Physical and mechanical properties of the wood of coffee trunks and branches

Abstract

Knowledge of the physical and mechanical properties of coffee plants is essential to the development of mechanisms that perform the harvesting of their fruits by the principle of mechanical vibrations; however, these properties have yet to be determined in the laboratory. In this context, the present study aimed to determine the mechanical and physical properties of coffee plants through tensile and compression tests by means of a universal testing machine.Elasticity modulus, Poisson’s ratio, and specific mass were determined for specimens developed from the trunks and branches of 20 samples whole coffee plants, Coffea arabica variety, Catuai Vermelho cultivar. The elasticity modulus was determined by the slope of the secant line in the elastic region of the stress-strain curve. Poisson’s ratio was determined by direct measurements in regions previously marked on the specimens. The conventional specific mass was obtained by the ratio between the mass of specimens and their volume. The methodology allowed the studied properties and a database to be obtained, and they can be used as a basis for the development and operation of the mechanism used in the mechanical and semi mechanical harvesting of coffee fruits. The results obtained indicate the following values for elasticity modulus of the trunk, performed from compression tests: 1090.94 MPa in the longitudinal direction and 108.60 MPa in the cross-sectional direction. For elasticity modulus of the branches, performed from tensile testsin the longitudinal direction: 507.72 MPa. For Poisson’s ratio, determined by direct measurements: 0.25 for the trunk and 0.09 for the branches. And for specific mass: 1070.05 kg.m-3 for the trunk and 1036.33 kg.m-3 for the branches. Key words: Elasticity modulus; Poisson’s ratio; Specific mass; Geometrical properties.