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Photoelasticity is particularly suitable for the analysis of the stress state in structural materials that are transparent and birefringent. Some techniques of digital photoelasticity (phase shifting and RGB) are applied to the analysis of stress field in two classes of structural materials. The first one consists of tempered glasses, such as those used in the automotive and architectural fields. The second one consists of thermoset polymers, typically used as matrices in fiber reinforced plastic structural composites. The birefringence of such resins is, in particular, exploited to investigate the development of swelling stresses and changes in fracture toughness as induced by water uptake aging

The present work investigates the fracture toughness behaviour of Single Edge Notched Bending (SENB) samples of epoxy systems subject to water uptake aging. Two epoxy systems with a significantly different Glass Transition Temperature, Tg, are in particular considered: a typical commercial non-aeronautical grade resin matrix for composite applications, reaching aTgof 90°C, and a DGEBA+DDS epoxy system achieving a Tg of 230°C.The materials have been conditioned by hydrothermal aging in a thermal bath at the temperature of 50°C. TransmissionPhotoelastic Stress Analysisis carried outon SENB samples during water aging, monitoring the presence and evolution of swelling stresses. The KIC Fracture toughness is measured and correlated with the internal stress field, with the water diffusion kinetics evaluated by gravimetric tests, and with the data from DMTA analyses. Results have highlighted significant differences in the fracture behaviour ofthe two epoxy systems