Nonlinear viscoelastic plastic model of the fruits under quasi-static compressive loading

It is commonly difficult to characterize the properties and model of a nonlinear viscoelastic plasticity of fruits. Based on the deformation characteristics of the fruits under constant rate quasi-static compression, a general rheological model of a nonlinear viscoelastic plastic solid was developed. The model is composed of three nonlinear springs, one viscous damper and one slide damper elements. The method for defining and determining the parameters of the model was proposed by combining the testing curves of stress versus strain with the model characteristics. The quasi-static compression testing was performed with two kinds of pear specimens of full flesh and flesh with a core. The parameters of the nonlinear viscoelastic plastic model were computed. The results show that theoretical model is well agreed with the test results, the viscoelastic plasticity of the fruit was influenced by the fruit core. The model can accurately and conveniently be used to determine the rheological parameters of pears and other fruits with similar properties.