Monitoring by a single fiber Bragg grating of the process induced chemo-physical transformations of a model thermoset

Strain build up during the non-isothermal curing of a model epoxy resin in an aluminum mold has been investigated by using a single fiber optic Bragg grating. The curing process as well as the cooling down stage, the de-molding phase and the intrinsic strain relaxation have been successfully monitored and analyzed. In non-isothermal curing, the gelification point has been clearly identified as the thermal apparent strain onset. The fiber optic system was efficient in measuring as the strain build up in cooling down as the de-molding stresses due to the thermal expansion coefficients mismatch between the resin and the aluminum mold. The frozen strain relaxation has been measured in repeated heating/cooling cycles and relaxation progression monitored by the evolution of the glass transition temperature in the aged sample. In addition, the thermal expansion coefficients of aluminum, glass and rubbery state resin have been estimated in good accordance with literature data. (C) 2004 Elsevier B.V. All rights reserved.