Hi all. I have something of a problem in my understanding of a current lab experiment that I am doing in my second year. The experiment is set such that we explore the elastic properties of an elastic band through small and large deformations and measure the force that it exerts on the mountings (that are moveable in order to defore the material). We are to observe a stress/strain curve, and work out the young's modulus, The hysterisis curve, and ultimate deviations from Hookean behaviour. The later part of the lab is to observe how the elastic properties change when at different temperatures. (I.E., hold a constant deformation, and vary the temperature) Note: the band is deformed linearly along its length, no force is applied in the plane of the cross section. My question is this. The stress/strain curve exhibits three stages, each having an almost perfect fit to a linear line along that part. The first i know is a Hookean type behaviour, where F=-kX. The second and third stage I have no idea what property of the band they represent. Does anyone know what they are meant to reveal? I understand that there are two dependancies that a band has in terms of its elasticity, those being an energy and entropic depenance. Can anyone shed some light on this problem for me? I would very much appreciate it :) Woody PS, this isnt homework, it is simply a question of understanding.