Development Of A Physically Based Methodology For Predicting Material Variability In Fatigue Crack Initiation And Growth Response
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Development Of A Physically Based Methodology For Predicting Material Variability In Fatigue Crack Initiation And Growth Response
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Author :
language : en
Publisher:
Release Date : 2004
Development Of A Physically Based Methodology For Predicting Material Variability In Fatigue Crack Initiation And Growth Response written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2004 with categories.
The report summarizes the results of an interdisciplinary program aimed at developing a computational methodology for treat material variability in the fatigue crack initiation and growth responses of aerospace structural alloys. In this three-year program, physics-based fatigue crack initiation and growth models were developed and integrated into a probabilistic micromechanical code for treating fatigue life variability resulting from material variations. Dubbed MicroFaVa (Micromechanical Fatigue Variability), the code is based on a set of physics-based fatigue models that predict fatigue crack initiation life, fatigue crack growth life, fatigue limit, fatigue crack growth threshold, crack size at initiation, and fracture toughness. Using microstructure information as material input, the code is capable of predicting the average behavior and the confidence limits of the crack initiation and crack growth lives of structural alloys under LCF or HCF loading. The code has been integrated and utilized with DARWIN, a probabilistic design and life-prediction code developed at Southwest Research Institute (SwRI), to treat fatigue life variability in a Ti rotor due to variation in the microstructure. The probabilistic micromechanics code has been verified and validated against two benchmark problems with known solutions, as well as comparisons against an extensive database of fatigue life and fatigue crack growth data.
Extension Of A Microstructure Based Fatigue Crack Growth Model For Predicting Fatigue Life Variability
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Author : MP. Enright
language : en
Publisher:
Release Date : 2004
Extension Of A Microstructure Based Fatigue Crack Growth Model For Predicting Fatigue Life Variability written by MP. Enright and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2004 with Fatigue crack growth categories.
Most of the existing crack growth models rely on empirical constants derived from curve fits of data at specific test conditions. Although statistical information can be obtained for many of these constants, multiple experimental tests typically must be performed to represent the wide range of the response. In this paper, an alternative approach is presented that links fatigue crack growth parameters to material and microstructural size parameters via a microstructure-based fatigue crack growth (FCG) model. In addition, variation of initial crack size due to microstructural variation is modeled in terms of a crack-size-based fatigue crack initiation model. Variations of microstructural parameters are described in terms of a probabilistic framework. The probabilistic, microstructure-based, FCG approach is illustrated for a Ni-based superalloy in which the influence of changes in the main descriptors of the individual microstructural parameters on initial crack size, crack growth rate, and fatigue life is shown. Stochastic model results are compared with existing experimental data to illustrate the feasibility of the approach for predicting da/dN variability due to microstructure variations.
Metallic Materials With High Structural Efficiency
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Author : Oleg N. Senkov
language : en
Publisher: Springer Science & Business Media
Release Date : 2006-04-11
Metallic Materials With High Structural Efficiency written by Oleg N. Senkov and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006-04-11 with Technology & Engineering categories.
In the fall of 1998, Prof. Sergey Firstov invited me to the Frantcevych Institute for Problems of Materials Science (IPMS) in Kyiv, Ukraine to discuss possible collaborations in the area of advanced metals research. During this visit, a strong mutual interest was evident in a broad range of structural metals technologies, and a quick friendship was established. Countless subsequent emails and a reciprocal visit to the U. S Air Force Research Laboratory by Prof. Firstov and a team of scientists from IPMS ensued to discuss and detail a broad collaboration in the area of structural metals. Two years after the initial visit, a major investment by the U. S. Air Force Office of Scientific Research (AFOSR) was established to pursue the technologies defined by these interactions. The annual reviews of the AFOSR Ukrainian Metals Initiative were held in late May, a most beautiful time in Kyiv when the lilacs are in bright display and the air is scented with the smell of falling blossoms from the chestnut trees that line the major streets and many parks. The sunny days and mild evenings provide a welcome break from winter, and on weekend evenings festive crowds spill onto the Khreshchatyk, Kyiv’s downtown boulevard, to listen to street musicians, watch jugglers and comedians, or simply to celebrate with friends. The annual reviews featured long days of intensive discussion of technical progress, followed in the evenings by the warm hospitality of the Ukrainian hosts.
Probabilistic Aspects Of Life Prediction
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Author : W. Steven Johnson
language : en
Publisher: ASTM International
Release Date : 2004
Probabilistic Aspects Of Life Prediction written by W. Steven Johnson and has been published by ASTM International this book supported file pdf, txt, epub, kindle and other format this book has been release on 2004 with Technology & Engineering categories.
As fatigue and fracture mechanics approaches are used more often for determining the useful life and/or inspection intervals for complex structures, realization sets-in that all factors are not well known or characterized. Indeed, inherent scatter exists in initial material quality and in material performance. Furthermore, projections of component usage in determination of applied stresses are inexact at best and are subject to much discrepancy between projected and actual usage. Even the models for predicting life contain inherent sources of error based on assumptions and/or empirically fitted parameters. All of these factors need to be accounted for to determine a distribution of potential lives based on combination of the aforementioned variables, as well as other factors. The purpose of this symposium was to create a forum for assessment of the state-of-the-art in incorporating these uncertainties and inherent scatter into systematic probabilistic methods for conducting life assessment.
Methods And Models For Predicting Fatigue Crack Growth Under Random Loading
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Author :
language : en
Publisher: ASTM International
Release Date :
Methods And Models For Predicting Fatigue Crack Growth Under Random Loading written by and has been published by ASTM International this book supported file pdf, txt, epub, kindle and other format this book has been release on with categories.
Probabilistic Aspects Of Life Prediction
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Author :
language : en
Publisher: ASTM International
Release Date :
Probabilistic Aspects Of Life Prediction written by and has been published by ASTM International this book supported file pdf, txt, epub, kindle and other format this book has been release on with categories.
Microstructure Based Approach For Predicting Crack Initiation And Early Growth In Metals
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Author :
language : en
Publisher:
Release Date : 2009
Microstructure Based Approach For Predicting Crack Initiation And Early Growth In Metals written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.
Fatigue cracking in metals has been and is an area of great importance to the science and technology of structural materials for quite some time. The earliest stages of fatigue crack nucleation and growth are dominated by the microstructure and yet few models are able to predict the fatigue behavior during these stages because of a lack of microstructural physics in the models. This program has developed several new simulation tools to increase the microstructural physics available for fatigue prediction. In addition, this program has extended and developed microscale experimental methods to allow the validation of new microstructural models for deformation in metals. We have applied these developments to fatigue experiments in metals where the microstructure has been intentionally varied.
Multiscale Fatigue Crack Initiation And Propagation Of Engineering Materials Structural Integrity And Microstructural Worthiness
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Author : George C. Sih
language : en
Publisher: Springer
Release Date : 2009-08-29
Multiscale Fatigue Crack Initiation And Propagation Of Engineering Materials Structural Integrity And Microstructural Worthiness written by George C. Sih and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009-08-29 with Technology & Engineering categories.
What can be added to the fracture mechanics of metal fatigue that has not already been said since the 1900s? From the view point of the material and structure engineer, there are many aspects of failure by fatigue that are in need of attention, particularly when the size and time of the working components are changed by orders of magnitude from those considered by st traditional means. The 21 century marks an era of technology transition where structures are made larger and devices are made smaller, rendering the method of destructive testing unpractical. While health monitoring entered the field of science and engineering, the practitioners are discovering that the correlation between the signal and the location of interest depends on a priori knowledge of where failure may initiate. This information is not easy to find because the integrity of the physical system will change with time. Required is software that can self-adjust in time according to the monitored data. In this connection, effective application of health monitoring can use a predictive model of fatigue crack growth. Earlier fatigue crack growth models assumed functional dependence on the maximum stress and the size of the pre-existing crack or defect. Various possibilities were examined in the hope that the data could be grouped such that linear interpolation would apply.
Physically Based Models For Elevated Temperature Low Cycle Fatigue Crack Initiation And Growth In Rene
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Author : Kip Owen Findley
language : en
Publisher:
Release Date : 2005
Physically Based Models For Elevated Temperature Low Cycle Fatigue Crack Initiation And Growth In Rene written by Kip Owen Findley and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2005 with Elastomers categories.
The aircraft engine industry is constantly striving to increase the operating temperature and stresses in hot section engine components, a goal that can only be achieved by accurately modeling and predicting damage mechanisms of potential engine materials. The objective of this work is to develop physically-based models that are able to accurately predict the high temperature crack initiation behavior of Rene 88DT, a commonly used aircraft engine disk material, under low cycle fatigue (LCF) conditions. Two different microstructural conditions were produced by subjecting the material to two separate heat treatments; the heat treatments were selected so that grain size remains the same but the size distribution of the strengthening gamma prime precipitate is different between the two conditions. LCF experiments were performed on specimens from each condition at 650C and R = -1 under strain ranges of 0.66%, 0.75%, and 1.5%. A third microstructural condition with a similar grain size but different gamma prime size distribution was tested by another source at 650C and R = 0 under strain ranges of 0.66%, 0.79%, 0.94%, and 1.14%. The results indicate that there are two competing crack initiation mechanisms: initiation from a microstructural defect such as an inclusion and initiation from slip band cracking. A physically based model, in the form of a modified Fatemie-Socie parameter, is utilized to predict the crack initiation mechanism and approximate cycles to failure based on the microstructure of the material and applied strain. Long crack growth models are also developed to model crack growth from subsurface inclusions and surface semi-elliptical cracks. These models predict that long crack growth is a small portion of the total fatigue life in these conditions, which suggests that the majority of the fatigue life is spent initiating a dominant fatigue crack.
Fatigue Damage Crack Growth And Life Prediction
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Author : F. Ellyin
language : en
Publisher: Springer
Release Date : 2011-09-15
Fatigue Damage Crack Growth And Life Prediction written by F. Ellyin and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011-09-15 with Technology & Engineering categories.
Fatigue failure is a multi-stage process. It begins with the initiation of cracks, and with continued cyclic loading the cracks propagate, finally leading to the rupture of a component or specimen. The demarcation between the above stages is not well-defined. Depending upon the scale of interest, the variation may span three orders of magnitude. For example, to a material scientist an initiated crack may be of the order of a micron, whereas for an engineer it can be of the order of a millimetre. It is not surprising therefore to see that investigation of the fatigue process has followed different paths depending upon the scale of phenomenon under investigation. Interest in the study of fatigue failure increased with the advent of industrial ization. Because of the urgent need to design against fatigue failure, early investiga tors focused on prototype testing and proposed failure criteria similar to design formulae. Thus, a methodology developed whereby the fatigue theories were proposed based on experimental observations, albeit at times with limited scope. This type of phenomenological approach progressed rapidly during the past four decades as closed-loop testing machines became available.