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ASTM Selected Technical Papers
Toughened Composites
By
NJ Johnston
NJ Johnston
1
NASA-Langley Research Center
,
Hampton, VA; symposium chairman and editor
Search for other works by this author on:
ISBN-10:
0-8031-0934-2
ISBN:
978-0-8031-0934-6
No. of Pages:
495
Publisher:
ASTM International
Publication date:
1987

Various configurations of edge delamination tension (EDT) test specimens were manufactured and tested to assess the usefulness of each configuration for measuring interlaminar fracture toughness. Tests were performed on both brittle (T300/5208) and toughened-matrix (T300/BP907) graphite reinforced composite laminates. The mixed-mode interlaminar fracture toughness Gc was measured during tension tests of (30/−302/30/90n)s, n = 1 or 2; (35/−35/0/90)s; and (35/0/−35/90)s layups designed to delaminate at low tensile strains. Laminates were made without inserts so that delaminations would form naturally between the central 90° plies and the adjacent angle plies. Laminates were also made with Teflon® inserts implanted between the 90° plies and the adjacent angle (θ) plies at the straight edge to obtain a planar fracture surface. In addition, Mode I interlaminar tension fracture toughness GIc was measured from laminates with the same layups but with inserts in the midplane, between the central 90° plies, at the straight edge. All of the EDT configurations were useful for ranking the delamination resistance of composites with different matrix resins. Furthermore, the variety of layups and configurations available yield interlaminar fracture toughness measurements, both pure Mode I and mixed mode, needed to generate delamination failure criteria.

The influence of insert thickness and location, and coupon size on Gc values were evaluated. For toughened-matrix composites, laminates with 1.5-mil (38.1-μm) thick inserts yielded interlaminar fracture toughness numbers consistent with data generated from laminates without inserts. Coupons of various sizes yielded similar Gc values. The influence of residual thermal and moisture stresses on calculated strain energy release rate for edge delamination was also reviewed. Edge delamination data may be used to quantify the relative influence of residual thermal and moisture stresses on interlaminar fracture for different composite materials.

1.
O'Brien
,
T. K.
, “
Characterization of Delamination Onset and Growth in a Composite Laminate
,” in
Damage in Composite Materials
, ASTM STP 775,
Reifsnider
K. L.
, Ed.,
American Society for Testing and Materials
,
Philadelphia
,
1982
, pp. 140-167.
2.
O'Brien
,
T. K.
,
Johnston
,
N. J.
,
Morris
,
D. H.
, and
Simonds
,
R. A.
, “
A Simple Test for the Interlaminar Fracture Toughness of Composites
,”
SAMPE Journal
, Vol.
18
, No.
4
, July/Aug. 1982, p. 8.
3.
Johnston
,
N. J.
,
O'Brien
,
T. K.
,
Morris
,
D. H.
, and
Simonds
,
R. A.
, “
Interlaminar Fracture Toughness of Composites II—Refinement of the Edge Delamination Test and Application to Thermoplastics
,” in
Proceedings of the 28th National SAMPE Symposium and Exhibition
,
Society for the Advancement of Material and Process Engineering
,
Corina, CA
,
1983
, p. 502.
4.
O'Brien
,
T. K.
, “
Mixed-Mode Strain-Energy-Release Rate Effects on Edge Delamination of Composites
,” in
Effects of Defects in Composite Materials
, ASTM STP 836,
American Society for Testing and Materials
,
Philadelphia
,
1984
, pp. 125-142.
5.
O'Brien
,
T. K.
,
Johnston
,
N. J.
,
Morris
,
D. H.
, and
Simonds
,
R. A.
, “
Determination of Interlaminar Fracture Toughness and Fracture Mode Dependence of Composites using the Edge Delamination Test
,” in
Proceedings of the International Conference on Testing, Evaluation, and Quality Assurance of Composites
,
Feest
T.
, Ed.,
Butterworth Scientific, Ltd.
,
Kent, England
,
1983
, p. 223.
6.
Whitney
,
J. M.
,
Browning
,
C. E.
, and
Hoogsteden
,
W.
, “
A Double Cantilever Beam Test for Characterizing Mode I Delamination of Composite Materials
,”
Journal of Reinforced Plastics and Composites
, Vol.
1
, No.
4
,
1982
, p. 297.
7.
Whitney
,
J. M.
and
Knight
,
M.
, “
A Modified Free-Edge Delamination Specimen
,” in
Delamination and Debonding of Materials
, ASTM STP 876,
Johnson
W. S.
, Ed.,
American Society for Testing and Materials
,
Philadelphia
,
1985
, pp. 298-314.
8.
Ho
,
T.
and
Schapery
,
R. A.
, “
The Effect of Environment on the Mechanical Behavior of AS/3501-6 Graphite Epoxy Material—Phase IV
,”
Naval Air Systems Command (ATC) Report
R-92000/3CR-9,
02
1983
.
9.
Whitcomb
,
J. D.
and
Raju
,
I. S.
, “
Analysis of Interlaminar Stresses in Thick Composite Laminates With and Without Edge Delamination
,” in
Delamination and Debonding of Materials
, ASTM STP 876,
Johnson
W. S.
, Ed.,
American Society for Testing and Materials
,
Philadelphia
,
1985
, pp. 69-94.
10.
O'Brien
,
T. K.
,
Raju
,
I. S.
, and
Garber
,
D. P.
, “
Residual Thermal and Moisture Influences on the Strain Energy Release Rate Analysis of Edge Delamination
,”
Journal of Composites Technology and Research
, Vol.
8
, No.
2
, Summer
1986
, pp. 37-47.
11.
Wang
,
S. S.
, “
The Mechanics of Delamination in Fiber-Reinforced Composite Materials—Part III
,”
NASA CR
,
1985
.
12.
Chai
,
H.
, “
Bond Thickness Effect in Adhesive Joints and Its Significance for Mode I Interlaminar Fracture of Composites
,” in
Composite Materials: Testing and Design (Seventh Conference)
, ASTM STP 893,
Whitney
J. M.
, Ed.,
American Society for Testing and Materials
,
Philadelphia
,
1986
, pp. 209-231.
13.
Hunston
,
D. L.
, “
Composite Interlaminar Fracture: Effect of Matrix Fracture Energy
,”
Composites Technology Review
, Vol.
6
, No.
4
, Winter
1984
, pp. 176-186.
14.
Bascom
,
W. D.
,
Boll
,
D. J.
,
Fuller
,
B.
, and
Phillips
,
P.
, “
Fractography of the Interlaminar Fracture of Carbon Fiber Epoxy Composites
,” in this volume, pp. 131-149.
15.
Johnson
,
W. S.
, and
Mangalgari
,
P. D.
, “
Influence of Resin on Interlaminar Fracture
,” in this volume, pp. 295-315.
16.
Adams
,
D. F.
,
Zimmerman
,
R. S.
, and
Odem
,
E. M.
, “
Determining Frequency and Load Ratio Effect on the Edge Delamination Test in Graphite/Epoxy Composites
,” in this volume, pp. 242-259.
17.
Murri
,
G. B.
and
O'Brien
,
T. K.
, “
Interlaminar GIIc Evaluation of Toughened-Resin Matrix Composites Using the End-Notched Flexure Test
,” in
Proceedings of the 26th AIAA/ASME/ASCE/AHS Structures, Structural Dynamics, and Materials Conference
,
American Institute of Aeronautics and Astronautics
,
New York
,
04
1985
, pp. 197-202.
18.
O'Brien
,
T. K.
, “
The Effect of Delamination on the Tensile Strength of Unnotched, Quasi-Isotropic, Graphite/Epoxy Laminates
,” in
Proceedings of the SESA/JSME 1982 Joint Conference on Experimental Mechanics, Hawaii, Part I
,
Society for Experimental Stress Analysis
,
Brookfield, CT
,
05
1982
, p. 236.
19.
O'Brien
,
T. K.
,
Ryder
,
J. T.
, and
Crossman
,
F. W.
, “
Stiffness, Strength, and Fatigue Life Relationships for Composite Laminates
,” in
Proceedings of the Seventh Annual Mechanics of Composites Review
,
U.S. Airforce Wright Aeronautical Laboratory (AFWAL)
,
Dayton, OH
, Oct., 1981.
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