Fracture mechanism in randomly oriented discontinuous carbon fiber reinforced borosilicate glass matrix composites

摘要

Fracture mechanisms in randomly oriented discontinuous carbon fiber reinforced borosilicate glass matrix composites are experimentally characterized. Two types of composite specimens with identical constituents but different microstructure wereproduced. The first type shows the three-stage behavior in the tensile stress-strain curve. In the second type which has the initial cracks, the stress - strain response is almost linear, but the initial Young's modulus is lower than that of the firsttype. Monotonic and static cyclic tensile and four point bend tests are conducted on those two specimens to measure the microcrack density, Young's modulus and Poisson's ratio as a function of applied strain. The experimentally determined crack density is used to estimate the interfacial shear stress. In the bend tests, evolution of microcracking on the tensile surface and through the thickness has been studied. Acoustic emission (AE) during the tests is monitored to understand the fracture mechanisms. Itis proved that the difference in fracture mode between the two specimens is due to the difference in microstructure and the presence of initial defects. The AE behavior shows good correlation with the evolution of microcracking and can explain thefracture processes. Young's modulus can be a damage parameter to estimate the microcrack density. Microcracking during the flexural tests begins on the tensile surface and the cracks progress gradually towards the neutral axis.