The effects of fibre prestressing have been investigated on the flexural properties of glass-epoxy composites. Fibre prestressed composites were made by applying and maintaining a known amount of tension on the fibres during the curing process of the epoxy resin. In the next step, bending tests were conducted on a tensile machine using four point bending. In this study the modulus and strength of the fibre prestressed composite increased up to 33%. The experimental data also indicated that there existed a fibre prestressing level at which the flexural properties reached their maximum values. This prestressing level was found to be a function of the curing temperature. A mechanism has been proposed to explain the improvement of the flexural properties by the use of fibre prestressing during the cure process.

By applying the appropriate tension to the fibers during the curing process, the impact strength of glass-epoxy composites is improved up to 33%. Charpy tests show that the increase of the fiber prestressing increases the impact strength up to a particular level. Beyond this level, however, the increase of prestressing reduces the impact strength. The fiber prestressed samples indicate splitting breakage within the polymer that creates more new surfaces as compared with unprestressed composites. This results in the sample absorbing more energy during the impact. The splitting breakage is explained by the formation of the residual stresses in the polymeric matrix. Those stresses are controlled and promoted by fiber prestressing during the curing process.

In the present work, micro-residual stresses are measured in fiber prestressed composites. This is carried out by evaluation of residual strains in the fibers subsequent to the curing process. The force-strain curve for the glass fiber before, during and after setting of the epoxy resin shows that some part of the fibers' strain, caused by pretension, is not recovered when the tension is removed at the end of the curing process. The unrecovered strain in the fibers is used to assess the micro-residual stresses in the composite. Experimental results indicate that the micro-residual stresses in the fibers are linear functions of the applied pretension on the fibers during cure.

A new method is introduced to measure the dimensional changes of the polymeric resins while they go through the curing process. The dimensional change of the resin can be detected by implanting two markers into the resin and looking at the relative movement of them under an optical microscope. In the next part of this study, a partially-filled polymer specimen was made with continuous fibers. The measurement of the residual strain in the un-reinforced polymer phase of the specimen and comparison of it to the shrinkage value, indicated that only 3.3% of the resin shrinkage remained as residual strain in the polymer. Furthermore, the reheating of the bi-layer sample revealed that the stress free temperature is much lower than the curing temperature of the composite.