Fatigue Damage Accumulation Process Research Articles

A new fatigue cumulative damage model based on material parameters and stress interaction

In order to evaluate the fatigue damage accumulation process of materials under different stress levels and to predict the fatigue lives, a new fatigue accumulation damage model based on material parameters and stress interaction is proposed. The parameters of the material required for the action coefficient introduced by the proposed model are the slope of the S-N characteristic curve and the ultimate stress. In addition, the fatigue cumulative damage of the previous level and the ratio of adjacent stresses are also taken into consideration. Besides, we have conducted extensive experiments by utilizing the two-level stress experimental data of steel 300CVM, 16Mn steel, LY12CZ, and AL-2024-T42, the three-level stress experimental data of LY12CZ material, the four-level and five-level stress experimental data of Aluminum alloy material, respectively. Especially, we calculate and compare the fatigue prediction results of our proposed model with those of the 6 existing models, i.e., Manson-Halford model, YG model, Yue model, Haghgouei model, Subramanyan model and Hashin model. These materials used for verification, in addition to the fatigue test data of high cycle lives, also include the combination of high cycle and low cycle multi-level stress test data. Finally, we compare the cumulative fatigue life of each model via two-level to five-level stress tests, and calculate the difference between the fatigue damage prediction results and the test results to evaluate the advantage of the proposed model. The predicted results show that the model proposed in this paper is in great agreement with the real testing results. Besides, the prediction effect of the proposed model is significantly superior to that of the existing 6 models, especially when both the fatigue low-cycle and high-cycle mixed stresses are used, which validates the high robustness of the proposed model under various complex stress conditions.

The effect of the fatigue damage accumulation process on the damping and stiffness properties of adhesively bonded composite structures

Wind turbine blade spar cap to shear web adhesively bonded connections can suffer from damage at the bond-line which can propagate through the structure compromising blade integrity. This study investigates changes in the stiffness and damping of a thick adhesive joint test specimen during a fatigue test. The stiffness is calculated using an extensometer and damping is determined using vibration and thermography. Fatigue tests showed three distinct phases of damage. Firstly, transverse cracks and delamination initiate and grow with little change in stiffness observed while damping increases by 18.6% and 17.8% inferred from the vibration and thermographic methods, respectively. In the second phase, the number of transverse cracks increases reaching saturation and the stiffness reduces by 4.7%. The increase in the loss factor is 65.7% and 95.6% from the vibration and thermographic methods, respectively. In the final phase, the crack density remains constant whilst de-bonding of the joint begins and grows until failure. The loss factor increases by 111.4% and 116.9% from the vibration and thermographic methods, respectively though the stiffness shows a cumulative reduction of only 8.6%. The results show the potential for monitoring changes in damping to infer incipient damage in an adhesively bonded composite joint structure.

Low-cycle fatigue behavior of austenitic stainless steels with gradient structured surface layer

Low-cycle fatigue behavior of gradient structured (GSed) 316L steels is investigated. The results show that both the homogeneous and gradient structures exhibit first cyclic hardening then cyclic softening. The GSed surface layer can, however, speed up cyclic hardening and extend cyclic softening processes. The analyses using hysteresis energy-based criterion indicates that the former phenomenon can be attributed to the reduced fatigue damage capacity, while the latter to the improved ability of damage defusing. This finding accordingly pinpoints that the retarded fatigue damage accumulation process has been acting as the main contributor to the enhanced fatigue performance of GSed 316L steels.

ЧИСЛЕННОЕ МОДЕЛИРОВАНИЕ УСТАЛОСТНОЙ ДОЛГОВЕЧНОСТИ ЭЛЕМЕНТОВ КОНСТРУКЦИЙ ПРИ ТЕРМОЦИКЛИЧЕСКОМ НАГРУЖЕНИИ

The paper considers processes of fatigue life of materials and structures in the exploitation conditions characterized by multiparametric nonstationary thermal-mechanical effects In the framework of mechanics of damaged media, a mathematical model is developed that describes processes of thermal-plastic deformation and fatigue damage accumulation in materials with degradation according to low- and high-cycle fatigue mechanisms (accounting for their interaction). The model consists of three interconnected parts: relations determining cyclic thermal-plastic behavior of a material, accounting for its dependence on the failure process; equations describing kinetics of fatigue damage accumulation; a strength criterion of the damaged material. The version of the defining relations of thermal plasticity is based on the notion of the yield surface and the principle of orthogonality of the plastic strain rate vector to the yield surface at the loading point and reflects the main effects of the process of cyclic plastic deformation of the material for arbitrarily complex trajectories of combined thermal-mechanical loading. The version of kinetic equations of fatigue damage accumulation is based on introducing a scalar parameter of damage degree and on energy-based principles, and takes into account the main effects of the nucleation, growth and merging of microdefects under arbitrarily complex loading regimes. A generalized form of an evolutionary equation of fatigue damage accumulation in low-cycle and high-cycle fatigue regions is introduced. The condition when the damage degree reaches its critical value is taken as the strength criterion of the damaged material. To assess the reliability and the scope of applicability of the developed defining relations of mechanics of damaged media, processes of thermal-plastic deformation and fatigue damage accumulation have been numerically analyzed, and the numerical results obtained have been compared with the data of full-scale experiments for a particular applied problem. The effect of the dropping frequency of a distillate on thermal cyclic fatigue life of the material of a heated surface of a tube has been numerically analyzed. The computational results for the fatigue damage accumulation processes under thermal pulsed loading are compared with experimental data. It is shown that the developed model describes both qualitatively and, accurately enough for engineering purposes, quantitatively the experimental data and can be effectively used for evaluating thermal-cyclic fatigue life of structures working in the conditions of multiaxial non-proportional regimes of combined thermal-mechanical loading.

РАСЧЕТНО-ЭКСПЕРИМЕНТАЛЬНАЯ МЕТОДИКА ОЦЕНКИ ОСТАТОЧНОГО РЕСУРСА ГАЗОПРОВОДА ПО УСТАЛОСТНОЙ ПРОЧНОСТИ

Актуальность. В реальных эксплуатационных условиях газопроводы работают при переменном уровне давления, которое в общем случае является величиной случайной, с неизвестным законом распределения. Также случайной является и температура окружающей среды. Вследствие отмеченных условий напряжения, возникающие в стенках трубы, не могут быть описаны законами, исследованными в рамках теории параметрической статистики. Основой прогнозирования ресурса газопровода является кривая усталости материала трубы, связывающая амплитуду действующих напряжений не со временем работы испытываемых до разрушения образцов, а с числом циклов их деформирования. Для определения в процессе эксплуатации газопровода остаточного ресурса во времени необходимо оценивать накопление в его материале усталостных повреждений при любом законе распределения напряжений независимо от его сложности. В настоящее время методики прогнозирования остаточного ресурса газопроводов, учитывающие фактический спектр изменения внешних нагрузок и процессы накопления от них усталостных повреждений в стенке трубы, отсутствуют. Поскольку газопроводы являются потенциально опасными объектами, определение их остаточного ресурса по времени эксплуатации является задачей важнейшей. Цель: определение во временном диапазоне остаточного ресурса газопровода с заданной вероятностью неразрушения, подвергающегося в процессе эксплуатации воздействию случайного спектра внешних нагрузок независимо от сложности спектра, с учетом процессов накопления усталостных повреждений в газопроводе. Методы: кинетическая теория механической усталости, методы непараметрической статистики, измерение циклических деформаций с помощью датчиков деформаций переменной чувствительности. Результаты. Разработана расчетно-экспериментальная методика, основанная на комплексном использовании: кинетической теории механической усталости, учитывающей накопление повреждений в процессе циклического деформирования изделий; методов непараметрической статистики, обеспечивающих восстановление функции плотности распределения напряжений независимо от сложности закона их изменения в процессе эксплуатации газопровода; оригинальных средств измерения циклических деформаций – датчиков деформаций переменной чувствительности. Рассмотрены основные этапы реализации методики. По зафиксированной в процессе эксплуатации газопровода на датчике величине перемещения границы его реакции (первых «темных пятен») на основе разработанных в рамках кинетической теории усталости уравнений получены математические зависимости решения задачи определения эквивалентных по повреждающему воздействию чисел циклов нагружения для восстановления длительности ступеней блока напряжений, расчета эквивалентных по повреждающему воздействию напряжений. На примере реализации методики установлена зависимость остаточного ресурса газопровода в зависимости от величины реакции на датчике, позволяющая оперативно оценивать остаточный ресурс различных участков газопровода в условиях эксплуатации. Показан вариант использования результатов реализации методики для определения влияния коррозионного дефекта газопровода на его остаточный ресурс.

Stochastic analysis of fatigue of concrete bridges

A novel method is proposed in this work for the assessment of the remaining fatigue life and fatigue reliability of concrete bridges subjected to random loads. The fatigue reliability of a bridge is a function of the fatigue damage accumulation; a stochastic fatigue damage model (SFDM) with physical mechanism is introduced for deriving the fatigue damage process. In order to implement the probabilistic analysis, based on the probability density evolution method (PDEM), the generalised density evolution equation (GDEE) for the remaining fatigue life is developed. Finally, a prestressed concrete continuous beam bridge located in China is illustrated. The random fatigue load acting on the bridge is modelled as the compound Poisson process, and the simulation of the random load uses the stochastic harmonic function (SHF) method. To simplify the reliability analysis, an equivalent constant-amplitude (ECA) load process is introduced based on energy equivalence. By employing SFDM, the finite element analysis of the bridge under the fatigue loading is performed. Then, the fatigue damage accumulation process of the bridge under the fatigue loading is obtained. Through solving the probability density evolution equation for the remaining fatigue life, the probability density functions (PDFs) of the remaining fatigue life evolving with time is obtained. The fatigue reliability is then calculated by integrating the PDF of the corresponding remaining life.

МОДЕЛИРОВАНИЕ УСТАЛОСТНОЙ ДОЛГОВЕЧНОСТИ ПОЛИКРИСТАЛЛИЧЕСКИХ КОНСТРУКЦИОННЫХ СПЛАВОВ ПРИ СОВМЕСТНОМ ДЕЙСТВИИ МЕХАНИЗМОВ МАЛО- И МНОГОЦИКЛОВОЙ УСТАЛОСТИ

Processes of fatigue life of polycrystalline structural alloys under a combined effect of low- and high-cycle fatigue are considered. In the framework of mechanics of damaged media (MDM), a mathematical model is developed, which describes processes of plastic deformation and fatigue damage accumulation. The MDM model consists of three interrelated parts: relations defining cyclic elastoplastic behavior of the material, accounting for its dependence on the failure process; equations describing fatigue damage accumulation kinetics; a strength criterion of the damaged material. The version of defining relations of elastoplasticity is based on the notion of yield surface and the principle of orthogonality of the plastic strain rate vector to the yield surface at the loading point. This version of equations of state reflects the main effects of the cyclic plastic deformation process of the material for arbitrarily complex loading trajectories. The version of kinetic equations of damage accumulation is based on introducing a scalar parameter of damage degree. The construction uses energy-based principles and accounts for the main effects of the process of nucleation, growth and merging of microdefects under arbitrarily complex multiaxial loading regimes. A combined form of the evolutionary equation of fatigue damage accumulation in the regions of low-cycle (LCF) and high-cycle (HCF) fatigue is proposed. It is shown that, under regular cyclic loading of the material, the stress amplitude of the cycle decreases by degrees during the transition from LCF to HCF and depends on the physical interaction of these mechanisms in the transition zone. The condition when the damage degree attains its critical value is taken as the strength criterion of the damaged material. A methodology of numerically determining parameters of the evolutionary equation of fatigue damage accumulation in the conditions of HCF is presented. To assess the reliability and the limits of applicability of the defining relations of MDM, processes of plastic deformation and fatigue damage accumulation in a number of structural alloys in cyclic tests have been numerically studied, and the obtained numerical results have been compared with the data of full-scale experiments. The results of comparison of the numerical and experimental data reveal that the developed model of mechanics of damaged media adequately describes durability of structures subjected to a combined effect of low- and high-cycle fatigue mechanisms. It is shown that the introduced MDM model qualitatively and, accurately enough for practical engineering purposes, quantitatively describes the main effects of the processes of plastic deformation and fatigue damage accumulation in structural alloys under cyclic loading.

Modeling fatigue life of structural materials under block-type nonsymmetrical loading

In the framework of mechanics of damaged media (MDM), a mathematical model describing processes of thermo-plastic deformation and fatigue damage accumulation under low-cycle loading is developed. The MDM model consists of three interconnected parts: relations defining cyclic thermoplastic behavior of the material included for its dependence on the failure process; equations describing damage accumulation kinetics; a strength criterion of the damaged material.To assess the reliability and the scope of applicability of the defining relations of MDM, processes of plastic deformation and damage accumulation in a number of structural steels in low-cycle tests have been numerically analyzed, and the obtained results have been compared with the data from full-scale experiments. It is shown that the proposed MDM model qualitatively and, accurately enough for engineering purposes, quantitatively describes the main effects of the processes of plastic deformation and fatigue damage accumulation in structural alloys under block-type nonstationary nonsymmetrical low-cycle loading.

Diagram and Parameters of Fatigue Sensitivity for Evaluating the Residual Strength of Layered GFRP Composites After Preliminary Cyclic Loadings

In this paper, the questions concerning the investigation of fatigue characteristics of composite materials are discussed and the changes in their static deformation and strength properties caused by preliminary cyclic actions are estimated. The aim of the work was to obtain new experimental data on damage accumulation processes in GFRP composite materials under combined cyclic and quasistatic loadings. An analysis of processes of fatigue damage accumulation in the composite materials is performed, and stages of change in the residual mechanical properties of the materials during cyclic loadings are noted. Temperature fields in the working section of samples are analyzed, and the characteristics features of temperature distribution in their destruction zone are revealed. Functions describing damage accumulation and changes in the strength and stiffness properties of the composites are introduced, which can be used to describe the behavior of the materials under fatigue loadings. A new form of representation of experimental data in the form of a fatigue sensitivity diagram is proposed, which can be employed to analyze the residual strength of structures made from composite materials. The characteristic stages of change in their residual static strength are presented in relation to the degree of preliminary cycling. It is proposed to use new material characteristics — the fatigue sensitivity threshold and the coefficient of static strength preservation.

3D characterization of fatigue damage mechanisms in a cast aluminum alloy using X-ray tomography

Specimens of an Al-Cu-Si alloy were manufactured using die casting without additional machining. These specimens contained various kinds of natural defects were subjected to fatigue loading. The role of these defects was analyzed using fractography, X-ray tomography, and Finite Element simulations. Special emphasis was placed on the interaction between shrinkage pores and gas pores, and on internal flaw extension. It was found that multiple cracks can be initiated from shrinkage pores, and that lifetime is reduced considerably, if gas pores and shrinkage pores interact. Otherwise, the almost defect free casting skin restricted crack extension from shrinkage pores to internal crack advance with corresponding low crack growth rates. The role of the different defect categories in the fatigue damage accumulation process can be explained from a Finite-Element analysis of typical defects which showed that similar values of the stress concentration factor occurred at several locations on a typical shrinkage pore, and at irregular shaped gas pores.

ЧИСЛЕННЫЙ АНАЛИЗ ТЕРМОЦИКЛИЧЕСКОЙ ДОЛГОВЕЧНОСТИ МОДЕЛЕЙ ЖАРОВЫХ ТРУБ С РАЗЛИЧНЫМИ УГЛАМИ НАКЛОНА ОХЛАЖДАЮЩИХ КАНАЛОВ

The issue of evaluating strength and service life of critical engineering objects, whose exploitation properties are characterized by multi-parametric nonstationary thermal-mechanical effects, is discussed. Basic degradation mechanisms of structural materials (metals and alloys) characteristic of such objects are considered. The main criteria for mathematical models of fatigue damage accumulation are formulated. Based on the developed version of defining equations of damaged medium mechanics, the effect of the angle of inclination of the cooling channels on thermal-cyclic life of the models of flue tubes of combustion chambers gas turbine engines is numerically analyzed. Special attention is paid to studying the processes of complex thermal-cyclic deformation and fatigue damage accumulation, accompanied by rotation of the main sites of stress tensors, complete and plastic deformations, as well as the processes of fatigue damage accumulation. Comparison of the obtained numerical results with experimental data shows that the developed model of damaged medium mechanics adequately and accurately enough for engineering calculations quantitatively describes experimental data and can be effectively used for evaluating thermal-cyclic life of materials and structures under multiaxial non-proportional modes of thermal-cyclic loading. Keywords: thermal-cyclic life, damaged medium mechanics, complex deformation, models of flue tubes, cooling channel, inclination, macroscopic crack, strength, fracture.

Evaluating fatigue life of materials and structures under low-cycle loading

The problem of evaluating strength and fatigue life of critical engineering objects, the operational properties of which are characterized by multi-parametric nonstationary thermal-mechanical effects, is discussed. The main degradation mechanisms of structural materials (metals and their alloys) characteristic of such objects are considered. The main requirements for mathematical models of fatigue damage accumulation are formulated. To evaluate the stress-strained state (SSS) and fatigue life of critical engineering facilities (CEF) in the framework of modern achievements of mechanics of damaged media (MDM), a mathematical model is developed which describes the processes of cyclic thermal-plastic deformation and fatigue damage accumulation in structural alloys subject to multiaxial non-proportional paths of combined thermal-mechanical loading. The MDM model consists of three interconnected parts: thermal plasticity constitutive equations, accounting for their dependence on the failure process; an evolution equation of damage accumulation and a strength criterion of a damaged material. To qualitatively and quantitatively assess the constitutive relations of MDM for low-cycle modes of thermal-cyclic loading, the numerical and experimental results for the fatigue life of a notched compact sample in a non-uniaxial stress state under block modes of thermal-cyclic loading were compared, which supported the validity of the constitutive relations of the MDM model for thermal fatigue. An approach based on the Palmgren-Miner rule of linear summation of damage, when used for evaluating the fatigue life of structural elements, may result in both conservative and non-conservative estimates. This conclusion is confirmed by the experimental and theoretical studies of foreign and domestic authors. The results of numerical modeling of the fatigue durability of a compact specimen with an obtuse notch are presented for two loading histories. It is shown that several cycles of more intensive loading at the beginning of the strain history are the reason why the rule of linear summation of damage can overestimate or underestimate the value.

Modeling of Deformation and Failure of Heat-Resistant Alloys under Cyclic Thermal-Mechanical Loading

The results of numerically modeling fatigue damage accumulation in heat-resistant alloys (Nimonic 80A, Haynes 188) under combined thermal mechanical loading are presented. Special attention is paid to the issues of modeling the processes of cyclic thermal plastic deformation and fatigue damage accumulation for complex deformation processes accompanied by the rotation of the main sites of stress and strain tensors.

Experimental Investigation of the Three-point Bending Fatigue Properties of Carbon Fiber Composite Laminates

The three point bending fatigue properties of carbon fiber epoxy matrix composite laminates were compared for fatigue loading stress levels of 75, 80 and 85%, and fatigue loading frequencies of 10, 15 and 20Hz, respectively. The experimental results showed that: the bending fatigue life of the composites obviously decreased with the increase of the fatigue loading stress level or the loading frequency. The fatigue damage accumulation process could be divided into three distinct stages according to the accumulation rate: fast, slow and then fast. When the loading stress level was increased from 75 to 85%, the duration of the third stage decreased from 40 to 10% of the overall fatigue life. When the loading frequency was increased from 10 to 20Hz, the duration of the third stage increased from 20 to 40% of the overall fatigue life. Matrix cracking, fiber breaking, interface debonding and delamination were identified as the main three-point bending fatigue damage modes of the carbon fiber composite material, and the stress level and the loading frequency were found to significantly influence the fatigue failure properties of the composites.

Experimental investigation of the three-point bending fatigue properties of carbon fiber composite laminates

The three-point bending fatigue properties of carbon fiber epoxy matrix composite laminates were compared for fatigue loading stress levels of 75, 80 and 85%, and fatigue loading frequencies of 10, 15 and 20 Hz, respectively. The experimental results showed that the bending fatigue life of the composites obviously decreased with the increase of the fatigue loading stress level or the loading frequency. The fatigue damage accumulation process could be divided into three distinct stages according to the accumulation rate: fast, slow and then fast. When the loading stress level was increased from 75 to 85%, the duration of the third stage decreased from 40 to 10% of the overall fatigue life. When the loading frequency was increased from 10 to 20 Hz, the duration of the third stage increased from 20 to 40% of the overall fatigue life. Matrix cracking, fiber breaking, interface debonding and delamination were identified as the main three-point bending fatigue damage modes of the carbon fiber composite material, and the stress level and the loading frequency were found to significantly influence the fatigue failure properties of the composites.

ОЦЕНКА УСТАЛОСТНОЙ ДОЛГОВЕЧНОСТИ КОМПАКТНОГО ОБРАЗЦА С КОНЦЕНТРАТОРАМИ ПРИ ТЕРМОЦИКЛИЧЕСКОМ НАГРУЖЕНИИ В УСЛОВИЯХ НЕОДНОРОДНОГО НАПРЯЖЕННОГО СОСТОЯНИЯ

The basic physical laws of the processes of inelastic deformation and fatigue damage accumulation in structural materials (metals and their alloys) for various complex modes thermocyclic loading and main approaches to modeling these processes are considered. It is noted that the rule of linear summation of damage (hypothesis Palmgren - Miner) in the calculation of the fatigue life when block mode thermocyclic loading can lead to both conservative (with a stock) and non-conservative estimate. The results of numerical modeling of the block thermocyclic deformation and fatigue damage accumulation in compact specimens with concentrators in a nonuniform stress state are given. Particular attention is paid to the study of complex processes thermocyclic deformation and fatigue damage accumulation, accompanied by the rotation of the main areas of stress tensor, and full of plastic deformation and fatigue damage accumulation processes. Comparison of the results of calculations carried out with experimental data showed that the model used in the article damaged the environment (MEAs) fairly describes the experimental data and can be effectively used for calculating the kinetics of fatigue damage accumulation in materials and structures under block mode thermocyclic loading. Keywords: thermocyclic strength, mechanic damaged the environment, difficult deformation, fatigue life, strength, macroscopic crack, destruction. &nbsp

МОДЕЛИРОВАНИЕ СЛОЖНОГО ПЛАСТИЧЕСКОГО ДЕФОРМИРОВАНИЯ И НАКОПЛЕНИЯ УСТАЛОСТНЫХ ПОВРЕЖДЕНИЙ В ЖАРОПРОЧНЫХ СПЛАВАХ ПРИ КОМБИНИРОВАННОМ ТЕРМОМЕХАНИЧЕСКОМ НАГРУЖЕНИИ

The main physical laws of complex thermal-plastic deformation and fatigue damage accumulation in structural materials (metals and their alloys) under various modes of combined thermal-mechanical loading are considered, as well as mathematical models of such processes. Results of numerically modeling cyclic thermal-plastic deformation and fatigue damage accumulation in heat-resistant alloys (Haynes 188) under combined thermal-mechanical loading are presented. Special attention is paid to the issues of modeling processes of cyclic thermal-plastic deformation and fatigue damage accumulation for complex deformation processes accompanied by rotation of the main sites of stress and strain tensors. The presented model of damaged medium is shown to describe, accurately enough for engineering computations, the processes of cyclic isothermal and non-isothermal deformation and fatigue damage accumulation under combined thermal-mechanical loading and makes it possible to analyze low-cycle fatigue life of heat-resistant alloys for arbitrary strain paths. Keywords: modeling, thermocyclic strength, difficult deformation, mechanical damaged the environment, fatigue life, strength, destruction, resource. &nbsp

Probabilistic Model of Fatigue Damage Accumulation in Rubberlike Materials

The paper presents a mathematical model of the non-localized fatigue damage accumulation process in rubberlike materials. A relation for the determination of the constants of the corresponding equation with allowance for known fatigue curve characteristics, in particular for their random spread, is proposed. Computational relationships for the determination of the probabilistic characteristics of damage have been derived. Experimental data for the determination of realization of the fatigue accumulation process in rubber specimens, which are in good agreement with theoretical results, are considered.

ЭКСПЕРИМЕНТАЛЬНО-ТЕОРЕТИЧЕСКОЕ ИССЛЕДОВАНИЕ УСТАЛОСТНОЙ ДОЛГОВЕЧНОСТИ СТАЛИ 08Х18Н10Т ПРИ РЕГУЛЯРНОМ И БЛОЧНЫХ ЦИКЛИЧЕСКИХ НАГРУЖЕНИЯХ

The results of the experimentally and theoretically studying the fatigue life of the 08Х18Н10Т austenitic steel under regular and block cyclic modes of low-cycle loading are presented. In the frame of damaged medium mechanics, processes of fatigue damage accumulation for low-cycle fatigue are modeled. The presented model of the methodology for evaluating fatigue life of structural steels has been verified by comparing the results of numerically modeling deformation and failure processes in laboratory specimens with experimental data. The comparison of computational and experimental data makes it possible to corroborate the adequacy of the determining relations of damaged medium mechanics and the methodology for determining material parameters under the effect of the low-cycle fatigue mechanism. A number of characteristic features accompanying the fatigue failure process under block modes of low-cycle loading are noted. Keywords: stressed-strained state, plasticity, fatigue, failure, damage accumulation, number of cycles to failure, fatigue life, resource.

Review of Studying on Fatigue Damage of Concrete Bridge

Fatigue is the decay process of the structure stress performance under the action of repeated load. The fatigue essence is the material fatigue damage accumulation process along with the increase in the number of fatigue loading. Because of the structural fatigue damage caused by the great dangers, the fatigue damage problem has been studied by many researchers at home and abroad. In this paper, it systematically reviews the research status of fatigue damage of concrete bridges on the basis of previous studies and the problems for further research are discussed. From the bridge component materials perspective, the paper analyses the status and the development direction of the dynamic constitutive models. At the same time, the paper summarizes the fatigue cumulative damage theory and analyses the advantages and disadvantages of the various theories. The main contents of this paper include: the research history and status of fatigue damage of concrete bridges, the damage variable selection, the fatigue cumulative damage theory, the problems for further research on the fatigue damage of concrete bridge.