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Title: Combined macroscopic and microscopic approach to the fracture of metals. Annual progress report, 1980-1981

Abstract

Recent progress was achieved in refining and generalizing the methods previously developed for treating the stable crack growth problem, with particular attention to the approximate asymptotic solution of Rice, Drugan and Sham for stress and deformation fields near the tip of a growing crack. The microstructural aspects of ductile fracture were studied in dual-phase steels and high-strength 4340 steels. Very interesting results were obtained in the work on hydrogen effects in steels. In medium strength steels, the ductility-reducing effect of hydrogen is tentatively attributed to the accumulation of hydrogen at internal interfaces with a resulting loss in the resistance to interfacial separation. Extension of Needleman and Rice's work on the growth of cavities at elevated temperatures to the investigation of the effects of triaxial stressing relates the rate of void growth by grain boundary diffusion and dislocation creep to the triaxiality. It provides a good model to analyze the growth of macro-cracks in polycrystals by the mechanisms of growth and coalescence of micro-voids.

Authors:
; ; ;
Publication Date:
Research Org.:
Brown Univ., Providence, RI (USA). Div. of Engineering
Sponsoring Org.:
USDOE
OSTI Identifier:
6458491
Report Number(s):
DOE/ER/10556-85
ON: DE81025544; TRN: 81-012200
DOE Contract Number:
AC02-80ER10556
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; STEELS; FRACTURE PROPERTIES; DUCTILITY; HYDROGEN; MICROSTRUCTURE; RESEARCH PROGRAMS; ALLOYS; CRYSTAL STRUCTURE; ELEMENTS; IRON ALLOYS; IRON BASE ALLOYS; MECHANICAL PROPERTIES; NONMETALS; TENSILE PROPERTIES; 360103* - Metals & Alloys- Mechanical Properties; 360102 - Metals & Alloys- Structure & Phase Studies

Citation Formats

Asaro, R. J., Gurland, J., Needleman, A., and Rice, J. R. Combined macroscopic and microscopic approach to the fracture of metals. Annual progress report, 1980-1981. United States: N. p., 1981. Web. doi:10.2172/6458491.
Asaro, R. J., Gurland, J., Needleman, A., & Rice, J. R. Combined macroscopic and microscopic approach to the fracture of metals. Annual progress report, 1980-1981. United States. doi:10.2172/6458491.
Asaro, R. J., Gurland, J., Needleman, A., and Rice, J. R. Mon . "Combined macroscopic and microscopic approach to the fracture of metals. Annual progress report, 1980-1981". United States. doi:10.2172/6458491. https://www.osti.gov/servlets/purl/6458491.
@article{osti_6458491,
title = {Combined macroscopic and microscopic approach to the fracture of metals. Annual progress report, 1980-1981},
author = {Asaro, R. J. and Gurland, J. and Needleman, A. and Rice, J. R.},
abstractNote = {Recent progress was achieved in refining and generalizing the methods previously developed for treating the stable crack growth problem, with particular attention to the approximate asymptotic solution of Rice, Drugan and Sham for stress and deformation fields near the tip of a growing crack. The microstructural aspects of ductile fracture were studied in dual-phase steels and high-strength 4340 steels. Very interesting results were obtained in the work on hydrogen effects in steels. In medium strength steels, the ductility-reducing effect of hydrogen is tentatively attributed to the accumulation of hydrogen at internal interfaces with a resulting loss in the resistance to interfacial separation. Extension of Needleman and Rice's work on the growth of cavities at elevated temperatures to the investigation of the effects of triaxial stressing relates the rate of void growth by grain boundary diffusion and dislocation creep to the triaxiality. It provides a good model to analyze the growth of macro-cracks in polycrystals by the mechanisms of growth and coalescence of micro-voids.},
doi = {10.2172/6458491},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jun 01 00:00:00 EDT 1981},
month = {Mon Jun 01 00:00:00 EDT 1981}
}

Technical Report:

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  • The final results of the recently completed theoretical study of the stress and deformation fields near a growing crack are presented. The shear-lag model has been successfully used to estimate stress in the hard martensite constituent of dual-phase steels under load. The stress values were correlated with the measured strain. In related work, the effect of the size and distribution of hard carbide particles on fracture initiation and fracture toughness was studied in high strength steels, 4140 and 4340, with particular attention to the mode of crack tip advance. The continuing study of the hydrogen assisted fracture of carbon steelsmore » was extended to a high carbon steel, i.e., 1095 spheroidized. This steel shows a transition of fracture mode from ductile to cleavage as a function of charging current density. In the area of elevated temperature rupture, a micromechanical model is proposed for creep crack growth by the mechanism of grain boundary void nucleation, growth, and coalescence with the macro-crack.« less
  • The following results are reported: (1) extremely good theoretical-experimental correlation was found between our theoretical predictions based on asymptotic analysis with numerical finite element studies and the experimentally monitored crack growth for a large range of stable crack growth in 4140 steel; (2) a theoretical model was developed for the critical conditions of crack initiation at rigid particles as a precursor of ductile rupture in steels; (3) as part of environmentally sensitive fracture mechanisms, it was found that hydrogen can promote a ductile-to-brittle fracture transition with increasing charging current density in low carbon steel; and (4) a new variational principlemore » has been established for the combined processes of plastic creep flow and grain boundary diffusion and has been constructively applied to the problem of cavity growth under creep conditions.« less
  • A finite element study of the strain hardening of a simple composite model was conducted which shows that the work hardening behavior can be understood by the effects of geometric and material properties on the development of slip regions. The fracture of dual-phase steels is now being treated theoretically by examining models for the description of the limits of ductilities in uniform elongation and post-uniform elongation. Detailed studies continue on the effects of tempering on aluminum and titanium-killed steels. A new correlation is shown between measured K/sub IC/ values and those calculated using our model based on a criteria ofmore » critical strains achieved over a critical distance, the former being identified with the measured plane strain ductility, the latter with the average particle spacing. Work on the role of hydrogen in the fracture of steels has been carried out on initially smooth and circumferentially notched specimens of a 1015 steel modified with Mn. Finite element studies of notched bend specimens have been carried out which exhibit the large strains and localized shearing modes in the highly deformed notch tip region often observed in high strength steels. In the case of fully plastic crack problems, we have given a concise derivation of a volume integral expression for the local energy release rate that can be applied to three-dimensional as well as two-dimensional cracked bodies. Numerical results have been obtained that illustrate the computational advantage of this approach. We have obtained solutions in short crack and deep crack limits, which are of interest since the design life of a structure is generally estimated from short crack solutions while the fracture resistance (or creep crack growth rate) is typically determined from deep cracked specimens. Also, comparison of these solutions with known limiting solutions permits the accuracy as well as consistency of the numerical results to be assessed.« less
  • Significant progress was achieved in the development of accurate solutions for crack tip stress and deformation fields. Finite element studies were initiated. In the area of microstructural aspects of fracture processes in ductile alloys, we have begun an experimental study of load transfer as a strain hardening mechanism in two-phase alloys, in parallel with a finite element analysis of deformation of two-phase alloys. Work on the fracture process in dual-phase steels continues. As part of the continuing study of the fracture toughness of high strength steels, an attempt was made to interpret the fracture results in terms of the micro-fracturemore » process beneath a crack or notch by which voids or microcracks initiate and link with the main crack. The study of hydrogen induced ductility losses has been extended to include the effects of strain state and level of triaxiality on the ductile rupture of a 1015-type steel.« less
  • The work reported includes studies on: (1) The role of particles and interfaces in the initiation of fracture, including fundamentals of brittle versus ductile response of interfaces and observations on cavity growth by the cracking of grain or sub-grain boundaries adjacent to carbides in spheroidized steels; (2) Environment sensitive fracture mechanisms, particularly the effect of hydrogen in reducing tensile ductility by acceleration of the crack-like mode of cavity growth along grain boundaries in steels; (3) Models for elevated temperature diffusive processes of cavity growth on grain interfaces, including non-equilibrium effects and crack-like growth modes; (4) Localization of plastic deformation andmore » the inception of ductile rupture; and (5) Elastic-plastic stress analysis, by finite elements, of growing cracks and examination of criteria for stable crack growth.« less