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Stress intensity factor (SIF) is one of the parameters in determining the stress at the crack tip caused by crack nucleation. Prediction of stress at the crack tip using LEFM (Linear Elastic Fracture Mechanics) and EPFM (Elastic Plastic Fracture Mechanics) approaches through SIF and J-integral becomes very important in estimating crack propagation, life and energy release rate. This study aims to analyze the SIF simulation (mode I and mode III), fatigue crack growth rate and J-Integral on leaf spring failure using ANSYS. The initial simulation carried out is preprocessing including crack design 5 mm, crack tip meshing with sphere radius = 10 mm and element size = 0.5 mm, while the boundary condition for the applied force is 3500 N. Failure will be dominated in the opening mode because mode I has the highest SIF value of KI = 469.67 MPa √mm compared and KIII = 386.27 MPa √mm. This is in accordance with the calculation of the analysis of the number of cycles and the fatigue crack growth rate where mode I has a lower number of cycles, namely 187500 cycles compared to mode III of 29000 cycles, while the fastest fatigue crack growth rate is produced by mode I. The decrease in strength is also analyzed based on the J-Integral analysis where, mode I produces a value of 3.809 mJ/mm2 and mode II 3.790 mJ/mm2 [ABSTRACT FROM AUTHOR]

Crack analysis on coil spring is intended to simulate stress, fatigue life, SIF mode I, II, J-Integral, and fatigue crack growth rate. Simulations were carried out using the Ansys Static Structural approach. The material used was tested for its composition and obtained SAE 9260 steel material is. The simulation results in conditions without crack show that the stress concentration point occurs in the 2nd coil according to the location of the coil spring fracture with an equivalent value of von misses 1236.1 MPa below the ultimate tensile strength value of SAE 9260 material. The results of the stress intensity factor value show that mode II shows the highest value was KII=171.11 MPa mm , compared to the value of KI=97.175 MPa mm . This is following the analysis of the number of cycles and the fatigue crack growth rate in mode II which has a lower number of cycles of 97500 cycles compared to mode I which is 677700 cycles, while in mode II it has a critical crack size value of 10.28 mm followed by a drastic decrease in strength. The maximum value of J-Integral for the given crack is 0.33962 mJ/mm2 which is located at the end of the crack. [ABSTRACT FROM AUTHOR]

There are various models out there, both theoretical and experimental, which are used to predict the fatigue crack growth in metals. Machine learning based computational models have been recently developed to predict such crack growth rate in a more comprehensive manner. This paper presents a supervised machine learning model with a better accuracy than the existing machine learning models. The experimental data obtained from the fatigue test carried out on CT specimen of material SA516Gr70 is used to test and train the model. The machine learning model XGBoost, which is implemented in this paper, is not only more accurate but also less likely to over fit when exposed to unseen data. Three alternative algorithms are investigated and by the process of elimination, best one is chosen. The paper shows the results received from some of those models, which were important in order to select the best one. The metrics used to filter and tune the model's performance are R2 score and mean squared error. The procedure for finding the optimal model and its results have been discussed. [ABSTRACT FROM AUTHOR]

The processes of fatigue crack propagation in titanium compressor and fan disks of contemporary gas-turbine engines are generalized. As it was shown, the cracks in a disk material can initiate and propagate at the micro-, meso- and macroscale level depending on the crack origination location, namely, rim or hub part of disks. Crack growth mechanisms are determined by the dominant mechanism of wave process of plastic deformation for titanium alloys, which appears during forging of compressor and fan disks. This process results in creation of filament-type structure with alternating brittle and ductile filaments of two-phase titanium alloys. The features of titanium alloy fracture in the regions of high-cycle and very-high-cycle fatigue are considered. The instances of in-service failure for fan and compressor disk from titanium alloys are demonstrated, and both the duration of fatigue crack growth, and equivalent stress level are estimated. [ABSTRACT FROM AUTHOR]

Acoustic emission is widely used in various industries as a method of non-destructive testing. However, to improve material properties and durability in complex and difficult working conditions, surface modification of materials is required, which affects the reliability of AE testing. In this work, uncoated 1163 aluminum alloy and micro-arc oxidation (MAO) coated 1163 aluminium alloy are used. These specimens were subjected to cyclic loading with simultaneous recording of acoustic emission signals. The experimental results of the comparative analysis show that the behaviour of fatigue damage can be characterized by the parameters of AE signals. The changes in fatigue damage mechanism due to the presence of MAO coatings and the reflection of the changes in acoustic emission signal parameters were also investigated. Using the acoustic emission parameter KWD, the fatigue life prediction of uncoated aluminium alloy and MAO coated aluminum alloy was carried out. [ABSTRACT FROM AUTHOR]

Elastic-plastic analysis is realized by finite element method, has been performed to study the compressive stress and stress ratio effect of tension-compression loading on the regularities of the local residual compressive stress formation in the fatigue crack tip. The results showed that the course of cyclic plastic deformations in the half-cycle compression is accompanied by a further redistribution of stresses in the crack tip, which causes a decrease in the residual compressive stresses formed in the half-cycles tension during unloading. Local residual compression stresses at the crack tip change with the level of applied compressive stresses and stress ratio of the tension-compression loading. As the load increases in the half-cycles tension, the residual compressive stresses formed after the application of the compressive load part cycle loading in the crack tip are superimposed by stresses from the external load. As a result, the tensile stresses increase. The compressive stress and stress ratio effect of tension-compression loading on the fatigue cracks growth is explained from the position of interaction of local residual compressive stresses the near crack tip with external stresses in the half-cycles tension. It is shown that the use of the effective stress intensity factor range in the Paris equation instead of the nominal one makes it possible to take into account the influence of tension-compression loading on the parameters of the material's resistance to the fatigue crack growth. [ABSTRACT FROM AUTHOR]

Composite materials using natural rubber as the main matrix are popular these days because of the wide applications of rubber materials in modern industries. Rubber materials also have damping properties, energy absorption, and exposure to continuous loads and different environmental conditions. In this research, properties of composite materials using natural rubber with epoxy resin and also prediction of fatigue life and crack growth have been studied using De Mattia Flexing Machine Test. Epoxy resin has been added to composite materials of natural rubber dough, epoxy has been added in different percentages with respect to the carbon as (0%, 10%, 20%, 30%, 40%). The effect of adding on the mechanical properties of rubber, especially the fatigue life when repeated loads have been applied on the specimen. Improvement of the qualifications of epoxy-reinforced rubber compounds when applied repeated loads on it, in bridges pad for example, and to make it suitable for all difficult conditions. [ABSTRACT FROM AUTHOR]

Although several models addressing microstructurally small fatigue crack behavior have been presented, there is work to be done in developing models that are based on the directly measured crack driving forces. The current study proposes a new method that combines high-resolution and high sample-rate digital image correlation analyses, optical crack length measurements, and microstructural information from electron backscatter diffraction analysis (EBSD). Microstructurally small fatigue crack growth was studied using a dual-microscope setup. The crack growth rate, cyclic crack-tip opening displacement (ΔCTOD), and full-field shear strain were measured over multiple grains, starting from sub-grain crack length up to seven times the grain size. A novel crack length analysis method was developed for the high- resolution optical measurement data, and the ΔCTOD was defined at a length scale smaller than the grain size. The grain structure from EBSD was combined with the strain measurements, exposing the influence of microstructural features on the shear strain accumulation during the fatigue crack growth. The developed methodology was used to study the propagation of a microstructurally small crack in Fe-18%Cr ferritic stainless steel. The results show that the developed method enables high-fidelity investigations on the effect of the grain boundaries and the shear strain localization on the microstructurally small fatigue crack behavior. [ABSTRACT FROM AUTHOR]

Damage assessment due to fatigue crack growth is an important element for assuring structural safety and fitness for service of mechanical components. Under cyclic loading due to the opening and closing of crack, material damage ahead of the crack tip depends on the crack tip blunting, its re-sharpening and the size of cyclic plastic zone. In present parametric study, size of the cyclic plastic zone is evaluated for CT specimen using finite element analysis. Chaboche non-linear kinematic hardening model is used to model elastic-plastic material constitutive behavior. It is observed that cyclic plastic zone size depends on load ratio, load range, load maxima and crack size. The size of monotonic and cyclic plastic zone is compared and found that monotonic plastic zone is approximately three to four times larger than the cyclic plastic zone due to crack closure effect. It is observed that material within the cyclic plastic zone undergo ratchetting. [ABSTRACT FROM AUTHOR]

The development of more environmentally friendly corrosion inhibitor such as nitrate (NO3-) as an alternative to chromium-based compounds is needed, especially for aircraft aluminium alloys. This paper presents a comparative study on nitrate (NO3-) and chromate (CrO42-) inhibitions of corrosion fatigue crack growth of aircraft AA7050 aluminium alloy in 3.5% NaCl solution. Corrosion fatigue tests were conducted using centre-crack tension (CCT) specimens immersed in 3.5% NaCl solution with and without NO3- and CrO42- inhibitors at the frequency, f of 10 Hz and stress ratio, R of 0.1. To gain better understanding to the corrosion inhibition mechanism of nitrate and chromate, corrosion tests were also conducted using potentiodynamic polarisation technique. Results showed that nitrate could behave as inhibitor and it slows down the fatigue crack growth rate similar to that of chromate owing to its capability of forming passive film despite its oxidising effect is lower compared to chromate inhibitor. [ABSTRACT FROM AUTHOR]

The theoretical foundations of fatigue crack growth kinetics in aircraft structures are presented. The influence of different cycles and modes of loading on crack growth rate is investigated. Modeling of the fatigue cracks propagation is carried out taking into account many factors. A semiphenomenological model of fatigue crack growth kinetics prediction is considered and refined, the possibility of its application to aircraft structures is shown. [ABSTRACT FROM AUTHOR]

A structural member subjected to cyclic loading leads to a structural failure due to fatigue phenomenon, where strength of the structure gets degrades by the damage initiation which eventually leads to failure. This paper is about the prediction of crack growth rate experimentally and assessments of fatigue crack growth rates on steel and aluminium plates. The experiments are conducted using MTS 100KN land mark fatigue test machine. In this work we analyse the crack growth rate due to fatigue loading through the characterisation on the dissipative process of fatigue crack tip zone. The crack growth tests are conducted on the steel and aluminium alloy for the stress ratio of 0.3 with the stress level of 60% of its ultimate stress. The properties of steel and aluminium alloys are estimated from the quasi static testing and their average values are taken for the studies. Here we used extensometer to find the crack growth rate and also found manually by measuring the crack length and respective time and their results are mutually agree with each other. [ABSTRACT FROM AUTHOR]

The paper presents an experimental methodology for estimating the very high cycle life of the AMG-6 aluminum alloy subjected to preliminary deformation, using an in-situ method for determining the accumulation of irreversible fatigue damage, based on an analysis of the nonlinear dynamics of free-end vibrations. The specified method allows us to set the kinetics of the accumulation of fatigue damage and to separate the stages of nucleation and growth of a fatigue crack. Based on the data on the surface morphology and established patterns, a kinetic equation is constructed for the nucleation and growth of fatigue cracks in the very high cycle loading range. This equation, based on empirical parameters related to the structure of the material, will allow us to determine the number of cycles for the nucleation of an internal crack and its emergence to the surface. [ABSTRACT FROM AUTHOR]

A method for modeling thermal destruction of periclase-carbon refractories is proposed. The method is based on the growth of fatigue cracks at elevated temperatures. The stress-strain state of the refractory under the influence of thermal and mechanical factors was determined in dynamics throughout the entire operation cycle. Chemical and abrasive wear of the material were not considered. For calculations, the finite element method was used. Energy criterion was used for calculations of crack growth. The probability of crack growth was determined using the results obtained previously for the stress-strain state of typical defects of refractory materials under the action of a tensile load. Thermal, energy and deformation criteria were formulated that determine the probability of the onset of cracks growth. [ABSTRACT FROM AUTHOR]

The paper presents the results of determining the characteristics of fatigue crack propagation resistance of a promising pipe steel of the 26KhMFA type. It has been found that at room temperature this type of steel has high values of fracture toughness resistance regardless of the orientation of the crack propagation path relative to the pipe axis. Anomalous stability of the fatigue crack propagation rate in the linear Paris law section with an increase in the effective range of the stress intensity factor in the range of ΔK=15–20 MPa m1/2 is revealed. The obtained experimental data characterize this steel as a material with increased resistance to fatigue crack propagation in the studied range. [ABSTRACT FROM AUTHOR]

Residual fatigue lifetime assessment of a cracked structure is a common task for engineering and scientific community. Fatigue crack may appear on the surface or in the initial defect, e.g. pores in weldments. Such a structure needs to be examined, whether is it safe to be operated. Various assessment methods of different difficulties exist. In this paper, numerical and experimental study on fatigue crack propagation is presented. Propagation of a fatigue crack starting from an initial surface defect of semi-elliptical shape through the flat specimen is considered. Two load ratios were employed in order to compare their effects, as loading at low asymmetry R = 0.1 ensures presence of a plasticity induced crack closure, while at load ratio R = 0.6 fatigue crack growth without premature closure is expected. Beach marks were created on the fracture surface in order to study the fatigue crack evolution, number of cycles spent for fatigue growth and also the influence of premature closure on the crack front evolution. One of the well-known methods was applied for numerical fatigue lifetime evaluation and estimated number of cycles required for crack growth through the body was compared to the experimentally measured data. Second part of the paper deals with fatigue crack front curvature, which is always affected at the vicinity of the free surface due to the corner singularity of the stress field. However, when crack closure appears, fatigue crack propagation is retarded and furthermore, crack front is curved even more at the free surface as a result of earlier closure than in the middle of the body. Separation of these two effects allows direct comparison of their impact on fatigue crack front propagation. [ABSTRACT FROM AUTHOR]

The procedure of using the elastoplastic model of the growth of fatigue cracks for various metals used for vessels operating under pressure is described. The growth rate of fatigue cracks is associated with the fracture at the tip of the fatigue crack due to embrittlement of the metal ahead of the crack front. Using steel 10G2 as an example, it was considered a method for determining the constants of an equation that describes the growth rate of cracks according to the results of standard fatigue tests of samples. To model thick-walled vessels and research the stress state in the crack area, the finite element method performed in the ANSYS software package was used. The cylindrical part of the pressure vessel with the biaxial stress state of the shell in the crack area is considered. For a semielliptical crack, the stress state at the crack tip was studied and average stresses ahead of the crack front were determined when the vessel was loaded to maximum pressure and unloaded to zero pressure. The crack growth rate was determined under biaxial loading of the crack growth zone under the conditions of elastoplastic behavior of the material, taking into account the residual stresses per loading cycle. The proposed method for applying the elastoplastic model of fatigue crack growth makes it possible to control the degree of danger of a registered surface crack in the wall of a pressure vessel under conditions of an variable loading cycle. [ABSTRACT FROM AUTHOR]

During the past decades, increasing demand in aircraft industry for high-performance, lightweight structures have stimulated a strong trend towards the development of refined models for fibre-metal laminates (FMLs). Fibre metal laminates are hybrid composite materials built up from interlacing layers of thin metals and fibre reinforced adhesives. The most commercially available fibre metal laminates (FMLs) are ARALL (Aramid Reinforced Aluminium Laminate), based on aramid fibres, GLARE (Glass Reinforced Aluminium Laminate), based on high strength glass fibres and CARALL (Carbon Reinforced Aluminium Laminate), based on carbon fibres. Taking advantage of the hybrid nature from their two key constituents: metals (mostly Aluminium) and fibre-reinforced laminate, these composites offer several advantages such as better damage tolerance to fatigue crack growth and impact damage especially for aircraft applications. Metallic layers and fibre reinforced laminate can be bonded by classical techniques, i.e. mechanically and adhesively. Adhesively bonded fibre metal laminates have been shown to be far more fatigue resistant than equivalent mechanically bonded structures. [ABSTRACT FROM AUTHOR]

The paper presents the results of fatigue crack growth simulation of the transition joint for S235JR steel and A5083 aluminum with the Grade 1 titanium interlayer coat and A1050 aluminum. Calculations were performed using ANSYS software. The publication presents the crack growth phenomena observed during fatigue testing. Additionally, calculations of residual stresses distributions induced by the process of joining materials during welding were carried out. Results of crack length calculations were comparable with experimantal data. [ABSTRACT FROM AUTHOR]

Probable reasons for the nucleation of a fatigue crack are shown for asymmetric constant-sign bending on the inner surface during the test of hollow cylinder parts made from hot-rolled tubes. It is shown that the decrease of the roughness of the inner surface to Rmax ≤ 10 μm in combination with the structure of the outer layer (martensite + troostite-martensite) at a depth of 2 mm creates conditions for a maximal increase in the durability of hollow parts under different kinds of loading. [ABSTRACT FROM AUTHOR]

The paper presents the investigation results of fatigue behavior of three types of materials: (i) wrought Ti-6Al-4V, (ii) Ti-6Al-4V fabricated using selective laser melting and (iii) Ti-6Al-4V fabricated using selective laser melting (SLM) with subsequent post-build processing by Ultrasonic Impact Treatment (UIT). The deformation behavior and fracture pattern of the specimens under cyclic loading was studied by means of scanning electron microscopy of the fracture surfaces and digital image correlation (DIC). The results obtained show that the proposed technique for post-build treatment of SLM specimen increases their fatigue durability by ∼60%. Moreover, the latter tends to exceed the lifetime of wrought Ti-6Al-4V. SEM and DIC studies witness the increase in ductility of the post-build treated material, which is supported by more ductile fracture surface pattern and larger strain of the specimen during cyclic loading. [ABSTRACT FROM AUTHOR]

It is important to understand the fatigue crack growth in order to avoid failure of components, especially in aerodynamic applications. Here ΔK, crack growth rate and fatigue life values for a non-cold expanded hole with cracked hole is evaluated using FEA and the results of the same is compared with classical method. The percentage difference between the FEA solution and classical solution for SIF is 3.4 %. Similarly the percentage difference between the FEA solution and classical solution for crack growth rate is 10.71 %. The fatigue life test results from classical solution is 1.844×10³ cycles and that obtained through FEA is 1.844×10³ cycles. It is same for FEA solution because of the fact that crack growth is neglected. It is evident that the variation of the FEA results of ΔK, crack growth rate and fatigue life are good agreement with that obtained from classical solution and hence the above FE Method can be successfully used to predict the FCG for non-cold expanded hole. [ABSTRACT FROM AUTHOR]

Among various cold expansion methods, Split Sleeve Cold Expansion technique is widely used. This method induces a zone of compressive residual stresses by pulling an oversized mandrel followed by removal through the hole. An appropriate amount of compressive residual stress reduces the severity of tensile stresses acting on the components there by retarding the fatigue crack growth rate or extending the service life of the components. It has been observed that either extensive testing or special computer codes (AFGROW) are required to determine fatigue crack growth life around residual stress fields. There was no generalized procedure to predict fatigue crack growth life around residual stress fields of cold expanded holes. An attempt has been made in this work to develop a systematic, simplified method to predict fatigue crack growth life around cold expanded holes by combining finite element method and Willenborg’s model. This method was in very good agreement to the classical approach and the variation of predication of fatigue crack growth was about 5.77% compared to the classical approach. The outcome of this work is the development of a systematic and simple procedure for predicting fatigue crack growth life around cold expanded fastener holes. This procedure helps in recommending appropriate inspection intervals and extending the service life of fatigue prone fastener holes. [ABSTRACT FROM AUTHOR]

Evolution of plastic deformation at a crack tip is observed using infrared and optical cameras, and the obtained images are processed with corresponding mathematical algorithms. The accuracy of displacement measurements is less than 1 micron, and the accuracy of temperature increments is less than 0.25 °C. Based on the experimental data, a theoretical model of heat dissipation at the fatigue crack tip tested under uniaxial and biaxial loading conditions is developed. The energy flux from the crack tip is described as a sum of two functions corresponding to energy dissipation in monotonic and reversible plastic zones. The efficiency of the model is illustrated by the experimental study of fatigue crack propagation in flat samples made of stainless steel AISI 304. [ABSTRACT FROM AUTHOR]

The paper studies the effect of ultrasonic forging of the surface layers of linear friction welded joints of the VT8-1 titanium alloy on their fatigue life. Low-cycle fatigue tests report a 2.5-fold increase in the service life of the welded joint after ultrasonic forging of its surface layers. The fractographic analysis of the fracture surfaces shows that, after ultrasonic forging, cracks initiate from the lateral surface of a specimen and have a radial front without river markings and with scarcely visible tear ridges. The microrelief of the initiation and growth zone of the main crack indicates a more ductile pattern of the fatigue crack growth in the material after ultrasonic forging. Ultrasonic forging of the surface layers of the VT8-1 welded joint increases its fatigue life and presents an effective method for improving the service life of welded joints, thus excluding a complex thermomechanical treatment. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental verification of a numerical solution to the problem of fracture of a cast-iron plate with a central hole, obtained by finite element modeling and an original author's technique. Experimental verification is performed by real-time laser dynamic speckle interferometry using a software-hardware complex developed by the authors. The moments of transition from the stage of fatigue crack initiation to the stage of stable growth and subsequent brittle fracture of the plate are defined. [ABSTRACT FROM AUTHOR]

This paper presents a technique for in-situ detection of fatigue damage initiation and growth in a prestrained aluminum-magnesium alloy in the very high cycle fatigue regime by analyzing the nonlinearity of the feedback signal of an ultrasonic fatigue system. Analysis has revealed anomalies in the elastic behavior of the examined material and the nonlinearity effects in amplitude oscillations. It has been found that these effects increase with fatigue crack initiation and growth. The validity of the method is verified by investigating the behavior of aluminum alloy samples, which were prestrained to different levels, so that the fatigue crack initiation time can be determined. The developed technique can be used for early detection of fatigue cracks both inside the material and on its surface. [ABSTRACT FROM AUTHOR]

High cycle and very high cycle fatigue is the most important fundamental and engineering problem for a variety of applications. A series of accidents caused by gas turbine engine failure, along with high costs of service life estimation and potential costs of the development of new constructions, has stimulated advanced concepts of national programs for high cycle and very high cycle fatigue, as being based on new fundamental results of fatigue evaluation. The programs aim at developing approaches using basic research findings, modern methods of laboratory modeling, and quantitative analysis of structural changes in order to reveal fracture stages and “criticality” mechanisms in transition to macroscopic fracture. A strong interest in the gigacycle range (109 cycles) of fatigue loads is provided by the progress in the creation of new (nano- and submicrostructural) materials with very high cycle fatigue life and by breakthrough tendencies in technologies requiring very high cycle fatigue life in aviation motor industry. [ABSTRACT FROM AUTHOR]

In the paper, experimental results of fatigue crack growth were presented. The main object of authors' investigation was a fatigue crack path determined under mixed mode (I+II) loading condition. For this purpose the CTS (compact tension shear) specimens were used. The tests were performed under the load ratio R = 0.1 and constant amplitude loading for a different mixity level. An experimental results were described using ΔK stress intensity factor range. In the paper, the experimental procedure was described and the kinetic fatigue fracture diagrams were constructed. After the fatigue tests the fractal dimension for the fracture surface was determined. According to the obtained results, the fractal dimension is not sensitive for different mixity level of loading (I+II) for structural steel S355J0. [ABSTRACT FROM AUTHOR]

Fatigue crack growth life as a function of crack length is essential for the prevention of catastrophic failures from damage tolerance perspective. In damage tolerance design approach, principles of fracture mechanics are usually applied to predict the fatigue life of structural components. Numerical prediction of crack growth versus number of cycles is essential in damage tolerance design. For cracks under mixed mode I/II loading, modified Paris law ( d a d N = C ( Δ K e q ) m ) along with different equivalent stress intensity factor (ΔKeq) model is used for fatigue crack growth rate prediction. There are a large number of ΔKeq models available for the mixed mode I/II loading, the selection of proper ΔKeq model has significant impact on fatigue life prediction. In the present investigation, the performance of ΔKeq models in fatigue life prediction is compared with respect to the experimental findings as there are no guidelines/suggestions available on the selection of these models for accurate and/or conservative predictions of fatigue life. Within the limitations of availability of experimental data and currently available numerical simulation techniques, the results of present study attempt to outline models that would provide accurate and conservative life predictions. Such a study aid the numerical analysts or engineers in the proper selection of the model for numerical simulation of the fatigue life. Moreover, the present investigation also suggests a procedure to enhance the accuracy of life prediction using Paris law. [ABSTRACT FROM AUTHOR]

In industrial hot forging processes, the forging dies underlie cyclic thermo-mechanical loads, which can lead to failure of the tools. Besides die wear (abrasive and adhesive) on the surface, fatigue crack initiation with a following fracture of the tool is one of the most frequent failures occurring in hot forging processes. In this study an industrial hot forging process is considered for fatigue analysis. Tool geometry is designed for a defined life time until crack initiated failure of the tool. Material characterization tests in form of tensile tests as well as cylindrical compression tests and low cycle fatigue tests were carried out. The data will be implemented in a commercial software-system to realize a qualitative good prediction of die life regarding crack wiation. [ABSTRACT FROM AUTHOR]

Results are presented from laboratory experiments and simulations that demonstrate the ability to localize fatigue cracks around fastener holes using spherically focused ultrasonic probes for shear-wave inspections. For the experiments, fatigue cracks were created in aluminum plates in a testing frame under cyclic loading. With the exceptions of one specimen with a mid-bore crack and another with a "through" crack, the remaining specimens contain surface-breaking cracks. All of the specimens were inspected for the cracks intersecting the back wall, and some were flipped over and re-inspected with the crack intersecting the front surface. Parameter and variable sensitivity studies were performed using CIVA Simulation Software. In contrast to C-scans where detection and localization of small cracks can be very difficult, modeling and initial experimental results demonstrate that cracks can be accurately located in "True" B-scans (B-scans projected in the part along the beam path). Initial results show that small-amplitude diffracted/scattered signals from the crack tips and edges are essential in obtaining clear crack traces in the True B-scans. It is important therefore that experimental data be acquired with sufficient gain to capture the diffracted/scattered signals. In all of the cases studied here, saturating the high-amplitude specular reflections from the fastener hole and crack enhanced the crack trace in the True B-scans. [ABSTRACT FROM AUTHOR]

The paper reports on the results of a complex study of the structural structure changes in the prefracture zone and the formation of fatigue cracks under multicycle fatigue loading for the steels Kh12F1 and 12Kh18N10T ion the state of metastable and stable austenite. It is demonstrated by electron-backscatter diffraction (EBSD) analysis that before crack initiation and during crack evolution there is strain localization characterized by martensitic transformation. Magnetic characteristics show that, both for chromium-nickel steel with stable austenite and for chromium steel with metastable austenite, the process of crack nucleation and growth is accompanied by the formation of the magnetic a- phase. [ABSTRACT FROM AUTHOR]

Markov model is one of the reliable method to describe the growth of the crack from the initial until fracture phase. One of the important subjects in the crack growth models is to obtain the transition probability matrix of the fatigue. Determining probability transition matrix is important in Markov Chain model for describing probability behaviour of fatigue life in the structure. In this paper, we obtain transition probabilities of a Markov chain based on the Paris law equation to describe the physical meaning of fatigue crack growth problem. The results show that the transition probabilities are capable to calculate the probability of damage in the future with the possibilities of comparing each stage between time. [ABSTRACT FROM AUTHOR]

When determining the characteristics of the fatigue crack growth rate, it is necessary, inter alia, to measure the crack length growth which must be combined with the number of accumulated load cycles. The length of the crack is determined using different testing methods. Recently, there is an increased interest in optical systems based on digital image correlation methods. These methods have however some limitations as regards, inter alia, the sharpness of pictures taken during tests e.g. at cryogenic temperatures. This paper presents a comparative analysis of the crack length "a" as a function of a crack-opening-displacement "d" obtained by experimental and numerical method. The tests were performed under ambient temperature for CT type specimens made of Ti6Al4V titanium alloy. Numerical research was carried out by finite element method using ABAQUS software. Satisfactory results were obtained which gave the reasons for establishing a hybrid methods for the crack length determination. [ABSTRACT FROM AUTHOR]

In this paper, the theoretical and experimental results of fatigue crack growth in AISI 5140 steel have been presented. According to the previous theoretical background - the energy parameter ΔH is introduced as a crack driving force in construction of fatigue crack growth rate (FCGR) diagrams. The physical explanation of this model is also presented. In experimental parts of this work, the kinetics fatigue fracture diagrams (KFFD) for AISI 5140 steel were constructed. The main goal of experimental works was to investigate the influence of microstructure on kinetics of fatigue crack growth. The AISI 5140 steel were tested in three different heat treatment conditions. As it has been confirmed, the energy parameter H describes the kinetics of fatigue crack growth much more synonymously than the classical stress intensity factor - ΔK. [ABSTRACT FROM AUTHOR]

In this paper we investigated the influence of consecutive dynamic and gigacycle fatigue loads on the lifetime of aluminum-magnesium alloy AlMg6. Preloading of samples was achieved during dynamic tensile tests in the split-Hopkinson bar device. Fatigue tests were conducted on Shimadzu USF-2000 ultrasonic fatigue testing machine. The New-View 5010 interferometer-profiler of high structural resolution (resolution of 0.1 nm) was used for qualitative fracture surface analysis, which provided the data allowing us to find correlation between mechanical properties and scale-invariant characteristics of damage induced roughness formed under dynamic and gigacycle fatigue loading conditions. Original form of the kinetic equation was proposed, which links the rate of the fatigue crack growth and the stress intensity factor using the scale invariant parameters of fracture surface roughness. The scale invariance characterizes the correlated behavior of multiscale damage provides the link of crack growth kinetics and the power exponent of the modified Paris law. [ABSTRACT FROM AUTHOR]

The role of cyclic plastic zone in front of the crack tip was studied in high strength steels. Estimated plastic zone size would be compared with actual observation. Strain controlled fatigue tests of the steels were carried out to obtain cyclic stress-strain curves for plastic zone estimation. Observations of plastic zone were carried out using in situ SEM fatigue crack growth tests under a constant-ΔK. Hard microstructures in structural steels showed to inhibit the extent of plastic deformation around the crack tip. The rate of crack growth can be correlated with the size of plastic zone. The smaller the plastic zone size, the slower the fatigue crack growth. [ABSTRACT FROM AUTHOR]

Varying loading conditions of aircraft structures result in stress concentration at fastener holes, where multilayered components are connected, possibly leading to the development of fatigue cracks. High frequency guided waves propagating along the structure allow for the non-destructive testing of such components, e.g., aircraft wings. However, the sensitivity for the detection of small, potentially hidden, fatigue cracks has to be ascertained. The type of multilayered model structure investigated consists of two adhesively bonded aluminium plate-strips. Fatigue experiments were carried out. The sensitivity of the high frequency guided wave modes to monitor fatigue crack growth at a fastener hole during cyclic loading was investigated, using both standard pulse-echo equipment and laser interferometry. The sensitivity and repeatability of the measurements were ascertained, having the potential for fatigue crack growth monitoring at critical and difficult to access fastener locations from a stand-off distance. [ABSTRACT FROM AUTHOR]

Fatigue (high- and gigacycle) crack initiation and its propagation in titanium alloys with coarse and fine grain structure are studied by fractography analysis of fracture surface. Fractured specimens were analyzed by interferometer microscope and SEM to improve methods of monitoring of damage accumulation during fatigue test and to verify the models for fatigue crack kinetics. Fatigue strength was estimated for high cycle fatigue regime using the Luong method [1] by "in-situ" infrared scanning of the sample surface for the step-wise loading history for different grain size metals. Fine grain alloys demonstrated higher fatigue resistance for both high cycle fatigue and gigacycle fatigue regimes. Fracture surface analysis for plane and cylindrical samples was carried out using optical and electronic microscopy method. High resolution profilometry (interferometer-profiler New View 5010) data of fracture surface roughness allowed us to estimate scale invariance (the Hurst exponent) and to establish the existence of two characteristic areas of damage localization (different values of the Hurst exponent). Area 1 with diameter ~300 μm has the pronounced roughness and is associated with damage localization hotspot. Area 2 shows less amplitude roughness, occupies the rest fracture surface and considered as the trace of the fatigue crack path corresponding to the Paris kinetics. [ABSTRACT FROM AUTHOR]

Source location is an important feature of acoustic emission (AE) damage monitoring in nuclear piping. The ability to accurately locate sources can assist in source characterisation and early warning of failure.This paper describe the development of a novel AE source location technique termed " Wavelet Transform analysis and Modal Location (WTML)" based on Lamb wave theory and time-frequency analysis that can be used for global monitoring of plate like steel structures. Source location was performed on a steel pipe of 1500 mm long and 220 mm outer diameter with nominal thickness of 5 mm under a planar location test setup using H-N sources. The accuracy of the new technique was compared with other AE source location methods such as the time of arrival (TOA) technique and DeltaT location.The results of the study show that the WTML method produces more accurate location results compared with TOA and triple point filtering location methods. The accuracy of the WTML approach is comparable with the deltaT location method but requires no initial acoustic calibration of the structure. [ABSTRACT FROM AUTHOR]

Fatigue crack growth rate (FCGR) measurement data for high strength austenitic alloys at cryogenic environment suffer in general from a high degree of data scatter in particular at ΔK regime below 25 MPa√m. Using standard mathematical smoothing techniques forces ultimately a linear relationship at stage II regime (crack propagation rate versus ΔK) in a double log field called Paris law. However, the bandwidth of uncertainty relies somewhat arbitrary upon the researcher's interpretation. The present paper deals with the use of the uncertainty concept on FCGR data as given by GUM (Guidance of Uncertainty in Measurements), which since 1993 is a recommended procedure to avoid subjective estimation of error bands. Within this context, the lack of a true value addresses to evaluate the best estimate by a statistical method using the crack propagation law as a mathematical measurement model equation and identifying all input parameters. Each parameter necessary for the measurement technique was processed using the Gaussian distribution law by partial differentiation of the terms to estimate the sensitivity coefficients. The combined standard uncertainty determined for each term with its computed sensitivity coefficients finally resulted in measurement uncertainty of the FCGR test result. The described procedure of uncertainty has been applied within the framework of ITER on a recent FCGR measurement for high strength and high toughness Type 316LN material tested at 7 K using a standard ASTM proportional compact tension specimen. The determined values of Paris law constants such as C0 and the exponent m as best estimate along with the their uncertainty value may serve a realistic basis for the life expectancy of cyclic loaded members. [ABSTRACT FROM AUTHOR]

Successful determination of residual fatigue life requires a comprehensive understanding of the fatigue related material deformation mechanism. Neither macroscopic continuum mechanics nor micromechanic observations provide sufficient data to explain subsequent deformation structures occurring during the fatigue life of a metallic structure. Instead mesomechanic deformation on different scaling levels can be studied by applying fractal analysis of various means of nondestructive inspection measurements. The resulting fractal dimension data can be correlated to the actual material damage states, providing an estimation of the remaining residual fatigue life before macroscopic fracture develops. Recent efforts were aimed to apply the fractal concept to aerospace relevant materials AA7075-T6 and Ti-6Al-4V. Proven and newly developed fractal analysis methods were applied to eddy current (EC) measurements of fatigued specimens, with the potential to transition this approach to an aircraft for an in-situ nondestructive inspection. The occurrence of mesomechanic deformation at the material surface of both AA7075-T6 and Ti-6Al-4V specimens could be established via topography images using confocal microscopy (CM). Furthermore, a pulsed eddy current (PEC) approach was developed, combined with a sophisticated new fractal analysis algorithm based on short pulse excitation and evaluation of EC relaxation behavior. This paper presents concept, experimental realization, fractal analysis procedures, and results of this effort. [ABSTRACT FROM AUTHOR]

This paper presents measurements of relative nonlinear acoustic parameter (βrel), ahead of a notch in Al 7075-T651 dog bone samples, subjected to fatigue. It is compared with crack growth measurements on the same samples. Measurements performed on two samples subjected to identical fatigue conditions that failed at vastly different number of fatigue cycles are described. The βrel measurement for both samples as a function of fatigue cycles was fit a Boltzmann curve. The role of changing βrel ahead of a notch is explored as a possible approach for remain life evaluation. [ABSTRACT FROM AUTHOR]

The objective of this paper is to present a comprehensive approach to image processing for Giant Magnetoresistive (GMR) array sensors with sheet current sources for the inspection of fatigue cracks in complex metallic structures. The approach incorporates optimal phase angle adjustment, array sensitivity compensation, fastener site identification, an adaptive edge evaluation and removal algorithm and a classification metric. Processing examples are presented that highlight the benefits of these algorithms for improving crack detection for challenging edge and fastener spacing conditions. [ABSTRACT FROM AUTHOR]

Giant Magnetoresistive (GMR) sensing arrays have been developed to detect fatigue cracks in thick, multi-layered metallic structures. As part of a program conducted by the U.S. Air Force Research Laboratory, fatigue crack specimens were fabricated to provide inspection targets for a GMR array. These specimens were mounted to simulate a wing structure and inspected using a Boeing Mobile Automated Scanner (MAUS). Probability of Detection (POD) from inspections and the results of capability studies are presented. [ABSTRACT FROM AUTHOR]

This study presents a systematical method for probabilistic fatigue life prediction using ultrasonic inspection data. A probabilistic model to correlate the ultrasonic inspection reported size and the actual size is proposed based on historical data of rotor flaw sizing. Both of the reported size and the actual size are quantified in terms of the equivalent reflector diameter. The equivalent initial flaw size (EIFS) is then calculated based on the actual size for fatigue propagation analysis. All major uncertainties, such as EIFS uncertainty, fatigue crack growth model parameter uncertainty, and experimental data measurement uncertainty are explicitly included in the fatigue life prediction. Bayesian parameter estimation is used to estimate fatigue crack growth model parameters and measurement uncertainties using a limited number of fatigue testing data points. The overall procedure is demonstrated using a Cr-Mo-V rotor segment with ultrasonic inspection data. Interpretations of the probabilistic prediction results are given. [ABSTRACT FROM AUTHOR]

Over the past twenty years acoustic emission (AE) has been studied for applications to the structural health monitoring (SHM) of metallic structures. The success of AE for prognosis of in-service steel bridges depends on the reliability of the received AE signals. The emphasis of this paper is on the characterization of acoustic emission source mechanisms for ASTM A572 grade 50 steel. The source characterization was aided by Digital Imaging Correlation (DIC) and Scanning Electronic Microscopy (SEM). The results indicate that both ductile and brittle mechanisms can produce AE during fatigue crack growth in the steel. However, the fracture mechanisms are predominately ductile. A key preliminary finding is that fatigue crack extension does not generally produce AE events in the early stage of fatigue crack growth for the steel bridge material investigated. [ABSTRACT FROM AUTHOR]

In Tokamak fusion reactors, such as ITER, superconducting strands are subjected to repeated Lorentz force loading and unloading which may degrade performance over time. The Cu matrix which surrounds the brittle Nb3Sn filaments allows the possibility of some elastic-plastic deformation that can initiate filament cracking. We seek to understand if there are strand design variables that might ameliorate such degradation but before being able to do such experiments, we need to establish procedures that can unambiguously detect the cracking caused by loading, rather than by subsequent metallographic examination. Here we make a first report of our procedures after fatigue testing at 77K. Filament crack densities were quantified from large montages covering ≈20 mm length of strand. Three types of cracks were present. The most common were cracks transverse to the filament axis adjacent to voids. Cracks away from voids were of low density until close to the fracture strain. A third kind of crack which generally initiates at unreacted Nb cores of filaments extends radially and in the plane parallel to the wire axis. Example results on one bronze strand fatigued for 1000 loading cycles at axial strains from 0.4% to 1.14% are shown. [ABSTRACT FROM AUTHOR]

In cable-in-conduit conductor (CICC) magnets, such as the ITER TF coils, the conduit is the primary structural component. This function creates requirements for 4 K strength, toughness, fatigue crack resistance, and ductility after exposure to the superconductor's reaction heat treatment. The tensile ductility of a steel is a quality factor related to fatigue and fracture resistance that can be evaluated more economically with tensile tests rather than fatigue and fracture tests. Here we subject 316LN modified base metal and welds to a range of cold work from 0% to 20% and a subsequent Nb3Sn reaction heat treatment to evaluate the effects on the tensile properties. With the addition of cold work, the 4 K yield strength increases while tensile elongation decreases in both the base metal and weld. The results are compared to previously published data on the same alloy to evaluate the use of tensile ductility parameters as a materials qualification specification in magnet design. [ABSTRACT FROM AUTHOR]