The Influence of Porosity and Its Modeling on Fatigue Behavior of High Pressure Die Cast Aluminum Including the Effects of Mean Stress, Stress Gradient and Specimen Size PDF Download
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Author: Bohua Zhang
Publisher:
ISBN:
Category : Aluminum
Languages : en
Pages : 135
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Book Description
High pressure die casting (HPDC) aluminum has been widely employed in many industries for its superb cast ability, productivity, flexibility and especially the high strength to weight ratio. The use of aluminum as a light metal reduces weight and the employ of HPDC aluminum enables mass production of thin-walled, complex, intricate components with near net shape. However, one disadvantage of this technology is the inevitable presence of various defects, particularly porosity. The objective of this study was to evaluate and characterize the fatigue behavior of HPDC aluminum with effects of defects. Porosity was the main defect studied. Tensile tests and load-controlled fatigue tests were conducted to generate data for this investigation. The material, A380 HPDC aluminum, was provided by Eaton Corporation, as the sponsor of this study. Tensile tests were performed to obtain basic mechanical properties of the material. Fatigue tests were performed for different conditions to characterize fatigue behavior and evaluate the effects of porosity level, specimen size, mean stress and stress gradient. Two different size specimens were tested under the same condition to evaluate the influence of specimen size on fatigue behavior, and specimens were divided into four levels according to the amount of porosity to study the effect of porosity level on fatigue behavior. As for mean stress, R = 0 tests were conducted to compare to the results of R = -1 tests and rotating bending tests were added for stress gradient evaluation. Stress-life curves were employed for generating relation between stress amplitude and fatigue life, while the significant scatter in the experimental data necessitated a statistical analysis. The fracture surfaces of failed specimens were also examined for crack initiation location and size of defects present.
Author: Bohua Zhang
Publisher:
ISBN:
Category : Aluminum
Languages : en
Pages : 135
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Book Description
High pressure die casting (HPDC) aluminum has been widely employed in many industries for its superb cast ability, productivity, flexibility and especially the high strength to weight ratio. The use of aluminum as a light metal reduces weight and the employ of HPDC aluminum enables mass production of thin-walled, complex, intricate components with near net shape. However, one disadvantage of this technology is the inevitable presence of various defects, particularly porosity. The objective of this study was to evaluate and characterize the fatigue behavior of HPDC aluminum with effects of defects. Porosity was the main defect studied. Tensile tests and load-controlled fatigue tests were conducted to generate data for this investigation. The material, A380 HPDC aluminum, was provided by Eaton Corporation, as the sponsor of this study. Tensile tests were performed to obtain basic mechanical properties of the material. Fatigue tests were performed for different conditions to characterize fatigue behavior and evaluate the effects of porosity level, specimen size, mean stress and stress gradient. Two different size specimens were tested under the same condition to evaluate the influence of specimen size on fatigue behavior, and specimens were divided into four levels according to the amount of porosity to study the effect of porosity level on fatigue behavior. As for mean stress, R = 0 tests were conducted to compare to the results of R = -1 tests and rotating bending tests were added for stress gradient evaluation. Stress-life curves were employed for generating relation between stress amplitude and fatigue life, while the significant scatter in the experimental data necessitated a statistical analysis. The fracture surfaces of failed specimens were also examined for crack initiation location and size of defects present.
Author: C. Oberwinkler
Publisher:
ISBN:
Category : El-Haddad
Languages : en
Pages : 16
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Book Description
Aluminium high pressure die casting is used to reduce costs and weight of various components in the automotive industry. The main problem of components made by pressure die casting is connected with inherent flaws (porosity, oxide skins, etc.), which can hardly be avoided. Today the fatigue calculation of aluminium high pressure die cast parts is usually performed using two S/N curves--one account for the flawed basic material and one for the pore-free surface layer. This does not provide an accurate estimate for the computation of the lifetime or safety against failure of the component. In a cast component the number and size of pores increases towards the center. As a consequence the fatigue strength decreases. This inhomogeneous distribution throughout the component has to be taken into account for a realistic estimation of the fatigue strength. To do so, two models are required--one to compute the pore size distribution in the component [Oberwinkler, C., Leitner, H., and Eichlseder, W. "Improvement of an Existing Model to Estimate the Pore Distribution for A Fatigue Proof Design of Al HPDC Components," TMS 2009, Shape Casting: 3rd Int. Symposium, 2009] and a material model [Oberwinkler, C., Leitner, H., and Eichlseder, W. "Computation of Fatigue Safety Factors for High-Pressure Die Cast (HPDC) Aluminium Components Taking into Account the Pore Size Distribution," SAE World Congress 2009], which describes the influence of the defect size on the fatigue strength. This paper focuses on the definition of the correlation between the fatigue strength and the pore size. The lifetime of a component is defined by the crack growth if the crack initiation period can be neglected. Casting defects usually show high stress concentration factors due to their irregular shapes where cracks initiate. In this case the defect size is a part of the total crack length. Pores can be considered as physically short cracks because of their size of approximately 10-500 μm. The El-Haddad equation [El Haddad, M. H., Smith, K. N., and Topper, T. H., "Fatigue Crack Propagation of Short Cracks," ASME Transactions, Volume 101, 1979, pp. 42-46] has been used to describe the influence of the defect size on the fatigue strength. Short crack experiments have been performed to show that due to the shorter cracks the threshold stress intensity factor decreases below the threshold stress intensity factor of long cracks.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 1146
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Book Description
Author: Yukitaka Murakami
Publisher: Elsevier
ISBN: 0080496563
Category : Technology & Engineering
Languages : en
Pages : 384
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Book Description
Metal fatigue is an essential consideration for engineers and researchers who are looking at factors that cause metals to fail through stress, corrosion, etc. This is an English translation of a book originally published in Japan in 1993, with an additional two chapters on the fatigue failure of steels and the effect of surface roughness on fatigue strength. The methodology is based on important and reliable results and may be usefully applied to other fatigue problems not directly treated in this book.
Author: D. N. Williams
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages : 22
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Book Description
The effects of environment on fatigue behavior are quite intimately related to such test variables as stress intensity, cyclic frequency, and temperature. The effect of these variables has been shown to be quite complex. However, a consistent pattern of behavior is beginning to emerge which, it is hoped, will lead to a considerably changed understanding of the corrosion-fatigue process. It is considered probable that an increased understanding of the corrosion-fatigue process will also contribute measureably to an improved understanding of general fatigue processes. Material variables such as composition, directionality of properties, and microstructure, have important effects on corrosion-fatigue behavior of aluminum alloys. However, it appears that these variables, at least in gaseous environments, may be important largely because of their effects on the mechanical behavior of aluminum alloys. On the other hand, studies in seawater suggest that these variables become increasingly important as the corrosive nature of the environment increases. This memorandum discusses in detail the effects of both test variables and material variables on corrosion fatigue. In addition, current theories of corrosion-fatigue mechanisms are outlined, and several methods of preventing corrosion fatigue are suggested. (Author).
Author: F. V. Lawrence
Publisher:
ISBN:
Category :
Languages : en
Pages : 11
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Book Description
It appears that the characteristics of the toe of the weld controls the fatigue crack initiation and propagation phenomena in the as welded specimens; and the size, and distribution and possibly location of the largest pore(s) control the fatigue crack initiation and propagation phenomena in weld reinforcement removed specimens.
Author: Kyle Michael Sigl
Publisher:
ISBN:
Category :
Languages : en
Pages : 216
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Book Description
Author: W. S. Hyler
Publisher:
ISBN:
Category : Aluminum powder
Languages : en
Pages : 52
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Book Description
Author: Phalgun Nelaturu
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages : 87
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Book Description
Metal fatigue is a recurring problem for metallurgists and materials engineers, especially in structural applications. It has been responsible for many disastrous accidents and tragedies in history. Understanding the micro-mechanisms during cyclic deformation and combating fatigue failure has remained a grand challenge. Environmental effects, like temperature or a corrosive medium, further worsen and complicate the problem. Ultimate design against fatigue must come from a materials perspective with a fundamental understanding of the interaction of microstructural features with dislocations, under the influence of stress, temperature, and other factors. This research endeavors to contribute to the current understanding of the fatigue failure mechanisms. Cast aluminum alloys are susceptible to fatigue failure due to the presence of defects in the microstructure like casting porosities, non-metallic inclusions, non-uniform distribution of secondary phases, etc. Friction stir processing (FSP), an emerging solid state processing technique, is an effective tool to refine and homogenize the cast microstructure of an alloy. In this work, the effect of FSP on the microstructure of an A356 cast aluminum alloy, and the resulting effect on its tensile and fatigue behavior have been studied. The main focus is on crack initiation and propagation mechanisms, and how stage I and stage II cracks interact with the different microstructural features. Three unique microstructural conditions have been tested for fatigue performance at room temperature, 150 °C and 200 °C. Detailed fractography has been performed using optical microscopy, scanning electron microscopy (SEM) and electron back scattered diffraction (EBSD). These tools have also been utilized to characterize microstructural aspects like grain size, eutectic silicon particle size and distribution. Cyclic deformation at low temperatures is very sensitive to the microstructural distribution in this alloy. The findings from the room temperature fatigue tests highlight the important role played by persistent slip bands (PSBs) in fatigue crack initiation. At room temperature, cracks initiate along PSBs in the absence of other defects/stress risers, and grow transgranularly. Their propagation is retarded when they encounter grain boundaries. Another major finding is the complete transition of the mode of fatigue cracking from transgranular to intergranular, at 200 °C. This occurs when PSBs form in adjacent grains and impinge on grain boundaries, raising the stress concentration at these locations. This initiates cracks along the grain boundaries. At these temperatures, cyclic deformation is no longer microstructure- dependent. Grain boundaries don't impede the progress of cracks, instead aid in their propagation. This work has extended the current understanding of fatigue cracking mechanisms in A356 Al alloys to elevated temperatures.
Author: Theodore Nicholas
Publisher: Elsevier
ISBN: 0080458874
Category : Science
Languages : en
Pages : 657
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Book Description
Dr Theodore Nicholas ran the High Cycle Fatigue Program for the US Air Force between 1995 and 2003 at Wright-Patterson Air Force Base, and is one of the world's leading authorities on the subject, having authored over 250 papers in leading archival journals and books. Bringing his plethora of expertise to this book, Dr Nicholas discusses the subject of high cycle fatigue (HCF) from an engineering viewpoint in response to a series of HCF failures in the USAF and the concurrent realization that HCF failures in general were taking place universally in both civilian and military engines. Topic covered include: - Constant life diagrams - Fatigue limits under combined LCF and HCF - Notch fatigue under HCF conditions - Foreign object damage (FOD) - Brings years of the Author's US Air Force experience in high cycle fatigue together in one text - Discusses HCF in the context of recent international military and civilian engine failures
