Fatigue Life Prediction of Composites and Composite Structures

Download Fatigue Life Prediction of Composites and Composite Structures PDF Online Free

Author :
Publisher : Woodhead Publishing
ISBN 13 : 0081025769
Total Pages : 766 pages
Book Rating : 4.0/5 (81 download)

DOWNLOAD NOW!


Book Synopsis Fatigue Life Prediction of Composites and Composite Structures by : Anastasios P. Vassilopoulos

Download or read book Fatigue Life Prediction of Composites and Composite Structures written by Anastasios P. Vassilopoulos and published by Woodhead Publishing. This book was released on 2019-10-08 with total page 766 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fatigue Life Prediction of Composites and Composite Structures, Second Edition, is a comprehensive review of fatigue damage and fatigue life modeling and prediction methodologies for composites and their use in practice. In this new edition, existing chapters are fully updated, while new chapters are introduced to cover the most recent developments in the field. The use of composites is growing in structural applications in many industries, including aerospace, marine, wind turbine and civil engineering. However, there are uncertainties about their long-term performance, including performance issues relating to cyclic fatigue loading that hinder the adoption of a commonly accepted credible fatigue design methodology for the life prediction of composite engineering structures. With its distinguished editor and international team of contributors, this book is a standard reference for industry professionals and researchers alike. - Examines past, present and future trends associated with the fatigue life prediction of composite materials and structures - Assesses novel computational methods for fatigue life modeling and prediction of composite materials under constant amplitude loading - Covers a wide range of techniques for predicting fatigue, including their theoretical background and practical applications - Addresses new topics and covers contemporary research developments in the field

Fatigue Damage, Crack Growth and Life Prediction

Download Fatigue Damage, Crack Growth and Life Prediction PDF Online Free

Author :
Publisher : Springer Science & Business Media
ISBN 13 : 0412596008
Total Pages : 490 pages
Book Rating : 4.4/5 (125 download)

DOWNLOAD NOW!


Book Synopsis Fatigue Damage, Crack Growth and Life Prediction by : F. Ellyin

Download or read book Fatigue Damage, Crack Growth and Life Prediction written by F. Ellyin and published by Springer Science & Business Media. This book was released on 1996-11-30 with total page 490 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Multiaxial Fatigue

Download Multiaxial Fatigue PDF Online Free

Author :
Publisher : SAE International
ISBN 13 : 0768065100
Total Pages : 510 pages
Book Rating : 4.7/5 (68 download)

DOWNLOAD NOW!


Book Synopsis Multiaxial Fatigue by : Darrell Socie

Download or read book Multiaxial Fatigue written by Darrell Socie and published by SAE International. This book was released on 1999-12-15 with total page 510 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides practicing engineers, researchers, and students with a working knowledge of the fatigue design process and models under multiaxial states of stress and strain. Readers are introduced to the important considerations of multiaxial fatigue that differentiate it from uniaxial fatigue.

Fatigue Damage

Download Fatigue Damage PDF Online Free

Author :
Publisher : MDPI
ISBN 13 : 3038426245
Total Pages : 211 pages
Book Rating : 4.0/5 (384 download)

DOWNLOAD NOW!


Book Synopsis Fatigue Damage by : Filippo Berto

Download or read book Fatigue Damage written by Filippo Berto and published by MDPI. This book was released on 2018-07-02 with total page 211 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is a printed edition of the Special Issue "Fatigue Damage" that was published in Metals

Introduction to Unified Mechanics Theory with Applications

Download Introduction to Unified Mechanics Theory with Applications PDF Online Free

Author :
Publisher : Springer Nature
ISBN 13 : 3030577724
Total Pages : 452 pages
Book Rating : 4.0/5 (35 download)

DOWNLOAD NOW!


Book Synopsis Introduction to Unified Mechanics Theory with Applications by : Cemal Basaran

Download or read book Introduction to Unified Mechanics Theory with Applications written by Cemal Basaran and published by Springer Nature. This book was released on 2021-02-02 with total page 452 pages. Available in PDF, EPUB and Kindle. Book excerpt: This text describes the mathematical formulation and proof of the unified mechanics theory (UMT) which is based on the unification of Newton’s laws and the laws of thermodynamics. It also presents formulations and experimental verifications of the theory for thermal, mechanical, electrical, corrosion, chemical and fatigue loads, and it discusses why the original universal laws of motion proposed by Isaac Newton in 1687 are incomplete. The author provides concrete examples, such as how Newton’s second law, F = ma, gives the initial acceleration of a soccer ball kicked by a player, but does not tell us how and when the ball would come to a stop. Over the course of Introduction to Unified Mechanics Theory, Dr. Basaran illustrates that Newtonian mechanics does not account for the thermodynamic changes happening in a system over its usable lifetime. And in this context, this book explains how to design a system to perform its intended functions safely over its usable life time and predicts the expected lifetime of the system without using empirical models, a process currently done using Newtonian mechanics and empirical degradation/failure/fatigue models which are curve-fit to test data. Written as a textbook suitable for upper-level undergraduate mechanics courses, as well as first year graduate level courses, this book is the result of over 25 years of scientific activity with the contribution of dozens of scientists from around the world including USA, Russia, Ukraine, Belarus, Spain, China, India and U.K.

Fatigue Design

Download Fatigue Design PDF Online Free

Author :
Publisher : Elsevier
ISBN 13 : 1483155226
Total Pages : 617 pages
Book Rating : 4.4/5 (831 download)

DOWNLOAD NOW!


Book Synopsis Fatigue Design by : Carl C. Osgood

Download or read book Fatigue Design written by Carl C. Osgood and published by Elsevier. This book was released on 2013-10-22 with total page 617 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fatigue Design, Second Edition discusses solutions of previous problems in fatigue as controlled by their particular conditions. The book aims to demonstrate the limitations of some methods and explores the realism and validity of the resulting solutions. The text is comprised of four chapters that tackle a specific area of concern. Chapter 1 provides the introduction and covers the scope, level, and limitations of the book. Chapter 2 deals with the characteristics of design approach, and Chapter 3 talks about the prediction of fatigue life. The last chapter discusses the general factors in fatigue. The book will be of great interest to researchers and professionals concerned with fatigue analysis, such as engineers and designers.

Fatigue Life Analyses of Welded Structures

Download Fatigue Life Analyses of Welded Structures PDF Online Free

Author :
Publisher : John Wiley & Sons
ISBN 13 : 1118614704
Total Pages : 442 pages
Book Rating : 4.1/5 (186 download)

DOWNLOAD NOW!


Book Synopsis Fatigue Life Analyses of Welded Structures by : Tom Lassen

Download or read book Fatigue Life Analyses of Welded Structures written by Tom Lassen and published by John Wiley & Sons. This book was released on 2013-03-01 with total page 442 pages. Available in PDF, EPUB and Kindle. Book excerpt: Avoiding or controlling fatigue damage is a major issue in the design and inspection of welded structures subjected to dynamic loading. Life predictions are usually used for safe life analysis, i.e. for verifying that it is very unlikely that fatigue damage will occur during the target service life of a structure. Damage tolerance analysis is used for predicting the behavior of a fatigue crack and for planning of in-service scheduled inspections. It should be a high probability that any cracks appearing are detected and repaired before they become critical. In both safe life analysis and the damage tolerance analysis there may be large uncertainties involved that have to be treated in a logical and consistent manner by stochastic modeling. This book focuses on fatigue life predictions and damage tolerance analysis of welded joints and is divided into three parts. The first part outlines the common practice used for safe life and damage tolerance analysis with reference to rules and regulations. The second part emphasises stochastic modeling and decision-making under uncertainty, while the final part is devoted to recent advances within fatigue research on welded joints. Industrial examples that are included are mainly dealing with offshore steel structures. Spreadsheets which accompany the book give the reader the possibility for hands-on experience of fatigue life predictions, crack growth analysis and inspection planning. As such, these different areas will be of use to engineers and researchers.

The Proceedings of the 2018 Asia-Pacific International Symposium on Aerospace Technology (APISAT 2018)

Download The Proceedings of the 2018 Asia-Pacific International Symposium on Aerospace Technology (APISAT 2018) PDF Online Free

Author :
Publisher : Springer
ISBN 13 : 981133305X
Total Pages : 3091 pages
Book Rating : 4.8/5 (113 download)

DOWNLOAD NOW!


Book Synopsis The Proceedings of the 2018 Asia-Pacific International Symposium on Aerospace Technology (APISAT 2018) by : Xinguo Zhang

Download or read book The Proceedings of the 2018 Asia-Pacific International Symposium on Aerospace Technology (APISAT 2018) written by Xinguo Zhang and published by Springer. This book was released on 2019-06-08 with total page 3091 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is a compilation of peer-reviewed papers from the 2018 Asia-Pacific International Symposium on Aerospace Technology (APISAT 2018). The symposium is a common endeavour between the four national aerospace societies in China, Australia, Korea and Japan, namely, the Chinese Society of Aeronautics and Astronautics (CSAA), Royal Aeronautical Society Australian Division (RAeS Australian Division), the Korean Society for Aeronautical and Space Sciences (KSAS) and the Japan Society for Aeronautical and Space Sciences (JSASS). APISAT is an annual event initiated in 2009 to provide an opportunity for researchers and engineers from Asia-Pacific countries to discuss current and future advanced topics in aeronautical and space engineering.

Metal Fatigue Analysis Handbook

Download Metal Fatigue Analysis Handbook PDF Online Free

Author :
Publisher : Elsevier
ISBN 13 : 0123852048
Total Pages : 634 pages
Book Rating : 4.1/5 (238 download)

DOWNLOAD NOW!


Book Synopsis Metal Fatigue Analysis Handbook by : Yung-Li Lee

Download or read book Metal Fatigue Analysis Handbook written by Yung-Li Lee and published by Elsevier. This book was released on 2011-08-17 with total page 634 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understand why fatigue happens and how to model, simulate, design and test for it with this practical, industry-focused reference Written to bridge the technology gap between academia and industry, the Metal Fatigue Analysis Handbook presents state-of-the-art fatigue theories and technologies alongside more commonly used practices, with working examples included to provide an informative, practical, complete toolkit of fatigue analysis. Prepared by an expert team with extensive industrial, research and professorial experience, the book will help you to understand: Critical factors that cause and affect fatigue in the materials and structures relating to your work Load and stress analysis in addition to fatigue damage-the latter being the sole focus of many books on the topic How to design with fatigue in mind to meet durability requirements How to model, simulate and test with different materials in different fatigue scenarios The importance and limitations of different models for cost effective and efficient testing Whilst the book focuses on theories commonly used in the automotive industry, it is also an ideal resource for engineers and analysts in other disciplines such as aerospace engineering, civil engineering, offshore engineering, and industrial engineering. The only book on the market to address state-of-the-art technologies in load, stress and fatigue damage analyses and their application to engineering design for durability Intended to bridge the technology gap between academia and industry - written by an expert team with extensive industrial, research and professorial experience in fatigue analysis and testing An advanced mechanical engineering design handbook focused on the needs of professional engineers within automotive, aerospace and related industrial disciplines

The Mechanics of Constitutive Modeling

Download The Mechanics of Constitutive Modeling PDF Online Free

Author :
Publisher : Elsevier
ISBN 13 : 0080525695
Total Pages : 700 pages
Book Rating : 4.0/5 (85 download)

DOWNLOAD NOW!


Book Synopsis The Mechanics of Constitutive Modeling by : Niels Saabye Ottosen

Download or read book The Mechanics of Constitutive Modeling written by Niels Saabye Ottosen and published by Elsevier. This book was released on 2005-09-28 with total page 700 pages. Available in PDF, EPUB and Kindle. Book excerpt: Constitutive modelling is the mathematical description of how materials respond to various loadings. This is the most intensely researched field within solid mechanics because of its complexity and the importance of accurate constitutive models for practical engineering problems. Topics covered include: Elasticity - Plasticity theory - Creep theory - The nonlinear finite element method - Solution of nonlinear equilibrium equations - Integration of elastoplastic constitutive equations - The thermodynamic framework for constitutive modelling – Thermoplasticity - Uniqueness and discontinuous bifurcations • More comprehensive in scope than competitive titles, with detailed discussion of thermodynamics and numerical methods. • Offers appropriate strategies for numerical solution, illustrated by discussion of specific models. • Demonstrates each topic in a complete and self-contained framework, with extensive referencing.

Fatigue and Durability of Metals at High Temperatures

Download Fatigue and Durability of Metals at High Temperatures PDF Online Free

Author :
Publisher : ASM International
ISBN 13 : 1615030549
Total Pages : 277 pages
Book Rating : 4.6/5 (15 download)

DOWNLOAD NOW!


Book Synopsis Fatigue and Durability of Metals at High Temperatures by : S. S. Manson

Download or read book Fatigue and Durability of Metals at High Temperatures written by S. S. Manson and published by ASM International. This book was released on 2009 with total page 277 pages. Available in PDF, EPUB and Kindle. Book excerpt: From concept to application, this book describes the method of strain-range partitioning for analyzing time-dependent fatigue. Creep (time-dependent) deformation is first introduced for monotonic and cyclic loading. Multiple chapters then discuss strain-range partitioning in details for multi-axial loading conditions and how different loading permutations can lead to different micro-mechanistic effects. Notably, the total-strain method of strain-range partitioning (SRP) is described, which is a methodology that sees use in several industries. Examples from aerospace illustrate applications, and methods for predicting time-dependent metal fatigue are critiqued.

Towards a Unified Fatigue Life Prediction Method for Marine Structures

Download Towards a Unified Fatigue Life Prediction Method for Marine Structures PDF Online Free

Author :
Publisher : Springer
ISBN 13 : 3642418317
Total Pages : 289 pages
Book Rating : 4.6/5 (424 download)

DOWNLOAD NOW!


Book Synopsis Towards a Unified Fatigue Life Prediction Method for Marine Structures by : Weicheng Cui

Download or read book Towards a Unified Fatigue Life Prediction Method for Marine Structures written by Weicheng Cui and published by Springer. This book was released on 2014-11-04 with total page 289 pages. Available in PDF, EPUB and Kindle. Book excerpt: In order to apply the damage tolerance design philosophy to design marine structures, accurate prediction of fatigue crack growth under service conditions is required. Now, more and more people have realized that only a fatigue life prediction method based on fatigue crack propagation (FCP) theory has the potential to explain various fatigue phenomena observed. In this book, the issues leading towards the development of a unified fatigue life prediction (UFLP) method based on FCP theory are addressed. Based on the philosophy of the UFLP method, the current inconsistency between fatigue design and inspection of marine structures could be resolved. This book presents the state-of-the-art and recent advances, including those by the authors, in fatigue studies. It is designed to lead the future directions and to provide a useful tool in many practical applications. It is intended to address to engineers, naval architects, research staff, professionals and graduates engaged in fatigue prevention design and survey of marine structures, in fatigue studies of materials and structures, in experimental laboratory research, in planning the repair and maintenance of existing structures, and in rule development. The book is also an effective educational aid in naval architecture, marine, civil and mechanical engineering. Prof. Weicheng Cui is the Dean of Hadal Science and Technology Research Center of Shanghai Ocean University, China. Dr. Xiaoping Huang is an associate professor of School of Naval Architecture, Ocean and Civil Engineering of Shanghai Jiao Tong University, China. Dr. Fang Wang is an associate professor of Hadal Science and Technology Research Center of Shanghai Ocean University, China.

Fatigue Testing and Analysis

Download Fatigue Testing and Analysis PDF Online Free

Author :
Publisher : Elsevier
ISBN 13 : 0080477690
Total Pages : 417 pages
Book Rating : 4.0/5 (84 download)

DOWNLOAD NOW!


Book Synopsis Fatigue Testing and Analysis by : Yung-Li Lee

Download or read book Fatigue Testing and Analysis written by Yung-Li Lee and published by Elsevier. This book was released on 2011-04-18 with total page 417 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fatigue Testing and Analysis: Theory and Practice presents the latest, proven techniques for fatigue data acquisition, data analysis, and test planning and practice. More specifically, it covers the most comprehensive methods to capture the component load, to characterize the scatter of product fatigue resistance and loading, to perform the fatigue damage assessment of a product, and to develop an accelerated life test plan for reliability target demonstration. This book is most useful for test and design engineers in the ground vehicle industry. Fatigue Testing and Analysis introduces the methods to account for variability of loads and statistical fatigue properties that are useful for further probabilistic fatigue analysis. The text incorporates and demonstrates approaches that account for randomness of loading and materials, and covers the applications and demonstrations of both linear and double-linear damage rules. The reader will benefit from summaries of load transducer designs and data acquisition techniques, applications of both linear and non-linear damage rules and methods, and techniques to determine the statistical fatigue properties for the nominal stress-life and the local strain-life methods. - Covers the useful techniques for component load measurement and data acquisition, fatigue properties determination, fatigue analysis, and accelerated life test criteria development, and, most importantly, test plans for reliability demonstrations - Written from a practical point of view, based on the authors' industrial and academic experience in automotive engineering design - Extensive practical examples are used to illustrate the main concepts in all chapters

Fatigue Damage, Crack Growth and Life Prediction

Download Fatigue Damage, Crack Growth and Life Prediction PDF Online Free

Author :
Publisher : Springer Science & Business Media
ISBN 13 : 9400915098
Total Pages : 484 pages
Book Rating : 4.4/5 (9 download)

DOWNLOAD NOW!


Book Synopsis Fatigue Damage, Crack Growth and Life Prediction by : F. Ellyin

Download or read book Fatigue Damage, Crack Growth and Life Prediction written by F. Ellyin and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 484 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Fatigue Design of Components

Download Fatigue Design of Components PDF Online Free

Author :
Publisher : Elsevier
ISBN 13 : 0080531601
Total Pages : 239 pages
Book Rating : 4.0/5 (85 download)

DOWNLOAD NOW!


Book Synopsis Fatigue Design of Components by : G. Marquis

Download or read book Fatigue Design of Components written by G. Marquis and published by Elsevier. This book was released on 1997-12-10 with total page 239 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume contains a selection of papers presented at Fatigue Design 95 held in Helsinki, Finland from 5-8 September 1995. The papers have been peer reviewed and present practical aspects for the design of components and structures to avoid fatigue failure. Topics covered include: fatigue design experiences, ground vehicle components, component reliability, multiaxial fatigue, notch analysis, service loading, welded structures, probabilistics aspects in fatigue, fatigue design optimization.

Advances in Wind Turbine Blade Design and Materials

Download Advances in Wind Turbine Blade Design and Materials PDF Online Free

Author :
Publisher : Elsevier
ISBN 13 : 0857097288
Total Pages : 485 pages
Book Rating : 4.8/5 (57 download)

DOWNLOAD NOW!


Book Synopsis Advances in Wind Turbine Blade Design and Materials by : Povl Brondsted

Download or read book Advances in Wind Turbine Blade Design and Materials written by Povl Brondsted and published by Elsevier. This book was released on 2013-10-31 with total page 485 pages. Available in PDF, EPUB and Kindle. Book excerpt: Wind energy is gaining critical ground in the area of renewable energy, with wind energy being predicted to provide up to 8% of the world's consumption of electricity by 2021. Advances in wind turbine blade design and materials reviews the design and functionality of wind turbine rotor blades as well as the requirements and challenges for composite materials used in both current and future designs of wind turbine blades.Part one outlines the challenges and developments in wind turbine blade design, including aerodynamic and aeroelastic design features, fatigue loads on wind turbine blades, and characteristics of wind turbine blade airfoils. Part two discusses the fatigue behavior of composite wind turbine blades, including the micromechanical modelling and fatigue life prediction of wind turbine blade composite materials, and the effects of resin and reinforcement variations on the fatigue resistance of wind turbine blades. The final part of the book describes advances in wind turbine blade materials, development and testing, including biobased composites, surface protection and coatings, structural performance testing and the design, manufacture and testing of small wind turbine blades.Advances in wind turbine blade design and materials offers a comprehensive review of the recent advances and challenges encountered in wind turbine blade materials and design, and will provide an invaluable reference for researchers and innovators in the field of wind energy production, including materials scientists and engineers, wind turbine blade manufacturers and maintenance technicians, scientists, researchers and academics. - Reviews the design and functionality of wind turbine rotor blades - Examines the requirements and challenges for composite materials used in both current and future designs of wind turbine blades - Provides an invaluable reference for researchers and innovators in the field of wind energy production

Failure Mechanisms of Advanced Welding Processes

Download Failure Mechanisms of Advanced Welding Processes PDF Online Free

Author :
Publisher : Elsevier
ISBN 13 : 1845699769
Total Pages : 331 pages
Book Rating : 4.8/5 (456 download)

DOWNLOAD NOW!


Book Synopsis Failure Mechanisms of Advanced Welding Processes by : X Sun

Download or read book Failure Mechanisms of Advanced Welding Processes written by X Sun and published by Elsevier. This book was released on 2010-07-15 with total page 331 pages. Available in PDF, EPUB and Kindle. Book excerpt: Many new, or relatively new, welding processes such as friction stir welding, resistance spot welding and laser welding are being increasingly adopted to replace or improve on traditional welding techniques. Before advanced welding techniques are employed, their potential failure mechanisms should be well understood and their suitability for welding particular metals and alloys in different situations should be assessed. Failure mechanisms of advanced welding processes provides a critical analysis of advanced welding techniques and their potential failure mechanisms.The book contains chapters on the following topics: Mechanics modelling of spot welds under general loading conditions and applications to fatigue life predictions, Resistance spot weld failure mode and weld performance for aluminium alloys, dual phase steels and TRIP steels, Fatigue behaviour of spot welded joints in steel sheets, Non-destructive evaluation of spot weld quality, Solid state joining - fundamentals of friction stir welding, Failure mechanisms in friction stir welds, Microstructure characteristics and mechanical properties of laser weld bonding of magnesium alloy to aluminium alloy, Fatigue in laser welds, Weld metal ductility and its influence on formability of tailor welded blanks, Joining of lightweight materials using reactive nanofoils, and Fatigue life prediction and improvements for MIG welded advanced high strength steel weldments.With its distinguished editor and international team of contributors, Failure mechanisms of advanced welding processes is a standard reference text for anyone working in welding and the automotive, shipbuilding, oil and gas and other metal fabrication industries who use modern and advanced welding processes. - Provides a critical analysis of advanced welding techniques and their potential failure mechanisms - Experts in the field survey a range of welding processes and examine reactions under various types of loading conditions - Examines the current state of fatigue life prediction of welded materials and structures in the context of spot welded joints and non-destructive evaluation of quality