Effect of the natural aging process on the shear strength of FRP composite single lap joints

The aim of this paper is to investigate the effects of fiber reinforced plastic (FRP) adherends in single lap joints subjected to an aging process. The adherends used a FRP laminate configuration of [901, 01, 01, 901], while the length and thickness of the adhesive bond were held constant. A two-part methacrylate adhesive was used for the bonding. The aging procedure applied to single lap joints was developed under natural conditions (in Temuco, Chile) for twelve months. Climate conditions of aging showed marked seasonal variations corresponding to cold, warm and hot months. The un-aged and aged adhesive behavior was assessed through Fourier Transform Infrared Spectroscopy (FT-IR). In addition, the degradation degree of the adhesive tested was investigated via thermal properties measured by thermogravimetric analysis (TGA) and Dynamic thermomechanical analysis (DMA). Three adhesive joints batches have been tested, without aging, nine month aging and twelve month aging. Tensile tests to the single lap joint (SLJ) were performed according to standard ASTM D 1002-01, at room temperature. The static tensile test revealed an incremental degradation of the mechanical strength in the adhesive joint compared to SLJ without aging. For the maximum displacement of the SLJ tested, a stiffening of the joint is appreciated, reducing the displacement in 72% and 65% for nine and twelve aging months, regarding the SLJ without aging. The results of the TGA and DMA tests of the adhesive barely changed after 365 days of exposure. The failure modes of the adhesive joints were classified as light fiber tear failure for all SLJ tested. It is important to highlight that the adhesive joints with FRP adherends suffer a significant mechanical strength decrease under environmental/climate degradation.