Dissipation hypothesis of energy under cyclic loads conditions was used to characterize the behavior of berry fruit. The possibility of dissipation of energy as a result of plastic deformations (Dawidenkow hypothesis) or visco-elastic deformations (Voigt hypothesis) was considered. Tests of hysteresis of whole fruit squeezed among two rigid plates for various levels of load and with various speeds of deformation of samples for two directions of load application were conducted for verification of the usefulness of both hypotheses. The strength tests were preceded by the test of hysteresis, the mass and the geometry of fruit were determined additionally as well as conventional density and moisture was counted. A mutual relation of average values of the coefficients of elasticity EC was accepted as the measure of dissipation of energy as a result of changes in the angle of inclination of the curve in the springy return phase. Voigt hypothesis was confirmed as useful within the range of small speeds of deformation and lack of usefulness of the Dawidenkow hypothesis was proved.
The selected physical properties as well as mechanical proprieties of kumquat and cape gooseberry fruit kept in the temperature of 12°C for 3 days, 8°C for 6 days and 4°C for 9 days were studied. The mass and size of fruit in three perpendicular directions were determined and density and moisture of tested material were calculated. Compressive tests of whole fruit were conducted for two directions of load application in order to determine the unit work WP an apparent coefficient of elasticity, stress σ and strain ε. The growth of inputs of the deformation work with expansion of the storage time was confirmed with regard to kumquat fruit which is related to the decrease of their conventional density. The decrease of the stress and elasticity values coefficient of cape gooseberry fruit with higher temperatures of storing expressed with the change of the slope angle of curves of the relation of stress-deformation was proved.
Gabriel Czachor, Jerzy Bohdziewicz and Krzysztof Kawa
The usefulness of raw material obtained from oak leaves, waste from paper mass and fragments of Miscanthus was verified with regard to pellet production. A batch of pellets produced therefrom was subjected to technological shear tests with the use of prototype equipment. Also pellets produced by well-known Polish producers were tested. The suggested method of technological shear enables obtaining credible results through standardization of tests conditions. Statistical processing of results proved that there are significant differences in the values of shear strength and unit shear work obtained for both group of pellets. An experimental batch of pellets has a lower density and thus lower shear strength which limits the scope of industrial application. The research which was carried out proved that there is a strong correlation between mechanical strength and density.