Statistical Inference of Defect Population for the Study and Simulation of the Low-Cycle Fatigue of a Cast Aluminium Alloy PDF Download
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Author: Pablo Wilson
Publisher:
ISBN:
Category :
Languages : fr
Pages : 0
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Book Description
Dans une optique d'allègement, les alliages d'aluminium de fonderie représentent une excellente solution technique. Ainsi, pour les culasses automobiles, les alliages d'aluminium Al-Si-Cu (Aluminium-Silicium-Cuivre) sont souvent choisis pour leurs performances mécaniques ainsi que leur bonne coulabilité. L'objectif de cette étude est d'améliorer la compréhension des mécanismes en fatigue oligocyclique pour définir un critère de fatigue adapté. Cet objectif est réalisé en combinant des essais (en fatigue oligocyclique à température ambiante et élevée), de nombreuses observations (microscopie à balayage électronique, microtomographie 3D rayons-X de laboratoire, suivi de fissure) et des simulations (génération de population de défauts et calculs éléments finis). À l'aide d'outils spécialement développés, la population de défauts (défauts de fonderie) est analysée en détails : la taille de défaut est modélisée par une distribution de Pareto généralisée et leurs positions par un processus ponctuel de type agrégé (démontrant que les défauts ne sont pas spatialement distribués de manière totalement aléatoire). Les processus ponctuels marqués permettent de montrer que tailles et positions de défauts ne sont pas corrélées. En utilisant ces informations statistiques, il est démontré que seuls les défauts proches de la surface sont critiques pour la fatigue oligocyclique. Un critère de fatigue basé sur l'énergie de déformation est utilisé pour prévoir la durée de vie en fatigue. Par la suite, un modèle de propagation de fissure permet de prendre en compte la taille de défaut dans la prévision de la durée de vie. Combiné à la statistique des défauts, ce modèle permet d'estimer la dispersion des essais. En dernier lieu, des essais et des simulations sur éprouvettes entaillées montrent que l'étude de la population de défauts est d'autant plus critique que le volume fortement sollicité mécaniquement devient plus faible.
Author: Pablo Wilson
Publisher:
ISBN:
Category :
Languages : fr
Pages : 0
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Book Description
Dans une optique d'allègement, les alliages d'aluminium de fonderie représentent une excellente solution technique. Ainsi, pour les culasses automobiles, les alliages d'aluminium Al-Si-Cu (Aluminium-Silicium-Cuivre) sont souvent choisis pour leurs performances mécaniques ainsi que leur bonne coulabilité. L'objectif de cette étude est d'améliorer la compréhension des mécanismes en fatigue oligocyclique pour définir un critère de fatigue adapté. Cet objectif est réalisé en combinant des essais (en fatigue oligocyclique à température ambiante et élevée), de nombreuses observations (microscopie à balayage électronique, microtomographie 3D rayons-X de laboratoire, suivi de fissure) et des simulations (génération de population de défauts et calculs éléments finis). À l'aide d'outils spécialement développés, la population de défauts (défauts de fonderie) est analysée en détails : la taille de défaut est modélisée par une distribution de Pareto généralisée et leurs positions par un processus ponctuel de type agrégé (démontrant que les défauts ne sont pas spatialement distribués de manière totalement aléatoire). Les processus ponctuels marqués permettent de montrer que tailles et positions de défauts ne sont pas corrélées. En utilisant ces informations statistiques, il est démontré que seuls les défauts proches de la surface sont critiques pour la fatigue oligocyclique. Un critère de fatigue basé sur l'énergie de déformation est utilisé pour prévoir la durée de vie en fatigue. Par la suite, un modèle de propagation de fissure permet de prendre en compte la taille de défaut dans la prévision de la durée de vie. Combiné à la statistique des défauts, ce modèle permet d'estimer la dispersion des essais. En dernier lieu, des essais et des simulations sur éprouvettes entaillées montrent que l'étude de la population de défauts est d'autant plus critique que le volume fortement sollicité mécaniquement devient plus faible.
Author: R. E. Little
Publisher: ASTM International
ISBN: 9780803107168
Category : Technology & Engineering
Languages : en
Pages : 156
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Book Description
It is commonly assumed in analysing fatigue data that there is a definite functional relationship between life in number of cycles and stress level. However, as has been pointed out several times (1, 2), an examination of the data shows considerable scatter. Even with carefully prepared smooth specimens, all from the same heat of steel, treated in the same manner and tested in the same laboratory, a range of 2 to 1 in number of cycles for failure at the same stress level is normal (1) and a range of 10 to 1 is not unusual (2). If the specimens are tested by different laboratories, slightly varying techniques will introduce further scatter (3).
Author: Hüseyin Özdeș
Publisher:
ISBN:
Category : Aluminum alloys -- Fatigue -- Forecasting
Languages : en
Pages :
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Book Description
Cast aluminum alloys are common in automotive and aerospace applications due to their high strength-to-density ratio. Fracture data for cast aluminum alloys, such as fatigue life, tensile strength and elongation, are heavily affected by the structural defects, such as pores and bifilms. There have been numerous studies in which either fatigue performance or tensile deformation were characterized and linked to casting defects. However, a comprehensive study that correlates tensile and fatigue properties has not been reported. The present study is motivated to fill this gap. The main objective of the investigation is to analyze the link between tensile and fatigue performance of commonly used cast aluminum alloys, and determine whether fatigue performance of cast aluminum alloys can be predicted. To accomplish this task, four research questions were developed: (i) how well do equations developed to account for mean stress effects perform in cast aluminum alloys, especially in datasets with various levels of structural quality, (ii) is the strong correlation between fatigue life and structural quality index obtained from tensile data reported for A206 alloy castings applicable to other aerospace and automotive casting alloys, (iii) how do methods to estimate high cycle fatigue from tensile data perform with aluminum castings, and (iv) can the axial fatigue performance of an A356-T6 casting be predicted from rotating beam fatigue data. Among the three mean stress correction models analyzed by using seven datasets from the literature, the one developed by Walker with an adjustable exponent has provided the best fit. It has been hypothesized that the adjustable Walker parameter is related to the structural quality index, QT, estimated from tensile data. Results have shown that there is indeed a strong correlation between QT and the Walker parameter. Moreover the parameters of the xvi Weibull distribution estimated from corrected data have been found to be strongly influenced by the mean stress correction method used. Tensile and fatigue life data for 319, D357 and B201 aluminum alloy castings reported in the literature have been reanalyzed by using a maximum likelihood method to estimate Basquin parameters in datasets with run-outs, Weibull statistics for censored data and mean stress correction. After converting tensile data to QT, a distinct relationship has been observed between the expected fatigue life and mean quality index for all alloys. Moreover, probability of survival in fatigue life has been found to be directly linked to the proportions of the quality index distributions in two different regions, providing further evidence about the strong relationship between elongation, i.e., structural quality, and fatigue performance [1]. Specimen geometry has been found to make the largest difference whereas the two aerospace alloys, B201 and D357, with distinctly different microstructures, have followed the same relationship, reinforcing the findings in the literature that fatigue life in aluminum castings is mainly determined by the size distribution and number density of structural defects. Six methods to predict fatigue life from tensile data have been compared by using data from the literature as well as the experimental A356 data developed in this study. Results have shown that none of the six methods provide reliable results. The consistently poor performance of the methods developed for steels and wrought alloys can be attributed to the major structural defects, namely bifilms, in aluminum castings. A new method to estimate the S-N curve from tensile data have been developed by using data for seventy-one S-N curves have been collected and Basquin parameters have been determined. Analysis showed that there is a strong relationship between QT and the Basquin exponent. xvii The Basquin parameters estimated by using the empirical relationships developed in the present study have provided better fits to the same datasets tested for the six methods. Hence the model developed in this study is proposed as the most reliable method to estimate high cycle fatigue properties. Finally, three methods to convert rotating bending fatigue test results to uniaxial fatigue data have been investigated by using the data developed in this study. Results have indicated that the method developed by Esin, in which both the fatigue life and alternating stress are corrected, provide the best estimate. Analyses of fracture surfaces of broken specimens via scanning electron microscopy have shown that tensile, axial fatigue and rotating beam fatigue properties are all strongly influenced by the same structural defects, confirming the validity of the approach taken in this study.
Author: Claude Amzallag
Publisher: ASTM International
ISBN:
Category :
Languages : en
Pages : 658
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Author: Eugene C. Naumann
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages : 32
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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: Jamal Ibrahim Awad
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages : 148
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Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 1368
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Author:
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ISBN:
Category : Metallurgy
Languages : en
Pages : 1602
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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.
