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Most of the models used for taking into account the influence of mean stress on fatigue life work on the basis of the correction of stress amplitudes of particular loading cycles. This can be done directly on the amplitudes or through the modification of the reference S-N curve. The mentioned procedure is also applicable for variable amplitude loading where, after rainflow cycle counting, all loading cycles described by amplitude and mean-stress value are designated. Mean-stress correction can be difficult to apply in stochastic fatigue-damage accumulation, also called the spectral method, where the load and the stress level is defined in the frequency domain using the appropriate power spectral density (PSD) function. The PSD function by itself does not give information to the user about the level of mean stress and only provides us with some statistical information of the fluctuating part of the random loading processes. The aim of the paper is to present how we can perform the mean-stress effect correction directly on a PSD function of stress using well-known models, such as proposed by Gerber, Goodman, Soderberg, or Morrow. The correction can be performed depending on the frequency component, which is a significant advantage of the presented method. The theoretical elaborations were used to develop a computer simulation used to compare the frequency-domain with the time-domain computation path. To show the effectiveness of the presented method, fatigue life has been estimated and compared with experimental fatigue test results for S355JR steel.
This book presents selected contributions from ICMFM XX and the Polish National Conference—KKMP. The XX International Colloquium on Mechanical Fatigue of Metals (ICMFM XX) was organized on 15–17 September 2021, in the Faculty of Mechanical Engineering of the Wroclaw University of Science and Technology, in Wrocław City, Poland, in a remote form. Its aim was to facilitate and encourage the exchange of knowledge and experiences among the different communities involved in both basic and applied research in the field of fatigue of metals, looking at the problem of fatigue from a multiscale perspective, and exploring analytical and numerical simulative approaches, without losing the perspectives of the application. The Polish National Conference—KKMP 2021—was organized remotely with 50–80 prominent international participants from the fracture mechanics community.
Mean-stress effects on fatigue life are critical in isothermal and thermomechanically loaded materials and composites. Unfortunately, existing mean-stress life-prediction methods do not incorporate physical fatigue damage mechanisms. An objective is to examine the relation between mean-stress induced damage (as measured by acoustic emission) and existing life-prediction methods. Acoustic emission instrumentation has indicated that, as with static yielding, fatigue damage results from dislocation buildup and motion until dislocation saturation is reached, after which void formation and coalescence predominate. Correlation of damage processes with similar mechanisms under monotonic loading led to a reinterpretation of Goodman diagrams for 40 alloys and a modification of Morrow's formulation for life prediction under mean stresses. Further testing, using acoustic emission to monitor dislocation dynamics, can generate data for developing a more general model for fatigue under mean stress. Berkovits, Avraham Glenn Research Center NASA-TM-101311, E-4307, NAS 1.15:101311 RTOP 582-01-11...
Time-Dependent Reliability Theory and Its Applications introduces the theory of time-dependent reliability and presents methods to determine the reliability of structures over the lifespan of their services. The book contains state-of-the-art solutions to first passage probability derived from the theory of stochastic processes with different types of probability distribution functions, including Gaussian and non-Gaussian distributions and stationary and non-stationary processes. In addition, it provides various methods to determine the probability of failure over time, considering different failure modes and a methodology to predict the service life of structures. Sections also cover the applications of time-dependent reliability to prediction of service life and development of risk cost-optimized maintenance strategy for existing structures. This new book is for those who wants to know how to predict the service life of a structure (buildings, bridges, aircraft structures, etc.) and how to develop a risk-cost, optimized maintenance strategy for these structures. Presents the basic knowledge required to predict service life and develop a maintenance strategy for infrastructure Explains how to predict the remaining safe life of the infrastructure during its lifespan of operation Describes how to carry out maintenance for an infrastructure to ensure its safe and serviceable operation during the designed service life
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
Comprehensive in scope and readable, this book explores the methods used by engineers to analyze and predict the mechanical behavior of materials. Author Norman E. Dowling provides thorough coverage of materials testing and practical methods for forecasting the strength and life of mechanical parts and structural members.
This book provides background and guidance on the use of the structural hot-spot stress approach to fatigue analysis. The book also offers Design S-N curves for use with the structural hot-spot stress for a range of weld details, and presents parametric formulas for calculating stress increases due to misalignment and structural discontinuities. Highlighting the extension to structures fabricated from plates and non-tubular sections. The structural hot-spot stress approach focuses on cases of potential fatigue cracking from the weld toe and it has been in use for many years in tubular joints. Following an explanation of the structural hot-spot stress, its definition and its relevance to fatigue, the book describes methods for its determination. It considers stress determination from both finite element analysis and strain gauge measurements, and emphasizes the use of finite element stress analysis, providing guidance on the choice of element type and size for use with either solid or shell elements. Lastly, it illustrates the use of the recommendations in four case studies involving the fatigue assessment of welded structures using the structural hot-spot stress