Hyperplasticity

Hyperplasticity is a new approach to plasticity theory in which thermodynamic principles play a central role. The most important feature of the new approach is that the entire constitutive behaviour can be derived from two scalar potentials. The approach has its roots in the work of Ziegler, who applied this technique to modelling a wide variety of dissipative materials, but principally those which exhibit viscous behaviour.

Plastic materials (i.e. those which are rate-independent) were only briefly treated in Ziegler's book "An Introduction to Thermomechanics". The application of these ideas to soils was, however, explored in the thesis by Houlsby (1981). At that stage the theories were mainly expressed in terms of kinematic variables (e.g. strains), whilst conventional plasticity theories are more commonly expressed in terms of stresses. The re-casting of the theory in terms of stresses was achieved by Collins and Houlsby (1997), who made much use of the Legendre transformation, which proves to be a very powerful technique in this area. Collins and Houlsby demonstrated the formal links between different potential functions (e.g. the dissipation function and the yield surface).

Houlsby and Puzrin (1999) generalised the above work to explore the full variety of different ways of expressing the theories (including also temperature effects). Most recently the same authors have been working on an approach called "continuous hyperplasticity" in which smooth transitions between elastic and plastic behaviour can be modelled.

The work involves co-operation with:

Publications on hyperplasticity.