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. 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. Roughnessinduced crack closure in the threshold region. Effect of residual stress on fatigue crack propagation. 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.
The simplest prediction procedures are based on crack growth material characteristics. Langley research center, hampton, virginia may 2000 the nasa sti program office. Full text of a practical engineering approach to predicting. Region ii most of the current applications of lefm concepts to describe crack growth behavior are associated with region ii. Comparative study of prediction methods for fatigue life evaluation of. 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. Plasticzone region refined 20 elements in plastic zone instead of 10 elements. This means that the region i crack growth law is a function of the test geometry.
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. 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. Evolution of residualstrain distribution through an. Their values are selected to fit the growth rate curve to experimental data. 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.
Left mwmarray measured magnetic permeability curves and fatigue crack growth curve from fastran analysis. Cfd fastran is highly flexible which means you can employs stateoftheart numerical and physical models, and advanced pre and postprocessing modules. Two types of specimens were used in the fatiguecrackgrowth studies. Of note is the observation that both fighter and transport aircraft display this same behaviour throughout the entire crack growth prediction. The constraint loss region is associated with the transition from flat tensile mode to slant shear mode crack growth as shown in fig. 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. 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.
It supports all grid technologies including multiblock structured, general polyhedral unstructured, chimeraoverset and adaptive cartesian. At the lowershelf, the maximum damage value is very small and hence, there are no regions of stable crack growth. Fatigue crack growth simulation of aluminium alloy. The ability of fatigue crack growth prediction is one of the most critical points in light of inspection intervals evaluation.
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. There are many prediction models that are used for fatigue crack growth prediction. 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. Modelling combined hcflcf fatigue crack growth under the. Fastranii a fatigue crack growth structural analysis program sudoc nas 1. Fatigue and crackgrowth analyses of riveted lapjoints in. 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. Fastran and dkeff are based on the same stress opening function, and thus are strongly dependent on the constraint loss region where crack growth changes from flat to slant growth. Experimental investigation and numerical prediction of.
Roughnessinduced crack closure in the threshold region for. Finally, in the region iii, at high dk values, crack growth rates are extremely high and little fatigue life is involved. The discovery of crack closure by elber 16 was another major step in the. Fatigue and crackgrowth behavior in a titanium alloy under. Study on the stop crack growth for shaft by using drilling hole. Region iii is characterized by rapid, unstable crack growth. Specimens the material used in the current study was obtained from the research group in poland m. Hence, the data required would have to be obtained by experimental means. C, analyses of fatigue crack closure during simulated threshold testing, fatigue crack growth thresholds. Konset, at which the hcf cycles commence to contribute to the crack growth rate. Analyses of fatigue crack growth databases for use in a damage.
Fastran models accelerations and retardation and other variable amplitude loading effects in crack growth using a crack closure model. Fatigue crack growth under variableamplitude loading. 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. Fatiguecrack growth in two aluminum alloys and crackclosure. Application of a stripyield model to predict crack growth under. Fracture mechanics and fatigue crack growth analysis. As an example of the efforts to codify the knowledge in this area, this report. Fatigue and stress monitoring with magnetic sensor arrays. Fracture mechanics and fatigue crack growth analysis software. Cfdfastran is the industryleading commercial cfd software for aerodynamic and aerothermodynamic applications. Anomalous fatigue crack growth phenomena in highstrength. Newman 5 predicted the life of various notched specimens based on the small crack growth curve with the aid of fastran software 6. A fatigue crack growth analysis computer code fastran based on plasticity induced closure has been developed. I or an accelerated growth region iii paris law cannot adequately describe these regions.
Fatigue crack growth simulation of aluminium alloy under cyclic sequence effects. 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. Afgrow, fastran, and nasgrow, since they do not apply to the materials from. 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. The attractiveness of the crack closure model for engine applications is its ability to accurately predict crack growth of small flaws. Similitude and the paris crack growth law similitude and the paris crack growth law jones, r molent, l pitt, s. The objective of this paper is to apply the fastran crackclosure model 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. Stable crack growth an overview sciencedirect topics. 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. Anomalous fatigue crack growth phenomena in highstrength steel. 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. To account for plasticity, a portion of the dugdale cyclicplasticzone length. 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.
One of the earliest crack growth equations based on the stress intensity factor range of a load cycle is the pariserdogan equation. 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. The growth of fatigue cracks can result in catastrophic failure, particularly in the case of aircraft. A computer controlled decreasing stress intensity technique for low rate fatigue crack growth testing, journal of testing and evaluation, v. The critical importance of correctly characterising. 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. In this paper, a fatigue crack growth prediction code, fastran, based on newmans plasticity induced closure model, is employed to facilitate the estimation. They had conducted crackgrowth tests on mt specimens fig. The stresslevel effect on fatiguecrack growth under. Fatigue and crackgrowth behavior in a titanium alloy. This, in turn, means that similitude does not hold in region i. Damage tolerance based life assessment for helicopter. Pdf fatigue crack growth simulation of aluminium alloy. Prediction of crack growth under variableamplitude.
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. 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. Fatigue crack growth and life predictions under variable. The presence of the large plastic zone in the crack tip induces the retardation of crack. 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. Pdf fatigue based structural design optimization implementing a. Fastran ii a fatigue crack growth structural analysis program sudoc nas 1. Evaluation of the c model for addressing short fatigue crack. 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.
Fatigue and crackgrowth behavior in a titanium alloy under constantamplitude and spectrum loading. A crack growth equation is used for calculating the size of a fatigue crack growing from cyclic loads. 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. Prediction of crack growth under variableamplitude loading. Study on the stop crack growth for shaft by using drilling hole ouday kudom mohammad. Crack closure is an important factor affecting fatigue crack growth in high strength alloy materials. The coefficient p controls the curve in the low growth rate threshold region, and q controls the curve in the high growth rate region. Newman while at nasa and is an acronym derived from nasa fatigue crack growth structural analysis. 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. Fastran is a computer program for calculating the rate of fatigue crack growth by combining. Fracture mechanics and fatigue crack growth analysis software nasa jsc team royce forman dr. Subcycle fatigue crack growth formulation for constant and. A crack growth equation can be used to ensure safety, both in the design phase and during operation, by predicting the size of cracks. A simple fatigue life prediction algorithm using the.
Since the model describes the interaction of microstructure, mechanism, and. In many practical engineering situations this region may be ignored because it does not affect the total crack propagation life. The paris law is normally applicable to the crack growth in region 2. 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. Both compression precracking and loadreduction methods were used. Two types of specimens were used in the fatigue crack growth studies. 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 crack growth rate for an example material is shown below using the nasgro equation. They had conducted crack growth tests on mt specimens fig. Our crack growth modeling capabilities are among the best in the industry. Study on the stop crack growth for shaft by using drilling. Unique to fracturelab is an outstanding enhancement to the nasgro equation that we call the perturbed nasgro pn model. Fastranii a fatigue crack growth structural analysis program. 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.
Fracture mechanicsbased life prediction of a riveted lap. The final analysis addressed the role of roughness induced crack closure on fatigue crack growth in the near. 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. Similitude and the paris crack growth law, international. 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. Region ii encompasses data where the rate of crack growth changes roughly. Fatigue crack growth based on fastran model for all load cases. The regions of stable crack growth are represented by regions of damage value exceeding 0. 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. 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 crack growth rate accelerates as the maximum stress intensity factor approaches the fracture toughness of the material.
Both options were used and the article stated that no analysis option enabled to reproduce crack growth retardation. Evolution of residualstrain distribution through an overload. 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. Fastrana fatigue crack growth life prediction code based on the crackclosure concept. 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. The application of overload also enhances the stress intensity range. 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. Fastranii a fatigue crack growth structural analysis. Sambi mettu joachim beek leonard williams feng yeh southwest research institute team dr. The critical importance of correctly characterising fatigue.
Fatiguecrack growth in two aluminum alloys and crack. Oct 01, 2008 similitude and the paris crack growth law similitude and the paris crack growth law jones, r molent, l pitt, s. 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 significance of fatigue crack closure 1971 citeseerx. 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. The fastran lifeprediction code, using either the crackclosure model or lefm procedures, and the afgrow code, which uses only lefm procedures, were. It has been demonstrated from the crack growth data under both the constant amplitude loads and the spectrum loads that the small crack growth rates are higher than those for long cracks. Higher crack growth rates result in nonconservative predictions of fatigue. 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. Fastran is an advanced lifeprediction code based on the physics of the growth of micro and macrocracks in metallic materials. Craig mcclung joe cardinal source of acquisition nasa johnson space center o. Crackgrowthrate tests were conducted on compact, ct, specimens made of 7075t7351 aluminum alloy over a wide range of constantamplitude loading r pminpmax 0.
In the nasgro database 23, 24, some typical values of can be used here. Currently, for large cracks, the threshold crack growth regime is experimentally defined by using american society for testing and materials astm standard e647, which has been shown to exhibit anomalies due to load reduction lr test procedures, which prematurely slows down crack growth and produce an abnormally high threshold for. An analytical model for the identification of the threshold. It is estimated that the crack must grow several compressive plasticzone sizes before. Damage tolerance based life assessment for helicopter components. It adds flexibility to the ordinarily straight line in region ii. Advances in materials science and engineering 2017 article. Fcg life prediction codes of fastran and afgrow, which are modified using the enhanced. The fastran code is wellknown for fatigue crack growth prediction and has. Analytical models based on the plasticity induced closure concept have been very successful in. It supports most of the commonly used data formats.
A simple fatigue life prediction algorithm using the modified. Paris law also known as the pariserdogan equation is a crack growth equation that gives the rate of growth of a fatigue crack. Crack closure and slip irreversibility in the fatigue crack growth of 316l stainless steel were investigated using digital image correlation dic. Standardised test methods such as the load reduction technique in astm e647 introduce a range of problems including load history effects and remote closure.
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