A Decohesion Model of Hydrogen Assisted Crack Propagation PDF Download

Author: Sam Lai Lee
Publisher:
ISBN:
Category : Metals
Languages : en
Pages : 146

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Author: Alexander Robert Troiano
Publisher: ASM International
ISBN: 9781615031788
Category : Technology & Engineering
Languages : en
Pages : 356

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Author: Blaise Bourdin
Publisher: Springer Science & Business Media
ISBN: 1402063954
Category : Technology & Engineering
Languages : en
Pages : 173

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Presenting original results from both theoretical and numerical viewpoints, this text offers a detailed discussion of the variational approach to brittle fracture. This approach views crack growth as the result of a competition between bulk and surface energy, treating crack evolution from its initiation all the way to the failure of a sample. The authors model crack initiation, crack path, and crack extension for arbitrary geometries and loads.

Author: M. Gao
Publisher:
ISBN:
Category :
Languages : en
Pages : 5

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A hydrogen partitioning model has been developed to account for the pressure and temperature dependence for hydrogen-assisted crack growth. The model gives explicit recognition to the role of hydrogen-microstructure interactions in determining the distribution (or partitioning) of hydrogen among the various microstructural elements (principally between the prior-austenite grain boundaries and the matrix) and the rate of crack growth along the elements. It also takes into account the role of various rate controlling processes in determining the rate that hydrogen is being supplied to the fracture process (or embrittlement) zone. Quantitative assessment of the model indicates very good agreements between the model predictions and the observed crack growth responses for AISI 4340 and 4130 steels tested in hydrogen and for AISI 4340 steel tested in hydrogen sulfide. This model accurately characterizes the reduction in crack growth rate and the concomitant change in fracture mode at high temperatures. Through its integration with the earlier models, based on rate controlling processes, the model predicts the pressure and temperature dependence for K-independent crack growth over the entire range of environmental conditions.

Author: David J. Unger
Publisher: Elsevier
ISBN: 0080527191
Category : Technology & Engineering
Languages : en
Pages : 317

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Book Description
Fracture mechanics is an interdisciplinary subject that predicts the conditions under which materials fail due to crack growth. It spans several fields of interest including: mechanical, civil, and materials engineering, applied mathematics and physics. This book provides detailed coverage of the subject not commonly found in other texts.Analytical Fracture Mechanics contains the first analytical continuation of both stress and displacement across a finite-dimensional, elastic-plastic boundary of a mode I crack problem. The book provides a transition model of crack tip plasticitythat has important implications regarding failure bounds for the mode III fracture assessment diagram. It also presents an analytical solution to a true moving boundary value problem for environmentally assisted crack growth and a decohesion model of hydrogen embrittlement that exhibits all three stages of steady-state crack propagation.The text will be of great interest to professors, graduate students, and other researchers of theoretical and applied mechanics, and engineering mechanics and science. - Presents the only analytical proven solution technique amenable to the second-order nonlinear partial differential equation governing a mode I elastoplastic crack problem - Places emphasis on the near crack tip partial differential equations governing plasticity and process zone theory in environmental cracking phenomena - Provides fundamental solutions of linear elastic fracture mechanics - Explains how transport-controlled stage II environmental crack growth can be mapped onto the classic Stefan problem - Predicts failure curves on fracture assessment diagram for mode III crack problem as transition occurs from plastic strip to finite-dimensional plastic zone - Gives a summary of pertinent equations of linear elasticity and plasticity

Author: Nilesh Raykar
Publisher:
ISBN:
Category :
Languages : en
Pages : 336

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Book Description
Modelling of hydrogen assisted stress corrosion cracking (HASCC) within the framework of mechanics is very important for its control and avoidance. The main focus of this study is to develop suitable approach for modelling and analysis of stable crack growth through high strength steels under HASCC. A new strategy based on combined analytical/numerical solution and finite element based cohesive zone model (CZM) has been developed. This has helped to couple analysis of hydrogen diffusion and crack growth during HASCC. The strategy has been applied to study crack growth in compact tension (CT) specimens. The solution to diffusion process is obtained through either an analytical or a numerical solution to the governing differential equation. The crack growth is analysed by CZM. For the analytical solution, both one- and two-dimensional approximations of the domain have been considered. The new CZM strategy, termed as hydrogen concentration dependent cohesive zone model (HCD-CZM), has been used for both CT and circumferentially notched tensile (CNT) round specimens. The CNT specimen has been employed for the first time to obtain the fracture toughness data of high strength steel under internal and external supply of hydrogen. The experimental scheme involving CNT specimen under slow strain rate loading is demonstrated as a valid experimental procedure for study of HASCC for high strength steels. Both types of HASCC, internal hydrogen assisted cracking (IHAC) and hydrogen environment assisted cracking (HEAC), are found to induce a proportionate drop in fracture toughness under higher hydrogen concentration near the crack tip. The experimentally obtained lowest fracture toughness data compare favourably with lower range of published threshold values for the similar material. The experimental average crack growth rates too agree with the reported data for the material. For CT specimens, both schemes of analysis of diffusion, excluding or including the effect of hydrostatic stress and plastic strain, predict variation of crack opening displacement with crack growth with good accuracy. Diffusion solution based on one- and two-dimensional analyses do not significantly alter the prediction of crack growth. The effect of hydrostatic stress on the distribution of hydrogen concentration is observed to be significant as long as plastic strain is less than 5%. The study has given rise to an important correlation between hydrogen concentration dependent strength reduction and plastic strain rate. A new modelling technique is presented for the CNT specimen with eccentrically placed ligament using two-dimensional finite element approximations; this has considerably simplified analysis of the problem which otherwise would require a three-dimensional solution. For CNT specimens, the HCD-CZM approach employing both analytical and finite difference based diffusion solutions predicted the critical fracture toughness in agreement with experimental results. In this case too, the inclusion of hydrostatic stress in the diffusion analysis has been found to have not so significant influence on the prediction of experimental observations. The K-resistance curve obtained for the case is included. The proposed HCD-CZM has been found to satisfactorily handle variation in specimen geometry, material and source of hydrogen supply. The thesis is divided into six chapters dealing sequentially with introduction, literature review, experiments with CNT specimen, analysis of CT specimens, modelling of CNT specimens and conclusions.

Author: Khlefa Alarbe Esaklul
Publisher:
ISBN:
Category :
Languages : en
Pages : 536

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Author: Richard P Gangloff
Publisher:
ISBN:
Category :
Languages : en
Pages : 624

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Author: David J. Unger
Publisher: Courier Corporation
ISBN: 0486143856
Category : Technology & Engineering
Languages : en
Pages : 338

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Book Description
"Analytical Fracture Mechanics should prove to be a valuable resource to both the new student and the experienced researcher in fracture mechanics. It is recommended." — Applied Mechanics Review One of the central concerns of engineering is the failure of materials. Addressing this concern, fracture mechanics — an interdisciplinary subject spanning mechanical, civil, and materials engineering, applied mathematics, and physics — predicts the conditions under which such failure will occur due to crack growth. This valuable self-contained text by an expert in the field supplements standard fracture mechanics texts by focusing on analytical methods for determining crack-tip stress and strain fields. Following a comprehensive 120-page introduction — which provides all the background necessary for understanding the remaining chapters — the book is organized around a series of elastoplastic and hydrogen-assisted crack-tip problems and their solutions. The first chapter presents the only proven solution technique for the second order nonlinear partial differential equation governing a mode I elastoplastic crack problem. Other chapters deal with plastic zone transitions, environmental cracking, and small-scale yielding versus exact linear elastic solutions. One of the excellent features of this book is the clarity with which groups of problems are presented and related to each other. Another is the careful attention it gives to the various modes of fracture (I, II, and III) and to showing the circumstances under which information from a solution for one mode may be used to infer information in another mode. For this edition, the author has added a new appendix, "Stress Across an Elastoplastic Boundary of a Mode I Crack: Parabolic to Hyperbolic Plasticity Transition."

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 25

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Book Description
Both internal and hydrogen environment assisted cracking continue to seriously limit high performance structural alloys and confound quantitative component prognosis. While intergranular H cracking assisted by impurity segregation can be minimized, other mechanisms promote IG cracking and transgranular H cracking modes have emerged; new alloys suffer serious H cracking similar to old materials. Micromechanical models of crack tip H localization and damage by decohesion predict important trends in threshold and subcritical crack growth rate behaviour. H diffusion appears to limit rates of cracking for monotonic and cyclic loading; however, uncertain%adjustable parameters hinder model effectiveness. It is necessary to better define conditions within 0.1-5 micronmeter of the crack tip, where dislocations and microstructure dominate continuum mechanics, and chemistry is localized. Nano-mechanics modeling and experimental results show very high levels of H accumulated in the crack tip fracture process zone, as necessary for interface decohesion. Contributing mechanisms include high crack tip stresses due to dislocation processes such as strain gradient plasticity, as well as powerful H production and trapping proximate to the electrochemically reacting crack tip surface. New sub- micrometer resolution probes of crack tip damage will better define features such as crack path crystallography (EBSD + Stereology) and surface morphology (high brightness, dual detector SEM), local H concentration (%IDS and NRA), and validate crack tip mechanics modelling (micro-Laue x-ray diffraction and EBSD).