produce damage that should not be neglected in the fatigue analysis.Originality/valueToday’s building design code allows large plastic deformation to occur in steel frames during an earthquake. However, the pre-Northridge earthquake steel frames showed fatigue cracks without the expected substantial plastic deformation at beam flanges. Proposed solutions to this problem were the reduced beam section neglecting the existence of the cracks at beam–column connections. This study considered the fatigue phenomenon in steel frames and provided the first set of tested fatigue damage values for steel components subjected to realistic earthquake loadings, which offered a possible method of dealing with fatigue cracks in the steel components of a building structure.

Evaluation of fatigue behavior of asphalt binders containing reclaimed asphalt binder using simplified viscoelastic continuum damage approach

Several fatigue damage analysis approaches have been introduced for asphalt binders and mixtures. In this study, using three modifiers including softer bitumen, a rejuvenator and waste polymer modified bitumen, fatigue behavior of RAB-containing binder mixes was evaluated based on the simplified viscoelastic continuum damage mechanics (S-VECD). In addition, correlations between the S-VECD parameters and the other fatigue failure criteria were investigated. For this purpose, the time sweep test was used to evaluate fatigue behavior of various asphalt binders in controlled-strain mode. Results showed that the rejuvenator and softer bitumen had the greatest effect in terms of prioritization on the improvement of the fatigue resistance of the RAB-containing binder mixes. Moreover, the results showed that good unique relationships between plateau value (PV) and Nf50 and between rate of change of total released pseudo strain energy (GR) and Nf50 were established in the RAB-containing binder mixes. Furthermore, there was a good relationship between the two concepts of the dissipated energy approach used for determination of the PV and the dissipated pseudo strain energy approach which used for calculation of the GR values.

Flexural fatigue damage analyses of recycled rubber‐modified epoxy‐based composites reinforced with alumina fibres

AbstractManufacturers have been working towards finding clean and cost‐efficient solutions by utilizing recycled materials to produce new components. Recycled rubber is one such material widely used in aeronautic and automotive industries. In this study, fresh scrap ethylene‐propylene‐diene‐monomer (EPDM) rubber is mixed with epoxy to manufacture novel composites with the addition of alumina (Al2O3) fibres. These composites can potentially be used to manufacture components subjected to cyclic loading, and to ensure reliability of such components, fatigue behaviour of these composites should be evaluated. This article describes the manufacturing of recycled rubber‐modified epoxy‐based ternary composites and their fatigue behaviour as well as toughening mechanisms. Dynamic mechanical analysis (DMA) was performed to determine thermomechanical properties. Three‐point bending and flexural fatigue tests and Shore D hardness measurements were carried out to determine mechanical properties. After static/fatigue fracture, fracture surfaces were observed with scanning electron microscope (SEM) to determine toughening mechanisms in these composites.

Comparison of two points of view when developing reliability-based topology optimization model: Validation on fatigue damage analysis

The classical topology optimization leads to a prediction of the structural type and overall layout configuration, and gives a rough shape description of the outer as well as inner boundaries of the structure. While, the Reliability-Based Topology Optimization (RBTO) model leads to several reliability-based topologies with high performance levels. Several strategies have been developed in this area considering two points of view: topology optimization and reliability analysis. In this work, a literature review of this different developments considering the two points of view over the last 20 years is presented to show that the different developments considering the point of view 'topology optimization' generate several reliability-based topologies, however, the other developments considering the point of view 'reliability analysis' lead to a single configuration. A numerical application on fatigue damage analysis is considered as a validation of the developed methods taking the point of view 'topology optimization' into account.

Fatigue damage analysis of offshore wind turbine monopile weldments

Offshore wind turbines (OWT) are subjected to harsh environmental conditions in addition to the variable service loads. The present study is aimed at performing a realistic fatigue life estimation of the monopile structure using operational service loads recorded by online monitoring systems. Fatigue damage analysis has been conducted at the circumferential weld joints using finite element (FE) method by considering geometrical and material property discontinuities. Global-local modelling of the OWT was performed in as-welded condition to capture the local stress range at the weld toe, which acts as the critical site where cracks are most likely to initiate and propagate. The S-N fatigue design approach and maximum stress range at the weld toe have been used to determine the fatigue crack initiation life in monopiles. The results from the proposed approach show that a realistic life assessment can be made on monopile structures by accounting for the geometrical effects at the circumferential welds.

Analysis of Fatigue Strain, Fatigue Modulus and Fatigue Damage for the Model Formulation of Concrete Based on Strain Life Approach

Analysis of fatigue strain, fatigue modulus and fatigue damage for the modeling of concrete plays a vital role in the evolution material behaviour which is heterogeneous and anisotropic in nature. The Level-S nonlinear fatigue strain curve, fatigue modulus curve, residual strain curve of concrete in compression, tension, flexure and torsional fatigue loading were proposed using strain life approach. The parameters such as physical meaning, the ranges, and the impact on the shape of the curve were discussed. Then, the evolution model of fatigue modulus was established based on the fatigue strain, fatigue modulus, residual strain and secondary strain evolution model. The hypothesis of fatigue modulus is inversely related with the fatigue strain amplitude. The fatigue evolution of concrete damages the bond between material grains, changed the orientation of structure of molecules and affects the elastic properties resulting in the reduction of material stiffness and modulus by formation of microcracking, macro cracking, cracking and finally damage. This paper presents the fatigue strain life model and analysis of fatigue strain, fatigue modulus and damage parameters of concrete which is capable of predicting stiffness degradation, inelastic deformation, and strength reduction under fatigue loading and experimental results were employed for the validation of the theoretical model.