RHEOLOGICAL CHARACTERIZATION OF APPLE CORTEX

The incremental creep and recovery theory was used to develop a constitutive relationship for apple cortex without assuming the nature and the characteristics of the material. Successive loading and unloading cycles of increasing duration were applied on the cylindrically shaped specimens of apple cortex. The elastic strain component was linear with stress. The viscoelastic and permanent strain components were time dependent and nonlinear functions of stress.
Three-step creep tests and stress-strain tests at various deformation rates were also conducted on cylindrically shaped specimens of apple cortex. Prediction of strains under these loading histories by using the constitutive equation showed a close agreement between the theoretical and experimental strains. An equivalence between the critical creep stress (found from the incremental creep and recovery tests) and the ultimate stress, obtained from the stress-strain tests at various deformation rates, were also established.