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Failure Criteria Of Fibrous Composite Materials

1.0. Introduction

This report was prepared during the two-month period the author spent at the Impact Dynamics
Research Facility at NASA Langley Research Center and was completed at the University of Seville
Engineering School, Seville, Spain.

The work developed at NASA Langley was originally conceived in two phases:

1. Evaluation of existing composite failure criteria in the MSC.Dytran code, a nonlinear finite
element code used for crash simulation and other transient dynamic structural problems.

2. Exploration of the possibilities for modification of material and failure models to account for
large deformations, and progressive failure and interaction of damage accumulation with stress-
strain response of laminated composites.

The greater part of the time at NASA Langley, after an inspection of the MSC.Dytran user manual,
was devoted to performing a bibliographical review of existing failure criteria of composites. The need
for this revision was also motivated by the lack of a theoretical manual supporting the aforementioned
program.

The papers considered most interesting for the objective of this report have been commented upon
in section 2.

The failure criteria included in the code under consideration are discussed in section 3. Some deci-
sions made in this code do not immediately indicate apparent consequences; therefore, it was necessary
to perform some calculations and to represent some graphs to show the implications of such decisions.
This information is presented in section 3.

A critical summary of the present procedures to perform analysis and design of composites is pre-
sented in section 4.

The study of the most important historical proposals presented to consider failure of the lamina of a
fibrous composite and the more recent modifications proposed created some doubts for this author
about the adequacy of the existing failure criteria. Also, some numerical analyses needed to be per-
formed to answer pertinent questions concerning the basis for some of the proposed criteria. A summary
of these ideas, which is a proposal of studies to be developed, is presented in section 5.

Finally, the most noteworthy aspects of the report, as well as some ideas for future developments,
are summarized in section 6.

2.0. Review of Recent Works

A review of recent publications (refs. 1—53) connected with the research topic featured in this report
has been completed. Initially, the study covered work done from 1993 to 1998. About 400 references
appeared in the initial review, from which approximately 100 were selected. When studying this infor-
mation, selected older papers were required and were included in the review.

Finally, 53 references have been included in this report. To facilitate the reading of this information,
a certain classification of the papers has been attempted, while recognizing the limitations from which
any classification can suffer. To facilitate the connection among the ideas in the different papers, the
references have been organized by date (within each group), although with some exceptions, particu-
larly when they refer to the same author.

All the references reviewed represent excellent works in their own field of application. The majority
of comments that might have negative connotations are connected with the aspects of interest in this
review, which obviously might or might not be of interest to the authors of the works reviewed.

The comments that appear in this section were generated when reading each of the papers. Some of
them may seem to be repetitive when the report is read in its entirety. They might have been comple-
mented or envisaged differently in the course of drawing up this report, as can be appreciated by reading
the rest of it.