Specific objectives were to evaluate capabilities for analyzing spectrum crack growth in lugs and to assess the effects on crack growth of kic and cold working the material surrounding the lug holes. Recent advances in fatigue crack growth modeling 167 1. Monitoring and prediction of fatigue cracks show great application potential and economic benefit in shortening aircraft downtime, prolonging service life, and enhancing maintenance. Introduction lugs are the connector type of elements widely used for structural supports in airframe structure. Crack growth analysis main cargo door primary and continuing damage 3. References appendices aindustry survey results and priority list bfatigue crack growth data and curve fits cfatigue crack growth database software operation. Stressintensity factor solutions for tapered lugs with. However, the fatigue crack growth process is a nonlinear. Simulation of wingfuselage attachment bracket lug for. Therefore, this experimental work is aimed to critically determine the influence of various variables listed below on the fatigue life of bolt. However, when normalized by youngs modulus all metals exhibit. Fatigue crack growth analysis can be carried out on the wing fuselage lug attachment bracket in the bottom skin of the wing. Solid mechanics fatigue crack propagation anders ekberg 5 20 crack growth in region ii and iii region ii for larger magnitudes of.
Jul 22, 2014 fatigue crack growth analysis can be carried out on the wing fuselage lug attachment bracket in the bottom skin of the wing. A structural testing of the wing fuselage lug attachment bracket can be carried out for the. The model was used to correlate crack growth rates under constantamplitude loading and to predict crack growth under aircraft spectrum loading on 2219t851 aluminum alloy plate material. Analyses of fatigue crack growth and closure near threshold. In this book, the authors present current research in the study of the mechanisms, behaviour and analysis of fatigue crack growths. Two different relationships for crack growth rate need to be analyzed. Discrete dislocation modeling of fatigue crack propagation. For some components the crack propagation life is neglected in design because stress levels are high, andor the critical flaw size small. Numerical simulation of fatigue crack growth in straight lugs equipped with efficient structural. Crack growth and residual strength analyses lap joint.
Referenced papers involve the extended finite element method, aerospace structures and fatigue crack growth, or any combination thereof. Specific objectives were to evaluate capabilities for analyzing spectrum crack growth in lugs and to assess the effects on crack growth of kic and cold working the material. Analytical and experimental investigations were conducted to determine the crack growth behavior in lug joints subjected to a randomized flightby flight spectrum. A fatigue crack normally initiates from the location maximum tensile stress in the structure. An overview of the mechanical, fracture, and fatigue crack growth properties for the selected material is provided, as shown below. 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.
The fatigue crack growth model of attachment lug subjected to oblique pinload is established, offering an analytical as well as experimental method for assessing and designing damage tolerant attachment lugs. Further, in order to calculate the stress intensity factor, fracture mechanics based analytical and numerical approaches are applied. The fatigue crack growth prognosis is used for rul prediction. The below figure represents the modeling of wing to fuselage lug attachment of both the cases in solid edge v193. Damage tolerance evaluation for the lug can be carried out for given load spectrum. Fatigue crack growth modeling of attachment lugs sciencedirect. The fatigue crack growth rates for al and ti are much more rapid than steel for a given.
Input of the prognostic algorithm consists of the crack length observed. Scope for future work fatigue crack growth analysis can be carried out on the wing fuselage lug attachment bracket in the bottom skin of the wing. Fatigue life prediction under random loading conditions in. Ctod 81 8 discussion 89 9 conclusions 93 10futurework 95 11acknowledgement 97. Numerical method for fatigue life of aircraft lugs under.
A uniform initialization gaussian mixture modelbased guided. The structural fatigue failure of a common connecting joint used to attach aircraft wingfuselage components was investigated too. Fatigue crack growth prediction of the attachment lug. Damage tolerance evaluation for the lug can be carried out for given. Finally, to demonstrate the compatibility of developed model. The structural fatigue failure of a common connecting joint used to attach aircraft wing fuselage components was investigated too. Using the randomized equation approach, the fatigue crack growth model, given by equation 3 has the following form. I damage tolerance analysis ofa cracked attachment lug usingbem. Fatigue crack growth prediction of the attachment lug based.
Mechanisms, behavior and analysis mechanical engineering theory and applications ping tang, jm leor zhang on. The analysis of fatigue crack growth relies on the concepts of fracture mechanics which are discussed on this page. K region ii, the crack growth rate will be governed by a power law such as paris law the crack growth rate is fairly insensitive to the microstructure however, the constants m and c are, of course. Hence, the stress ratio dependence crack growth model is taken into account to assess the fatigue strength of damaged lug. Stress analysis and fatigue life prediction of wing. It begins with the initiation of cracks, and with continued cyclic loading the cracks propagate, finally leading to the rupture of a component or specimen. Stress analysis and fatigue life prediction of wing fuselage. This paper discusses an analytical and experimental investigations of the fatigue crack growth behavior in attach ment lugs subjected to a randomized. Prediction of fatigue crack growth in airframe structures. Cracks had been found on wing attachment lugs before the predicted fatigue life was reached in a full scale fatigue test. Much of the observed experimental behavior such as the effects of notches, maximum applied stress, crack length, inplane biaxiality, outofplane constraint, and transient loadings can be explained based on crack closure concepts. The contact pinlug has been studied with nonlinear contact analysis. Simulation of wingfuselage attachment bracket lug for fighter. Study on fatigue crack growth model of attachment lug.
K are calculated by the sif equation to get the values of the paris constants. Much of the observed experimental behavior such as the effects of notches, maximum applied stress, crack length, inplane biaxiality, out of plane constraint, and transient loadings can be explained based on crack closure concepts. Citeseerx efficient computation method in fatigue life. In the fe model, the load is applied through three different methods including the model with cosine pin pressure, constant pin pressure and actual pin. Fatigue crack growth computer program nasgro version 3. An application of the energy release rate concept to crack growth in attachment lugs. Fatigue damage, crack growth and life prediction f.
Moreover, the crack growth path for the lug with quarterelliptical crack is simulated. In 1970, paris 1 proposed a method to determine very slow fatiguecrackgrowth rates and showed the development of a fatiguecrackgrowth threshold, akth. Computational fatigue analysis of the pinloaded lug with. As shown, most of the life of the component is spent while the crack length is relatively small. The attachment lug demands careful fatigue life analysis especially in crack growth phase. Dtdhandbook afgrow air force growth fracture mechanics. In order to quantify the effects of fatigue damage, each period of the fatigue life is associated with a unique assessment method, an. Knowing the c and m, fatigue crack growth rate could be obtained by using pariss equation 7.
International journal of applied fatigue 42, 88a94. Fatigue cracks will appear at the location of high tensile stress locations. However, crack closure cannot be used to explain the overloadinduced retardation effects found in this work under planestrain, where both crack arrest and delays were associated to anincrease in keff. The dt analysis is carried out to determine the crack propagation life for the part using the finite. Boljanovic and maksimovic identified attachment lugs fatigue crack growth modeling and considered the lug with single throughthethickness crack as well as single quarterelliptical corner. In this article, the training stability problem when constructing the guided wavehidden markov model initialized by usually adopted kmeans clustering method and its influence to damage evaluation were researched first by applying it to fatigue crack. Inthis study, fatigue andfatigue crack growth behavior of krupp 2510 steel was investigated in. A wing to fuselage attachment fitting is considered for fatigue load analysis. That is why the 7475t7351 aluminum alloy has been chosen for fatigue crack growth prediction analysis performed to confirm the accuracy of the rms model for fatigue crack growth prediction under. The concept of the crack growth prognostic algorithm is shown in figure 4. Crack growth due to cyclic loading is called fatigue crack growth and is the focus of this page. Fatigue crack growth assessments in welded components including crack closure effects. The fatigue cracks are simultaneously generated by cracking of carbides, debonding of carbide metallic matrix interfaces or by crack initiationinthematrix4.
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 assessment of the wingfuselage attachment was the subject of several pieces of research in the near past. However, when normalized by youngs modulus all metals exhibit about the same behavior. In addition, the crack growth rate increases with increased applied stress. The rul is defined by the crack length reaching its critical size limit. The presence of the through crack at the attachment lug hole is not. In section 3, the fatigue test of attachment lugs is presented and used for validation. The predicted crack growth lives agreed well with experimental data. Improved pf based fatigue crack growth prediction 2. Fatigue crack growth modeling of attachment lugs request pdf. Dotfaaar0515 fatigue crack growth database for damage.
Such an investigation examines the stress analysis and the residual life estimation through a computational model here proposed in which suitable fracture. Fatigue crack growth assessments in welded components. K region ii, the crack growth rate will be governed by a power law such as paris law the crack growth rate is fairly insensitive to the microstructure however, the constants m and c are, of course, different for. As far as the lug configuration with quarterelliptical corner crack is concerned, the crack extension in depth and surface directions must be investigated. Stress intensity solutions were developed for cracks radiating from lug holes using bueckners weight function approach for various stress. For the above prediction, both constant and variable amplitude loads were.
The crack length, a, is plotted versus the corresponding number of cycles, n, at which the crack was measured. In the current project, an attempt will be made to predict the fatigue life of wingfuselage attachment bracket in a transport airframe. May 23, 20 take a closer look at fatigue and fracture. Crack growth in a hostile environment is called environmental crack growth and is not discussed here. Recent advances in fatigue crack growth modeling springerlink. The ratio of predictedtoexperimental lives ranged from 0.
A uniform initialization gaussian mixture modelbased. To obtain efficient algorithm in crack growth analysis here is derived. The reliability of the proposed procedures is verified using experimental fatigue crack growth data. Fatigue crack growth and steadystate creep duration.
Design and analysis on aircraft wing to fuselage lug. Topics discussed in this compilation include the unified fatigue crack growth. Design and analysis on aircraft wing to fuselage lug attachment. Discrete dislocation modeling of fatigue crack propagation v. Fatigue crack growth behavior of al7050t7451 attachment. Keywords wing to fuselage lug attachment, stress concentration, fatigue life, sn data, factor of safety, occurrence, exceedence and damage tolerance. Crack growth analysis main cargo door msd cracks 1. In this article, the training stability problem when constructing the guided wavehidden markov model initialized by usually adopted kmeans clustering method and its influence to damage evaluation were researched first by applying it to fatigue crack propagation evaluation of an attachment lug. Fatigue crack growth analysis can be carried out on the model. The residual life estimation of cracked lugs is analyzed by employing the crack growth law based on a twoparameter driving force model. American institute of aeronautics and astronautics, reston, virginia 1981.
In this paper for modeling catia v5 software is used and for analysis tool msc. Triangular and prismatic quadratic isoparametric elements, formed by collapsing one side and placing the mid. Crack growth simulation with residual stresses a paper addressing the effects of residual stresses was presented at the recent asip conference in san antonio, tx. A concise summary is presented of analysis methods and their correlation with test results from 236 fatigue crack growth and 16 residual strength tests of attachment lugs covering a wide variety. For analyses of fatigue damage, the fatigue life is split into two different periods of analyses. Xfem based analysis of fatigue crack growth in damaged. The demarcation between the above stages is not welldefined. Fatigue cracks are one of the common failure types of key aircraft components, and they are the focus of prognostics and health management phm systems. A crack closure model for predicting fatigue crack growth. Fatigue crack growth behavior of al7050t7451 attachment lugs. Residual life estimation of cracked aircraft structural components. The effect of height of the lug head and thickness on the fatigue failure behavior of damaged lug finally, for the fatigue critical wingfuselage attachment lug, the effect of height of the lug head and thickness on the residual life is analyzed. Apr 03, 2012 fatigue crack growth and steadystate creep duration. On the dominant role of crack closure on fatigue crack.
I damage tolerance analysis ofa cracked attachment lug. Fatigue life prediction of cracked attachment lugs using. Crack growth and fatigue life of single throughthickness and single quarter elliptical corner cracks in attachment lug are estimated and then compared with the available experimental data. It represents the top view, side view and front view of fitting. Fatigue test the fatigue test, named ft312, was designed to locally test the wing fold aftspar sheartie and simulate the initial crack nucleation. In 1970, paris 1 proposed a method to determine very slow fatigue crack growth rates and showed the development of a fatigue crack growth threshold, akth. In a metallic structure fatigue manifests itself in the form. For other components the crack growth life might be a substantial portion of the total life of the assembly. In the fatigue crack growth and fracture analysis of lugs, accurate calculation of the stress intensity factor k is essential. Analysis of fatigue crack growth in an attachment lug based on the weight function technique and the unigrow fatigue crack growth model. Following this work, in the early 1970s, elber 23 pioneered the concept of premature. Based on this study a crack growth prediction has been performed with a proper analytical model. Fatigue and fatigue crack growth behavior of tool steel. Fatigue damage analysis of wingfuselage attachment lug.
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