The Reliability of a Component Under Several Distributed Cyclic Numbers at the Corresponding Constant Cyclic Stress Levels

2017 ◽  
Vol 4 (2) ◽  
Author(s):  
Xiaobin Le
Keyword(s):  
Cyclic Loading ◽  
Fatigue Damage ◽  
Cyclic Stress ◽  
New Method ◽  
Reliability Calculation ◽  
Stress Levels ◽  
Relative Errors ◽  
Number Of Cycles ◽  
Unsolved Issue ◽  
Loading Spectrum

The probabilistic stress-number of cycles curve (P-S-N curve) approach is widely accepted for describing the fatigue strengths of materials. It is also a widely accepted fatigue theory for determining the reliability of a component under fatigue loadings. However, it is an unsolved issue in the P-S-N curve approach that the calculation of reliability of a component under several distributed cyclic numbers at the corresponding constant cyclic stress levels. Based on the commonly accepted concept of the equivalent fatigue damage, this paper proposes a new method to determine the reliability of the component under several distributed cyclic numbers at the corresponding constant cyclic stress levels. Four examples including two validation examples will be provided to demonstrate how to implement the proposed method for reliability calculation under such fatigue cyclic loading spectrum. The relative errors in validation examples are very small. So, the proposed method can be used to evaluate the reliability of a component under several distributed cyclic number at different stress levels.

The Reliability of a Component Under Multiple Cyclic Stress Levels With Distributed Cyclic Numbers

2016 ◽  
Author(s):  
Xiaobin Le
Keyword(s):  
Fatigue Life ◽  
Probabilistic Models ◽  
Random Variable ◽  
Fatigue Loading ◽  
Cyclic Stress ◽  
Initial Crack ◽  
Stress Levels ◽  
Single Constant ◽  
Unsolved Issue ◽  
Loading Spectrum

Fatigue damage is initiated through some “defects” on the surfaces of and/or inside the component and induced by the fatigue cyclic loadings. These “defects” are randomly scattered in components, and one of these “defects” will be randomly “activated” and finally developed to become the initial crack which causes the final fatigue failure. Therefore, the fatigue strength is inherently a random variable and should be treated by probabilistic models such as typical P-S-N curves. The fatigue cyclic loading could be presented or described in any form. But the fatigue loading spectrum can generally be grouped as and described by these five models: (1) a single constant cyclic stress (loading) with a given cyclic number, (2) a single constant cyclic stress with a distributed cyclic number, (3) a distributed cyclic stress (loading) at a given fatigue life (cyclic number), (4) multiple constant cyclic stress levels with given cyclic numbers, and (5) multiple constant cyclic stress levels with distributed cyclic numbers. The approaches for determining the reliability of components under fatigue loading spectrum of the models 1∼4 are available in literature and books. But few articles and books have addressed an approach for determining the reliability of components under the fatigue loading spectrum of the model 5. This paper will propose two approaches for addressing this unsolved issue. Two examples will be presented to implement the proposed approaches with detailed procedures.

scholarly journals Study on the Influence of Different Prophase Stress Levels on the Fatigue Damage Characteristics of Granite

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Tianzuo Wang ◽  
Mengya Xue ◽  
Peng Sha ◽  
Fei Xue ◽  
Linxiang Wang
Keyword(s):  
Fatigue Damage ◽  
Stress Level ◽  
Development Trend ◽  
Cyclic Stress ◽  
Tangent Modulus ◽  
Dissipated Energy ◽  
Upper Limit ◽  
Stress Levels ◽  
Number Of Cycles ◽  
The Development Trend

In order to reveal the influence of prophase stress levels on the fatigue damage characteristics of granite, uniaxial fatigue tests of granite with different prophase stress levels were carried out on the basis of the MTS 815.04 rock mechanics test system. The results show that, under the same number of cycles, the failure degree increases with the increase of the prophase stress level. Under the low upper limit of cyclic stress, the tangent modulus and dissipated energy increase significantly with the increase of prophase stress level at the early stage of the cycle loading, while the increasing trend is not obvious with the increase of prophase stress level at the late stage. Under the high upper limit of cyclic stress, the tangent modulus and dissipated energy are less affected by the prophase stress level. The development trend of elastic release energy is not obvious with the increase of prophase stress level, which is less affected by the number of cycles. From the damage parameters defined by dissipative energy, under the low upper limit of cyclic stress, the initial damage is less affected by the prophase stress level. With the increase of the number of cycles, the influence of the prophase stress level on the development trend of the damage variable increases gradually. And the development trend of damage variables shows “C-shaped” damage.

Cumulative fatigue damage for 3-D angle-interlock woven composite under three-point bending cyclic loading

2012 ◽  
Vol 22 (1) ◽  
pp. 3-16 ◽  
Author(s):  
Limin Jin ◽  
Baozhong Sun ◽  
Bohong Gu
Keyword(s):  
Cyclic Loading ◽  
Fatigue Damage ◽  
Stress Level ◽  
Three Dimensional ◽  
Woven Composite ◽  
Damage Development ◽  
Static Test ◽  
Three Point Bending ◽  
Cumulative Fatigue Damage ◽  
Number Of Cycles

This article presents the quantitative characterization of cumulative fatigue damage behavior for the three-dimensional angle-interlock woven composite undergoing three-point bending cyclic loading. The S–N curve was obtained to demonstrate the fatigue life of the three-dimensional angle-interlock woven composite under different stress levels. The increment of cycles for each 5% interval of stress level was reported to show the difference of fatigue resistance performances of the three-dimensional angle-interlock woven composite among the high, middle, and low intervals of stress level. In addition, the Cumulative Fatigue Damage versus Number of Cycles (D–N) curve and the Deflection Index versus Number of Cycles (F–N) curve were deduced to characterize the three-stage cumulative fatigue damage. Furthermore, the damage morphologies of the three-dimensional angle-interlock woven composite after fatigue tests were photographed to compare with those in quasi-static test. The cracks initiation and propagation in the three-dimensional angle-interlock woven composite during the process of cyclic loading were summarized to find the mechanisms of fatigue damage development.

A Novel Application of the Principles of Linear Elastic Fracture Mechanics (LEFM) to the Fatigue Behavior of Tendon Tissue

2004 ◽  
Vol 126 (5) ◽  
pp. 641-650 ◽  
Author(s):  
Samer M. Adeeb ◽  
Michelle L. Zec ◽  
Gail M. Thornton ◽  
Cyril B. Frank ◽  
Nigel G. Shrive
Keyword(s):  
Tensile Strength ◽  
Cyclic Loading ◽  
Fracture Mechanics ◽  
Ultimate Tensile Strength ◽  
Fatigue Behavior ◽  
Cyclic Stress ◽  
Linear Elastic Fracture Mechanics ◽  
Linear Elastic ◽  
Elastic Fracture ◽  
Number Of Cycles

Background: Experiments on the fatigue of tendons have shown that cyclic loading induces failure at stresses lower than the ultimate tensile strength (UTS) of the tendons. The number of cycles to failure Nf has been shown to be dependent upon the magnitude of the applied cyclic stress. Method of approach: Utilizing data collected by Schechtman (1995), we demonstrate that the principles of Linear Elastic Fracture Mechanics (LEFM) can be used to predict the fatigue behavior of tendons under cyclic loading for maximum stress levels that are higher than 10% of the ultimate tensile strength (UTS) of the tendon (the experimental results at 10% UTS did not fit with our equations). Conclusions: LEFM and other FM approaches may prove to be very valuable in advancing our understanding of damage accumulation in soft connective tissues.

MONITORING OF FAILURE MECHANISMS IN A COMPOSITE BENDING ACTUATOR DURING CYCLIC LOADING BY ACOUSTIC EMISSION

2010 ◽  
Vol 24 (15n16) ◽  
pp. 2339-2344
Author(s):  
SUNG-CHOONG WOO ◽  
NAM SEO GOO
Keyword(s):  
Cyclic Loading ◽  
Fatigue Damage ◽  
Event Rate ◽  
Piezoelectric Composite ◽  
Transgranular Fracture ◽  
Bending Actuator ◽  
Performance Reduction ◽  
Composite Actuator ◽  
Electromechanical Loading ◽  
Number Of Cycles

The objective of this work is to investigate the influence of electromechanical cyclic loading on the performance of a bending piezoelectric composite actuator. We have analyzed the fatigue damage mechanisms in terms of the behavior of the AE event rate. It was found that whether the actuators are subjected to purely electric loading or electromechanical loading, the initial fatigue damage of the bending piezoelectric composite actuator was caused by the transgranular fracture in the PZT ceramic layer; the final failure was caused only in the case of PCAWB under electromechanical loading by a local discharge, which critically affected the performance reduction of the actuators. As the number of cycles increased, a large reduction in displacement performance coincided with a high AE event rate, which was identified via microscopic observations.

Fatigue properties by “self-heating” method: Application to orthodontic Ni-Ti wires after hydrogen charging

2018 ◽  
Vol 29 (16) ◽  
pp. 3242-3253 ◽  
Author(s):  
Maha Rokbani ◽  
Luc Saint-Sulpice ◽  
Shabnam Arbab Chirani ◽  
Tarak Bouraoui
Keyword(s):  
Cyclic Loading ◽  
Fatigue Behavior ◽  
Cyclic Stress ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Orthodontic Wires ◽  
Heating Method ◽  
Hydrogen Charging ◽  
Self Heating ◽  
Number Of Cycles

Ni-Ti superelastic alloys have been successfully used in orthodontic clinics thanks to their good biomechanical and biochemical behavior. However, during treatment, some orthodontic wires may break in the oral cavity. The susceptibility of these alloys to cyclic loadings and to hydrogen embrittlement is supposed to be main causes of these unexpected failures. This study presents a contribution to studying the effect of hydrogen, obtained after cathodically charging in 0.9% NaCl solution, on the fatigue behavior of Ni-Ti commercial orthodontic wires subjected to high-cycle fatigue. Fatigue tests were analyzed using self-heating method based on observing thermal effects under mechanical cyclic loading. The results obtained with self-heating approach imply that the increase in hydrogen charging time is connected with an increase in the mean stabilized temperature and a decrease in the fatigue life. Self-heating method allows a rapid prediction of the endurance limit with a good reproducibility of fatigue tests at high number of cycles. Furthermore, cyclic stress–induced transformations and conventional fatigue tests under strain control are considered in this work to investigate the effect of hydrogen on cyclic loading type and to acquire for a better understanding of the interaction between hydrogen and thermo-mechanical mechanisms in Ni-Ti alloys.

The Reliability Calculation of Components Under Any Cyclic Fatigue Loading Spectrum

2017 ◽  
Author(s):  
Xiaobin Le
Keyword(s):  
Stress Amplitude ◽  
Fatigue Loading ◽  
Cyclic Fatigue ◽  
Cyclic Stress ◽  
Fatigue Reliability ◽  
Cycle Number ◽  
New Approach ◽  
Systematic Description ◽  
Reliability Calculation ◽  
Loading Spectrum

The fatigue failure of metal components is due to cyclic fatigue loading. The typical cyclic fatigue loading spectrums described in the literature includes only a few simple cyclic loadings such as a constant amplitude of cyclic fatigue loading with a given cycle number, several constant amplitudes of cyclic fatigue loadings with given cycle numbers, and a distributed stress amplitude of a cyclic stress with a given cycle number or an infinite life. The systematic description of cyclic fatigue loading spectrums is necessary and wasn’t presented in the literature. This paper will present a systematic description of all possible types of cyclic fatigue loading spectrums, which includes 6 different cyclic fatigue loading spectrum models. The P-S-N curve fatigue theory is widely accepted not only for describing the fatigue test data, but also for estimating the reliability of components under cyclic fatigue loading spectrum. However, the reliability calculation of a component under several distributed stress levels with corresponding given cyclic numbers has not been solved according to the literature review. This paper presents a new approach to estimate the reliability of components under such cyclic fatigue loading spectrum. With the contribution of this paper, the P-S-N curve fatigue theory now becomes a complete fatigue reliability theory and can be used to estimate the reliability of components under any type of cyclic fatigue loading spectrum.

Cyclic Loading of Piles Using the P-Y Method

2019 ◽  
Vol 13 (2) ◽  
Author(s):  
Matt Bristow
Keyword(s):  
Cyclic Loading ◽  
Soil Depth ◽  
Large Diameter ◽  
Reference Conditions ◽  
Numerical Procedure ◽  
New Method ◽  
Shear Stresses ◽  
Applied Loading ◽  
Cyclic Degradation ◽  
Laterally Loaded

A new analytical method is presented to determine the effects of cyclic loading on laterally loaded piles. The method uses a new numerical procedure to quantify the effects of the cyclic loading at each soil depth and convert that to a set of cyclic p-y modifiers. The reduced foundation stiffness associated with the cyclic loading can be determined, including the residual static capacity and an estimate of the accumulated displacement. The new method introduces the concept of cyclic degradation damage, which is defined as sum of the cyclic degradation that is occurring at each soil depth. Cyclic degradation calculations are based on the shear stresses in the soil. Consequently, anything that causes the shear stresses to change (e.g. pile length, pile diameter, applied loading, etc.) will automatically be included in the calculation of cyclic p-y modifiers. The method has been validated by comparing the cyclic p-y curves produced using the new method with established cyclic p-y curves derived from fielding testing. The new method has also been used to investigate what happens to the cyclic p-y modifiers as one moves away from the reference conditions used to determine the established cyclic p-y curves in API RP2A (2000). The new method shows that every application (e.g. combination of cyclic loading, pile properties, and soil characteristics) has its own unique set of cyclic p-y curves, though most p-y curves fit within an upper and lower bound range. Examples are provided for large diameter monopiles.

scholarly journals Investigation of Deformation Inhomogeneity and Low-Cycle Fatigue of a Polycrystalline Material

2021 ◽  
Vol 11 (6) ◽  
pp. 2673
Author(s):  
Mu-Hang Zhang ◽  
Xiao-Hong Shen ◽  
Lei He ◽  
Ke-Shi Zhang
Keyword(s):  
Cyclic Loading ◽  
Low Cycle Fatigue ◽  
Strain Tensor ◽  
Equivalent Strain ◽  
Differential Entropy ◽  
Strain Components ◽  
Deformation Inhomogeneity ◽  
Standard Deviations ◽  
Number Of Cycles ◽  
The Relationship

Considering the relationship between inhomogeneous plastic deformation and fatigue damage, deformation inhomogeneity evolution and fatigue failure of superalloy GH4169 under temperature 500 °C and macro tension compression cyclic loading are studied, by using crystal plasticity calculation associated with polycrystalline representative Voronoi volume element (RVE). Different statistical standard deviation and differential entropy of meso strain are used to measure the inhomogeneity of deformation, and the relationship between the inhomogeneity and strain cycle is explored by cyclic numerical simulation. It is found from the research that the standard deviations of each component of the strain tensor at the cyclic peak increase monotonically with the cyclic loading, and they are similar to each other. The differential entropy of each component of the strain tensor also increases with the number of cycles, and the law is similar. On this basis, the critical values determined by statistical standard deviations of the strain components and the equivalent strain, and that by differential entropy of strain components, are, respectively, used as fatigue criteria, then predict the fatigue–life curves of the material. The predictions are verified with reference to the measured results, and their deviations are proved to be in a reasonable range.

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