Newman 5 predicted the life of various notched specimens based on the small crack growth curve with the aid of fastran software 6. Prediction of crack growth under variableamplitude loading. Fatigue and crackgrowth behavior in a titanium alloy under. They had conducted crack growth tests on mt specimens fig. It adds flexibility to the ordinarily straight line in region ii. A fatigue crack growth analysis computer code fastran based on plasticity induced closure has been developed. Crackgrowthrate tests were conducted on compact, ct, specimens made of 7075t7351 aluminum alloy over a wide range of constantamplitude loading r pminpmax 0. Newman while at nasa and is an acronym derived from nasa fatigue crack growth structural analysis. Read crackgrowth calculations in 7075t7351 aluminum alloy under various load spectra using an improved crackclosure model, engineering fracture mechanics on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at.
Fcg life prediction codes of fastran and afgrow, which are modified using the enhanced. Fatigue crack growth simulation of aluminium alloy under cyclic sequence effects. Fatiguecrack growth in two aluminum alloys and crackclosure. At the lowershelf, the maximum damage value is very small and hence, there are no regions of stable crack growth. The fastran lifeprediction code, using either the crackclosure model or lefm procedures, and the afgrow code, which uses only lefm procedures, were. Pdf fatigue crack growth simulation of aluminium alloy. The constraint loss region is associated with the transition from flat tensile mode to slant shear mode crack growth as shown in fig. This, in turn, means that similitude does not hold in region i. Experimental investigation and numerical prediction of. Cfdfastran is the industryleading commercial cfd software for aerodynamic and aerothermodynamic applications. Evaluation of the c model for addressing short fatigue crack growth executive summary the accurate modelling of fatigue crack growth in high strength metallic aircraft structures is an essential requirement for the structural integrity management of the aircraft fleets of the royal australian air force.
Fastranii a fatigue crack growth structural analysis program. 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. A computer controlled decreasing stress intensity technique for low rate fatigue crack growth testing, journal of testing and evaluation, v. Roughnessinduced crack closure in the threshold region for high strength aircraft structural alloys a thesis submitted in fulfilment of the requirement for the degree of doctor of philosophy kevin frank walker beng aero with distinction msc school of aerospace mechanical and manufacturing engineering college of science engineering and health. Our crack growth modeling capabilities are among the best in the industry. Fastranii a fatigue crack growth structural analysis. Fastranii a fatigue crack growth structural analysis program sudoc nas 1. The crack growth rate for an example material is shown below using the nasgro equation. There are many prediction models that are used for fatigue crack growth prediction. Konset, at which the hcf cycles commence to contribute to the crack growth rate. The code was developed over the past 40 years, at nasa langley research center and mississippi state university, and it is used worldwide in numerous aircraft companies, research organizations, and other industries. A crack growth equation can be used to ensure safety, both in the design phase and during operation, by predicting the size of cracks.
Unique to fracturelab is an outstanding enhancement to the nasgro equation that we call the perturbed nasgro pn model. One of the earliest crack growth equations based on the stress intensity factor range of a load cycle is the pariserdogan equation. The objective of this paper is to apply the fastran crackclosure model to correlate constantamplitude crackgrowth rate data on 2024t3 aluminum alloys and to predict crack growth under variableamplitude loading and a commercial transport wing spectrum. Stable crack growth an overview sciencedirect topics. Advances in materials science and engineering 2017 article. Damage tolerance based life assessment for helicopter. Crack closure was first observed by wolf elber as propping open a crack tip resulting in a reduction of the full stress intensity range or crack tip driving force. Anomalous fatigue crack growth phenomena in highstrength. Cfd fastran is highly flexible which means you can employs stateoftheart numerical and physical models, and advanced pre and postprocessing modules. Fatigue and crackgrowth behavior in a titanium alloy. Modelling combined hcflcf fatigue crack growth under the. Subcycle fatigue crack growth formulation for constant and. Finally, in the region iii, at high dk values, crack growth rates are extremely high and little fatigue life is involved.
Fatiguecrack growth in two aluminum alloys and crack. Indeed, for the d6ac steel considered in 8 and also in 4 forth and jones 9 have shown that crack growth in regions i and ii. As elber 3 concluded in a 1970 paper, at the present stage,it appears that theoretical calculation of the crack closure phenomenon presents great difficulties. In many practical engineering situations this region may be ignored because it does not affect the total crack propagation life. Crack closure is an important factor affecting fatigue crack growth in high strength alloy materials. Standardised test methods such as the load reduction technique in astm e647 introduce a range of problems including load history effects and remote closure. Comparative study of prediction methods for fatigue life evaluation of.
Both options were used and the article stated that no analysis option enabled to reproduce crack growth retardation. Since then, several crack propagation models were proposed, such as the priddle equation 14 and the forman model 15, and the crack growth behavior was divided into three stage. Anomalous fatigue crack growth phenomena in highstrength steel. Fastrana fatigue crack growth life prediction code based on the crackclosure concept. Right detail of the measurement grid precomputed sensor responses indicating response of mwmarray channels 1 and 4 within selected ranges of load cycles channel 1. The regions of stable crack growth are represented by regions of damage value exceeding 0. Study on the stop crack growth for shaft by using drilling hole.
Neutron diffraction was employed to investigate the crack growth retardation phenomenon after a single tensile overload by mapping both onedimensional and twodimensional residualstrain distributions around the crack tip in a series of compacttension specimens representing various crack growth stages through an overloadinduced retardation period. 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 simplest prediction procedures are based on crack growth material characteristics. The significance of fatigue crack closure 1971 citeseerx. The application of overload also enhances the stress intensity range. Study on the stop crack growth for shaft by using drilling. A widely recognized propagation life prediction code, based upon the crack closure model, is fastran ii developed by newman 4 at the nasa langley research center. Analyses of fatigue crack growth databases for use in a damage. A crack growth equation is used for calculating the size of a fatigue crack growing from cyclic loads. The objective of this paper is to apply the fastran crack closure model to correlate constantamplitude crack growth rate data on 2024t3 aluminum alloys and to predict crack growth under variableamplitude loading and a commercial transport wing spectrum.
The stresslevel effect on fatiguecrack growth under. Fatigue and crackgrowth behavior in a titanium alloy under constantamplitude and spectrum loading. Study on the stop crack growth for shaft by using drilling hole ouday kudom mohammad abstract the aim of this search is study the effect of the hole for control on crack growth for the rotation shaft,provide rotating shaft in which test work is applied, provide the electrical drill for drilling, the shaft at. Indeed, for the d6ac steel considered in 8 and also in 4 forth and jones 9 have shown that crack growth in regions i and ii conforms to a nonsimilitude based growth law. Fatigue and crackgrowth analyses of riveted lapjoints in. In the nasgro database 23, 24, some typical values of can be used here. Fatigue crack closure due to surface roughness and plastic. They had conducted crackgrowth tests on mt specimens fig. Afgrow air force grow is a damage tolerance analysis dta framework that allows users to analyze crack initiation, fatigue crack growth, and fracture to predict the life of metallic structures. Fastran is a computer program for calculating the rate of fatigue crack growth by combining.
C, analyses of fatigue crack closure during simulated threshold testing, fatigue crack growth thresholds. Since the model describes the interaction of microstructure, mechanism, and. Left mwmarray measured magnetic permeability curves and fatigue crack growth curve from fastran analysis. If a crack fails to grow perceptibly in say 10,000,000 cycles, the alternating stress intensity is often taken as an operational fatigue threshold. Region iii is characterized by rapid, unstable crack growth. Fracture mechanicsbased life prediction of a riveted lap. Application of a stripyield model to predict crack growth under. Fatigue and stress monitoring with magnetic sensor arrays.
Fatigue crack growth under variableamplitude loading. The results of the analysis show that universally crack growth predictions under typical aircraft load spectra utilize a significant portion of the crack growth rate curve close to the threshold region. Originally developed by the air force research laboratory, afgrow is mainly used for aerospace applications, but can be applied to any type of metallic structure that experiences fatigue cracking. Evolution of residualstrain distribution through an. The crackgrowth model, fastran, was used to calculate fatigue lives and crack growth in laboratory lapjoint specimens made of a thinsheet clad aluminum alloy to establish appropriate crack configurations and to select equivalent initial flaw sizes eifs. Region i is taken as either very slow crack growth region or nearthreshold region since the sif range of the sigmoidal curve in this region. The coefficient p controls the curve in the low growth rate threshold region, and q controls the curve in the high growth rate region. Fracture mechanics and fatigue crack growth analysis software nasa jsc team royce forman dr. Fatigue crack growth simulation of aluminium alloy. To account for plasticity, a portion of the dugdale cyclicplasticzone length.
Right detail of the measurement grid precomputed sensor responses indicating response of mwmarray channels 1 and 4 within selected ranges of load cycles channel 1 was monitoring a. The fastran lifeprediction code, using either the crackclosure model or lefm procedures, and the afgrow code, which uses only lefm procedures, were used to make crackgrowth predictions from an initial crack size to failure in the mt specimens. It supports all grid technologies including multiblock structured, general polyhedral unstructured, chimeraoverset and adaptive cartesian. Roughnessinduced crack closure in the threshold region. The stress intensity factor k \displaystyle k characterises the load around a crack tip and the rate of crack growth is experimentally shown to be a function of the range of stress intensity. Fracture mechanics and fatigue crack growth analysis software.
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. Fatigue crack growth based on fastran model for all load cases. The ability of fatigue crack growth prediction is one of the most critical points in light of inspection intervals evaluation. The threshold and very low growth rate region poses a number of challenges including small crack behaviour, k max effects and the apparent breakdown of similitude. Fracture mechanics and fatigue crack growth analysis. Langley research center, hampton, virginia may 2000 the nasa sti program office. Fastran ii a fatigue crack growth structural analysis program sudoc nas 1. Hence, the data required would have to be obtained by experimental means. The discovery of crack closure by elber 16 was another major step in the. Plasticzone region refined 20 elements in plastic zone instead of 10 elements. Region ii most of the current applications of lefm concepts to describe crack growth behavior are associated with region ii.
Sambi mettu joachim beek leonard williams feng yeh southwest research institute team dr. Damage tolerance based life assessment for helicopter components. Prediction of crack growth under variableamplitude. Fatigue crack growth and life predictions under variable. A polycrystalline and a 001 oriented specimen were tested to study mode i fatigue crack growth, while 111 oriented specimens were used to study mixed mode i and ii fatigue crack growth. Nov 01, 2004 read crack growth calculations in 7075t7351 aluminum alloy under various load spectra using an improved crack closure model, engineering fracture mechanics on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. The attractiveness of the crack closure model for engine applications is its ability to accurately predict crack growth of small flaws. Higher crack growth rates result in nonconservative predictions of fatigue. Afgrow, fastran, and nasgrow, since they do not apply to the materials from. Similitude and the paris crack growth law similitude and the paris crack growth law jones, r molent, l pitt, s.
The growth of fatigue cracks can result in catastrophic failure, particularly in the case of aircraft. Craig mcclung joe cardinal source of acquisition nasa johnson space center o. Roughnessinduced crack closure in the threshold region for. The fastran code is wellknown for fatigue crack growth prediction and has. Pdf fatigue based structural design optimization implementing a.
Region i is taken as either very slow crack growth region or nearthreshold region since the sif range of the sigmoidal curve in this region asymptotically approaches. It supports most of the commonly used data formats. Their values are selected to fit the growth rate curve to experimental data. The paris law is normally applicable to the crack growth in region 2. As an example of the efforts to codify the knowledge in this area, this report. It is estimated that the crack must grow several compressive plasticzone sizes before. It denes a value below which the fatigue crack will cease to grow or the growth rate is nucleation and the smallcrack growth consume most.
Evolution of residualstrain distribution through an overload. An analytical model for the identification of the threshold. Fastran is an advanced lifeprediction code based on the physics of the growth of micro and macrocracks in metallic materials. Study on the stop crack growth for shaft by using drilling hole ouday kudom mohammad. Neutron diffraction was employed to investigate the crackgrowth retardation phenomenon after a single tensile overload by mapping both onedimensional and twodimensional residualstrain distributions around the crack tip in a series of compacttension specimens representing various crackgrowth stages through an overloadinduced retardation period. A simple fatigue life prediction algorithm using the modified. Crack closure and slip irreversibility in the fatigue crack growth of 316l stainless steel were investigated using digital image correlation dic. As the crack grows, the strips are cut and leave a region of raised plastic material in the crack wake that prevents the complete closure of a crack. This means that the region i crack growth law is a function of the test geometry. Crack growth rate tests were conducted on compact, ct, specimens made of 7075t7351 aluminum alloy over a wide range of constantamplitude loading r pminpmax 0. Fastran models accelerations and retardation and other variable amplitude loading effects in crack growth using a crack closure model. The presence of the large plastic zone in the crack tip induces the retardation of crack.
The final analysis addressed the role of roughness induced crack closure on fatigue crack growth in the near. 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. The critical importance of correctly characterising fatigue. For the reason that the crack growth data in the threshold region are not sufficient or even not available, an initial value of is guessed. The critical importance of correctly characterising. Full text of a practical engineering approach to predicting. Analytical models based on the plasticity induced closure concept have been very successful in.
Oct 01, 2008 similitude and the paris crack growth law similitude and the paris crack growth law jones, r molent, l pitt, s. The crackopening stresses, as a function of load history and crack length, are calculated from the model and the effective stressintensity factor range, used to correlate fatiguecrack growth rates, may be either elastic or modified for plastic yielding at the crack tip. Specifically designed to support the aerospace industry, it employs stateoftheart multiple moving body capability for simulating the most complex aerospace problems including missile launch, maneuvering and. The objective of this paper is to apply the fastran crackclosure model to. Specimens the material used in the current study was obtained from the research group in poland m. Two types of specimens were used in the fatiguecrackgrowth studies. Both compression precracking and loadreduction methods were used. I or an accelerated growth region iii paris law cannot adequately describe these regions. Evaluation of the c model for addressing short fatigue crack. Comparative study of prediction methods for fatigue life. The crack growth rate accelerates as the maximum stress intensity factor approaches the fracture toughness of the material. A simple fatigue life prediction algorithm using the.