Influence of artificial UV degradation on the performance of steel/GFRP single-lap joints during exposure time

Metal structures can be repaired with composites using adhesives. However, because it involves polymeric materials, the environmental conditions of the structure can modify the behavior of the material, making its use unfeasible. Ultraviolet radiation (UV) is a degradation agent that has strong action on the polymeric materials, which are present in the adhesives and matrix of composites. In this work, it is studied the behavior of steel/GFRP single-lap joints using epoxy adhesive when exposed to UV radiation for different time intervals, to understand their behavior. The joint behavior was evaluated by shear testing and the adhesive was analyzed by DMA, FTIR and TGA. A decline of up to 32.5% in shear strength was observed with increasing UV exposure time. The Tg of the adhesive also showed a reduction. The FTIR spectra of the adhesive indicated a reduction in peaks related to epoxy functional groups when the exposure time was increased. This revealed degradation of the polymeric chains of the adhesive, a fact that can be associated with the reduction in Tg and the reduction in the shear strength of the joint. Thus, the application of such material in places exposed to UV radiation should consider the poorer performance regarding degradation.

Automated summary

Metal structures can be repaired with composites using adhesives. However, exposure to ultraviolet radiation can degrade the polymeric materials in the adhesive, leading to a decline in shear strength and a reduction in the adhesive's glass transition temperature (Tg). The degradation of the adhesive's polymeric chains is associated with the reduction in Tg and shear strength of the joint. Therefore, the application of such materials in UV-exposed areas should consider their poorer performance regarding degradation.