Fatigue crack growth and applications springerlink. Recent advances in fatigue crack growth modeling 167 1. The nascrac software employs crack growth analysis methods based on linear elastic fracture mechanics and utilizes the cracktip. In this paper it is estimated that crack closure phenomenon arises because tensile plastic zone at crack tip is compressed by surrounding elastic zone. Pdf a fatigue life prediction method based on strain. Gangloff university of virginia, charlottesville, virginia nasacr194982rew computer modeling the fatigue crack growth rate behavior of metals in corrosive environments final report. One of the earliest crack growth equations based on the stress intensity factor range of a load cycle is the pariserdogan equation. Crack closure is important because it tends to alter the relationship between the applied stress intensity factor range dk k max k min and that actually experienced by the crack tip dk eff k max k cl.
Nasgro has been developed and is distributed under the terms of a space act agreement a joint. Stress intensity factor crack length crack growth rate fatigue crack growth stress ratio these keywords were added by machine and not by the authors. Fatigue crack growth of ti62222 titanium alloy under. It is found in this study that when the ratio of low loading to high loading is. The aim of these models is to calculate only one cyclic stress intensity factor from the whole load spectrum, which can be used in order to characterize the crack growth adequately.
These fatigue countermeasures can improve flight crew performance and alertness. Development of the nasaflagro computer program for analysis. F fatigue crack growth universiti teknologi malaysia. We believe that crack closure phenomenon is the main problem in considering mechanism of crack propagation in the second stage. Using crack growth equations to solve for cyclic fatigue when stress is alternated in two different ways.
Fatigue research has been conducted in a variety of aerospace environments and. Predicting fatigue life is a critical aspect of the design cycle because virtually every product manufactured will wear out or break down. Recent advances in fatigue crack growth modeling 169 s a b 6 9 ii figure 1. Stp738 fatigue crack growth measurement and data analysis. The growth of fatigue cracks can result in catastrophic failure, particularly in the case of aircraft. However, when normalized by youngs modulus all metals exhibit about the same behavior. October 1995 preferred fracture mechanics practices. The software is developed jointly by southwest research institute swri and the national aeronautics and space administration nasa under a space act. Failure analysis and fatigue life prediction are necessary and critical for engineering structural materials. Dotfaaar0515 fatigue crack growth database for damage. Durability analysis using short and long fatigue crack. Fatigue life and crack growth prediction methodology j.
Environment enhanced fatigue crack propagation in metals. In this paper, a general methodology is proposed to predict fatigue life of smooth and circularhole specimens, in which the crack closure model and equivalent initial flaw size eifs concept are employed. Gangloff university of virginia, charlottesville, virginia nasa cr194982rew computer modeling the fatigue crack growth rate behavior of metals in corrosive environments final report. The fatigue crack growth rates for al and ti are much more rapid than steel for a given. Computer modeling the fatigue crack growth rate behavior of metals in corrosive environments edward richey iii, allen w. Durability analysis using short and long fatigue crack growth. Pdf common case studies of marine structural failures. Fatigue mechanismkey to the solution of the engineers second fundamental problemj. A model has been created to allow the quantitative estimation of the fatigue crack growth rate in steels as a function of mechanical properties, testspecimen characteristics, stressintensity range and testfrequency. Region iii is characterized by rapid, unstable crack growth. A deterministic method of estimating the fatigue crack growth durability of metallic airframes is presented, with particular reference to a civil transport aircraft. Following this work, in the early 1970s, elber 23 pioneered the concept of premature. Nasgro fracture mechanics and fatigue crack growth. The fatigue crack growth resistance of aerospace alloys is generally reduced by concomitant cyclic plastic deformation and exposure to a wide range of aggressive environments at ambient and elevated temperatures.
The analysis of fatigue crack growth mechanism and. An overview of the mechanical, fracture, and fatigue crack growth properties for the selected material is provided, as shown below. It is suggested that when this ligament was fractured, the observed sudden increase in crack length occurred. The fatigue crack growth calculator allows for fatigue crack growth analysis of a cracked part. Analyses of fatigue crack growth databases for use in a damage tolerance approach for aircraft. The development of this fcgd will begin the process of developing a consistent set of. Mechanisms, behavior and analysis mechanical engineering theory and applications ping tang, jm leor zhang on. A comprehensive, authoritative assessment of new developments in fatigue crack growth testing and of problems in the use of fatigue cracks growth rate information in materials evaluation, design, and reliability assessment. Fatigue test data and correlating with analytical data. A plot of the crack growth rate dadn curve is also provided, as well as the fracture toughness versus thickness curve for the selected material. Fatigue growth of small corner cracks in aluminum 6061t651. The fatigue loading used in the crack growth testing was of constantamplitude sinusoidal type. Introduction there have been numerous research studies on the characterization of fatigue crack growth using fracture mechanics since the work of paris and colleagues 1 in the early 1960s.
Eceanispi and oxidation and pbtigue life at elevated tehperatures final contractor report syracuse univ. For some components the crack propagation life is neglected in design because stress levels are high, andor the critical flaw size small. Fatigue crack growth rate model for metallic alloys r. These properties usually include values for fracture toughness, fatigue and sustained load crack growth rate, and crack growth. Fatigue crack growth how is fatigue crack growth abbreviated. Computer modeling the fatigue crack growth rate behavior. The mechanism of fatigue crack propagation scientific. Fatigue crack growth life calculations using nasaflagro were conservative. The software is developed jointly by southwest research institute swri and the national aeronautics and space administration nasa under a space act agreement, with additional support from the nasgro consortium and the federal aviation administration faa. Abstract the nasa flagro nasgro computer program was developed for fracture control analysis of space hardware and is currently the standard computer code in nasa, the u. A crack growth equation can be used to ensure safety, both in the design phase and during operation, by predicting the size of cracks. As a retardation of fatigue crack propagation occur under two step loading such as high to low loading, it is difficult to predictt the fatigue life in variable loading conditions.
Twodimensional crack growth problems with nasaflagro. The effect of temperature on the fatigue crack growth in a 150 mm class 12 unplasticized polyvinyl chloride upvc pipegrade material overa temperature range. Fatigue crack growth rates for the partthroughcracked specimens are compared with a base curve fitted from the data obtained using standard specimens. Fatigue crack growth of beta21s titanium alloy under. A model has been created to allow the quantitative estimation of the fatigue crack growth rate in steels as a function of mechanical properties, testspecimen characteristics. Pdf modified nasgro equation for physically short cracks. Fatigue crack growth computer program nasaflagro, developed by r. Fatigue crack growth life calculations using nasa flagro were conservative. Air force, and the european agency esa for this purpose. Fatigue crack growth computer program nasaflagro version 2.
The normalized equivalent stress intensity factor solution can be used for estimation of fatigue lives in a fatigue crack growth model under mixed mode loading conditions asim et. This defect distribution is combined with afatigue crack growth fcg nasa. A crack growth equation is used for calculating the size of a fatigue crack growing from cyclic loads. Dec 17, 2001 twodimensional crack growth problems with nasa flagro.
For other components the crack growth life might be a substantial portion of the total life of the assembly. Development of the nasaflagro computer program for. Nasa contractor report 182 129 the analysis of fatigue crack growth mechanism and oxidation and fatigue life at elevated temperatures a1sacb182129 the aijalysis of fulgue 8 8 2 29 87 crack groutfi f. The current nasa accepted practice in fracture mechanics analysis uses the computer program nasa flagro, which includes interaction effects. Fatigue life prediction based on crack closure and equivalent.
The suite of fracture mechanics and fatigue crack growth analysis programs known as nasgro is made available to the general public by southwest research institute with the goal of transferring nasadeveloped technology to industry. In this case, fatigue crack growth analysis is key to safe operation of the system. Because of this, the fatigue crack growth method based on linear. The development of this fcgd will begin the process of developing a consistent set of standard fatigue crack growth material properties.
Cyclic loading is applied in the form of a stress history. Pdf a typical fatigue crack growth curve consists of the threshold region, the paris region. Ghonem mechanics of materials laboratory, department of mechanical engineering university of rhode island, kingston, ri 02881 usa abstract fatigue crack growth experiments were performed on three different lamellar microstructures of ti 6242 at 520oc. Therefore, the mechanism of retardation was investigated by changing the ratio of two steploading in some materials in this paper. The crack growth rate accelerates as the maximum stress intensity factor approaches the fracture toughness of the material. The stress plot of the first vibration modal shape showed the peak stress of the blade occurred where crack initiated, also the crack direction growth shows the evidence of dominant bending stress, therefore it could be concluded that the first bending vibration mode was a possible cause of fatigue. Effects of temperature and frequency on fatigue crack. Nasa flagro fatigue crack growth computer program that provides an automated procedure for calculating the fatigue life of cyclically loaded structures with initial cracklike defects 31. Jones the fatigue crack growth behaviour of a ferritic stainless steel has been investigated as a function of test temperature, thermal exposure and frequency at intermediate growth.
Fatigue crack growth resistance and crack closure behavior. Nasgro fracture mechanics and fatigue crack growth analysis. Effects of temperature and frequency on fatigue crack growth in 18% cr ferritic stainless steel kamel makhlouf and j. The nasaflagro nasgro computer program was developed for fracture control analysis of space hardware and is currently the standard computer code in nasa, the u.
This type of initiation mechanism is not the only one to occur in material. Different effects of crack closure on small crack growth region and long crack. In the current version, the software was enhanced to suit the needs of the aircraft industry. Since its discovery by elber 1, fatigue crack closure has been an intensely studied parameter associated with fatigue crack growth behavior. Analyses of fatigue crack growth databases for use in a damage tolerance approach for aircraft propellers and rotorcraft. The crack growth rate is calculated at each stress cycle, and the crack is grown until failure. This information provides the necessary foundation for incorporating environmental effects in nasa flagro and will better enable predictions of aerospace component fatigue lives. Fatigue research has been conducted in a variety of aerospace environments and simulations, including the space shuttle. In this book, the authors present current research in the study of the mechanisms, behaviour and analysis of fatigue crack growths.
The esacrack package is the structural analysis software utilized by esa for damage tolerance evaluation of spaceflight structures. Nasa flagro v2 fatigue crack growth computer program developed as an aid in predicting the growth of preexisting flaws and cracks in structural components using a twodimensional model which predicts growth independently in two directions based on the calculation of stress intensity factors. Abstract the nasaflagro nasgro computer program was developed for fracture control analysis of space hardware and is currently the standard computer code in nasa, the u. Dotfaaar0749 analyses of fatigue crack growth databases. Nasa technical memorandum 109044 fatigue life and crack. Paris, threshold for fatigue crack growth propagation and effects of load ratio and frequency, in progress in flaw growth and fracture toughness testing, astm stp536, american society for testing and materials, philadelphia, pp. This approach to allowing and accounting for a safe level of crack growth during the operation of the system is referred to as damagetolerant design. The analyst can choose to use either a crack growth rate equation or a nonlinear interpolation routine based on tabular data.
Introduction one of the most important tasks in fracture control analysis is acquiring valid crack growth properties of the materials. Fong 3 fatigue mechanisman historical perspectivel. Specimen geometrys used in fatigue crack closure research. The nasa flagro nasgro computer program was developed for fracture control analysis of space hardware and is currently the standard computer code in nasa, the u. The fatigue crack growth rate behavior of an aluminum alloy is shown in figure q4. This package developed and distributed by esa consists of various analysis tools used to generate load and stress spectra, perform fracture mechanics analysis, generate stress intensity factor solutions and to perform fatigue analysis. Creep fatigue crack growth cfcg behavior, fracture mechanism, and microstructural evolution of g115 steel under different hold times and initial stress intensity factor ranges. Quantitative microscopy and direct observations at dislocation level quantitative microscopy and fatigue mechanismsf. Mmj13 fatigue and fracture mechanics sample test qustion. Fatigue crack growth nasaflagro computer program developed as aid in predicting growth of preexisting flaws and cracks in structural components of space.
Crack growth equations are used to predict the crack size starting from a given initial flaw and are typically based on experimental data obtained from constant amplitude fatigue tests. The software is developed jointly by southwest research institute swri and the national aeronautics and space administration nasa under a space act agreement, with additional support from the nasgro. The crack propagation durations increased significantly with decreasing. Results of an experimental investigation of the fatigue growth of small comer cracks emanating from. Global analyses models the global analyses models base on the statistical description of the load spectrum. Fatigue crack growth was transgranular with sem fracture surface morphology dependent upon both ak and temperature with significant increase in secondary cracking at 175. The arrhenius relationship between fatigue crack growth rate, dadn, and absolute temperature, t, was found to describe the experimental data very well independent of the applied stress intensity factor range. Various computer software packages for fatigue crack growth analysis have.
Sep 14, 2017 using crack growth equations to solve for cyclic fatigue when stress is alternated in two different ways. Fatigue crack growth mechanisms in fully lamellar ti6242 alloy at 520 oc f. Fatigue crack growth simulation in a generator fan blade. This problem involves the complex mechanism of smallcrack growth which is. At high stress intensities, crack growth rates are extremely high and little fatigue life is involved. The k and jintegral solutions in the nascrac program account for the effect of the presence of the crack on the input stress. Fatigue crack growth rate model for metallic alloys.
Limited correlative experiments indicate that dehumidified oxygen and hydrogen have no effect on the rate of fatiguecrack growth in this alloy, while distilled water. Fatigue life prediction based on crack closure and. Nasa flagro predicts crack growth using a twodimensional model which predicts growth independently in two directions based on the calculation of stress intensity factors. Nasa flagro, nasa, and materials branch report 86es51, houston, july. This process is experimental and the keywords may be updated as the learning algorithm improves.
Some systems may be designed to allow for some crack growth before repair and replacement. In an effort to understand the causal mechanism of the doubler tip. Nasgro is a suite of computer programs used to analyze fracture and fatigue crack growth fcg in structures and mechanical components. The nasaflagro nasgro computer program was developed for. The investigation determined that the mechanism of failure of the crankshaft was probably.
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