The Effects of Truncation and Marker Loads on Spectrum Fatigue Crack Growth PDF Download
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 45
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Book Description
The US Air Force is operating a large fleet of aging aircraft. Some examples of problems that aging aircraft can encounter are fatigue and corrosion. Throughout the Air Force and industry, many research efforts are being conducted to deal with the aging aircraft problems. Many of these efforts require a significant amount of fatigue testing, both constant amplitude testing, which can be relatively fast, and spectrum fatigue testing, which can take a significant amount of testing and inspection time. One of the main objectives of this research effort was to determine whether spectrum truncation has a noticeable effect on crack growth rates. In order to save valuable testing time, the duration of spectrum fatigue tests can be shortened by truncating the spectrum. When truncating a spectrum, small fatigue cycles that are not expected to contribute to the overall crack growth life of the specimen or structure, can be removed from the spectrum. By doing so, a significant amount of test time can be saved. It is very important though that by excluding these small fatigue cycles from the spectrum, the overall crack growth behavior will not change. Another important objective of this effort was to verify that the insertion of marker loads into a fatigue spectrum has no or a negligible effect on the crack growth rate when compared to a fatigue test without the marker loads. When running a fatigue test to determine crack growth rates, regular inspection is necessary to check the crack size versus cycle count, which can be very time consuming and might prevent running tests overnight. When inserting marker loads in a fatigue test, the test can be.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 45
Get Book Here
Book Description
The US Air Force is operating a large fleet of aging aircraft. Some examples of problems that aging aircraft can encounter are fatigue and corrosion. Throughout the Air Force and industry, many research efforts are being conducted to deal with the aging aircraft problems. Many of these efforts require a significant amount of fatigue testing, both constant amplitude testing, which can be relatively fast, and spectrum fatigue testing, which can take a significant amount of testing and inspection time. One of the main objectives of this research effort was to determine whether spectrum truncation has a noticeable effect on crack growth rates. In order to save valuable testing time, the duration of spectrum fatigue tests can be shortened by truncating the spectrum. When truncating a spectrum, small fatigue cycles that are not expected to contribute to the overall crack growth life of the specimen or structure, can be removed from the spectrum. By doing so, a significant amount of test time can be saved. It is very important though that by excluding these small fatigue cycles from the spectrum, the overall crack growth behavior will not change. Another important objective of this effort was to verify that the insertion of marker loads into a fatigue spectrum has no or a negligible effect on the crack growth rate when compared to a fatigue test without the marker loads. When running a fatigue test to determine crack growth rates, regular inspection is necessary to check the crack size versus cycle count, which can be very time consuming and might prevent running tests overnight. When inserting marker loads in a fatigue test, the test can be.
Author: Ralph Ivan Stephens
Publisher: ASTM International
ISBN:
Category : Alloys
Languages : en
Pages : 345
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Book Description
Author: Jaap Schijve
Publisher: Springer Science & Business Media
ISBN: 0306483963
Category : Science
Languages : en
Pages : 528
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Book Description
This book is primarily a textbook. It is written for engineers, students and teachers, and it should also be useful for people working on various topics related to fatigue of structures and materials. The book can be used for graduate and undergraduate courses and for short courses for people already working in the industry, laboratories, or research institutes. Furthermore, the book offers various comments which can be useful to research-workers in order to consider the practical relevance of laboratory investigations and to plan future research. An important theme of the book is the understanding of what happens in the material of a structure in service if the structure is subjected to a spectrum of cyclic loads. Knowledge of the fatigue mechanism in the material and how it can be affected by a large variety of practical conditions is essential for dealing with fatigue problems. The designer of a dynamically loaded structure must “design against fatigue”. This includes not only the overall concept of the structure with related safety and economic aspects, but also questions on detail design, joints, production and material surface quality. At the same time, the designer must try to predict the fatigue performance of the structure. This requires a knowledge of the various influencing factors, also because predictions on fatigue have their limitations and shortcomings. Similar considerations arise if fatigue problems occur after a long period in service when decisions must be made on remedial actions.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 1346
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Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 544
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Book Description
Author: Björn Palmberg
Publisher:
ISBN:
Category :
Languages : en
Pages : 58
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Book Description
Author:
Publisher:
ISBN:
Category : Mechanics, Applied
Languages : en
Pages : 1072
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Book Description
Author: R. P. Wei
Publisher:
ISBN:
Category :
Languages : en
Pages : 25
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Book Description
The importance of delay (or, retardation in the rate of fatigue crack growth) produced by load interactions in variable-amplitude loading on the accurate prediction of fatigue lives of aircraft and other engineering structures has been recognized for some time and has begun to receive greater attention in recent years. Recent investigations showed that the effects of delay can be quite large, and that these effects need to be taken into account in developing improved fatigue analysis procedures for aircraft and other engineering structures. A number of models (based on the concepts of crack closure, residual stress intensity factor, etc.) have been proposed to account for the effects of delay. These models, while successfully predicting trends in the rate of fatigue crack growth for randomized load spectra, appear to break down for ordered spectra. Several basic problems contributed to the lack of complete success, and needs to be resolved in the development of improved models for predicting load interaction effects (chiefly delay) on fatigue crack growth.
Author: Petit (M.)
Publisher:
ISBN:
Category : Closed loop control
Languages : en
Pages : 19
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Book Description
An automated data acquisition system has been developed that can be used as an independent watchdog to monitor the loads applied during a fatigue test. An algorithm to perform peak-picking based on a quadratic least squares approach has been shown to yield peak/valley magnitudes to within 1%. A damage parameter is described that assesses the impact of loading error on the resulting fatigue crack growth behavior. The peak-picking system has been validated for both constant amplitude as well as variable amplitude, spectrum loading. Overall test system performance is shown to vary significantly during the spectrum testing for the three different types of controllers: an analog controller with a computer control fatigue test system and two different types of digital controllers. This testing and analysis clearly demonstrates the importance of quantifying range error (this is not the same as end-level error), number of occurrences for each range, and overall damage content. Finally, the importance of standardizing performance metrics for spectrum testing methods is presented along with some potential recommendations for what these metrics could be and how they might be developed.
