The effect of spline material, adhesive type, and screw on bending moment capacity of the mitered frame corner joints made of medium-density fiberboard (MDF) under diagonal tension

Cabinets doors are usually made of medium-density fiberboard (MDF) as mitered frames connected with wooden dowels, biscuits, spline, or plastic keys with adhesive. Because of its rapidly curing and working, cyanoacrylate adhesive is usually used to connect frame members, but they separate after a while due to its brittle fracture, which is an unusual joining method. Therefore, this study was aimed to investigate the effects of Spline material (plywood, fiberboard, and poplar wood), type of adhesive (polyurethane (PU), and Polyvinyl acetate (PVAc)) with and without a mechanical fastener such as screw on the bending moment capacity of the mitered frame corner joints under diagonal tensile, then compared with frames cut with CNC. Loading was applied with a Hounsfield 0308 testing machine with a loading rate of 5 mm/min. The results showed that the changing of the spline materials, adhesive types, and mechanical fastener resulted in 79.2%, 69.1%, and 131.7% change in the strength of the joints, respectively. The least bending moment was observed in joints made with plywood spline and PU adhesive without any screw; on the contrary, the highest bending moment was related to both joints made with fiberboard and poplar spline with PU adhesive and screws (50.83 and 48.48 N.m, respectively). Late two mentioned joints tolerated higher bending moments than the CNC cut MDF frames (12.4% and 7.6%, respectively). Therefore, all frames are necessary to use spline with PU adhesive as well as screws to make the frame, to reduce the MDF offcuts caused by CNC cutting.