Damage characteristics analysis of GFRP-Balsa sandwich beams under Four-point fatigue bending

Four-point bending static and fatigue experiments were performed on composite sandwich beams with glass fiber reinforced polymer (GFRP) face sheets and Balsa wood cores. Specimens with various span-to-depth ratios were prepared using a vacuum-assisted resin transfer molding process. The results showed that the sandwich beams under both static and fatigue tests failed due to core shear and debonding. The S–N curves of sandwich beams were determined using an exponential empirical model. The study showed that to sustain at least one million cycles, the service load should be limited to 60% of the ultimate load. The deflection evolution of the sandwich beams were found to occur in three stages, namely, transient fall, stable evolution, and rapid failure. Furthermore, a fatigue damage model closely related to the possible detection of damage initiation and progression was proposed. The model was proved to be appropriate for describing the fatigue response of GFRP-Balsa sandwich beams.