Dependance of Damage Accumulation in Carbon Fibre Reinforced Epoxy Composites on Matrix Properties

摘要

Two types of fibre reinforced resin specimens have been tested, each having the same type of fibre but with very different resin systems. In this way the effect of matrix properties on carbon fibre reinforced resin systems has been studied. Steady loads on unidirectional specimens have confirmed that far from being the unresponsive purely elastic bodies that most measuring techniques suggest the acoustic emission technique reveals the continuous accumulation of internal damage. The acoustic emission behaviour is characterized by curves of ln(dt/dN) as a function of total accumulated emissions which typically shows two asymptotic slopes, one at the origin, the other at infinity. An analytical expression has been proposed to describe this behaviour involving four parameters. The rate of damage accumulation has been shown to be greatly influenced by the properties of the matrix, with an increased rate observed with a resin containing a high percentage of plasticizer. The histograms of the amplitude distributions reveal a peak at 25 db at low stresses which is seen to be displaced towards 40 db at higher applied loads. It is concluded that the peak at 40 db is due to fibre failure whereas the lower peak may be due to microcracking of the matrix. The study has revealed that period of overloading are equivalent to accelerated mechanical aging at lower loads.