FRACTURE ANALYSIS OF FATIGUE DAMAGE MECHANISMS IN FIBER REINFORCED COMPOSITE MATERIALS USING SCANNING ELECTRON MICROSCOPY

摘要

A variety of experimental and analytical methods have been used in attempting to characterize the fatigue damage processes in fiber reinforced composite materials. There has, however, been a distinct lack of SEM fractography applied to this area. In this report, composite SEM fractographs (approx. 70 - 80x) of two composite material systems (boron/epoxy and boron/aluminum) having the same fibers, layup and geometry, but drastically different matrix materials, are presented and discussed in detail. Both high and low frequency strain controlled fatigue tests and static test fractures are examined. Distinct differences between static and fatigue damage, and high and low frequency fatigue damage were observed. These various damage modes are detailed and summarized in several tables. A physical model describing the fracture process in these materials is presented by means of a flow chart. This model considers the cases of: static or fatigue loading, high or low cycling frequency, and weak or strong interface behavior.