Técnica de pulso ultrassônico para avaliação de danos mecânicos em grãos de café beneficiados

Abstract

The coffee has big economic importance for Brazil, but there aren't yet researches for storage so the grain’s quality will be kept during this period. The knowledge of physics characteristic to grain coffee would allow the transition of the conventional storage model to grain store and as an indirect measure of improving and preserving the quality of stored grain. The elasticity modulus allow to make comparison of strength material and the variations of this occurred by reason of your chemical composition, microstructure and material defects will can be used as indicator of physical integrity of grain. In this context, this work was realized with the intention of know the elasticity modulus of bulk grains of coffee, by the method of non-destructive testing. The ultrasonic pulse technique is a simple alternative for obtaining the modulus. Thus a silo model was built to reproducing the conditions of storage, and the values of the elastic modulus measured. The values obtained with the Stress Wave Timer are among 2,54 to 4,23 MPa, and maximum load applied was 8.32 kN and vertical pressure was calculated in 1,526 kPa. To assess the impact of storage conditions, laboratory tests generally applied to seeds, were performed. The tetrazolium test applied in endosperm to investigate external damage was able to find a increase because of the loads applied, however, the others tests, electrical conductivity and X- rays, didn't identify increase in external damage in grains after the loads, this indicates that the value of the vertical pressure may be used safely for storing coffee.