Mechanical properties of random packings of spheres

The mechanical behaviour of random packings of spheres submitted to an oedometric compression has been studied. The particles consist of charged polymeric gels which are swollen in salty water. The relation between the measured force F and the imposed deformation e is non linear, i. e. F = ɛ m , where m is greater than the exponent governing the microscopic Hertz law. This is due to the fact that the number of contacts between grains that transmit forces increases with the applied deformation. In order to study the viscoelastic behaviour of such packings, we have tested the effect of the duration τ of the cycles of compression on the global characteristic. Moreover, size and wall effects have also been considered.