Degree Of Fatigue Damage Research Articles

The Prediction for the Residual Life of Waste Drive Axle Housing Basing on Neural Network

In order to estimate the residual life of waste drive axle housing, the prediction model of waste axle housings with artificial neural networks is built in this paper. Take the deformation, residual stress and the gradient of magnetic intensity Kmax relating to axle housing’s fatigue damage degree as the input of neural network, and compare the testing residual life of the waste drive axle housing with its predicting residual life. The result demonstrates that: the deformation, residual stress and the gradient of magnetic intensity Kmax of axle housing as the characteristic parameter estimating the degree of fatigue damage, adopting trainbr training function can get good network performance and comparatively high precision of prediction. Besides, the longer the residual life of the waste axle housing is, the more precise the prediction life will be.

Metal magnetic memory effect caused by circle tensile-compressive stress

The variation of surface magnetisation, caused by applied stress under the geomagnetic field, can be potentially used to evaluate the degree of fatigue damage for ferromagnetic materials. Under lab conditions, the normal components of surface magnetisation induced by circle tensile-compressive stress are measured in rotary bending fatigue experiments. Based on the effective field theory and the law of approach, the results of experiments are discussed. This work confirms the J-A-S model.

EBSDによる低サイクル疲労損傷の観察（SUS316鋼およびSTS410鋼の微視組織的変化）

Electron backscatter diffraction (EBSD) technique was employed for observing the microstructural change in SUS316 and STS410 due to low-cycle fatigue. Samples of various degrees of strain amplitude and number of cycles were prepared for crystal orientation measurements. The cyclic straining caused local change in crystal orientations and the change was quantified by a parameter called local misorientation. In SUS316, the local misorientation exhibited stripe-like distribution, which emanated from slip deformation. On the other hand, in STS410, network-like distribution was formed. The cell structure which consisted of dislocations brought about the quasi-grain boundaries. Angular distribution of the power spectrum density obtained by Fourier transfer of the local misorientation distribution maps showed the dependency on loading axis. This suggested that it is possible to know the loading direction by the EBSD observation. It was also shown that the degree of fatigue damage could be estimated by the quantification of the local change in the crystal orientations.

Assessment of fatigue damage in solid plates through the ultrasonic Lamb wave approach

Changes (degradations) in the mechanical properties of solid plates induced by cyclic fatigue loading will influence the features of ultrasonic Lamb wave propagation, such as dispersion and attenuation. This paper has qualitatively analyzed the feasibility of using the amplitude-frequency characteristics and the stress wave factors (SWFs) of ultrasonic Lamb wave propagation to assess fatigue damage in solid plates. Liquid wedge transducers located on the surface of solid plates tested are used to generate and detect the Lamb wave signals. Based on the Ritec-SNAP ultrasonic measurement system, the experimental setup for assessing the degree of fatigue damage in solid plates using ultrasonic Lamb wave approach has been established. For several rolled aluminum sheets subjected to tension-tension cyclic loading, the experimental examinations have been performed for the relationships between the amplitude-frequency characteristics of ultrasonic Lamb wave propagation and the numbers of loading cycles (denoted by N), as well as the correlations between the Lamb wave SWFs and N. The experimental results show that the Lamb wave SWFs decrease monotonously and sensitively with the increment of cycles of fatigue loading. Based on the correlations between the Lamb wave SWFs and N, it is further verified that ultrasonic Lamb wave propagation combined with the Lamb wave SWFs can be used to effectively assess early fatigue damage in solid plates.

Research on Fatigue Damage of Ferromagnetic Material by Metal Magnetic Memory Methods

Tension–tension fatigue tests of notched 18CrNi4A steel specimens were carried out under three different fatigue stresses, and metal magnetic memory (MMM) signals were detected. The effects of fatigue damage and fatigue stress on MMM signals were investigated. The results show that the absolute values of the feature parameters Hp(y)max, Hp(y)min and Hp(y)sub increase with the aggravation of the fatigue damage. There is an inherent relationship between the fatigue stress and the values of the Hp(y)sub; the larger the fatigue stress is, the larger the absolute values of the Hp(y)sub is. Fatigue-damaged locations can be effectively predicated according to the mutational character of the Hp(y) curve and the K curve, and zero-crossing points of the Hp(y) curve, respectively. Fatigue damage degree can be effectively predicated according to the value of the Kmax and the Hp(y)max, Hp(y)min and Hp(y)sub.

The Fatigue Life Assessment of PZL-130 Orlik Structures Based on Historical Usage Data

Material fatigue is the basic factor limiting aircraft’s durability. It comes from the fact that changing loads affect aircraft structure as well as from the fact that aircraft’s mass restrictions do not allow for diminishing stress to the level when material fatigue does not occur. Estimating fatigue durability of a particular structure as well as its actual fatigue damage degree is possible when the history of loads affecting the structure is known. Accuracy of loads monitoring influences the accuracy of indicated fatigue wear. In case of older structures, which have been maintained according to safe life principle, the number of hours have been commonly used as a fatigue wear indicator. After aircraft structure reaches flying time estimated by the produces, it is considered as fatigue wear and it is no longer in service. In case of a lack of results of loads spectrum measurements, results of tests conducted for other aircraft (of similar structure and assignment) can be used. For this purpose, average loads spectrum has been elaborated for particular aircraft groups, for example, HELIX, FELIX, FALSTAFF, ENSTAFF, TWIST(10). In the case of small aircraft, the data from FAA (2) report have been often used. This article describes the way of fatigue wear estimation for PZL-130 Orlik aircraft on the basis of historical data from flight recorders.

Thermal fatigue resistance of a monocrystalline alloy

Specific features of thermal fatigue fracture of a monocrystalline alloy used in manufacturing of rotor blades of gas-turbine units are investigated. The dependences of the number of cycles to failure on the crystallographic orientation of the material, maximum temperature in a cycle, temperature range, and stress concentration are established. The effects of the pores and processes of recrystallization on the degree of thermal fatigue damage are analyzed.

Cyclic Fatigue of Alumina Ceramics as Evaluated by Modified Small Punch Tests

Fatigue behaviors of conventional alumina ceramics in cyclic loading with hemisphere and cylinder punches are investigated with modified small punch (MSP) tests. Residual strengths are used to quantify the degree of fatigue damage. The dependences of the residual MSP strength on loading mode, cyclic loading magnitude, frequency, and puncher shape have been discussed in detail. Fatigue behavior studies could be very convenient and effective because MSP tests could perform the cyclic loading and then evaluate the residual strength consistently and effectively.

A STUDY ON FATIGUE DAMAGE OF SHAPE MEMORY ALLOY COMPOSITE USING NDE TECHNIQUE

TiNi shape memory alloy was used to recover the shape of transformed objects using its shape memory effect. This shape memory effect plays an important role inside metal matrix composite. A composite using shape memory alloy has a large advantage that can control crack initiation and propagation, when compared with other composites due to the shape memory effect of shape memory alloy under high temperature. In this study, TiNi/Al6061 and TiNi/2024 shape memory composites were fabricated by the hot press method, and a fatigue test was performed to evaluate the fatigue damage for the shape memory composites under room temperature and high temperature. The relationship of the crack growth rate and the stress intensity factor for these shape memory composites were clarified at both temperature conditions. The delay effect of crack propagation due to shape memory alloy was also evaluated under high temperature. In addition, an acoustic emission technique was used to evaluate the crack initiation and the control of crack propagation by shape memory effect under fatigue test nondestructively. The relationship between AE parameter and the degree of fatigue damage of the shape memory composites was discussed.

A micro-cell model of the effect of microstructure and defects on fatigue resistance in cast aluminum alloys

Six different, industrially important, casting situations containing an array of typical microstructure and defects were investigated. Porosity, secondary dendrite arm spacing, Al-matrix, Si-particles, and Fe-rich intermetallics were experimentally identified as the major factors affecting the alloy’s resistance to fatigue. A micro-cell model was developed to quantitatively investigate the effect of these factors on fatigue resistance. The micro-cell captures the key microstructural features and is embedded into a macro material element at the specimen surface. A nonlinear isotropic/kinematic hardening law was used to describe the cyclic plastic behavior of the Al-matrix. This model enables the quantification of the accumulation and concentration of the microscale plastic deformation induced during fatigue loading by microstructural heterogeneities. The simulation results demonstrate that microscale plastic damage could occur even when the maximum far-field stress is below the nominal yield stress of the alloy. The degree of fatigue damage, in terms of the accumulation of plastic damage dissipation energy, was found to be sensitive to the microstructural features. Fatigue strength was estimated using the model and found to be in good agreement with experimental results.

Fatigue behaviour of mechanically fastened aluminium joints tested in spectrum loading

The objective of the present work was to investigate the fatigue behaviour of single overlap mechanically fastened aluminium joints tested in FALSTAFF spectrum. In order to induce varying degrees of fatigue damage, three joints were loaded with different number of spectrum blocks. Strain gauges were used to measure strain distribution between bolt rows and to determine the degree of secondary bending at certain points. Two instrumented bolts were employed to measure their axial and shear response during loading. The load transfer between the bolt rows was calculated using the measured strain distributions. The achieved results were then compared with the ones obtained from measurements done on the instrumented bolts. The overall test results indicated that the friction wear between the joint parts significantly affected the fatigue behaviour of the inspected joints.

Prolonging fatigue life of a damaged steel by annealing

This paper deals with the endurance life of fatigue failure (defined as a sudden drop of stress range) under constant total strain rate for a quenched and tempered (600 °C for 2 h) steel. The investigation is focused on the effect of annealing at 550 °C for 2 h on the residual fatigue life. Two influencing factors are studied: the fatigue damage degree of the material prior to annealing and the magnitude of the constant total strain amplitude. The total fatigue lives of the specimens with annealing were increased twice as that without annealing. The interpretation of the results is mainly based on TEM observations.

Fatigue Evaluation of Type 316 Stainless Steel Using Positron Annihilation Lineshape Analysis and β+-γ Coincidence Positron Lifetime Measurement

In order to non-destructively evaluate the degree of fatigue damage in type 316 stainless steel, frequently used in the primary system of nuclear power plants, positron annihilation lineshape analysis and β+-γ coincidence positron lifetime measurement were applied. In positron annihilation lineshape analysis, an energy spread of annihilation gamma ray peak was measured and expressed as the S-parameter. In positron lifetime measurement, mean lifetime analysis and two-component analysis were conducted. As a result, the S-parameter and the mean lifetime increased monotonously with fatigue life ratio. Strain-controlled fatigue increased more at the early stage of fatigue than stress-controlled fatigue. The S-parameter in the both stress- and strain-controlled fatigue reached almost the same value at the end of fatigue, and also the mean lifetime in the both stress- and strain-controlled fatigue reached almost the same value at the end of fatigue. In two-component analysis of positron lifetime measurement, the positron lifetime of the defect component did not change during fatigue, and the relative intensity of the defect component increased with fatigue life ratio. At the early stage, the relative intensity of defect component in the strain-controlled fatigue was larger than in stress-controlled fatigue, and both intensities reached almost the same value at the end of fatigue.

腐食疲労き裂先端で生じる応答電流からの腐食疲労損傷の検討

In the previous paper, the corrosion fatigue test of commercial pure iron had been performed in 5 mol/m3-chloride-containinig sodium borate and boric acid buffer solution of pH 8.39. The response current to the applied cyclical elastic deformation in two different strain waveforms, sinusoidal and trapezoidal was successfully simulated using two parameters, a decay factor and frequency of the applied strain waveform, where the decay factor is a parameter indicating the repassivation ability. The response current was found to be due mainly to charging or discharging current of electrical double layer before crack initiation and the current (damage current) due to iron dissolution and repassivation from the crack tips superimposed on the charging current after crack initiation. In this study, the effects of the decay factor and the frequency on the corrosion fatigue damage have been investigated.The simulation results showed that the amount of charge of the damage current increases with decreasing decay factor, and with increasing frequency under a constant period. The decrease in the decay factor implies the promotion of the anodic dissolution at the crack tip. In other words, the chemical process (corrosion) contributes largely to the crack propagation. On the other hand, since the increase in the frequency reduces the time factor for the progress of corrosion reaction in each strain cycle, the mechanical process becomes more important factor for the crack propagation in high frequency corrosion fatigue test.From the simulation results of the total current due both to the double layer charging or discharging and anodic dissolution (damage current), it was found that the increases in the ratio of the damage current increases the higher harmonic components in the response current and decreases the phase shift between the applied strain and the response current. Accordingly, the degree of corrosion fatigue damage can be detected by the monitoring of these harmonic components and phase shift.

陽電子消滅法による原子力発電所ステンレス鋼配管の疲労評価

Since positron annihilation lineshape analysis can evaluate the degree of fatigue damage, detecting defects such as dislocations in metals, we used the method to evaluate the degree of fatigue damage in a type 316 stainless steel pipe, which is used in the primary system of a nuclear power plant. Using 68Ge as a positron source, an energy spread of annihilation gamma ray peak from the material was measured and expressed as the S-parameter.Actual plant material cut from a surge line pipe of a pressurizer in a pressurized water type nuclear power plant was measured by positron annihilation lineshape analysis and the S-parameter was found. Comparing the S-parameter with a relationship between the S-parameter and fatigue life ratio of the type 316 stainless steel, we evaluated the degree of fatigue damage of the actual material. Furthermore, to verify the evaluation, microstructures of the actual material were investigated by TEM (transmission electron microscope) to observe dislocation densities. As a result, a change in the S-parameter of the actual material from standard as-received material (type 316 stainless steel) was in the range from −0.0013 to 0.0014, while variations in the S-parameter of the standard as-received material were about ±0.002; differences between the actual material and the as-received material were not significant. Moreover, the dislocation density of the actual plant material observed by TEM was almost the same as that of the as-received material. In conclusion, we could verify the evaluation of the positron annihilation lineshape analysis for fatigue damage.

Non‐destructive evaluation of fatigue and creep‐fatigue damage by means of the induced‐current focused potential drop technique

Quantitative evaluation of damage accumulation including crack initiation and propagation is one of the major concerns of industrial plant management and plant licence renewal. In order to develop a novel non‐destructive testing (NDT) and non‐destructive evaluation (NDE) technique for damage evaluation, the induced‐current focused potential drop (ICFPD), originally proposed for a defect inspection, was employed. In this study, ICFPD was successfully applied to a non‐destructive damage evaluation based on crack measurements. The measurements were taken on fatigued specimens with various degrees of fatigue damage. The ICFPD can clearly detect and differentiate the damage accumulation processes including crack initiation, small crack growth and subsequent macroscopic crack growth. In order to demonstrate the applicability of damage evaluation assessments based on small crack measurements, ICFPD has also been applied to creep–fatigue loading where damage evaluation of a fusion reactor material is based on small crack measurements by the ICFPD technique and a novel methodology is proposed.

突合せおよびスカーフ接着継手の繰返し荷重下における接着層の損傷挙動

Rubber modified epoxy adhesive has been widely used to structure fields due to its high toughness. The importance of fracture mechanism of the rubber-toughened epoxy is the void formation by rubber particles, where damage zone enclosing the voids propagates in the vicinity of the crack tip. Hence, in considering strength of the rubber modified epoxy, the damage behavior should be taken into account. However, there are few studies about the fatigue behavior of the rubber modified epoxy adhesive discussed from the viewpoint of damage mechanics.In this study, the damage behavior of the adhesively bonded butt and scarf joints under cyclic loading conditions has been studied using a rubber modified epoxy adhesive, where stress triaxiality in the adhesive layer can be varied in a wide range by changing the scarf angle. The strain and crack length of the adhesive layer were monitored by using strain and crack gages pasted on the adhesive layer. A damage parameter is introduced to depict the degree of fatigue damage. Based on these parameters, the effect of stress triaxiality on damage development behavior was discussed.

Fatigue damage evaluation of a power plant component from analysis of the dislocation structures

The paper presents a method for estimating the degree of fatigue damage in an engineering ferritic–bainitic steel. A dislocation microstructure chart is first established from laboratory fatigue tests. Misorientation measurements are carried out after fatigue failure between dislocation cells produced by cyclic loading in ferrite grains and between dislocation cells in bainite originated by the heat treatment. There is shown to be a clear dependence of these values on the strain amplitude. On this basis, the analysis of the microstructure of a steel taken from a component which failed in service allowed the determination of the strain amplitude value to which the component had been subjected.

A method for fatigue based reliability when the loading of a component is unknown

When the loading of a component is unknown, it is not possible to perform fatigue evaluation without some additional knowledge of the applied loading. A model is presented which considers problems of this type. In this situation, the components will have experienced some degree of fatigue damage during operation. However, the loading during use is unknown, and thus direct calculation of the remaining service life is not possible without additional data. The use of components removed from service to conduct fatigue tests can provide the required test data. The test data contains additional information associated with the loading which can be used to determine the residual fatigue damage resistance of the components. Comparing the residual fatigue damage resistance of the tested components with the fatigue damage resistance of new components can make it possible to, indirectly, describe the fatigue damage accumulation which has occurred in the components during the time in service. Thus, the fatigue damage accumulated in the components can be determined by additional fatigue tests, in spite of the absence of direct knowledge of applied service loading. The fatigue evaluation of untested components can be performed using the probabilistic fatigue model which is presented in this paper. The model is demonstrated by performing an evaluation of compressor blades for which the applied loading is unknown. The calculated results are shown to be close to the statistical results obtained in-service for the blades.

Damage of Al 2024 alloy due to sequential exposure to fatigue, corrosion and fatigue

Fatigue and corrosion are two major concerns of aging aircraft research. Metal corrosion and fatigue act synergistically in various ways. They may be present separately or simultaneously. In this study Al 2024-T3 alloy was intermittently subjected to sequential corrosion and fatigue processes. Specimens were first subjected to various degrees of fatigue damage in air, then immersed in a corrosive solution for a fixed amount of time, and subsequently further fatigued in air to failure. The results are compared with those subjected to fatigue in air, and to corrosion then fatigue in air. We find that the total fatigue life (sum of fatigue cycles before and after corrosion) exceeds that of the virgin samples, provided that the initial fatigue cycle has consumed more than half of life solely fatigued in air. It is believed that the blunting of microcracks and the removal of other surface damage, such as intrusions/extrusions created at the initial stage of fatigue, are the major reasons for this increased fatigue life.