Fatigue Damage Parameter Research Articles

Estimate of Fatigue Damage Parameter by Shin Steel Plate under Fluctuating Amplitude Loads and Remote Measurement of Crack Length in Shin Steel Plate

Estimate of Fatigue Damage Parameter by Shin Steel Plate under Fluctuating Amplitude Loads and Remote Measurement of Crack Length in Shin Steel Plate

Review of Multiaxial Fatigue Life Prediction Technology under Complex Loading

The research on multiaxial fatigue life prediction methods is reviewed in the present paper from two aspects of experiment and theory. It is pointed out that the reasonable methods of the critical plane determining, multiaxial cycle counting and multiaxial fatigue damage parameter fixing are necessary if the fatigue life prediction models established under the multiaxial constant amplitude loading were applied to the life prediction of the complex multiaxial load. The shortcomings of existing researches are discussed. In the aspect of experiment, it is devoid of the multiaxial fatigue test that the loading components acted with different frequencies, and in the aspect of theory, the additional hardening effect of the multiaxial out-of-frequency loading is not considered. Both in the theoretical research and practical engineering applications, the problem of the out-of-frequency multiaxial loading is a pressing issue.

A modification of Shang–Wang fatigue damage parameter to account for additional hardening

Based on the critical plane approach, the Shang–Wang fatigue damage parameter is analyzed. It is discovered that the effect of the additional cyclic hardening on fatigue life cannot be reflected by the normal strain excursion well. In order to solve this problem, this fatigue damage parameter is modified by using the Huber–Mises criterion. The modified damage parameter combined maximum shear strain range with normal strain range on the critical plane, and a new stress-correlated factor is introduced to account for the additional cyclic hardening. It is demonstrated that the modified criterion gives satisfactory results for all the six checked materials.

Fe-18Mn TWIP강의 Pre-strain에 따른 저주기 및 고주기 피로 수명 예측 모델

The influence of pre-strain on low cycle fatigue behavior of Fe-18Mn-0.05Al-0.6C TWIP steel was studied by conducting axial strain-controlled tests. As-received plates were deformed by rolling with reduction ratios of 10 and 30%, respectively. A triangular waveform with a constant frequency of 1 Hz was employed for low cycle fatigue test at the total strain amplitudes in the range of <TEX>${\pm}0.4\;{\sim}\;{\pm}0.6$</TEX> pct. The results showed that low-cycle fatigue life was strongly dependent on the amount of pre-strain as well as the strain amplitude. Increasing the amount of prestrain, the number of reversals to failure was significantly decreased at high strain amplitudes, but the effect was negligible at low strain amplitudes. A new model for predicting fatigue life of pre-strained body has been suggested by adding <TEX>${\Delta}E_{pre-strain}$</TEX> to the energy-based fatigue damage parameter. Also, high-cycle fatigue lives predicted using the low-cycle fatigue data well agreed with the experimental ones.

Material characterization of SS 316 in low-cycle fatigue loading

This study deals with simulation of low-cycle fatigue (LCF), followed by evaluation of fatigue parameters, which would be suitable for estimating fatigue lives under uniaxial loading. The cyclic elastic–plastic stress–strain responses were analyzed using the incremental plasticity procedures. Finite-element (FE) simulation in elastic–plastic regime was carried out in FE package ABAQUS. Emphasis has been laid on calibration of SS 316 stainless steel for LCF behavior. For experimental verifications, a series of low-cycle fatigue tests were conducted using smooth, cylindrical specimens under strain-controlled, fully reversed condition in INSTRON UTM (Universal Testing Machine) with 8,800 controller at room temperature. The comparisons between numerical simulations and experimental observations reveal the matching to be satisfactory in engineering sense. Based on the cyclic elastic–plastic stress–strain response, both from experiments and simulation, loop areas, computed for various strain amplitude, have been identified as fatigue damage parameter. Fatigue strain life curves are generated for fatigue life prediction using Coffin–Manson relation, Smith–Watson–Topper model, and plastic energy dissipated per cycle (loop area). Life prediction for LCF has been found out to be almost identical for all these three criteria and correlations between predicted and experimental results are shown. It is concluded that the improvement of fatigue life prediction depends not only on the fatigue damage models, but also on the accurate evaluations of the cyclic elastic–plastic stress/strain responses.

Fracture Characteristics of Asphalt Mixtures Containing Incinerator Bottom Ash Aggregate

The documented results form part of a larger research program to study the mechanical and environmental properties of asphaltic mixtures containing incinerator bottom ash aggregate (IBAA). The fracture characteristics of four mixtures containing 0%, 30%, 60%, and 80% IBAA by weight were investigated under monotonic and cyclic semi-circular bending conditions. The linear elastic fracture mechanics (LEFM) approach was used to evaluate crack resistance of the tested mixtures with the aim of investigating the effect of IBAA content on these properties. LEFM led to the determination of the stress intensity factor, the J-integral, fracture energy, and Paris law parameters. Crack propagation was monitored with a digital camera, and a program developed in-house was adopted in interpreting crack growth. In addition, a new approach was presented to obtain asphalt fatigue damage parameters from fracture tests. Results showed a benefit to be gained in adding IBAA up to a certain amount, beyond which cracking properties become close to those of the control mix.

Multiaxial fatigue damage parameter and life prediction under low cycle loading for GH4169 alloy and other structural materials

Combined tension–torsion fatigue tests were conducted on nickel-based alloy GH4169 under proportional and nonproportional loading at 650 °C. The fatigue cracks on the specimen surface were found basically initiating and propagating along the maximum shear plane. Taking into account the materials in elastic–plastic state under low-cycle fatigue, a multiaxial fatigue damage parameter based on SW model was proposed. The developed damage model can be reduced to the uniaxial Manson–Coffin equation, which was used to evaluate the low cycle multiaxial fatigue for GH4169 alloy, Haynes188 and mild steel. It is concluded that the predicted results with the proposed model can give satisfied results.

Application of the endochronic theory of plasticity for life prediction with asymmetric axial cyclic straining of AISI 304 stainless steel

In this paper, experiments of asymmetrical axial cyclic straining were conducted to explore the mean strain effects on the stable hysteresis loop and the fatigue life of AISI 304 stainless steel. The experimental results show that the imposed mean strain level has almost no influence on the shape of a stable hysteresis loop under the same strain amplitude condition. In terms of the mean strain effect on the fatigue life, at a strain amplitude greater than 0.6%, the imposed mean strain level was found to have no significant effect on the fatigue life, whereas a prominent effect on the fatigue life was found at low strain amplitude. Moreover, the endochronic theory of plasticity has been utilized to develop the stress–strain relationships to simulate the stable hysteresis curve in tension. A good agreement exists between the simulation curve and the experimental data. In this study, the fatigue damage parameter ( Δ W P ) T is applied to the predictions of fatigue life. The prediction life is obtained by the ( Δ W P ) T damage parameter calculated on the basis of the simulated hysteresis loop which has a good correlation with the experimental life.

An inverse analysis approach to determine fatigue performance of bituminous mixes

In pavement engineering, fatigue resistance is evaluated using different tests protocols and different specimen geometries. The dependency of the specimen shape geometry on fatigue performance does not allow the evolution of intrinsic material properties. This paper deals with the calibration of intrinsic fatigue damage parameters for bituminous materials. A fatigue damage model is implemented. The decrease of stiffness of the specimen during fatigue tests for different laboratory testing conditions is calculated from finite element computations. An inverse optimization technique is used in order to adjust the fatigue damage parameters on bending fatigue tests. A Levenberg-Marquardt algorithm is implemented to fit the finite element specimen global response on experimental results. An application on bending laboratory fatigue tests is presented to illustrate the applicability of the method for pavement engineering.

Fatigue life prediction of vulcanized natural rubber subjected to heat-aging

Fatigue life prediction and evaluation are the key technologies to assure the safety and reliability of automotive rubber components. In this paper, fatigue life prediction methodology of vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from fatigue test. Heat-aging effects on the fatigue life prediction of natural rubber were experimentally investigated. Fatigue test were performed using the 3-dimensional dumbbell specimen, which were aged different amounts. The Green-Lagrange strain at the critical location determined from the finite element method used for evaluating the fatigue damage parameter. Fatigue life prediction equation effectively represented by a single function using the Green-Lagrange strain. According to fatigue life prediction equation, fatigue life ambient temperature was longer than at 70 ∘C. Predicted fatigue lives of the rubber component were in fairly good agreements with the experimental fatigue lives within factor of two.

Prediction of fatigue lifetime under multiaxial cyclic loading using finite element analysis

Life prediction for GH4169 superalloy thin tubular and notched specimens were investigated under proportional and nonproportional loading with elastic–plastic finite element analysis (FEA). A strain-controlled tension–torsion loading was carried out by applying the axial and circular displacements on one end of the specimen in the cylindrical coordinate system. Uniaxial cyclic stress–strain data at high temperature were used to describe the multi-linear kinematic hardening of the material. The comparison between FEA and experimental results for thin tubular specimen showed that the built model of FE is reliable. A fatigue damage parameter was proposed to predict the fatigue crack initiation life for notched specimen. The results showed that a good agreement was achieved with experimental data.

Experimental characterisation and numerical simulation of contact evolution effect on fretting crack nucleation for Ti–6Al–4V

Contact evolution effects during fretting can be divided into two categories, namely, change of contact geometry due to wear and near-surface damage. In this paper a study on the effect of contact evolution on fretting crack nucleation in Ti–6Al–4V is carried out, based on a cylinder-on-flat contact fretting wear configuration. The fretted surfaces are carefully profiled so that the evolution of the contact geometry around fretting-induced cracks is identified. The evolution of the near-surface microstructure is identified by scanning electron microscopy. According to the experimental results, a predictive framework is presented to capture the competition and interaction between the contact evolution and crack initiation. The modelling of fretting wear is central to this approach, since it predicts not only the extent of wear damage, but also the concomitant change in fatigue pertinent stresses. The analysis of fretting wear tests, including partial slip and gross sliding conditions, without the substrate fatigue loading of fretting fatigue tests, provides an opportunity to investigate the crack initiation and thus validate predictions. A multi-axial fatigue damage parameter is employed within a cumulative fatigue-damage methodology to predict the wear-induced crack nucleation behaviour under different slip regimes.

Damage evolution in a [±45] 2S CFRP laminate under block loading conditions

Cyclic tests were conducted on [±45] 2 S angle ply carbon–epoxy specimens using stress ratios, R (minimum/maximum stress) of 0.1 and −1.0. Damage was monitored by measuring progressive strain changes in the loading direction. The fatigue damage parameter was found to satisfactorily describe the evolution of damage throughout life, facilitating fatigue life prediction. Two distinct stages of damage evolution were identified. In Stage I, the fatigue damage parameter and the density of matrix micro-cracking rapidly increased to a level dependent upon the stress (Characteristic Damage State). This was followed by Stage II which was a long period (∼90% life) of gradual increase in damage, involving crack coalescence, debonding and delamination. On subjecting the specimens to two step block loading tests, synergistic interaction occurred whereby the total fatigue life was greater than that predicted by the summation of the individual blocks of cycles. The effect of crack density and crack closure appeared to play important roles in extending the fatigue life. For the low to high stress level block transition, more cycles were required to reach the Characteristic Damage State, whereas for the high to low sequence, the presence of a large number of cracks and matrix debris within them resulted in closure at the lower stress. Again, the number of cycles to failure increased.

A unified method for the analysis of controlled-strain and controlled-stress fatigue testing

Fatigue cracking is one of the primary distresses in asphalt pavements. This study presents a method to characterize fatigue resistance of the fine portion of the asphalt mixture using the dynamic mechanical analyzer (DMA). Three mixtures were characterized in controlled-strain and controlled-stress modes of loading. The new method has several advantages as it requires reasonable testing time, uses a small amount of material, utilizes fundamental properties of the mixture, and is able to unify the results from controlled-strain and controlled-stress modes of loading. The unified method relies on identifying the different mechanisms of energy dissipation during fatigue cracking that are related to changes in the phase angle, changes in stiffness, and development of permanent deformation during the fatigue damage process. Two fatigue damage parameters are derived in this paper. The parameters are shown to have reasonable and lower coefficients of variation than conventional parameters such as number of loading cycles to failure and cumulative dissipated energy.

Cyclic Elastoplastic Analysis of Structures Concerning a Fatigue Assessment According to the Local Strain Approach: An Overview

This Technical Brief presents an overview about the current methodologies for elastoplastic calculation of structures undergoing cyclic loading, aiming a fatigue assessment according to the local strain approaches. The possibilities and limitations of the plasticity models available in most popular commercial finite element codes are discussed. Also, several methodologies for structural elastoplastic analysis, concerning the derivation of the stabilized material response, are also addressed highlighting their potentialities and drawbacks. The discussion proposed in this Technical Brief is intended as guidance for design engineers needing to ponder all calculation alternatives for assessing fatigue damage parameters before a rational decision is carried out, in the framework of local approaches to fatigue.

A new energy-based fatigue damage parameter in life prediction of high-temperature structural materials

A new life prediction model has been developed with the energy-based fatigue damage parameter of a non-dimensional plastic strain energy density (PSED). Tensile tests and low cycle fatigue tests of 316L austenitic stainless steel and 429EM ferritic stainless steel have been performed at elevated temperature for the prediction. While the cyclic stress response of a material is not stabilized during fatigue deformation, it was found that PSED is stabilized at the early stage of fatigue life and nearly invariant through the whole cycles. Hence, PSED can be regarded as a suitable fatigue parameter for the materials. The Morrow model using PSED gave a good correlation on low-cycle fatigue under isothermal conditions for both stainless steels. A fatigue damage parameter, which is defined as the PSED non-dimensionalized by material toughness, was proposed to account for temperature effect on the fatigue life. The developed model, in which the fatigue exponent is obtained from the universal slope method and the true toughness measured from the tensile test is used as a temperature-compensating parameter, provided a good prediction on the fatigue behaviors of both stainless steels over the temperature range.

Fatigue Life Evaluation of Automotive Engine Mount Insulator

Fatigue life of automotive engine mount insulator made of natural rubber was evaluated. In order to develop an appropriate fatigue damage parameter of the rubber material, a series of displacement controlled fatigue tests was conducted using 3-dimensional dumbbell specimens with different levels of mean displacement. It was shown that the maximum Green-Lagrange strain was a proper damage parameter, taking the mean displacement effects into account. Nonlinear finite element analyses of the rubber engine mount insulator and 3D dumbbell specimen were performed based on a hyper-elastic material model determined from the simple and equi-biaxial tension tests. Fatigue life prediction of the engine mount insulator was made by incorporating the maximum Green-Lagrange strain values, which was evaluated from the finite element analysis and fatigue tests, respectively. Predicted fatigue lives of the engine mount insulator showed a fairly good agreement with the experimental fatigue lives.

Two Models for Predicting Fatigue Crack Growth

In this investigation two fatigue crack growth models based on the different physical assumptions were systematically analyzed. One model makes use of the size of the stable damage distribution zone near crack as the major contributor to the fatigue crack growth. This model is based on the concept that a material point failures and a new crack will form when the fatigue damage value of the material point reach the critical damage. The other model supposes that fatigue growth can be described as a process with sequentially breaking small volume elements behind the crack tip. The fatigue crack growth can be regarded as successive crack re-initiation over a critical distance. The fatigue crack growth rate can be determined as the ratio of the critical distance to the average life within critical distance. Both models use macro parameter to describe the microscopic mechanism. An elastic-plastic finite element analysis (FEA) was used to obtain the detailed stress-strain history of the notched component with a detailed consideration of the cyclic plasticity of the material using a robust cyclic plasticity model. The fatigue damage distribution and the average damage within the critical distance near the crack tip can be obtained by combining the fatigue damage parameter with the stress strain distribution from the finite element analysis. These two models were evaluated using the experimental results obtained from the crack grow experiments on compact specimens made from 16MnR. The predicting results using these two models correlate well with the experimental data. The results show that two models can well describe the notch effect on the fatigue crack growth.

Fatigue crack orientation in NR and SBR under variable amplitude and multiaxial loading conditions

The orientations of cracks as they develop in a material indicate the planes that have experienced the maximum damage. For the purpose of fatigue life analysis and prediction, these planes are referred to as the failure or critical planes. In order to study the planes on which cracks develop for different types of loading, the development of cracks was observed during constant and variable amplitude experiments using the multiaxial ring specimen. Two filled rubber materials were compared in this study: NR, which strain crystallizes, and SBR, which does not. Multiaxial test signals composed of alternating blocks of axial and torsion cycles (each of which acts on different critical planes) produced crack orientations that fell between those occurring for signals composed only of axial or of torsion cycles. Plane-specific fatigue damage parameters of cracking energy density and normal strain were evaluated for their ability to predict the experimentally observed planes of crack development.

Fatigue Analysis of Asphalt Mixtures Independent of Mode of Loading

Fatigue cracking is a common form of distress in asphalt pavements. During the last four decades, significant research has been conducted to characterize fatigue damage in asphalt mixtures. This paper evaluates an analytical method that is independent of the mode of loading (controlled strain or controlled stress) to quantify the fatigue resistance of asphalt mixtures. The evaluation was based on fatigue tests conducted on the fine aggregate matrix (FAM) portion of an asphalt mixture by using a dynamic mechanical analyzer. A number of tests were performed by applying oscillatory torque under controlled-strain and controlled-stress conditions at a frequency of 10 Hz and a temperature of 25°C. The data from these tests were analyzed by using a fracture model for viscoelastic materials to calculate a fatigue damage parameter, R(N), which represents the influence of the numbers of cracks with equivalent crack radii on the material fracture behavior and which quantifies crack growth in FAM. This damage parameter has a coefficient of variation lower than the coefficients of variation of conventional parameters, such as the number of load cycles to failure and the cumulative dissipated energy. In addition, this parameter provides comparable results for a given material independent of the mode of loading.