The Steady-state Sinusoidal Dynamic Behaviour of Peach and Pear

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Foods are frequently subjected to dynamic loading during harvesting, handling, transportation, and processing. Accurate prediction of dynamic responses of foods under these loading conditions requires better understanding of their dynamic visco-elastic properties. In this article, dynamic equilibrium was determined according to sinusoidal stress–strain. When a visco-elastic specimen is subjected to a sinusoidal varying stress, the resulting strain will be a sinusoidal response of the same frequency as the stress, out of phase by a lag angle. Experiments were conducted to measure the complex modulus of intact Daguanshan peaches and Luyu pears, the phase angle by which the strain lags the stress, and their relationship with initial pre-loading and vibration input power over a range of frequencies. Both the complex modulus and the phase angle increased as the frequency increased from 20 to 200 Hz. Initial pre-loading had a significant effect on the complex modulus, but not on the phase angle. Vibration input power had no significant effect on the complex modulus and phase angle. The phase angle depends not only on internal friction but also on the inertia of intact fruit.