| The impact response of fiber composites was investigated to determine the effect of repetitive drop weight testing with increasing energy (RDTIE). The initiation and propagation of impact damage were traced by ultrasonic C-Scanning and sectioning through the damaged region. In thermosetting matrix composites, two or three distinct damage stages could be found from changes in stiffness and percent transferred energy. The first stage involved transverse cracking in the upper and/or bottom layers. In the second stage, the damage was through the sample thickness and in the third the damage propagated to the edge of the sample.; In thermoplastic matrix composites, the type of damage was not clearly delineated and many different fracture mechanisms (e.g., delamination, fiber breakage, etc.) occurred simultaneously.; Changes in stiffness with cumulative energy at which the damage occurred were affected by matrix, fiber, ply stacking sequence and sample geometry. A simple model was developed to predict these effects. The theory and experimental data were compared and showed reasonable agreement.; Static three-point bending test was performed in order to compare with the impact test. In the thermosetting matrix materials, the impact tests and static tests showed similar results. However, thermoplastic matrix composites showed different results between impact tests and static tests. The repetitive drop weight test with increasing energy was compared with fatigue impact test at constant energy. Finally, the effect of impact damage on residual tensile modulus was determined. |
