Measurement of micro-residual stresses in fiber-prestressed composites

In the present work, micro-residual stresses are measured in fiber pre-stressed 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 pre tension, 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.