Effect of size and shape on modulus of deformability

The effect of size and shape on the modulus of deformability was investigated and the analysis was extended to irregularly shaped cross-sections. Cylindrical specimens of raw potatoes with diameters (D) of 8.6 and 12.4 mm, heights (L) L=D and L=D/2 and water activity 0.94 were used as test materials. Their modulus of deformability was evaluated from a compression test. Multiplying the linear region moduli obtained from the stress-strain curves, by a modification factor of D/4L yielded a size-independent modulus. D/4L represents the ratio of the stress-bearing cross-sectional area that accounts for expansion to the stress-free surface area that accounts for material compressibility. The concept was further applied to samples with irregularly shaped cross-sections. Force-deformation data for these samples were converted to stress-strain data by using the cross-sectional area of the silhouettes of the samples. Modulus of deformability was evaluated from the stress-strain data and modified by multiplying with Df/4L where Df is the ferret diameter of the stress-bearing cross-section. Moduli of deformability for the irregularly shaped samples were found to behave similar to their cylindrical counterparts. This type of analysis should help to obviate the need for any other correction procedure and make comparative evaluation of deformation moduli more meaningful.