Micrographs of the fracture of vinyl ester composites cured by microwaves

Abstract

Vinyl esters (VE) in production exhibit shrinkage upon hardening which may be up to 10%. Shrinkage inherently sets up internal stresses within a material which are usually tensile in the core of the material and compressive on the surface (Ku, 2002). When these stresses act together with an applied load, they may cause premature failure of the composite component. Initial research by Ku has identified microwave technology as a possible solution to the shrinkage problem with initial tests revealing overall shrinkage results of around 1%. This has been achieved by selecting an optimum combination of initiator, input power of microwave energy and low profile additives. The aim of this project was to investigate the fracture behaviour of particulate reinforced vinyl ester composites cured by microwaves. To achieve this, a number of specimens were produced. These specimens were 33% by weight of the ceramic hollow spheres (envirospheres). Two types of tests have been performed, the drop weight impact test and the short bar fracture test. The drop weight impact and short bar tests yield fracture samples which were viewed under a scanning electron microscope (SEM) to investigate the mechanics of fracture. These SEM images or micrographs will provide further material and information on the fracture mechanics of VE/FLYASH cured under microwave conditions and will build on the knowledge base for this composite.