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Title: Some microstructural conditions for evaluating fracture toughness and R-curve behavior in platelet-reinforced composites

Abstract

The validity of K[sub Ic] fracture toughness determinations by various techniques usually employed and compared with each other is discussed in detail for two ceramic materials. They are a simple Si[sub 3]N[sub 4] material fracturing with transgranular crack propagation and a Si[sub 3]N[sub 4]-25vol% SiC-platelet measured by four different methods: single-edge V-notched beam (SEVNB), single-edge precracked beam (SEPB), indentation fracture (IF), and chevron-notched beam (CNB). It is generally recognized that, in platelet composites, K[sub Ic] values can be reliably obtained only by procedures adopting notched specimens in which the wake-zone of precracking is mechanically removed (SEVNB or renotched SEPB). In the present investigation the CNB method, in which the wake contribution to fracture resistance is generally small but not negligible, was also found to give stress-intensity factors at maximum load whose value was almost coincident with the K[sub Ic] determined by SEVNB method. Using stereological concepts, fractographic observations, and acoustic emission (AE) experiments, the microstructural conditions for negligible wake-contribution during the subcritical stable crack extension in the CNB experiment were worked out and applied to rationalize the behavior of the present composite. Apparent toughness values markedly higher than the true'' K[sub Ic] of the composite were measured both by themore » standard SEPB and IF method. Such a discrepancy is considered due, in the former case, mainly to traction forces between the precracked surfaces while, in the latter, to an insufficient account of the residual stress field associated with the indentation.« less

Authors:
;  [1];  [2]
  1. Osaka Univ. (Japan). Inst. of Scientific and Industrial Research
  2. Kyote Inst. of Tech., Kyoto (Japan). Dept. of Materials Engineering
Publication Date:
OSTI Identifier:
6147951
Resource Type:
Journal Article
Journal Name:
Journal of Testing and Evaluation; (United States)
Additional Journal Information:
Journal Volume: 21:5; Journal ID: ISSN 0090-3973
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COMPOSITE MATERIALS; FRACTURE PROPERTIES; SILICON CARBIDES; SILICON NITRIDES; CERAMICS; CRACK PROPAGATION; EXPERIMENTAL DATA; MICROSTRUCTURE; RESIDUAL STRESSES; CARBIDES; CARBON COMPOUNDS; DATA; INFORMATION; MATERIALS; MECHANICAL PROPERTIES; NITRIDES; NITROGEN COMPOUNDS; NUMERICAL DATA; PNICTIDES; SILICON COMPOUNDS; STRESSES; 360203* - Ceramics, Cermets, & Refractories- Mechanical Properties; 360603 - Materials- Properties

Citation Formats

Pezzotti, Giuseppe, Niihara, Koichi, and Nishida, Toshihiko. Some microstructural conditions for evaluating fracture toughness and R-curve behavior in platelet-reinforced composites. United States: N. p., 1993. Web.
Pezzotti, Giuseppe, Niihara, Koichi, & Nishida, Toshihiko. Some microstructural conditions for evaluating fracture toughness and R-curve behavior in platelet-reinforced composites. United States.
Pezzotti, Giuseppe, Niihara, Koichi, and Nishida, Toshihiko. 1993. "Some microstructural conditions for evaluating fracture toughness and R-curve behavior in platelet-reinforced composites". United States.
@article{osti_6147951,
title = {Some microstructural conditions for evaluating fracture toughness and R-curve behavior in platelet-reinforced composites},
author = {Pezzotti, Giuseppe and Niihara, Koichi and Nishida, Toshihiko},
abstractNote = {The validity of K[sub Ic] fracture toughness determinations by various techniques usually employed and compared with each other is discussed in detail for two ceramic materials. They are a simple Si[sub 3]N[sub 4] material fracturing with transgranular crack propagation and a Si[sub 3]N[sub 4]-25vol% SiC-platelet measured by four different methods: single-edge V-notched beam (SEVNB), single-edge precracked beam (SEPB), indentation fracture (IF), and chevron-notched beam (CNB). It is generally recognized that, in platelet composites, K[sub Ic] values can be reliably obtained only by procedures adopting notched specimens in which the wake-zone of precracking is mechanically removed (SEVNB or renotched SEPB). In the present investigation the CNB method, in which the wake contribution to fracture resistance is generally small but not negligible, was also found to give stress-intensity factors at maximum load whose value was almost coincident with the K[sub Ic] determined by SEVNB method. Using stereological concepts, fractographic observations, and acoustic emission (AE) experiments, the microstructural conditions for negligible wake-contribution during the subcritical stable crack extension in the CNB experiment were worked out and applied to rationalize the behavior of the present composite. Apparent toughness values markedly higher than the true'' K[sub Ic] of the composite were measured both by the standard SEPB and IF method. Such a discrepancy is considered due, in the former case, mainly to traction forces between the precracked surfaces while, in the latter, to an insufficient account of the residual stress field associated with the indentation.},
doi = {},
url = {https://www.osti.gov/biblio/6147951}, journal = {Journal of Testing and Evaluation; (United States)},
issn = {0090-3973},
number = ,
volume = 21:5,
place = {United States},
year = {1993},
month = {9}
}