Assessment of the mixed timber combination effect of finger-jointed timber species using flexural and tensile strength

Off-cut wood is one of the wastes dumped by sawmills, and inadequate length of sawn timber materials fail to fully utilize the wood supply. Finger joint, a method that connects two small pieces of timber, is identified as a sound technique to minimize wastage. Different timber species should be bonded at the finger joint production process for making finger-jointed mixed boards. When mixing the different timber species, timber pieces should be matched based on the mechanical strength. This study was, therefore, conducted to find the strength properties of mixed finger-jointed timber species of wood, namely, Grandis (Eucalyptus grandis), Jack (Aartocarpus heterophyllus), Kumbuk (Terminalia arjuna) and Pine (Pinus caribaea), commonly used in Sri Lanka in the manufacture of furniture. The tests were carried out on timber samples with 19 mm finger lengths made of two sections bonded with an adhesive containing polyvinyl acetate (PVAc). The tensile strength and variation of the flexural strength of the finger length of the samples were studied. BS 373: 1957 was the standard used for the flexural tests. A Universal Testing Machine (UTM 100 PC) was used for the mechanical tests. Timber combination categories are not significantly different for the MOR tests. Pine-Pine vs. Pine-Grandis combination category is significantly different for Bending tests. According to overall results, timber combination categories are significantly different for the tensile tests except for Pine and Kumbuk combinations. The findings of this study will directly benefit the finger joint manufacturers in Sri Lanka.