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Title: Determining fatigue crack opening loads from near-crack-tip displacement measurements

Abstract

The aim of this research was to develop a near-crack-tip measurement method that quantifies crack closure levels in the near-threshold fatigue crack growth regime--a regime where crack closure is not well characterized by remote compliance methods. Further understanding of crack closure mechanics was gained by performing novel crack growth experiments in conjunction with numerical simulations of three-dimensional crack-front propagation. Steady-state (i.e., constant growth rate) fatigue crack growth rates were characterized by performing constant cyclic stress intensity range ({Delta}K) experiments over a wide range of stress ratios (R). Near-crack-tip (less than 0.3 mm behind) load-versus-displacement measurements were conducted on the specimen surface using a novel noncontact experimental technique (Digital Imaging Displacement System--DIDS). The experiments and simulations revealed that the three-dimensional aspects of fatigue crack closure must be considered to determine correct opening load levels from near-crack-tip load-versus-displacement data. It was shown that near-crack-front, but increase near the free surface. The interior opening load was found to collapse closure-affected data to intrinsic rates, and thus shown to relate to the true crack-front driving force parameter. Surface opening load DIDS measurements made at an optimal distance behind the crack tip were used to correlate da/dN with {Delta}K{sub eff}. Opening load determinations made lessmore » than the optimal distance behind the crack tip were shown to be too high to correlate fatigue crack growth rates.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
DOT/Volpe National Transportation Systems Center, Cambridge, MA (US)
OSTI Identifier:
20005702
Resource Type:
Conference
Resource Relation:
Conference: Second Symposium on Advances in Fatigue Crack Closure Measurement and Analysis, San Diego, CA (US), 11/12/1997--11/13/1997; Other Information: PBD: 1999; Related Information: In: Advances in fatigue crack closure measurement and analysis: Second volume. ASTM special technical publication 1343, by McClung, R.C.; Newman, J.C. Jr. [eds.], 490 pages.
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 42 ENGINEERING; ALUMINIUM ALLOYS; FATIGUE; CRACK PROPAGATION; MECHANICAL TESTS; MEASURING METHODS; THREE-DIMENSIONAL CALCULATIONS; STRESS INTENSITY FACTORS; FINITE ELEMENT METHOD

Citation Formats

Riddell, W T, Piascik, R S, Sutton, M A, Zhao, W, McNeill, S R, and Helm, J D. Determining fatigue crack opening loads from near-crack-tip displacement measurements. United States: N. p., 1999. Web.
Riddell, W T, Piascik, R S, Sutton, M A, Zhao, W, McNeill, S R, & Helm, J D. Determining fatigue crack opening loads from near-crack-tip displacement measurements. United States.
Riddell, W T, Piascik, R S, Sutton, M A, Zhao, W, McNeill, S R, and Helm, J D. Thu . "Determining fatigue crack opening loads from near-crack-tip displacement measurements". United States.
@article{osti_20005702,
title = {Determining fatigue crack opening loads from near-crack-tip displacement measurements},
author = {Riddell, W T and Piascik, R S and Sutton, M A and Zhao, W and McNeill, S R and Helm, J D},
abstractNote = {The aim of this research was to develop a near-crack-tip measurement method that quantifies crack closure levels in the near-threshold fatigue crack growth regime--a regime where crack closure is not well characterized by remote compliance methods. Further understanding of crack closure mechanics was gained by performing novel crack growth experiments in conjunction with numerical simulations of three-dimensional crack-front propagation. Steady-state (i.e., constant growth rate) fatigue crack growth rates were characterized by performing constant cyclic stress intensity range ({Delta}K) experiments over a wide range of stress ratios (R). Near-crack-tip (less than 0.3 mm behind) load-versus-displacement measurements were conducted on the specimen surface using a novel noncontact experimental technique (Digital Imaging Displacement System--DIDS). The experiments and simulations revealed that the three-dimensional aspects of fatigue crack closure must be considered to determine correct opening load levels from near-crack-tip load-versus-displacement data. It was shown that near-crack-front, but increase near the free surface. The interior opening load was found to collapse closure-affected data to intrinsic rates, and thus shown to relate to the true crack-front driving force parameter. Surface opening load DIDS measurements made at an optimal distance behind the crack tip were used to correlate da/dN with {Delta}K{sub eff}. Opening load determinations made less than the optimal distance behind the crack tip were shown to be too high to correlate fatigue crack growth rates.},
doi = {},
url = {https://www.osti.gov/biblio/20005702}, journal = {},
number = ,
volume = ,
place = {United States},
year = {1999},
month = {7}
}

Conference:
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