Comportamento dinâmico do cafeeiro: um estudo sobre as propriedades físicas, mecânicas e modais de ramos plagiotrópicos

Abstract

Seeking to reduce the physical efforts of manual harvesting, increased operational capacity, as well as greater effectiveness in detachment, the mechanization of the harvesting operation has been increasingly used in the coffee production process. The objective of this study was to understand the dynamic behavior of the coffee plant to assist in the development of machines and to adapt parameters associated with this type of harvest. The work was based on the determination of the physical, mechanical, and modal properties of the plagiotropic branch of the specie Coffea arabica L., cultivar Catuaí Vermelho (IAC144). Different factors were considered: position in the plant (upper third, middle third and lower third), maturation stages (green fruits and ripe fruits) and study scenarios of the branches (without fruits and without leaves, without fruits and with leaves, with fruits and leaves). This work consists of three articles. In the first article, the mass, volume, specific mass and modulus of elasticity of specimens made from branches of the coffee plant were experimentally determined. The specimens of the branch presented mean specific mass equal to 0.945 g.cm-3 with standard deviation of 0.049 g.cm-3. The mean modulus of elasticity found was 1.24 GPa with a standard deviation of 0.13 GPa. In the second article, the experimental modal analysis was performed, using the Response and Frequency Function (FRF) obtained from the use of an impact hammer system and accelerometer. The mean natural frequencies, ratios and average damping coefficients were determined considering the different factors. For the leafless and fruitless branch, considering the position in the plant, a significant difference of the upper third was observed in relation to the other thirds of the plant for the first three natural frequencies. The upper third presents throughout its extension, younger biological material, in development and with new shoots. The lower stiffness, due to morphological characteristics of young wood, and lower mass, may influence the values of the average natural frequency of the branch, which may explain the values obtained. For the fruit-filled and leafless branch, in a synthesized way, the average natural frequencies were increased as the maturation stage evolved or towards the top of the plant in the upper third. In the study of the branch with leaves and fruits, it was observed, for the different positions in the plant, that there was no significant difference for the average natural frequencies. This result can be considered as an important machine regulation parameter, since it would not be necessary to use different frequencies throughout the plant for skid. In the third article, natural frequencies and modes of vibration of plagiotropic branches were determined by finite element analysis. The proposed models were statistically analyzed by linear regression analysis and correction test. The values of experimental and numerical natural frequencies showed linear correlation, indicating that the proposed models can predict the dynamic behavior of coffee when submitted to mechanical vibrations.