A VIDEO-BASED METHOD FOR DETERMINATION OF AVERAGE STRESS-STRAIN RELATIONS IN UNIAXIAL COMPRESSION OF SELECTED FOODS

A video-based method was applied to evaluate average stress-strain rel ationships during uniaxial compression experiments of selected food ma terials. The determination of apparent Poisson ratios of Gouda cheese resulted in numbers close to the theoretical value for incompressible materials of 0.5. In case of such foodstuffs, mathematically corrected compressional stress based on the consideration of constant specimen volume showed almost similar results to stress values estimated on the basis of the true cross-sectional area measured from lateral extensio n. For compressible materials such as apples or bread, which show a ce rtain reduction of volume under stress or strain, the apparent Poisson ratios were strain-dependent. Average stress values calculated from c ompressional force and actual specimen diameter were found to be diffe rent from either engineering stress and corrected stress.