An adhesively bonded Pi-/T-joint is a common ‘out-of-plane’ structural joint that connects a vertical (web) and a horizontal (base) load bearing substrates using an adhesive and a 3D-braided π (pi) preform. The stress-transfer between the substrates and the preform occurs through the adhesive bond-line via complex mechanisms that are governed by the loading condition and material properties of the substrates and the adhesive. Resistance strain gages and fiber optic sensors can only provide local/single-point measurement. Moreover, embedding them in the adhesive bond-line is impractical as they act as stress-concentrators and sites for the onset of failure. Optical techniques, especially the photoelasticity coating method, enables the full-field visualization of stress/strain fields. In this work, the Pi-/T-joints were made with aluminum substrates (both web and base) and a carbon fiber pi-preform using SC-15 resin as an adhesive. The joints were manufactured using the liquid resin transfer molding technique. The photoelasticity coating method was used to visualize and measure plane strains and stress directly on the joint using polarized light. The joints were experimentally tested in ‘out-of-plane’ (web pull-out) configuration until failure, and the isochromatic photoelasticity fringes or strain field images from the surface of the specimen were recorded. Force-displacement data were also characterized. Numerical models were developed using commercially available software ABAQUS®. Results show reasonably good agreement between the strain maps from photoelasticity and numerical simulations for similar load levels. Improvements in technique and modeling are suggested in order to improve agreement and to gain added insight into the complex behavior of these joints.
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