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Title: Polycrystal orientation effects on microslip and mixed-mode behavior of microstructural small cracks

Abstract

There are two sources of mode mixity--on a macro level (combined loading situation), and on the micro level--that affect the propagation of small crystallographic cracks. This work explores mode mixity on the micro level by utilizing a computational model to simulate microstructural influences on driving forces for the formation and growth of small cracks. Two-dimensional computational cyclic crystal plasticity calculations are conducted to study the distribution of cyclic slip and critical plane-type fatigue parameters in a material with nominal stress-strain characteristics of 4340 steel. Cases of applied cyclic tension-compression and cyclic shear are analyzed at strain amplitudes below macroscopic yielding. Emphasis is placed on stress state and amplitude dependence of the distribution of these parameters among grains. The role of anisotropic plasticity is isolated by assuming the elastic behavior of grains to obey homogeneous, isotropic linear elasticity. All grains are of equal dimension and are assigned a random orientation distribution. It is found that the distribution of the Fatemi-Socie critical plane fatigue parameter among grains is Weibull-distributed, and it is argued that it forms an improved linkage to cyclic crack tip displacement for microstructurally small cracks. The authors also present computed crack tip opening and sliding displacements as a functionmore » of maximum applied tensile strain (from well below to just above nominal yielding) for small cracks within surface grains surrounded by a nearly random orientation distribution of grains. Multiple realizations of the local microstructure are examined for each crack length for sub-grain size cracks, with results normalized to the ratio of crack length to grain size. Key results include a very strong role of the free surface on crack tip displacement, with opening displacement being much greater than the sliding for suitably small crystallographic cracks in the surface grains. There is also a strong effect of the orientation of the next grain ahead of the crack on local mode mixity of the crack tip displacements, which plays an increasingly influential role as the crack tip approaches the first grain boundary.« less

Authors:
;
Publication Date:
Research Org.:
Georgia Inst. of Tech., Atlanta, GA (US)
OSTI Identifier:
20000282
Report Number(s):
CONF-9805206-
ISBN 0-8031-2602-6
Resource Type:
Conference
Resource Relation:
Conference: Mixed-Mode Crack Behavior, Atlanta, GA (US), 05/06/1998--05/07/1998; Other Information: PBD: 1999; Related Information: In: Mixed-mode crack behavior. ASTM special technical publication 1325, by Miller, K.J.; McDowell, D.L. [eds.], 342 pages.
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; PLASTICITY; SLIP; MICROSTRUCTURE; FRACTURE MECHANICS; CRACK PROPAGATION; STEELS; FATIGUE

Citation Formats

Bennett, V, and McDowell, D L. Polycrystal orientation effects on microslip and mixed-mode behavior of microstructural small cracks. United States: N. p., 1999. Web.
Bennett, V, & McDowell, D L. Polycrystal orientation effects on microslip and mixed-mode behavior of microstructural small cracks. United States.
Bennett, V, and McDowell, D L. Thu . "Polycrystal orientation effects on microslip and mixed-mode behavior of microstructural small cracks". United States.
@article{osti_20000282,
title = {Polycrystal orientation effects on microslip and mixed-mode behavior of microstructural small cracks},
author = {Bennett, V and McDowell, D L},
abstractNote = {There are two sources of mode mixity--on a macro level (combined loading situation), and on the micro level--that affect the propagation of small crystallographic cracks. This work explores mode mixity on the micro level by utilizing a computational model to simulate microstructural influences on driving forces for the formation and growth of small cracks. Two-dimensional computational cyclic crystal plasticity calculations are conducted to study the distribution of cyclic slip and critical plane-type fatigue parameters in a material with nominal stress-strain characteristics of 4340 steel. Cases of applied cyclic tension-compression and cyclic shear are analyzed at strain amplitudes below macroscopic yielding. Emphasis is placed on stress state and amplitude dependence of the distribution of these parameters among grains. The role of anisotropic plasticity is isolated by assuming the elastic behavior of grains to obey homogeneous, isotropic linear elasticity. All grains are of equal dimension and are assigned a random orientation distribution. It is found that the distribution of the Fatemi-Socie critical plane fatigue parameter among grains is Weibull-distributed, and it is argued that it forms an improved linkage to cyclic crack tip displacement for microstructurally small cracks. The authors also present computed crack tip opening and sliding displacements as a function of maximum applied tensile strain (from well below to just above nominal yielding) for small cracks within surface grains surrounded by a nearly random orientation distribution of grains. Multiple realizations of the local microstructure are examined for each crack length for sub-grain size cracks, with results normalized to the ratio of crack length to grain size. Key results include a very strong role of the free surface on crack tip displacement, with opening displacement being much greater than the sliding for suitably small crystallographic cracks in the surface grains. There is also a strong effect of the orientation of the next grain ahead of the crack on local mode mixity of the crack tip displacements, which plays an increasingly influential role as the crack tip approaches the first grain boundary.},
doi = {},
url = {https://www.osti.gov/biblio/20000282}, journal = {},
number = ,
volume = ,
place = {United States},
year = {1999},
month = {7}
}

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