STUDY OF FATIGUE FAILURE OF COMPOSITE MATERIALS

Abstract

The use of composite materials in U.S. Navy aircraft and other vessels has become increasingly popular due to the composites’ high strength to weight ratio. The nature of these military structures causes them to be exposed to high amounts of vibrations and cyclic loads, which lead to fatigue and eventual failure. The main objective of this research is to develop a reliable model to predict fatigue failure of composite materials in order to determine the service life of these military structures. This study determined the correlation between the fatigue failure of the glass fiber and the fatigue failure of the fiber and epoxy matrix composite. Glass fiber and composites with differing orientations were tested at various strain rates from 0.03–0.07 and were compared. A mathematical expression was created to model the exponential decrease of the elastic modulus with the number of cycles and to predict the failure cycle. The mathematical model is able to predict the failure cycles within 12% of the experimental results and follows the same trend of decreasing elastic modulus for both the fiber and the composite, showing a correlation exists between the failure behavior of fibers and the failure behavior of composites.