Determination of bending modulus of elasticity of Pterygota macrocarpa K. Schum (Kyere) and Piptadeniastrum africanum (Dahoma) using two International testing norms

Abstract

Two different international testing norms, DIN52186 (1978) and ISO8375 (1985) were used to determine the bending modulus of elasticity (MOE) of Pterygota macrocarpa K. Schum (Kyere) and Piptadeniastrum africanum (Dahoma). The results from the two testing norms for each timber species were highly correlated, with correlation co-efficients of 0.92 and 0.96 obtained for Kyere and Dahoma respectively. The MOE determined using ISO 8375 (1985), employing deflections within loading points (i.e. within the shear free zone) was, however, significantly higher than that determined using DIN 52186 (1978), employing deflections along the whole specimen length, for both species at 5% probability level. The difference in MOE's may be attributed to the influence of shear stresses in bending, in the case of specimens tested using DIN 52186 (1978). The results indicate that, test standards which recommend computation of MOE using total deflection along the whole length of the test specimen may under-estimate the actual rigidity of a wooden member.



JOURNAL OF THE GHANA SCIENCE ASSOCIATION Volume 1 Number 3, July (1999) pp. 126-132