ANISOTROPIC MECHANICAL-PROPERTIES OF APPLES

Firmness is a critical aspect of apple quality. Knowledge of mechanica l properties of apple flesh and intact apples is needed to develop a m ethod to sort intact apples according to firmness. Little derailed inf ormation is available on the nonhomogeneous and anisotropic mechanical properties of apples. The objective of this study was to determine th e effects of ripeness and of specimen orientation and location within the apple on failure stress, strain, and energy, and apparent modulus of elasticity (Young's modulus). Compression tests were performed on ' Delicious', 'Golden Delicious', and 'Rome Beauty' apples using a unive rsal testing machine. The four mechanical properties were significantl y influenced by specimen orientation, latitude (location from stem to calyx), and depth (from skin to core) and, to a smaller extent, by the orientation x latitude, orientation x depth, and ripeness x depth int eractions. The other interactions were either quite small or not signi ficant. Failure stress was highest in the vertical direction and lowes t in the tangential direction. Young's modulus was significantly (P le ss than or equal to 0.05) higher in radial samples than in tangential and vertical samples. The largest values of failure stress and Young's modulus were obtained from the bottom sections and the smallest Young 's modulus values, from the top sections. Delicious apples varied more around their circumference than did Golden Delicious and Rome Beauty apples. The anisotropic properties of the apples were more pronounced in the middle (equatorial) sections than in the top (stem) or bottom ( calyx) sections.