Search Results for fracture mechanic crack growth

The separation of the fatigue process into crack initiation and propagation phases has been an important and useful advance in engineering. The combined approach of strain-control testing and the development fracture mechanics of fatigue crack growth rates is a key advance that allows better understanding and simulation of both crack nucleation and the subsequent crack growth mechanisms. This article reviews three basic types of fatigue properties: stress-life, strain life, and fracture mechanic crack growth.

This article offers an overview of fatigue fundamentals, common fatigue terminology, and examples of damage morphology. It presents a summary of relevant engineering mechanics, cyclic plasticity principles, and perspective on the modern design by analysis (DBA) techniques. The article reviews fatigue assessment methods incorporated in international design and post construction codes and standards, with special emphasis on evaluating welds. Specifically, the stress-life approach, the strain-life approach, and the fracture mechanics (crack growth) approach are described. An overview of high-cycle welded fatigue methods, cycle-counting techniques, and a discussion on ratcheting are also offered. A historical synopsis of fatigue technology advancements and commentary on component design and fabrication strategies to mitigate fatigue damage and improve damage tolerance are provided. Finally, the article presents practical fatigue assessment case studies of in-service equipment (pressure vessels) that employ DBA methods.

Understanding fatigue crack growth is critical for the safe operation of many structural components. This article reviews the standard fracture mechanics and methods to determine the crack growth rate for a material and loading condition experimentally. It also addresses the two most important aspects of crack-growth modeling: loading environment and crack geometry.

The approaches to spectrum life prediction in components can be classified into two types, namely, history-based methods, using the life-fraction rule or other damage rules, and postservice evaluation methods. This article discusses the variables affecting the material crack growth rate behavior and those essential elements in making spectrum crack growth life prediction. It provides information on life assessment for bulk creep damage.

Engineered components fail predominantly in four major ways: fracture, corrosion, wear, and undesirable deformation (i.e., distortion). Typical fracture mechanisms feature rapid crack growth by ductile or brittle cracking; more progressive (subcritical) forms involve crack growth by fatigue, creep, or environmentally-assisted cracking. Corrosion and wear are another form of progressive material alteration or removal that can lead to failure or obsolescence. This article primarily covers the topic of abrasive wear failures, covering the general classification of wear. It also discusses methods that may apply to any form of wear mechanism, because it is important to identify all mechanisms or combinations of wear mechanisms during failure analysis. The article concludes by presenting several examples of abrasive wear.

The cracking process occurs slowly over the service life from various crack growth mechanisms such as fatigue, stress-corrosion cracking, creep, and hydrogen-induced cracking. Each of these mechanisms has certain characteristic features that are used in failure analysis to determine the cause of cracking or crack growth. This article discusses the macroscopic and microscopic basis of understanding and modeling fracture resistance of metals. It describes the four major types of failure modes in engineering alloys, namely, dimpled rupture, ductile striation formation, cleavage or quasicleavage, and intergranular failure. Certain fundamental characteristics of fracture observed in precipitation-hardening alloys, ferrous alloys, titanium alloys are also discussed.

This article provides a brief description of the different types of micromechanisms of monotonic and cyclic fracture. General information on the material variables that have the most beneficial effect on resistance to failure is presented. The article discusses the various stages, growth rates, and striation spacings of fatigue crack. The mechanisms of fatigue striation formation are also discussed. The fatigue crack growth in duplex microstructures and cyclic crack growth in polymers are reviewed. The article also describes the mechanisms and models of fatigue crack closure.

This article summarizes the metallurgy of carbon and alloy steels, followed by discussions on their major mechanical properties, namely, static fracture toughness, dynamic fracture toughness, fatigue or sustained-load crack growth rates, and fatigue or sustained-load thresholds. It addresses fatigue crack propagation and sustained-load crack propagation, as well as the fundamental aspects of fracture in steels. The article illustrates the effects of variations in the alloy chemistry, microstructure, temperature, strain rate, and environment on various fracture toughness or crack growth rate parameters.

The fracture-mechanics technology has significantly improved the ability to design safe and reliable structures and identify and quantify the primary parameters that affect structural integrity of materials. This article provides a discussion on fracture toughness of notched materials by explaining the ductile-to-brittle fracture transition and by correlating KId, KIc, and Charpy V-notch impact energy absorptions. It highlights the effects of constraint, temperature, and loading rate on the fracture transition. The article discusses the applications of fracture mechanism in limiting of operating stresses. It describes the mechanisms, testing methods, and effecting parameters of two main categories of fracture mechanics: linear-elastic fracture mechanics and elastic-plastic fracture mechanics. The article concludes with a discussion on the three major progressive stages of fatigue: crack initiation, crack growth, and fracture on the final cycle.

This article summarizes the general fatigue and fracture properties of cast steels, namely, toughness, fatigue, and component design factors such as section size and discontinuities. It describes the various factors that influence fatigue of cast steels. These factors include section size, defect size, stress modes, and waveform types. The article discusses various fracture mechanics in cast steels: cyclic stress-strain behavior and low- and high-cycle fatigue life behavior; plane-stress fracture toughness; plane-strain fracture toughness; constant-amplitude fatigue crack initiation and growth; and variable-amplitude fatigue crack initiation and growth.

This article describes the fracture mechanics in fatigue. It discusses the fatigue crack growth rate (FCGR) testing that consists of several steps, beginning with selecting the specimen size, geometry, and crack length measurement technique. The two major aspects of FCGR test analysis are to ensure suitability of the test data and to calculate growth rates from the data. The article presents an analysis of the crack growth data. Optical, compliance, and electric potential difference are the most common laboratory techniques, and the article reviews their merits and limitations. Forced-displacement, forced-vibration, rotational-bending, resonance, and servomechanical systems for various loading conditions are also discussed.

This article is an atlas of fractographs that helps in understanding the causes and mechanisms of fracture of AISI/SAE alloy steels (4xxx steels) and in identifying and interpreting the morphology of fracture surfaces. The fractographs illustrate the brittle fracture, ductile fracture, impact fracture, fatigue fracture surface, reversed torsional fatigue fracture, transgranular cleavage fracture, rotating bending fatigue, tension-overload fracture, torsion-overload fracture, slip band crack, crack growth and crack initiation, crack nucleation, microstructure, hydrogen embrittlement, sulfide stress-corrosion failure, stress-corrosion cracking, and hitch post shaft failure of these steels. The components considered in the article include tail-rotor drive-pinion shafts, pinion gears, outboard-motor crankshafts, bull gears, diesel engine bearing cap bolts, splined shafts, aircraft horizontal tail-actuator shafts, bucket elevators, aircraft propellers, helicopter bolts, air flasks, tie rod ball studs, and spiral gears.

Corrosion fatigue refers to the phenomenon of cracking in materials under the combined actions of fatigue loading and a corrosive environment. This article focuses on the various mechanisms of corrosion fatigue, namely, hydrogen-assisted cracking, anodic dissolution, and surface energy reduction. It discusses the variables affecting corrosion fatigue. The effect of fatigue load frequency, environment, grain size, stress ratio, waveform, and temperature fatigue crack growth are also discussed.

This article illustrates the role that fracture mechanics can play in failure analysis. It describes the important failure criteria as relations between design and materials factors, which are used to correlate fracture mechanics analysis to the observations of a failure analysis. Descriptions include an indication of how the factors are typically evaluated. The article also provides information on subcritical fracture mechanics. Finally, a group of failure analysis examples explain how fracture mechanics parameters can be determined and how they may be fitted into an overall failure investigation.

This article reviews generalized test methodologies for fatigue characterization of polymers and examines fatigue fracture mechanisms in different engineering plastics. It provides detailed micromechanistic images of crack-tip processes for a variety of semicrystalline and amorphous engineering polymers. The article describes fracture mechanics solutions and approaches to the fatigue characterization of engineering polymers when dealing with macroscale fatigue crack growth. It includes mechanistic images for high-density polyethylene, ultrahigh-molecular-weight polyethylene, nylon 6, 6, polycarbonate, and polypropylene. The article describes the micromechanisms of toughening of plastics and uses a macroscale approach of applying fracture mechanics to the fatigue life prediction of engineering polymers, building on the mechanistic concepts. It also describes the factors affecting fatigue performance of polymers.

Many metal failures involve fracture, and fractography is an essential activity in many, if not most, failure analysis (FA) investigations. This article introduces and illustrates the role of fractography in an FA investigation. Basic guidelines are briefly presented for investigating a failure and how fractography helps the FA investigator determine evidence. Examples are given throughout this article on how the examination of fracture surfaces discerns various sources of crack initiation and mechanisms of crack growth. The procedures for analyzing fractures also include several steps and techniques that involve photographic documentation, proper specimen handling, and visual or microscopic examination. The article also briefly describes the use of metallography in fracture analysis along with case studies as illustrative examples of various fracture mechanisms and modes.

This article describes concepts and tools that can be used by the failure analyst to understand and address deformation, cracking, or fracture after a stress-related failure has occurred. Issues related to the determination and use of stress are detailed. Stress is defined, and a procedure to deal with stress by determining maximum values through stress transformation is described. The article provides the stress analysis equations of typical component geometries and discusses some of the implications of the stress analysis relative to failure in components. It focuses on linear elastic fracture mechanics analysis, with some mention of elastic-plastic fracture mechanics analysis. The article describes the probabilistic aspects of fatigue and fracture. Information on crack-growth simulation of the material is also provided.

The concepts of fracture mechanics are basic ideas for developing the methods of predicting the load-carrying capabilities of structures and components containing cracks. This article provides an introduction to the methodology for computing the onset of fracture and describes plane strain fracture toughness, denoted as K IC . It presents formulas for the stress-intensity parameter as a function of crack size, crack shape, applied stress (or load), and geometry of load application.

This article describes the fatigue properties of particle-reinforced metal-matrix composites (PR-MMCs) in terms of mechanisms of crack initiation, fatigue life, and fatigue crack growth. It reviews specimen preparation and microscopic procedures that are used in fatigue testing of MMCs. It also describes the evaluation of the long fatigue crack growth behavior of MMCs by using the test methods and specimens that are used for unreinforced metallic alloys. Fractography of MMCs under plane-strain conditions is also described with information on the observed features of MMC fatigue fracture surfaces and their observation methods.