The effects of welding direction on quasistatic and fatigue crack propagation behaviours are. This work is an attempt to theoreti cally model fatigue crack propagation induced by alternating cracktip plastic blunting and resharpening in the. The crack dimension has been identified as a crucial factor by a number of authors, because short fatigue cracks having a small length compared to the scale of local plasticity, or to the key microstructural dimension, or simply smaller than 12 mm in metals grow at faster rate and lower nominal stress compared to large cracks 72, 73. Fatigue crack propagation behavior of rc beams strengthened. On the theoretical modeling of fatigue crack growth. Anisotropic transient thermal fatigue crack propagation theory. In this paper, the crack propagation theory based fatigue assessment of ship structures is studied. The compact tension ct samples with and without a hole are designed. Fatigue crack propagation experiment and numerical simulation. A generalized theory of fatigue crack propagation nasaads. Phase transformation theory applied to predict fatigue crack.
The proposed fatigue damage model is experimentally verified using a specially designed fatigue crack growth code to simulate the crack propagation in a compact tension ct specimen with sinkhole and misshole meaning when the propagated crack is. Generally, fatigue crack growth rate dadn is presented as a function of stress intensity range deltak. A continuum model of crack extension is used to derive a crack propagation law for the case of constant plastic strain amplitude fatigue. An integral equation is derived which governs the growth of the fatigue crack. Topics discussed in this compilation include the unified fatigue crack growth. A stochastic theory of fatigue crack propagation aiaa journal. A numerical model of fatigue crack propagation based on the theory of critical distances has been developed in a previous paper engng fract mech 20. The determination of the fatigue crack propagation curve is an essential part of the fracture mechanics design approach. The fatigue crack growth model proposed by frost and dixon, based on the different crack tip geometries of a loaded and unloaded crack, is restated and extended using the stress intensity factor. In this report, we focus on the fatigue crack growth fcg theories in polycrystalline metallic materials with predominantly ductile fracture mode. Pdf the fatigue crack growth model proposed by frost and dixon, based on the different crack tip geometries of a loaded and unloaded crack. Fatigue failures, both for high and low cycle, all follow the same basic steps process of crack initiation, stage i crack growth, stage ii crack growth, and finally ultimate failure. Part of the problem for fatigue and fatiguecrack propagation is that these behaviors are influenced by a wide range of parameters that include cyclic stress.
Since the model describes the interaction of microstructure, mechanism, and. Fatigue crack propagation behaviour derived from sn data. The fatigue crack propagation rate predicted is compared with experimental data for different steels and aluminum alloys to demonstrate that the prediction of the theory agrees reasonably well with experimental results. Mastering the fatigue crack propagation law has important significance for predicting structural fatigue life. Abstract the crack propagation law was derived from the sn data in the very high cycle fatigue of a bearing steel. Fatigue crack propagation an overview sciencedirect topics. Crack closure effects on fatigue crack propagation rates hindawi. Fracture mechanics is an effective mechanism for characterizing the fatigue crack propagation. A simple theory is developed to assess quantitatively the mechanism of fatigue crack propagation in metals. For fatigue, fatiguecrack propagation, and fracture data, however, design allowable values are usually not available and the data are presented in terms of typical or average values. A stochastic theory of fatigue crack propagation aiaa. In recent years, stress intensity factor and jintegral were usually commonly calculated to investigate the thermal fatigue crack propagation behaviors of the isotropic materials such as tool steels and cast irons.
Aug 20, 2006 a simple theory is developed to assess quantitatively the mechanism of fatigue crack propagation in metals. Paris and erdogan correlate the stress intensity factor sif range with the fatigue crack growth rate, and propose this seminal model as equation 1. Studies on quasistatic and fatigue crack propagation. A new model for predicting fatigue damage university of. The model demonstrates the critical dependence of fatigue crack growth on the fatigue ductility exponent, the fatigue ductility coefficient, the elastic modulus and the fracture toughness. Most of these studies attempt to relate crack propagation rates with some function of the stress intensity, factor, based upon experimental data. May 17, 2012 uncertainty propagation method for probabilistic fatigue crack growth life prediction theoretical and applied fracture mechanics, vol. Fatigue strength assessment of ship structures based on the.
Finally one needs to decide on criteria to determine under which conditions the crack will propagate, as well as the direction of propagation. Cracks were found to converge when they propa gated into the farfield stresses. Phase transformation theory applied to predict fatigue. The applicable fatigue crack growth rate expression. Fatigue crack propagation behaviour derived from sn data in. Analytical prediction of fatigue crack propagation in. Mechanisms of fatiguecrack propagation in ductile and. Fatiguecrack propagation is another topic of fracture mechanics that is not well. To begin the process cracks must nucleate within a material. Volpe national transportation systems center cambridge, ma 021421 093 8 final report october 1993 i this document is available to the public through the national technical information service springfield, virginia 22161. Ckm where c and m are material parameters one of the first 1962 and most widely used fatigue crack propagation criteria oalgorithmo 1. In dynamic loading, we will still get fracture if the stress intensity factor, for some instant of.
Key words crack propagation fatigue crack crack initiation crack behavior fillet weldtjoint geometric. The fatigue crack growth model proposed by frost and dixon, based on the different crack tip geometries of a loaded and unloaded crack, is restated and. Find stress intensity factor for the current geometry 2. Fatigue crack propagation was modeled by using the cyclic plasticity material properties and fatigue constants for crack initiation. The life of a fatigue crack has two parts, initiation and propagation. Successive analytic approximations to the solution of the integral. The crack may then propagate in a direction perpendicular to the direct stress. Fracture mechanics is the field of mechanics concerned with the study of the propagation of cracks in materials. Transient thermal fatigue crack propagation behavior of a. Reduced master equations, stochastic differential equations, and applications. Fatigue crack propagation experiment and numerical. A new model for predicting fatigue damage university of arizona. Mode i opening mode a tensile stress normal to the plane of the crack, mode ii sliding mode a shear stress acting parallel to the plane of the crack and perpendicular to the crack front, and.
Fatigue crack propagation can also be quantitatively described by the stress intensity factor k. Lowcycle fatigue analysis in abaqusstandard allows the modeling of discrete crack growth along an arbitrary path based on the principles of linear elastic fracture mechanics with the extended finite element method. Fatigue crack propagation test fcp tests were performed by employing the singleedgenotched sen specimens, see figure 2. Jun, 20 fatigue crack propagation fcp analysis is a method to monitor the resistance of a material to crack inception and propagation under cyclical loading. Stress corrosion theory of crack propagation with applications to geophysics orson l.
He examined a number of alloys and realised that plots of crack growth rate against. The theory is also applicable to predict fatigue crack propagation in interconnects under cyclic stress with corresponding experimental data for solder and intermetallics. Fatigue crack propagation behavior of snagcu solder. By the use of fracture mechanics principles it is possible to predict the number of cycles spent growing a crack to some specified length or to final failure. Lowcycle fatigue analysis using the direct cyclic approach. The presence of a crack can significantly reduce the life of a component or structure. A series of fatigue crack propagation tests were carried out for the rc beams strengthened with cfl under high temperatures and high humidity 50c, 95% r h and indoor atmosphere 23c, 78% r h environment to obtain fatigue crack propagation curves curves.
Unified creepplasticity theory was incorporated in the model to predict the creep and hysteresis effects on fatigue crack propagation in solder. Discrete dislocation modeling of fatigue crack propagation. In crack propagation testing, fracture mechan ics methods are used to determine the crack growth rates of preexisting cracks under cyclic loading. The crack propagation testing under quasistatic and fatigue loads are performed. Solid mechanics fatigue crack propagation anders ekberg 2 20 stress intensity factors and fracture in static loading, the stress intensity factor for a small crack in a large specimen can be expressed as kf ai. Uncertainty propagation method for probabilistic fatigue crack growth life prediction theoretical and applied fracture mechanics, vol. An energy approach to predict fatigue crack propagation in. Theory life prediction for fatigue cracks was made very much easier and far more quantitative, in the 1960s when paris 1 postulated that the range of stress intensity factor might characterise subcritical crack growth under fatigue loading in the same way that k characterised critical, or fast fracture. An analytical model for fatigue crack propagation of long cracks in metals and metal alloys is presented. Under the fatigue load, the rate of change a of the crack length a with the number of cycles n, dadn, is the rate of fatigue crack growth, reflecting the speed of crack propagation. A mathematical model for fatigue crack propagation under the influence of residual stress has been developed which is remarkably applicable to the prediction of any kind of fatigue behaviors under residual stress fields. The theory is also applicable to predict fatigue crack propagation in interconnects under cyclic stress with corresponding. Department of transportation research and special progrems adninistration volpe national transportation systems center kcndell square, cdridge, ma 02162 8.
The accumulated plastic energy density at the critical distance point ahead of the crack tip is used as a measure of the fatigue damage. Fatigue failure is brittlelike relatively little plastic deformation even in normally ductile materials. Mechanisms, behavior and analysis mechanical engineering theory and applications ping tang, jm leor zhang on. The model is derived from the basic crack propagation theory and it uses a damage indicator. These discrete jumps each time the crack advances causes the oscillations observed in fig. Discrete dislocation modeling of fatigue crack propagation v. During a fatigue test, the relationship between the crack length a and the number of cycles n was recorded at appropriate time points, and the secant method was used to calculate the crack propagation rates dadn that were obtained at the different crack depths. Mechanisms of fatigue crack growth a critical digest of theoretical. This comprehensive overview of the whole field of fatigue and fracture of metallic materials covers both the theoretical background and some of the latest experimental techniques.
Nearthreshold fatigue crack propagation without oxide. In this book, the authors present current research in the study of the mechanisms, behaviour and analysis of fatigue crack growths. The basic laws governing fatigue are derived theoretically for failure in both the high and low stress regions, and the material parameters controlling crack propagation determined. Fundamentals of and applications to fatigue analysis on the web. You complete the definition of the crack propagation capability by defining a fracturebased surface behavior and specifying the. Numerical modeling of fatigue crack propagation based on. A numerical model based on the theory of critical distances has been developed to simulate the fatigue crack propagation for cast aluminum alloys under mode i loading. Fatiguecrackpropagation data are usually obtained from precracked or. A new continuum mechanics model is developed for predicting fatigue crack propagation rates using a fracture mechanics approach.
Numerical modeling of fatigue crack propagation based on the. The fatigue crack propagation rate in a snagcu solder was predicted using phase transformation theory. After fatigue crack propagation, the material ahead of the crack and in its wake exhibits a strong texture, which is eliminated by subsequent shapememory heat treatment, indicating that this texture is due to detwinning, the main deformation mechanism of niti. From this, the propagation lives could be predicted without considering the effect of the ini tial surface discontinuities. Materials whenever subjected to fatigue cracking may exhibit mean stress effects as well as crack closure effects. The majority of the fatigue life may be taken up in the propagation of a crack. Introduction fracture mechanics fatigue crack propagation. Effect of residual stress on fatigue crack propagation. The strengthened beams were placed in hotwet environment pretreatment and. To make life estimations for fatigue crack growth and damage tolerant design, the following information are often needed. Residual strength calculation procedures have obvious shortcomings, but the prediction of fatigue crack propagation characteristics is even less accurate, despite the vast amount of research that has been done on this subject. The peridynamic theory is applied to study the crack turning behaviour of fsw joints in this work.
Analysis of fatigue crack propagation behavior in fillet. The crack will continue to grow until it reaches a critical. In materials science, fatigue is the weakening of a material caused by cyclic loading that results in progressive and localised structural damage and the growth of cracks. Peridynamics pd has inherent advantages in calculating crack turning. It provides a summary of the complex interactions between material microstructure and cracks, classifying them with respect to the overall damage process with a focus on microstructurally short cracks and dynamic. Solid mechanics fatigue crack propagation anders ekberg 7 20 pariso law paris law can be written as d d a n.
The key features of the model are an extension of griffiths theory of fracture to include fatigue, a dislocation model for the crack tip opening displacement, and cyclic plasticityinduced closure. First, the calculation of stress intensity factor based on finite element analysis and weight function method are given, then paris model is used to predict the crack propagation life. A generalized theory of fatigue crack propagation is presented which is based on the linear accumulation of metallurgical damage in the plastic region. There are three ways of applying a force to enable a crack to propagate. As explained before, the fatigue crack propagation rate is calculated for each crack growth increment. Evolution of fatigue crack propagation rate estimated by numerical simulation.
Fatigue strength assessment of ship structures based on. Effect of residual stress on fatigue crack propagation book. Fracture is considered to have occurred when the damage at the crack tip exceeds a critical value. Solid mechanics fatigue crack propagation anders ekberg 20 crack closure r elber, in 1970, discovered that crack closure exists in cyclic loading, even for loads that are greater than zero this crack closure will decrease the fatigue crack growth rate by reducing the effective stress intensity range the stress intensity rate.
While on the subject of dislocations, it is appropriate to briefly discuss fatigue. The introduction of fatigue test methods meetyou carbide. A theory for fatigue crack propagation sciencedirect. Firstly, the fatigue crack propagation experiment is used to obtain the upper and lower thresholds value of type i fatigue crack propagation of 42crmo steel compact tensile specimen under the alternating load of stress ratio r 0. Fatigue crack propagation may be caused by cyclic stresses in a benign environ ment, or by the combined.
Ab mechanical deformation of a solid during fatigue cycling is broadly defined a phase transformation, because defects are produced that increase its internal energy. In experiments, crack propagation has been measured as a. It uses methods of analytical solid mechanics to calculate the driving force on a crack and those of experimental solid mechanics to characterize the materials resistance to fracture. Nj 08405 fracture mechanics fatigue crack propagation research and special programs administration john a. The propagation rate, dadn mcycle, of surface cracks was estimated to be a power. Analytical prediction of fatigue crack propagation in metals. Reduced master equations, stochastic differential equations, and. Once a fatigue crack has initiated, each loading cycle will grow the crack a small amount, typically producing striations on some parts of the fracture surface. Linear elastic fracture mechanics lefm, moreover, is the fundamental theory for establishing the analytical model of fatigue crack propagation. The second problem consists of the numerical computation of the fracture parameters, such as the stress intensity factors, the j integral, the energy release rate or another. Fatigue crack propagation according to the above results, excess oxides were not present on the fracture surfaces when the samples were tested at approximately 5. A conventional fatigue crack growth curve of dadn versus deltak can be divided into three regions, i. Mechanisms of fatiguecrack propagation in ductile and brittle solids 59 in general, ductile materials are toughened intrinsically, e. Reasonable agreement between theoretical predictions and experimental results was obtained.