Book Review: Fatigue of Composite Materials
Dateline: 10/06/97Last week, a reader wrote me and asked if I had any information on crack propagation mechanisms in composites. Having worked on several failure reviews, the short answer is that cracks follow the fiber direction and are turned by changes in fiber angle.
For a more theoretical answer, I was able to recommend two books. The first was Dynamic Loading and Characterization of Fiber-Reinforced Composites, which I reviewed last July.
The second book is Fatigue of Composite Materials, and I promised the reader a review of it this week.
This book is a collection of nine papers by Ramesh Talreja. An introductory chapter, written for the collection, gives a brief theoretical background to fatigue in composites and covers the topic from a qualitative viewpoint. Many different fatigue damage mechanisms can be found in composites, depending on the load direction and laminate sequence. For example, a unidirectional composites loaded in the fiber direction will show fiber breakage, interfacial debonding, matrix cracking, and interfacial shear failure.
The remainder of the book reads almost like a text, even though it is a collection of papers. Chapters two through four pick up where the introduction left off, with a detailed qualitative description of fatigue mechanisms in unidirectional composites and various laminates. Fatigue-life (S-N) diagrams are introduced which show not only load limit versus number of cycles, but also the different failure modes which may occur.
Chapters five through eight present a more theoretical view of fatigue and damage mechanisms. Using the qualitative models shown in the earlier chapters, modified constitutive equations which account for damage are developed. These models are used to determine the residual elastic properties in a laminate, and a few numerical examples are given.
In chapter nine, the author shows how to calculate the Weibull parameters for strength and fatigue life data. (For more information on Weibull parameters, see my earlier feature on Statistics and Strength.
Finally, it was is probably the most practical chapter, the author presents design criteria for both static and fatigue loads. He begins by describing damage propagation in a laminate, then shows how that changes as both the load and the layup change. The models developed in the second part of the book are then used to develop reliability criteria for composites.
As the author points out in his preface, a rigorous theory for fatigue in composites has not yet been developed. Research continues at a quick pace, and this book only covers the period of 1979--1984. It provides a good background in composite fatigue, but obviously cannot include the latest research.
Details: Fatigue of Composite Materials, by
Ramesh Talreja, published by
Technomic, 1987, ISBN 87762-516-6.
1. Fatigue Damage Mechanisms: Introduction; 2. Fatigue of Composite
Materials: Damage Mechanisms and Fatigue-Life Diagrams; 3. Damage
Models for Fatigue of Composite Materials; 4. A Conceptual Framework
for the Interpretation of Fatigue Damage Mechanisms in Composite
Materials; 5. Stiffness Based Fatigue Damage Characterization of
Fibrous Composites; 6. A Continuum Mechanics Characterization of
Damage in Composite Materials; 7. Residual Stiffness Properties of
Cracked Composites Laminates; 8. Transverse Cracking and Stiffness
Reduction in Composite Laminates; 9. Estimation of Weibull Parameters
for Composite Material Strength and Fatgiue Life Data; 10. On Design
Criteria for Composite Structures Under Static and Fatigue Loads