A Crack-closure Model for Predicting Fatigue-crack Growth Under Aircraft Spectrum Loading PDF Download
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 68
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 68
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Book Description
Author: JC. Newman
Publisher:
ISBN:
Category : Aluminum alloy
Languages : en
Pages : 32
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Book Description
Experiments on metallic materials have shown that fatigue cracks remain closed during part of the load cycle under constant- and variable-amplitude loading. These experiments have shown that crack closure is a significant factor in causing load-interaction effects (retardation and acceleration) on crack growth rates under variable-amplitude loading.
Author:
Publisher: ASTM International
ISBN:
Category :
Languages : en
Pages : 147
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 42
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Book Description
Author: Wolf Elber
Publisher: ASTM International
ISBN: 0803109962
Category : Fracture mechanics
Languages : en
Pages : 671
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Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781722193744
Category :
Languages : en
Pages : 50
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Book Description
The objective is to study the effects of constraint on fatigue crack growth under aircraft spectrum loading. A plasticity-induced crack-closure model that accounts for constraint variations during the transition from flat-to-slant crack growth was used to correlate crack-growth rate data under constant-amplitude loading and to calculate crack growth under simulated aircraft spectrum loading. The model was applied to several thin-sheet aluminum alloy materials. Under laboratory air conditions, the transition was shown to be related to the size of the cyclic plastic zone based on the effective stress-intensity factor range for several sheet materials and thicknesses. Results from three-dimensional, elastic-plastic, finite-element analyses of a flat, straight-through crack in a thin-sheet aluminum alloy specimen showed a constraint loss similar to that assumed in the model. Using test data and the closure model, the location of the constraint-loss regime in terms of growth rate and the value of the constraint factor at these rates were determined by trial and error. The model was then used to calculate crack growth under the TWIST spectrum. The calculated results agreed reasonably well with test data. In general, the model predicted shorter crack-growth lives than tests under the TWIST spectrum by about 40 percent. For the TWIST spectrum clipped at Level 3, the calculated lives were within about 20 percent. The results demonstrated that constraint variations, especially for thin-sheet alloys, should be accounted for to predict crack growth under typical aircraft spectra. Newman, J. C., Jr. Langley Research Center RTOP 538-02-10-01...
Author: EP. Phillips
Publisher:
ISBN:
Category : Alloys
Languages : en
Pages : 19
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Book Description
The present paper is concerned with the application of a plasticity-induced crack-closure model, FASTRAN, to predict fatigue-crack growth under various load histories in a thin-sheet Ti-62222 STA titanium alloy. This alloy was a leading candidate for a metallic High-Speed-Civil-Transport (HSCT) aircraft in the United States. The crack-growth model was based on the Dugdale strip-yield model but modified to leave plastically deformed material in the wake of the advancing crack. The model includes the influence of "constraint" on the development of plasticity and closure during constant- and variable-amplitude load histories. The model was used to correlate crack-growth-rate data under constant-amplitude loading over a wide range in crack-growth rates and stress ratios at two service temperatures (room temperature and 175°C). Tests on repeated spike overloads were used to help establish the constraint variations in the model. The model was then used to predict crack growth under two simulated aircraft spectrum load histories at the two temperatures. The spectra were a commercial HSCT wing spectrum and the Mini-TWIST (transport wing spectrum). This paper will demonstrate how constraint plays a leading role in the retardation and acceleration effects that occur under variable- amplitude and spectrum loading. The model was able to calculate the effects of repeated spike overloads on crack growth at the two temperatures, generally within about ± 30 %. Also, the predicted crack-growth behavior under the HSCT spectrum agreed well with test data (within 30 %). However, the model under-predicted the fatigue-crack-growth behavior under the Mini-TWIST spectrum by about a factor-of-two. Some of the differences may be due to fretting-product-debris-induced closure or three-dimensional effects, such as free-surface closure, not included in the model. Further study is needed on life predictions under the Mini-TWIST flight spectrum.
Author: D. Aliaga
Publisher:
ISBN:
Category : Damage tolerance
Languages : en
Pages : 14
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Book Description
This paper presents a new approach for calculating the crack growth under spectrum loading in various different industrial applications. The paper includes (1) An original model based on the crack closure concept. The model combines a cycle by cycle analysis with a conservative cycle counting method similar to the "rain flow" one. A rule that fixes the crack tip opening point at every cycle to take into account the R ratio effect and the retardation effects is developed. (2) A method used for the determination of parameters. The model requires only three parameters that can be obtained with two simple crack growth tests. These two tests give both the values of parameters and the K range where the model is valid. The three parameters depend on the material and the specimen thickness. (3) Some industrial applications--the results show a good correlation between tests and calculations for several different materials. Furthermore, calculation with standard fatigue spectra (TWIST, MINITWIST, FALSTAFF) are given for a range of parameters.
Author: JC. Newman
Publisher:
ISBN:
Category : Crack propagation
Languages : en
Pages : 23
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Book Description
The present paper is concerned with the application of an analytical crack-closure model in the study of crack growth under various load histories. The model was based on a concept like the Dugdale model, but modified to leave plastically deformed material in the wake of the advancing crack tip.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 34
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Book Description
A concept based on the crack-closure phenomenon was developed to replace random load spectra with constant amplitude loading in both analysis and tests. The maximum load and the crack opening load in the constant amplitude loading are chosen to be equal to those for the spectrum, so that both crack growth mode and the crack length at failure are equivalent to those under random load spectra. The number of cycles of constant- amplitude loading is chosen so that the amount of crack growth is equal to that due to a given sequence or block of the random spectrum loading. The concept was tested experimentally after predicting the equivalent number of constant-amplitude cycles for six different random load sequences. The agreement between predictions and test results was good.
