Method For Fatigue Life Research Articles

Numerical method for fatigue life of plane bolted joints under thermal load

In fatigue test, the fatigue life of metal components is affected by many factors, such as test temperature, stress ratio and loading frequency. In order to study the influence of temperature on fatigue life of bolted joints, thermal stress and fast coefficient are introduced. A numerical method of fatigue crack initiation life is proposed based on Manson-Coffin strain fatigue formula. The crack initiation life of 2024 aluminum alloy at different temperatures can be obtained by this method, which provides a theoretical basis for the fatigue life prediction of metals. Then, the stress severity factor SSF is introduced to calculate fatigue life of plane bolted joints. The data obtained from the model show that the crack initiation life of aluminum alloy specimen decreases significantly with test temperature rises, the same as the fatigue life of bolted joints.

Assessment of Fatigue Lifetime and Characterization of Fatigue Crack Behavior of Aluminium Scroll Compressor Using C-Specimen

Currently, a scroll compressor is used in many industrial fields; hence, research on its reliability is important. The major loading type during operation is pressure. However, unexpected contact between scroll compressors typically occurs, and thus, the severe loading condition should be considered. To consider this condition, the study modified the scroll compressor’s structure to a C-type specimen. The study applied cyclic axial load in the specimen. The main objective of the study is to define a proper fatigue life method for the aluminium scroll compressor and proper finite element method (FEM) modeling. To define the method, the study included a case study for various parameters, such as mean stress effects. Furthermore, a crack propagation study is presented. In the study, the Darveaux method that considers the Bauschinger effect of ductile material is used. It is expected that the consideration of the parameters can help define the fatigue life assessment of an aluminium scroll compressor.

Research on Fatigue Life of Lifting Equipment Based on Double Linear Cumulative Damage Theory

The lifting equipment is applied more and more extensively with the fast development of economy. The fatigue and safety problems of lifting equipment in service are more and more prominent. The stress spectrum monitoring data was analyzed by the two parameters rain-flow counting method for fatigue analysis. The calculation for cumulative damage and prediction for fatigue life of the lifting equipment’s hot region were calculated based on the double linear damage theory and the nominal stress method. According to the engineering application results, the real crack generation time is consistent with that of our estimation, which demonstrates that our prediction model and method for fatigue life are effective and give a method for the evaluation of the lifting equipment’s fatigue life. The double linear damage theory is recommended for use in fatigue and damage prediction of lifting equipment in service.

Fatigue Research on Excavator Boom Driven by Real Loads

The difficulty to simulate the complex loads in the fatigue analysis of excavator working device results in great error in the result, so a research method of fatigue life of working device that was completely driven by real loads was proposed. With a 20t excavator as the research object, a kinetic model of excavator working device was established using the D-H method. According to the hydraulic cylinders pressure and displacement data in the process of digging recorded by the sensors, the real working loads of booms hinge points were obtained combining the equation of forces. The life contour of boom was obtained by the fatigue analysis of boom using software MSC.Fatigue. The minimum fatigue life is 16.8 years, and the result of the study provides basis for designing excavator working device structure.

The Iterative Method for Reliability Estimation of Fatigue Life

The expression of reliability estimation method for fatigue life of machine parts was derived, and two kinds of stress cycles (reversed cycle and un-symmetric reversed cycle) were considered. An iteration method is presented and the corresponding computer program named STRENGTH-2 is developed for estimating reliable life of machine parts. The engineering application results show that the calculated results are close to experimental results. The proposed method can be convenient to carry out the fatigue reliability design for machine parts under the action of uni-axial and multi-axial loadings, and promote the popularization and application of existing anti-fatigue design method. It has the high value of engineering application.

Research on Fatigue Life of Autofrettaged Thick-Walled Cylinder in Probabilistic Fracture Mechanics

Based on the theory of probabilistic fracture mechanics and Monte Carlo simulation, reliability analysis method for fatigue life of autofrettaged thick-walled cylinder was given. The forms of fatigue cracks in bore of autofrettaged thick-walled cylinder were considered as semi-elliptical cracks. The autofrettage residual stress solution was suitable for the thick-walled cylinder made of steel with strain hardening and Bauschinger effect. The stress intensity factors of thick-walled cylinder were calculated according to weight function method. The analysis of the examples showed that lognormal distribution is the best fit for fatigue life. Finally, the fatigue life of autofrettaged thick-walled on the condition of different reliabilities and confidences were presented.

Method for Fatigue Life on the Facilities of Gate and Penstock

Method for Fatigue Life on the Facilities of Gate and Penstock

Load Spectrum Compiling and Practical Application of Output Flange for Wheel Loader Gearbox

To realize the structural light weighting design of the transmission components of engineering vehicles on the basis of life in control, this paper took wheel loader as an example, collected the time-domain load signals of the transmission system in typical working conditions, provided processing steps for load spectrum synthesis by a certain percentage, and generated the program load spectrum which consisted of various amplitudes and means. The load spectrum can be used for fatigue loading at the output flange of gearbox. Then, the finite element model of the flange was established, and the stress analysis was carried out in the stress concentration location such as fillet. The prediction method of fatigue life on the base of program load spectrum was given. After the fatigue life prediction based on the compiled load spectrum and the theory of cumulative fatigue damage, the fatigue life of outside fillet of the flange, where is of maximum stress, is obtained. It was possible to obtain adequately fatigue prediction results in engineering vehicle design, using load spectrum, finite element analysis, and a stress-life approach to fatigue damage calculations.

Fatigue Life of Main Shaft Bearing of Direct Drive Wind Turbine

A calculation method of fatigue life for main shaft bearing of direct drive wind turbine was proposed. The statics models of the bearing were established and a set of equilibrium equations were obtained. By solving the equilibrium equations, the displacements of the inner ring were obtained, and the rolling element loads were calculated further. Based on the load distribution of the rollers, the fatigue life of the bearing was calculated and the influences of the clearances on it were researched. Results show that the clearances of the bearing can influence its service life distinctly. Zero axial clearance is recommended for the bearing.

Estimation of Random Sonic Fatigue Life Based on Peak Probability Density of Von Mises Stress

As to the random sonic fatigue problem of thin walled structure of aerospace flight vehicle, estimation method for fatigue life based on Von Mises stress peak probability density is investigated. Assuming that Von Mises stress process satisfies three-parameter Weibull distribution, the peak probability density function of Von Mises stress is derived through the threshold crossing analysis and the peak distribution analysis of stationary random process. According to the Miner linear cumulative damage theory, the method for estimating the fatigue life in the frequency domain is established with the Von Mises stress peak probability density function applied. As an example, an aero-engine Combustor liner is considered, using coupled Finite Element Method (FEM) and Boundary Element Method (BEM) method, the structure vibration response to limited bandwidth Gaussian white noise is calculated. Based on the results, fatigue life of the structure is estimated by using the proposed method. Further more, the influences of the probability density function which is characterized by three-parameter Weibull distribution and two-parameter Weibull distribution respectivily for Von Mises stress response of the Combustor liner structure subjected to random accoustic loadings are discussed.

Hole Expansion by Using Al-Alloy Specimen and 0.45% Carbon Steel Specimen

The enhancement method of fatigue life and the crack initiate and growth behavior of a holed specimen was investigated by using the 2024 Aluminum alloy and 0.45% Carbon steel. The purpose of present study is to propose a simple technical method for enhancement of fatigue life in a notched specimen. Also, the effect of local plastic deformation by cold work on fatigue crack initiation behavior was examined. This paper presents a basic experimental kinematic cold expansion method by inserting and removing a pin through the specimen hole. The shape of cross-section of pin was a circle or an ellipse. It was shown that the fatigue life of the specimen with the cold-worked hole was longer than that of the specimen with non-cold-worked hole for the case of same stress level in aluminum alloy and carbon steel. Also, the fatigue strength was higher in the case of the cold expanded hole. In this study, a methodology of lengthening of fatigue life of holed specimen is shown. Also, the improvement conditions of fatigue life were significantly affected by shape of pin, local hardening and residual stress conditions. The fatigue life improvement of the damaged component of structures was studied.

Effect of Parameters of Notch on Fatigue Life of Shaft Based on Product Lifecycle Management

For designing the fatigue life of shaft with a circumferential notch exactly, the influencing factors have been analyzed completely. The modified mechanics model to estimate the fatigue life of shaft with a circumferential notch is set up. The assessment method of fatigue life for shaft with a circumferential notch is put forward. The effects of notch on stress concentration factor and fatigue life of shaft with a circumferential notch are discussed and the influencing parameters are obtained. The results show that the tip radius of notch has a great effect on fatigue life of shaft; on the other hand, the open angle of notch has a little effect on it. The results will establish the base of anti-fatigue design of shaft.

Effect of Wear on the Fatigue Life of Annular Notched Shaft Based on Product Lifecycle Management

Anti-fatigue design is a key content in product lifecycle management and there are many factors to affect the fatigue life of parts. For designing the fatigue life of shaft with a circumferential notch exactly, the influencing factors have been analyzed completely. The mechanics model for assessing the fatigue life of shaft is set up. The assessment method of fatigue life for shaft is set up according to the traditional fatigue life estimation. The effect of wearing parameter to fatigue life is analyzed and the results show that the wear is an important factor to affect the fatigue life.

Effect of Specimen Configuration and Loading Types on Fatigue Life of an Annealed 0.42% Carbon Steels

In the present study, a unified crack growth law based on the small fatigue crack growth law was investigated using specimens with different configurations and loading types for the annealed 0.42% carbon steel. Then, a convenient prediction method of fatigue life was proposed. This small fatigue crack growth rate was uniquely determined by the modified small crack growth law, , despite of changing for specimen configurations and loading types. The constants of can be estimated by an empirical equation of without stress/strain gradient. Considered the effect of stress gradient for different specimen configurations and loading types, the stresses under bending loadings and specimen configurations was calculated from that under push-pull loading. Therefore, the fatigue life of the specimens with different configuration and under different loading types can be simply estimated through the fatigue crack growth law based on the only tensile strength of carbon steels. The availability of proposed method was confirmed experimentally by the results of several carbon steels.

The Ability of Current Models for Fatigue Life Prediction of Shot Peened Components

It is well known that shot peening has a marked benefit on fatigue life for the majority of applications. This effect is attributed mainly due to the compressive residual stress state at the component’s surface due to shot peening. The present paper evaluates the ability of several fatigue life prediction models, commonly used for general analyses, to predict the behaviour of components with compressive residual stress due to shot peening. Advanced elastic-plastic finite element analyses were carried out in order to obtain stress, strain, strain energy and fracture mechanics parameters for cracks within a compressive residual stress field. With these results several total fatigue life prediction models (including critical distance methods) and fracture mechanics based models were applied in order to predict fatigue life. Fatigue life predictions were compared with several experimental fatigue tests carried out on specimens, representative of a critical region of a compressor disc in a gas turbine aero engine. The results obtained showed that total fatigue life methods, even if combined with critical distance methods, give conservative results when shot peening is considered. Fatigue life was successfully predicted using the method proposed by Cameron and Smith, by adding initiation life to crack propagation life. This last method was also successfully applied for the prediction of non-propagating cracks that were observed during the experimental tests.