| Popis: |
DETERMINATION of the axial compression com-plex modulus of spheroidal shaped foods by sinusoidal direct stress-direct strain is not possible using the Hertz contact theory because the contact surface area is not all caused by the sinusoidal forcing. A static preload is normally used to hold the specimen in place and a sinusoidal forcing superimposed. Inability to use the Hertz equation in this situation is demonstrated experi-mentally and an alternative equation sought. Using dimensional analysis and test data for 176 specimens involving a variety of fruits and vegetables (88 ellip-soidal specimens and 88 cylindrical specimens) tested at 2 Hz and 144 specimens tested at 80 Hz, the equation |E*| = 1.51 F/(D dc) for spheroidal specimens was developed where |E*| is the absolute value of the complex modulus, F is peak to peak force, D is peak to peak displacement and dc is the mean contact diameter (including both contact surfaces of an axially com-pressed spheroid). Any consistent set of units is suitable. Using this developed equation, the R2 value for the modulus was 0.97. |
