Fastran is a computer program for calculating the rate of fatigue crack growth by combining crack growth equations and a simulation of the plasticity at the crack tip. Comparative study of prediction methods for fatigue life evaluation of. Having glanced at the web site i can see that it might be useful to shed some light on fatigue crack growth and crack closure based concepts. They used a dugdale strip model as a basis for their analysis, and demonstrated that a wake in the form of a plastic layer could.
Jan 08, 20 the plasticityinduced crack closure model, fastran, was used to correlate the data over a wide range in stress ratios and crack growth rates from threshold to near fracture. Fastran ii is a lifeprediction code based on the crack closure concept and is used to predict crack length against cycles from a specified initial crack size to failure for many common crack configurations found in structural components fastran ii is an update of the previous fastran. Subcritical crack growth also leads to a time dependence of the strength, the slower the loading rate, the weaker the material. Fastran has a variety of crack growth equations built in along with piece wise linear equations that can be read from file. Test results from the literature on inconel 718 fabricated via a laserpowder bed fusion lpbf method and the plasticityinduced crack closure model fastran 12 are used to predict fatigue. The use of crack growth analysis tools based on plasitictyinduced crack closure model, such as fastran, cgap and afgrow, requires the conversion of. Aug 10, 2015 purpose the prediction of fatigue crack growth behaviour is an important part of damage tolerance analyses. Fastran is an advanced nonlinear lifeprediction code based on cyclic plasticity and the crack closure concept. The residual strength analysis methodology is based on the critical crack tipopeningangle fracture criterion that. To account for the very high crackclosure levels, a very low constraint factor, like planestress conditions, had to. Fastran is a computer program for calculating the rate of fatigue crack growth by combining crack growth equations and a simulation of the plasticity at the crack tip fastran models accelerations and retardation and other variable amplitude loading effects in crack growth using a crack closure model.
Prediction of fatigue lives in additively manufactured alloys. Fatigue life, finite element, fatigue crack growth, crack nucleation, bolted joints date received. Introduction experimental testing for baseline fatigue crack growth rate properties has traditionally been performed on laboratory coupons designed to promote modei crack growth, where cracking is perpendicular to the applied load. Aug 26, 2016 subcritical crack growth also leads to a time dependence of the strength, the slower the loading rate, the weaker the material. This model allows the calculation of the stress ratio or mean stress effect that gives rise to the increased rate of crack growth at higher stress ratios. Recently, the authors work has focused on evaluating the fastran retardation model. Fracture mechanicsbased life prediction of a riveted lap. Fatiguelife prediction methodology using a crackclosure. Fatigue lives in lapsplicejoint specimens and fatiguecrack growth in a structural fatigue test article agreed well with calculations from smallcrack theory and fatiguecrack growth analyses with the fastran code. Effect fracture resistance on retardation of crack growth. Fracture mechanics is the field of mechanics concerned with the study of the propagation of cracks in materials. Prediction of fatigue lives in additively manufactured.
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. Test results from the literature on inconel 718 fabricated via a laserpowder bed fusion lpbf method and the plasticityinduced crackclosure model fastran 12 are used to predict fatigue. Methodology for predicting the onset of widespread. Fatigue and crackgrowth behavior in a titanium alloy. Comparison of crack growth rate data from aircraft panels and agard small crack database 103 small crack data agard r 732.
The fastran code is wellknown for fatigue crack growth. Stress state factor evaluation based on a fractographic. K eff p 1k max k ie q where c 1i and c 2i are the coefficient and exponent for each linear segment i 1 to n, respectively. Crack closure is an important factor affecting fatigue crack growth in high strength alloy materials. This model is implemented in the afgrow code, which allows different retardation models to be compared. Assessment of residual stresses and hole quality on the fatigue behavior of aircraft structural joints. The science of fracture mechanics provides a logical framework for understanding the effect of subcritical crack growth on structural ceramics and for predicting lifetime. The residual stress theory schijve and broek 1962 assumes that compressive.
The program uses a strip yield model of the crack tip that was first proposed by d. Langley research center, hampton, virginia may 2000 the nasa sti program office. In the early 70s elber 1 hypothesised that the r ratio effect seen in constant amplitude fatigue tests was due to plasticity related crack closure and he presented an empirical formulation to account for this effect. Several stress analysis codes have been developed or enhanced to analyze the lapsplicejoint configuration. As an introductory course, the text is focused on the essential concepts and analytical methods of fracture mechanics, aiming at painting a broad picture of the theoretical background to fracture mechanics. The primary advantage of the model is that all input parameters, including.
In this paper, the terms fatigue life and crack growth life are used synonymously since all fatiguelife calculations were performed using the fastran crack growth methodology with the eifs concept and formulations based on small crack theory. The fastran crack growth retardation model uses stress state descriptors to consider the local stress state ahead of the crack tip. The nasgro equation is modified by introducing the concept of intrinsic effective threshold stress intensity factor sif range. 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 in modern materials science, fracture mechanics is an important tool used to improve the. Fatigue and crack growth in 7050t7451 aluminum alloy. This text is based on a series of lectures conducted on fracture mechanics. Comparative study of prediction methods for fatigue life evaluation. A simple fatigue life prediction algorithm using the.
One crucial way to address the concern is to explore physically reasonable expression of crack. An analytical model for the identification of the threshold. The model predictions are also compared with those of fastran 7 and afgrow 1 codes. Fatigue and crackgrowth behavior in a titanium alloy under. Fatigue lives in lapsplicejoint specimens and fatiguecrack growth in a structural fatigue test article agreed well with calculations from smallcrack theory and fatiguecrackgrowth analyses with the fastran code. The primary advantage of the model is that all input parameters, including those for an.
Fatigue crack growth rate and stressintensity factor. The lifeprediction method used in fastran ii is built around an analytical crack closure model. Computer modeling the fatigue crack growth rate behavior of metals in corrosive environments microform. Further studies are needed to develop a combined model of plasticity, roughness, and debris induced crack closure behavior. The fastran lifeprediction code was used to model crack growth from an initial microstructural size flaw to failure and the crackgrowth relation used is 5 dc dn c 1 i. Fatigue and crack growth in 7050t7451 aluminum alloy under. Subcycle fatigue crack growth formulation for constant and. Crack growth equation wikimili, the best wikipedia reader. Fracture mechanicsbased life prediction of a riveted lap joint. Purpose the prediction of fatigue crack growth behaviour is an important part of damage tolerance analyses.
Fatigue analyses of riveted lapsplice joints in a narrow. Defense technical information center compilation part notice. Comparison of crack growth rate data from aircraft panels and agard small crack database 103 small crack data agard r 732 105 104 agard rfti k 106 fatigue crack growth rate mmcycle panel data 107 skin thickness 6 50 100 m 1 10 100 0 108 crack length crack length m 31. Analytical models based on the plasticity induced closure concept have been very successful in.
Slow crack growth how is slow crack growth abbreviated. The objective of this paper is to present some of the efforts to conduct fatigue and crack growth analyses with the fastran lifeprediction code using small crack theory. Full text of a practical engineering approach to predicting. The fastran lifeprediction code was used to model crack growth from an initial microstructural size flaw to failure and the crack growth relation used is 5 dc dn c 1 i. Walker, fatigue crack growth from a notch under severe overload and underload, in proceedings of the international conference on structural integrity and failure, 2006. The crack growth concept is employed in this paper to predict the fatiguelife of am materials. Common case studies of marine structural failures intechopen.
Fatigue crack growth based on fastran model for all load. The objective of this paper is to apply the fastran crackclosure model to correlate constantamplitude crackgrowth rate data on 2024t3 aluminum alloys. The fatigue crack growth analysis methodology is based on small crack theory and a plasticity induced crack closure model, and the effect of a corrosive environment on crack growth rate is included. Calculated fatigue lives from fastran using smallcrack theory with an equivalentinitialflawsize of 9 microm in radius at the center of the semicircular edge notch fit the constantamplitude test data fairly well, but underpredicted the spectrum loading results by a factor of 2 to 3. Methodology for predicting the onset of widespread fatigue. Crack tip constraint factors, to account for threedimensional stateofstress effects, were selected to correlate large crack growth rate data as a function.
Newman 5 predicted the life of various notched specimens based on the small crack growth curve with the aid of fastran software 6. Calculated fatigue lives from fastran using small crack theory with an equivalentinitialflawsize of 9 microm in radius at the center of the semicircular edge notch fit the constantamplitude test data fairly well, but underpredicted the spectrum loading results by a factor of 2 to 3. The plasticityinduced crackclosure model, fastran, was used to correlate the data over a wide range in stress ratios and crackgrowth rates from threshold to near fracture. State commission on gambling various locations scg. An assessment on the impact of loose and tight rivets on the. Fastran a fatigue crack growth lifeprediction code based on the crackclosure concept version 5. Full text of a practical engineering approach to predicting fatigue crack growth in riveted lap joints see other formats nasatm2000210106 a practical engineering approach to predicting fatigue crack growth in riveted lap joints c. Cimprovements to fastranfatigue crack growth lifeprediction code. 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. Cracktip constraint factors, to account for threedimensional stateofstress effects, were selected to correlate largecrack growth rate data as a function. Pdf fatigue crack growth simulation of aluminium alloy. A crack growthbased individual aircraft monitoring method. Equivalent initial flaw size testing and analysis of. The fatiguecrack growth analysis methodology is based on smallcrack theory and a plasticity induced crackclosure model, and the effect of a corrosive environment on crackgrowth rate is included.
Design concept using smallcrack theory flaw size d smallnone 1 m. Theory, development, user guide and examples executive summary crack growth assessment is an essential element of the aircraft certification procedure for. Main problem of this method is the complexity of small crack theory. Plasticity is known to be the main driver of closure, but in some materials and at some stages other mechanisms such as fracture surface roughness and debris accumulation are also important.
Fatigue lives in lapsplicejoint specimens and fatigue crack growth in a structural fatigue test article agreed well with calculations from small crack theory and fatigue crack growth analyses with the fastran code. Nasgro is a suite of computer programs used to analyze fracture and fatigue crack growth fcg in structures and mechanical components. Two crack growth prediction codes, afgrow and fastran, were used to not only develop the eifs but also to compare the crack growth algorithms in each code. 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 concept. Using the fastran model implemented in the afgrow computing code, the descriptor is input into the retardation model as a constant tensile compressive constraint factor along with the corresponding crack growth rate. The residual strength analysis methodology is based on the critical cracktipopeningangle fracture criterion that. A simple fatigue life prediction algorithm using the modified. For the stressdominated crack growth, a powerlaw function has been empirically proposed to describe the.
The closure model has also been used to explain the increase rate of growth seen with small cracks known as the small crack effect. A fatigue crack growth structural analysis program. The griffiths equation describes the relationship between applied nominal stress and crack length at fracture, i. Griffith was concerned with the energetics of fracture, and considered the energy changes associated with incremental crack extension. Crack growth predictions are performed by using both the linear damage accumulation principle and the fastran retardation model. The damage model is compared against the results of an extensive coupon fatigue test programme for aluminium alloy 7050t7451. Thus, variableamplitude load histories did not have to be reordered to capture the damaging effects of major and minor load. The crackgrowth concept is employed in this paper to predict the fatiguelife of am materials. The eifs calculations are prone to compounding errors in the crack growth analysis due to the changing stress intensity factor solutions and stress fields as the crack gets longer. K eff p 1k max k ie q where c 1i and c 2i are the coefficient and exponent for each linear segment i. Fatigue crack closure due to surface roughness and plastic. Various computer software packages for fatigue crack growth analysis have been developed by nasa. In the mid1970s, the fastran ii lifeprediction code was developed by dr. He developed the theory for predicting plasticity induced crack closure and software fastran, which is widely used in the aircraft industry.
Fatigue crack growth simulation of aluminium alloy under spectrum. The model is based on plasticityinduced fatiguecrack closure and is used to. Fatigue and crackgrowth analyses on 7075t651 aluminum. In the mid1970s, the fastranii lifeprediction code was developed by dr. They used a dugdale strip model as a basis for their analysis, and demonstrated that a wake in the form of a plastic layer could obstruct closure and therefore reduce the effective range of the. In this article, a new crack growthbased tracking method is described that also includes a measure of the certified fatigue life consumed. One advantage of the proposed method is that the complex growth behavior analysis of small cracks can be.
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