Resistance of corn ears and grains of different maturity to quasi-static load

Abstract

Corn Zea mays L. is among the most remarkable cereal species, which has great importance in the human diet and animal feed in many parts of the world. Corn yield from one hectare can be from 50 to 70 tons of green mass or from 6 to 10 tons of grain. Corn for grain can be harvested using various technologies, provided the grains in ears are in physiological stage of maturity. Awareness of apparent properties such as rupture force, rupture energy etc. of agricultural seeds is important for predicting load-deformation behaviour, and must be taken into account when designing specific processing machines. This study was carried out with the aim to determine the physical and mechanical properties corn grains and corn ears during their different physiological maturity stages. The study of mechanical properties of corn grains and ears was performed applying quasi-static loads using Instron-5960. Corn ear deflection was tested applying different distances between the support beams: 60 mm and 120 mm. Corn ear rupture force decreases when the distance between the supports is increased. Grains were applied load at three different orientations: over the length, over the width and over the thickness. A single grain was placed between two parallel plates and gradually compressed while simultaneously recording the force and the corresponding deformation that occurred until the grain ruptured. At this point the force suddenly decreased, while deformation continued. In most cases, the initial portion of grain load-deformation curve was more or less linear up to certain points of deformation beyond which it became non-linear. The observed bioyield point represents the yield point in biological materials. This is an indication of initial cell rupture in the cellular structure of material. The results showed that provided moisture content was reducing from 50.94±1.64% to 36.21±0.52%, the maximum corn grain rupture force increased from 91.54±16.75 N to 200.67±18.43 N.