Failure Characteristics of Apple Tissue Under Cyclic Loading

Abstract

ABSTRACT THIS report is a study of the response of apple tissue to compressive cyclic loading. Experiments were performed in which cylindrical samples of apple tissue were subjected to cyclic loading, with the peak stress either remaining constant or slightly increasing with each cycle. For comparison, static loading tests were performed with comparable stress magnitudes. It was found that apple tissue can fail under cyclic or static loadings of magnitude insufficient to cause failure initially. Failure was apparently due to a propagation of cell wall ruptures in a plane perpendicular to the axis of the applied stress, as under ordinary constant-strain-rate tests. The failure characteristics in terms of tissue strength, strain at failure, and time to failure were not significantly different under cyclic and static loadings; however, the strain at failure was about 30% greater than that under constant-strain-rate loading. A statistical model for the number of cycles to failure indicates that the likelihood of imminent failure remained approximately constant with the number of cycles applied, and thus failure appeared to be primarily a random event rather than the result of damage accumulation. The results of a simple model of the parenchyma cell indicate that cell wall stresses are greatest in the initial application of load under cyclic or static loadings. Thus, it is theorized that the initiation of failure is caused by a random decay in cell wall strength under applied load