Effect of loading rate on the strength of SiCf/SiC composites

The dependency of the strength of SiC fiber reinforced SiC composites (SiCf/SiC) on the loading rate has been experimentally determined with respect to the fiber volume fraction and boron nitride or carbon fiber coating of different thickness. High strain rate tests were performed using a pendulum-type impact bending machine and the Split-Hopkinson pressure bar (SHPB) technique, which enable the measurement of the stress-strain relationship at strain rates around 200 s(-1). The tensile and bending strengths defined as the maximum stress in the stress-strain relationship were obtained as a function of the fiber volume fraction (20%-40%) and the strain rate. The composites with higher fiber volume fraction and with higher strain rate exhibited larger bending and tensile strengths. The fiber pull-out length increases with fiber volume fraction and coating thickness and decreases with loading rate. The fiber pull-out mechanism is explained by sliding at both the fiber/coating and the coating/matrix interfaces in combination with coating fracture.