In this study, the method of peanut shelling is selected as application of pressure on peanut bulk for the design of shelling machine and thus behavior of peanut bulk has been investigated. To this end, medium-size peanuts have been placed inside an iron cylinder of 70 mm height and 90 min diameter to form one, two and three layers, each singly at a time and have been subjected to the static pressure through a wooden piston fitted with the cylinder in a 20 ton universal testing machine under the constant loading speed. Values of loads and corresponding deformations have been recorded by the machine on a graph. The experimental data have been transformed into the linear and nonlinear models of stress-strain and pressure-density relationships. One observation regarding the bulk behavior is that at the beginning and ends of the loading there appear to be linear areas and a nonlinear domain in between them. The intersection of the extensions of the two linear areas, which falls inside the nonlinear domain, has been found to reflect the start of shelling. It has been concluded that the start of shelling on the basis of three layers requires a pressure of 0.278 N/mm(2) with zero damage and 4.45% breakage. On the other hand, shelling energy per volume has been found to vary from 36 x 10(-3) to 88 x 10(-3) Nmm/mm(3) involving three layers. The average bulk modulus has been determined to vary between 1.13 and 1.64 N/mm(2). (c) 2005 Elsevier Ltd. All rights reserved.