Fatigue Damage Accumulation Model Research Articles

Fatigue Damage Accumulation Modeling of Metals Alloys under High Amplitude Loading at Elevated Temperatures

This article presents an approach related to the modeling of the fatigue life of constructional metal alloys working under elevated temperature conditions and in the high-amplitude load range. The article reviews the fatigue damage accumulation criteria that makes it possible to determine the number of loading cycles until damage occurs. Results of experimental tests conducted on various technical metal alloys made it possible to develop a fatigue damage accumulation model for the LCF (Low Cycle Fatigue) range. In modeling, the material’s damage state variable was defined, and the damage accumulation law was formulated incrementally so as to enable the analysis of the influence of loading history on the material’s fatigue life. In the proposed model, the increment of the damage state variable was made dependent on the increment of plastic strain, on the tensile stress value in the sample, and also on the actual value of the damage state variable. The model was verified on the basis of data obtained from experiments in the field of uniaxial and multiaxial loads. Samples made of EN AW 2024T3 aluminum alloy were used for this purpose.

RETRACTED: Reliability analysis of mechanical components based on a nonlinear fatigue damage accumulation model

The dynamic reliability models of mechanical components with the failure mode of fatigue are mainly based on the linear damage accumulation theory, which is also called the Miner’s rule. But the Mi...

Nonlinear fatigue damage accumulation and life prediction of metals: A comparative study

AbstractFatigue damage modelling and life prediction of engineering components under variable amplitude loadings are critical for ensuring their operational reliability and structural integrity. In this paper, five typical nonlinear fatigue damage accumulation models are evaluated and compared by considering the influence of load sequence and interaction on fatigue life of P355NL1 steels. Moreover, a new nonlinear fatigue damage accumulation model is proposed to account for these two effects. Experimental datasets of pressure vessel steel P355NL1 and four other materials under two‐block loadings are used for model comparative study. Results indicate that the proposed model yields more accurate fatigue life predictions for the five materials than the other models.

Inhibition of apoptosis exacerbates fatigue-damage tendon injuries in an in vivo rat model.

Tendinopathy is a common and progressive musculoskeletal disease. Increased apoptosis is an end-stage tendinopathy manifestation, but its contribution to the pathology of the disease is unknown. A previously established in vivo model of fatigue-damage accumulation shows that increased apoptosis is correlated with the severity of induced tendon damage, even in early onset of the disease, supporting its implication in the pathogenesis of the disease. Consequently, this study aimed to determine: (1) whether apoptosis could be inhibited after fatigue damage and (2) whether its inhibition could lead to remodeling of the extracellular matrix (ECM) and pericellular matrix (PCM), to ultimately improve the mechanical properties of fatigue-damaged tendons. The working hypothesis was that, despite the low vascular nature of the tendon, apoptosis would be inhibited, prompting increased production of matrix proteins and restoring tendon mechanical properties. Rats received 2 or 5 d of systemic pan-caspase inhibitor (Q-VD-OPh) or dimethyl sulfoxide (DMSO) carrier control injections starting immediately prior to fatigue loading and were sacrificed at days 7 and 14 post-fatigue-loading. Systemic pan-caspase inhibition for 2 d led to a surprising increase in apoptosis, but inhibition for 5 d increased the population of live cells that could repair the fatigue damage. Further analysis of the 5 d group showed that effective inhibition led to an increased population of cells producing ECM and PCM proteins, although typically in conjunction with oxidative stress markers. Ultimately, inhibition of apoptosis led to further deterioration in mechanical properties of fatigue-damaged tendons.

Predicting the fatigue strength and life of 316L steel sinters of varying porosity for implants in a uniaxial loading state

This paper presents a new approach to predicting the fatigue strength and life of 316L steel sinters of varying porosity used in the production of implants. Uniaxial monotonic and periodically variable loads were taken into account. The research material consisted of sinters of 316L austenitic steel, with porosities p = 26%, p = 33% and p = 41%, obtained by powder metallurgy. Determined monotonic and fatigue curves within the range of uniaxial tension-compression made it possible to identify the process of fatigue damage growth and formulate numerical dependencies for predicting the fatigue life of porous materials. The variables of the porous sinter’s damage state were defined, and the law of damage accumulation (linear and non-linear approach) was formulated incrementally, so as to enable analysis of the influence of loading history on the material's fatigue life. In the proposed model, the increment of the damage state variable was made dependent on the increment of plastic strain and of the tensile stress value in the sample, and in the non-linear approach, also on the actual value of the damage state variable. The numerical model of fatigue damage accumulation was experimentally verified through tests performed by the authors on samples of porous sintered material with varying degrees of compaction.

Low cycle fatigue of metallic materials under uniaxialloading at elevated temperature

This paper reviews experimental tests of the fatigue life of metallic materials under uniaxial fatigue loading at elevated temperature. The influence of elevated temperature on the properties of different materials were investigated for monotonic and cyclic loads with high loading amplitude values. Models most commonly used to estimate the fatigue life of materials under these conditions are presented. Based on compiled results of experimental tests, an empirical model of fatigue damage accumulation was developed, making it possible to predict fatigue life under uniaxial, low-cycle loading conditions at elevated temperature. The model's structure was based on fatigue deformation curves obtained by way of experimental tests. The low number of material constants, which can be determined from fatigue tests at ambient temperature, is an advantage of the proposed model. The model was verified experimentally, and compiled test results were used for this purpose.

Probabilistic fatigue life prediction and reliability assessment of a high pressure turbine disc considering load variations

In the present work, a probabilistic framework for fatigue life prediction and reliability assessment of an engine high pressure turbine disc is proposed to incorporate the effects of load variations and mean stress, which provides a reference for engine structural design under a given target failure probability. Within this framework, a new probabilistic fatigue damage accumulation model under random loadings is elaborated based on a ductility exhaustion model, and probabilistic [Formula: see text] curves for the high pressure turbine disc under different flight missions are derived based on experimental data of turbine disc alloy GH4169. The influence of random load variations on fatigue reliability of the high pressure turbine disc has been investigated and quantified by combining the engine load spectrum with finite element analysis.

A new fatigue damage accumulation model considering loading history and loading sequence based on damage equivalence

In this study, a new nonlinear fatigue damage accumulation model is proposed to consider the effects of loading history and loading sequence under multi-level stress loading based on the Miner–Palmgren rule and S-N curve. By using damage equivalence, the new model is simplified and another form of the model is given. This model improves the application of the traditional Miner–Palmgren rule, by considering not only the loading sequence effect but also the loading history effect. The methods for calculating the degree of safety of specimens and cumulative damage of low-amplitude loads are also presented. Applicability of the new model is validated by predicting the fatigue life of 16Mn and 45 steel specimens under two-level stress loading. Further validation is carried out for the case of 41Cr4 and Aluminum alloys 6082 T6 under multi-level stress loading, and the strengthening and damaging effect of low-amplitude loads is considered. Comparing with the Miner–Palmgren rule and some new models, this new model gives more accurate and reliable prediction.

A one-parameter nonlinear fatigue damage accumulation model

A nonlinear model for fatigue damage accumulation under variable amplitude loading is presented. The known assumption that the isodamage curves are converging at the knee point of the S-N curve of the material, has been adopted. The proposed model does only require one parameter, in addition to the S-N curve of the material, in order to calculate the remaining fatigue life. A single value for the parameter has been found to give satisfying agreement with experimental data for four arbitrary selected steels, indicating a general trend.

Accumulation and mechanism of the fatigue damage for a nickel based superalloy

The fatigue damage accumulation investigations were performed for high and low cycle fatigue loading regime for the nickel based superalloy frequently used in the aviation industry. Definition of the damage parameter proposed by Johnson in [2], modified to be applicable for cyclic loading, was used to quantify damage. In the modified definition, the accumulated equivalent plastic strain was used as the damage indicator instead of axial strain. Analysis of the variations of hysteresis loop allowed to plot damage indicator as the function of load cycle number and finally to plot damage parameter as the function of the life ratio. This kind of plot, known as the Damage Curve, enables identification of the fatigue damage accumulation model appropriate for the investigated material and applied loading regime. Fractography and structural observations performed on damaged specimens allowed to identify damage mechanism for the alloy in question.

A statistically self-consistent fatigue damage accumulation model including load sequence effects under spectrum loading

A probabilistic methodology is proposed to evaluate fatigue damage accumulation and fatigue lives of specimens under variable amplitude loading. With probabilistic modifications in the present model, the calculative consistency is achieved between fatigue damage and fatigue life. The load sequence effects on fatigue damage accumulation are properly accounted for variable amplitude loading. The developed damage model overcomes the inherent deficiencies in the linear damage accumulation rule, but still preserves its simplicity for engineering application. Based on the Monte Carlo sampling method, numerical verification of this model is conducted under two kinds of spectrum loading. The predicted probabilistic distributions of fatigue lives are validated by fatigue tests on Al-alloy straight lugs. KEYWORDS. Fatigue damage; Fatigue life; Probabilistic statistical model; Load sequence effect; Statistical self-consistency.

Low cycle fatigue tests and damage accumulation models on the rolling shear strength of cross-laminated timber

This paper presents a study on rolling shear damage accumulation and duration of load of cross-laminated timber (CLT) with low cycle fatigue tests. The study of the duration-of-load (DOL) effect on strength properties of wood products is typically challenging; it may be more challenging for non-edge-glued CLT considering crosswise layups of wood boards, existing gaps, and non-uniform stress distributions in cross layers. In experimental studies, short-term ramp loading tests and low cycle trapezoidal fatigue loading tests were used to study the DOL behaviour of the CLT rolling shear. The ramp tests were performed to establish the short-term CLT rolling shear strength properties. The low cycle trapezoidal fatigue tests were performed to evaluate the damage accumulation process for the matched specimens under controlled rolling shear stress levels. A stress-based damage accumulation model was further used to investigate the rolling shear DOL effect with model parameters treated as random variables calibrated against one set of the test data. The calibrated model predicted well comparing with the other set of the test data. This verified model provides a robust tool to quantify the DOL effect on rolling shear strength in the core layers of CLT that can be used in future studies of DOL behaviour in CLT under arbitrary loading histories.

Combined Cycle Fatigue Investigation Based on Energy Principle

We present a modified energy-principle based model of fatigue damage accumulation in high temperature alloys usually used in gas turbine engine under combined high cycle fatigue and low cycle fatigue (LCF/HCF) loading conditions. Our model is based on the energy principle which includes a modified approximation formula that describes fatigue crack origin depending on the relative amplitude of stress intensity in the ranges of both high- and low-cycle fatigue under non-isothermal loading. Functional dependence that presents the influence of HCF mechanisms on a fatigue life of our structural material is gradual and it has not breaks of the curve that yields a possibility to rewrite the equation of the S-N curve with taking into account combined cycle fatigue loading. We used the same number of parameters as the initial model. Note, that new parameter interpretation gives clear physical picture. The proposed model is verified by comparing the computed results with the experimental data for one high temperature alloy GH4133.

A fatigue damage accumulation model based on stiffness degradation of composite materials

Many of the stiffness-based fatigue damage models contain four main limitations for composite materials life determination: (i) lack of capability in simulating the whole periods of damage evolution, (ii) applicability for a specific type of composite and in a limited range of loading levels, (iii) existence of many parameters in the models requiring substantial experimental data, (iv) application for constant amplitude loading only. In this paper, a stiffness-based fatigue damage model is proposed aiming to address the posed shortcomings. Nine sets of experimental data are utilized for this purpose. The results show that the model succeeds in dealing with these limitations. Then, a life prediction model is developed based on the damage model for two-stage loading. The model is assessed by three sets of experimental data and compared with some existing models. The comparison demonstrates that the model predictions are promising for remaining fatigue cycles in comparison with the studied models.

Residual life prediction based on nonlinear fatigue damage accumulation model

When a nonlinear fatigue damage accumulation model based on damage curve approach is used to get better residual life prediction results, it is necessary to solve the problem caused by the uncertain exponent of the model. Considering the effects of load interaction, the assumption that there is a linear dependence between the exponent ratio and the loading ratio is established to predict fatigue residual life of materials. Three experimental data sets are used to validate the rightness of the proposition. The comparisons of experimental data and predictions show that the predictions based on the proposed proposition are in good accordance with the experimental results as long as the parameters that represent the linear correlativity are set an appropriate value. Meanwhile, the accuracy of the proposition is approximated to that of an existing model. Therefore, the proposition proposed in this paper is reasonable for residual life prediction.

Damage accumulation modeling under uniaxial low cycle fatigue at elevated temperatures

The paper presents a fatigue damage accumulation model, which allows us to predict fatigue life under low cycle uniaxial loadings at elevated temperatures. The structure of the model has been based on the stress–strain curves obtained during the experimental study. The model has been verified experimentally by applying experimental studies carried out on ENAW-2024T3 aluminum alloy and 2Cr–2WVTa steel. Moreover, a comparison between the results of fatigue life prediction using the proposed damage accumulation model was done with the results obtained on the basis of various generally applied models, based on the Manson–Coffin dependency. Furthermore this paper presents the results of experimental studies carried out on the aluminum alloy ENAW 2024 T3 under uniaxial low cycle fatigue loadings in the conditions of elevated temperatures. In the course of the study, material constants and the parameters of the stress–strain curve in the range of low cycle fatigue for four levels of temperatures (20, 100, 200 and 300°C) were set.

Verification of Mathematical Models of Damaged Medium Mechanics in the System for the in-Service Monitoring of the Life of Reactor Plants*

The paper presents the main statements of a mathematical model of fatigue damage accumulation in structural materials of reactor plant equipment and systems, which was developed on the basis of methods of damaged medium mechanics, and the results of its verification.

Accumulation of Fatigue Damages for Block-Type Loads with Use of Material Memory Function

The paper proposes a new model of fatigue damage accumulation based on the memory of the material and developed on the basis of memorizing of the meaningless material. The comparison of damage accumulation between the classical and proposed models for chosen materials are in favor of the authors model.

A nonlinear fatigue damage accumulation model considering strength degradation and its applications to fatigue reliability analysis

Fatigue is a damage accumulation process in which the material property deteriorates and degenerates continuously under cyclic loading. The analysis of damage accumulation plays a key role in preventing the occurrence of fatigue failures, and the damage evolution mechanism is one of the important focuses of fatigue behavior. In this paper, a residual strength degradation model according to the stress–strength interference (SSI) model is introduced firstly; then a modified nonlinear fatigue damage accumulation model based on the Manson–Halford theory is proposed. Combining the proposed nonlinear damage accumulation model with the residual strength degradation model, a new method is developed for fatigue life prediction under constant and variable amplitude loading, which considers not only the effects of load interactions, but also the phenomenon of strength degradation of materials induced by loading history, and it can be used to predict the reliability and fatigue life of mechanical components. Moreover, the material parameter for the residual strength degradation can be obtained directly from S–N curve without running extra experiments. Finally, experimental data are used to compare with the predicted value in order to demonstrate the proposed residual strength degradation model. In addition, two sets of experimental data are also used to verify the proposed nonlinear fatigue damage accumulation model which is applied to predict fatigue life under two-stress level loading and reliability prediction under multi-stress level loading. The results show that the proposed method has a good agreement between the experimental data and predicted values.

Fatigue modeling of chopped strand mat/epoxy composites

In the present research, fatigue behavior of chopped strand mat/epoxy composites has been studied with two different techniques. First, the normalized stiffness degradation approach as a well-known model for unidirectional and laminated composites was utilized to predict the fatigue behavior of chopped strand mat/epoxy composites. Then, the capability of the fatigue damage accumulation model for chopped strand mat/epoxy composites was investigated. A series of tests has been performed at different stress levels to evaluate both models with the obtained results. The results of evaluation indicate a better correlation of the normalized stiffness degradation technique with experimental results in comparison with the fatigue damage accumulation model.