A study of press-glued and screw-glued stressed skin components with a gap-filling phenol resorcinol formaldehyde adhesive

The effect of screw-gluing and gap-filling phenol resorcinol formaldehyde (GPRF) adhesive using different glue line thickness values on the mechanical performance of stressed skin components (SSCs) including block shear strength were investigated experimentally. The use of screw-gluing fastening type and GPRF adhesive for the stressed skin and other panel products were determined. A new procedure was developed to fabricate pre-arranged gaps using steel shims, a testing machine that has a special apparatus, and wings made of maple for bending specimens and measure their thickness by utilizing the image analysis technique.; The bending properties of SSCs were investigated in relation to fastening types (press-gluing, screw-gluing, screwing-only, and no connection) and glue line thickness (0.1778–1.0160 mm). The results showed that neither modulus of rupture (MOR) nor slope among the fastening types was not significantly affected by different glue line thickness. No interaction found between two variables that proved satisfactory performance of and good gap-filling property the GPRF adhesive. Fastening only by screws is not recommended. Screw-glued and press-glued components performed similarly and showed similar deflection characteristics and failure patterns. The test data indicated that screw-glued components had better MOR and slope average than press-glued ones. The presence of screws increased the strength in bending and gave initial pressure to hold the skin and stringer in place to allow the glue curing. The results confirmed that the GPRF adhesive can be used to bond plywood to lumber into a structurally sound and efficient panel product. The technique can be used to fabricate larger panel products economically. The variables of modulus of elasticity of lumber and plywood, moisture content of lumber and plywood and specific gravity of lumber and plywood were used to build a realistic and practical model to calculate the MOR and slope. The block shear strength was decreased with increased glue line thickness. The screw-gluing fastening type was found as effective as the press-gluing type to provide necessary pressure for block shear assemblies.