STIFFNESS ASSESSMENT FROM JAGGED FORCE-DEFORMATION RELATIONSHIPS

Brittle and crunchy foods are notorious for their irregular and irreproducible force-deformation relationships which cannot be converted to stress-strain relationships because of geometric considerations. However, a fairly consistent assessment of their stiffness can still be extracted from their jagged force-deformation curves. For example, either the averaged force at a given deformation (e.g., 20%), determined directly or calculated by fitting the curves of several specimens with a polynomial model, can be considered a legitimate stiffness measure albeit a relative one. But since the magnitude of such parameters is affected by occasional force lows and minima as well as failure and sliding events at preceding deformations, they can only provide a low estimate of the material actual stiffness. Application of an algorithm that identifies the peak forces in the force-deformation relationship produces a new relationship that has a fairly regular and much smoother shape. Derivation of stiffness parameters from such curves is not only easier because of the regular shape and reduced number of points but also provides a closer estimate of the material actual stiffness.