Technological solutions that will ensure the economic viability
and environmental compatibility of a future High Speed Civil Transport
plane are currently being sought. Lighter structural materials
for both airframe primary structures and engine structure components
are being investigated. We believe that such objectives can be
achieved through the use of high-temperature composites as well
as other conventional, lighter weight alloys. One of the prime
issues for these structural components is assured long-term behavior
with a specified reliability.
An investigation was conducted to describe a computational simulation
methodology for predicting fatigue life (see the figure above),
reliability, and probabilistic long-term behavior of polymer matrix
composites. A unified time-, stress-, and load-dependent Multi-Factor
Interaction Equation (MFIE) model developed at the NASA Lewis
Research Center was used to simulate the long-term behavior of
polymer matrix composites.
To illustrate the application of the methodology, we chose a typical
composite system consisting of graphite fibers in an epoxy matrix
with a layup of (0°/±45°/90°)s. This methodology
can be applied to other types of polymer matrix composites as
well. The cumulative probability distribution functions for the
fatigue life cycles were computed for different thermal cycle
rates and constant applied stress. The laminate strength was evaluated
on the basis of first-ply failure criteria (hereinafter referred
to as laminate strength). First-ply failure criteria assumes that
a laminate has failed when any stress component in a ply exceeds
its respective allowable. Using these cumulative probability distribution
functions, one obtains a fatigue life cycle curve for a reliability
of 0.999 (as in the following figure). The results show that,
at low mechanical cyclic loads and low thermal cyclic amplitudes,
fatigue life for 0.999 reliability is most sensitive to the matrix
compressive strength, matrix modulus, thermal expansion coefficient,
and ply thickness. In contrast, at high mechanical cyclic loads
and high thermal cyclic amplitudes, fatigue life at 0.999 reliability
is more sensitive to the shear strength of the matrix, longitudinal
fiber modulus, matrix modulus, and ply thickness.
Previous articleLast updated April 30, 1997
Responsible NASA Official:
Gynelle.C.Steele@nasa.gov
216-433-8258
Point of contact for NASA Glenn's Research & Technology reports:
Cynthia.L.Dreibelbis@nasa.gov
216-433-2912
SGT, Inc.
Web page curator:
Nancy.L.Obryan@nasa.gov
216-433-5793
Wyle Information Systems, LLC
