Determination of physical properties and simulation of dynamic behavior of coffee plants

Abstract

The objective of this work was to study the dynamic behavior of coffee plants, in order to analyze their behavior during harvesting process, from numerical simulations, using a previously developed model. To support the simulations, the physical and mechanical properties (elasticity modulus, Poisson's ratio and specific mass) of specimens from the trunks and branches of coffee plants were determined in the laboratory, using tensile and compression tests in an universal testing machine. Such characteristics served as a basis to extract the natural frequencies and the modes of vibration (modal properties) from numerical simulations, which were performed using the deterministic Finite Element Method. To validate the model used, laboratory tests of free vibration using samples of whole plants were performed and the values found in the laboratory tests were compared statistically with the results found in the numerical simulations. The methodologies used in all stages of the research allowed evaluating the dynamic behavior of coffee plants when subjected to mechanical vibrations, which can assist in the development and adjustment in the use of mechanisms that perform mechanized harvesting in coffee plantations. The results obtained indicate values of elasticity modulus, for the trunk, of 1,090.94 MPa in the longitudinal direction and 108.60 MPa in the transversal direction; elasticity modulus of the branches, performed from tensile tests in the longitudinal direction, of 507.72 MPa. Poisson's ratio values, determined by direct measurements, were 0.25 for the trunk and 0.09 for the branches. Specific mass values found were 1070.05 kg.m-3 for the trunk and 1036.33 kg.m-3 for the branches. Frequency values found in the laboratory tests were concentrated in the range between 10 Hz and 30 Hz. This work took into account real aspects of coffee plants, such as their anisotropy and the use of a model built from reverse engineering, which represents an advance in research that simulates the dynamic behavior of coffee plants during the harvesting process.