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ASTM Selected Technical Papers
Composite Materials: Fatigue and Fracture, Second Volume
By
PA Lagace
PA Lagace
1
Associate Professor of Aeronautics and Astronautics
,
Technology Laboratory for Advanced Composites, Massachusetts Institute of Technology
;
symposium chairman and editor
Search for other works by this author on:
ISBN-10:
0-8031-1190-8
ISBN:
978-0-8031-1190-5
No. of Pages:
428
Publisher:
ASTM International
Publication date:
1989

The mode II delamination fracture toughness of a ductile and a brittle unidirectional graphite/epoxy composite has been studied using the end-notched flexure (ENF) test and the end-loaded split laminate (ELS) test. The stress field in the vicinity of the crack tip of a split laminate beam under mode I and mode II (ELS test) conditions has been determined by means of a finite-element analysis. Also, the micromechanics of mode II fracture have been studied during in situ and postmortem observations of the fracture process. Both the ENF and ELS tests give similar values for GIIc. However, because elastic material behavior is assumed in the analysis, the GIIc results for a ductile composite are somewhat uncertain because permanent deformation is observed. The ELS test provides a pure shear stress state in the vicinity of the crack tip. The formation of hackles in composites made with brittle resins provides a more tortuous path for the crack leading to an increased resistance to delamination under mode II conditions compared to mode I. However, extensive resin deformation and yielding play a more significant role in the fracture resistance for mode II loading of composites made using a rubber-toughened epoxy.

1.
Tse
,
M. K.
,
Hibbs
,
M. F.
, and
Bradley
,
W. L.
, “
Interlaminar Fracture Toughness and Real Time Fracture Mechanisms of Some Toughened Graphite/Epoxy Composites
,”
Toughened Composites, ASTMISTP 937
,
Johnston
N. J.
, Ed.,
American Society for Testing and Materials
,
Philadelphia
,
1987
, pp. 115–130.
2.
Murri
,
G. B.
, “
GIIc Measurement of Toughened Matrix Composites Using the End-Notched Flexure (ENF) Test
."
ASTM Committee D30.02 Task Group on Interlaminar Fracture Toughness
,
Dallas, TX
,
1984
.
3.
Vanderkley
,
P. S.
, “
Mode I-Mode II Delamination Fracture Toughness of a Unidirectional Graphite/Epoxy Composite.
" Master of Science thesis,
Texas A&M University
, College Station, TX,
12
1981
.
4.
Russell
,
A. J.
and
Street
,
K. N.
, “
The Effect of Matrix Toughness on Delamination: Static and Fatigue Fracture under Mode II Shear Loading of Graphite Fiber Composites
,”
Toughened Composites, ASTM/STP 937
,
Johnston
N. J.
, Ed.,
American Society for Testing and Materials
,
Philadelphia
,
1987
, pp. 275–293.
5.
Gillespie
,
J. W.
,
Carlsson
,
L. A.
, and
Pipes
,
R. B.
, “
Finite Element Analysis of the End-Notched Flexure Specimen for Measuring Mode II Fracture Toughness
,”
Composite Science and Technology
, Vol.
27
,
1986
, pp. 177–197.
6.
Carlsson
,
L. A.
,
Gillespie
,
J. W.
, and
Pipes
,
R. B.
, “
On the Analysis and Design of the End-Notched Flexure (ENF) Test Specimen for Mode II Testing
,”
Journal of Composite Materials
, Vol.
20
,
11
1986
, pp. 594–604.
7.
Specification Sheet of AS4/3502 Graphite/Epoxy Composite, Hercules, Inc., P.O. Box 98, Magna, UT 84044.
8.
Bulletin CFM4B, Celanese Corp., 26 Main Street, Chatham, NJ 07928.
9.
Jordan
,
W. M.
, “
The Effect of Resin Toughness on Fracture Behavior of Graphite/Epoxy Composites
,” Ph.D. dissertation,
Texas A&M University
, College Station, TX,
1985
.
10.
Barsoum
,
R. S.
,
International Journal for Numerical Methods in Engineering
 0029-5981, Vol.
10
,
1976
, pp. 25–37.
11.
Whitney
,
J. M.
,
Composites Science and Technology
, Vol.
23
,
1985
, pp. 201–219.
12.
Bradley
,
W. L.
and
Corleto
,
C. R.
, “
The Significance of Hackles in the Failure Analysis of Graphite/Epoxy Composite Materials
,” Mechanical Engineering Division of the Texas Engineering Experiment Station,
Texas A&M University
, College Station, TX,
1986
.
13.
Hibbs
,
M. F.
and
Bradley
,
W. L.
, “
Correlations Between Micromechanical Failure Processes and the Delamination Fracture Toughness of Graphite/Epoxy Systems
,” in
Fractography of Modern Engineering Materials: Composites and Metals, ASTM STP 948
,
Masters
J. E.
and
Joseph
J. Au
, Eds.,
American Society for Testing and Materials
,
Philadelphia
,
1987
, pp. 68–97.
14.
Nam
,
S. W.
,
Bradley
,
W. L.
, and
Chakachery
,
E.
A Study of Coating Cracking During In-Situ Fracture Studies in SEM
,” unpublished research, Department of Mechanical Engineering,
Texas A&M University
, College Station, TX,
1986
.
15.
Bradley
,
W. L.
and
Cohen
,
R.
, “
Matrix Deformation and Fracture in Graphite Reinforced Epoxies
,” in
Delamination and Debonding of Materials, ASTM STP 876
,
Johnson
W. S.
, Ed.,
American Society for Testing and Materials
,
Philadelphia
,
1985
, pp. 389–410.
16.
Jordan
,
W. M.
and
Bradley
,
W. L.
, “
Micromechanics of Fracture in Toughened Graphite-Epoxy Laminates
,” in
Toughened Composites, ASTM STP 937
,
Johnston
N. J.
, Ed.,
American Society for Testing and Materials
,
Philadelpia
,
1987
, pp. 95–114.
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