||New Standard Test of Composite Delamination Growth
ASTM D 6671, Standard Test Method for Mixed Mode I - Mode II Interlaminar
Fracture Toughness of Uni-Directional Fiber Reinforced Polymer
Matrix Composites, was approved May 10 to enable more precise
failure predictions. It was developed by members of ASTM Subcommittee
D30.06 on Interlaminar Properties, part of Committee D30 on Composite Materials.
Subcommittee chairman James R. Reeder, Ph.D., NASA Langley Research
Center, Hampton, Va., described its merit. The test method measures
a material property for which there was no standard test previously,
he said. This test method was standardized rather than other
possible tests because it offered several advantages. It can measure
toughness over a large range of mixed-mode ratios; data from the
test can be processed using simple closed-form equations (including
the division of the Mode I and Mode II toughness components);
and the preselected mixed-mode ratio stays essentially constant
as the delamination grows.
After Reeder and John H. Crews, Jr., Ph.D., developed the test
method at NASA Langley, Reeder conducted a round robin test activity
that refined the test protocol which was eventually balloted for
standardization by ASTM.
Reeder explained why D 6671 was developed as well as the improvements
it offers. Delamination is a primary failure criterion of composite
materials, he began. Delamination resistance is generally characterized
by the fracture toughness parameter. In the past, the only standard
for composite delamination growth was in Mode I where the delamination
grows by pulling the layers apart. Delaminations in real structures
would generally also be subjected to shear loading, and the fracture
toughness was known to change dramatically with the addition of
This new test method allows for the fracture toughness of composite
material to be measured with various amounts of opening and shear,
he noted. The new material data is leading to much more accurate
As in the standard Mode I test, the mixed-mode delamination test
uses a unidirectional composite test specimen, Reeder continued.
The results from the test are used to predict delamination growth
in general laminates that are not unidirectional. Composite laminates
are used in many different industries because of its high strength-to-weight
and stiffness-to-weight ratios.
D 6671 is available this month.
Technical comments may be directed to James R. Reeder, Ph.D., NASA Langley Research Center, Hampton, Va. (phone: 757/864-3456).
Committee D30 meets in Santa Barbara, Calif., Oct. 16-18 in conjunction
with MIL Handbook 17, and March 11-14 in Pittsburgh, Pa. For membership
or meeting details, contact James P. Olshefsky, manager, ASTM Technical Committee Operations (phone: 610/832-9714).
Copyright 2001, ASTM