A series of twenty four fatigue tests were performed on massproduced fiber reinforced plastic beams to evaluate their performance under cyclic loads. Combinations of sections which were joined by adhesives and bolts were also tested. Stiffness degradation and failure patterns were monitored in each specimen. It was observed that most of the composite beams exhibited a high resistance to fatigue under cyclic loading with strain range reaching levels as high as 84 % of the ultimate strain of the specimen. Theoretical prediction of fatigue resistance was not possible at this stage of the research program, but excellent correlation was observed between theoretical and experimental static deflections and strains. This paper describes a procedure to characterize the fatigue performance of glass-fiber/polyester resin composite beams and joints, but additional testing of specimens with different sizes and span lengths is suggested to have a better understanding of the material behavior.
Applications of fiber reinforced plastic (FRP) materials were limited, traditionally, to aerospace industries because only in the aerospace industry FRP's high manufacturing and assembling costs were justified by the high strength to weight ratio. However, recent improvements in manufacturing technologies and certain distinct advantages of glass FRPs over conventional materials offered the composite industry a broad spectrum of commercial applications such as automobiles, pedestrian bridges, roof decks, cooling towers, beach piers and many others. One of the distinct advantages of FRPs over conventional materials is their increased resistance to fatigue. Fatigue failure in composites does not necessarily imply breakage of a specimen into two or three pieces, but often can be observed as fiber breakage, matrix crushing, interfacial debonding or delamination (Talreja, 1987). Strain range versus number of cycles (S-N) diagrams are commonly used in composite materials to describe the expected fatigue behavior.
