Evaluation of the Major Failure Modes of the Nonstructural Finger Jointed Timber Species Under Tensile Test

Abstract

A study was undertaken to evaluate the tensile strength performance and major failure modes of the finger-jointed timber species used in nonstructural productions. Finger jointing is a process for recovering valuable natural resources. Finger joint technique is used to eliminate wood defects which weaken the strength of sawn wood plank and unused short pieces can even be used for obtaining defect free longer lengths of timber. A finger profile of 13 mm finger length, 4 mm pitch and 1 mm tip width were used in the study. The sections were joined by using PVA adhesive.BS 373: 1957 and BS EN 15497:2014 Standards were used for tests. The test for tensile properties were performed using Universal Testing Machine (UTM 100 PC) with loading plate moving speed of 01mm/min and load vs. displacement variation was obtained. Maximum load could be identified to calculate ultimate tensile strength. Seven timber species commonly used for furniture manufacturing industries in Sri Lanka, including softwood Pine (Pinus caribaea) and hardwood Grandis (Eucalyptus grandis), Jack (Artocarpus heterophyllies), Kumbuk (Terminalia arjuna), Mahogany (Swietenia macrophylla), Satin (Chloroxylon swietenia) and Teak (Tectona grandis) were used in this study. The major failure mode of the nonstructural finger jointed 7 timber species subjected to a tensile test was mainly due to glue line failure (47.14%), followed by wood grain failure (24.28 %) and fiber failure (15.71%). The least failure mode was weak finger joint (12.85 %). The highest mean finger joint strength was obtained from Grandis (50.23 N/mm2) timber species and least mean finger joint strength was recorded in Kumbuk (16.88 N/mm2) timber species.