Double‐surface plasticity for micropolar continuum

This work is concerned with the modeling of a cold‐box sand (CBS), a composition of sand grains and a resin binder. To this end, experiments are performed which show the following characteristics: localization phenomena in form of a shear band, softening behavior in the force‐displacement curve, asymmetric behavior for compression and tension. These complex characteristics require a sophisticated material model. For this purpose a micropolar continuum, which is a special case of the micromorphic continuum, is used. In addition to the degrees of freedom of a classical continuum, the micropolar model has additional degrees of freedom in the form of micro‐rotations, which represent the grains of sand in our analyzed material. The macro‐part of this model represents the binder of the CBS. In order to make the micropolar model as flexible as possible, two flow functions are introduced; one for the macro‐part and one for the micro‐part. This approach is called double‐surface plasticity. The two flow functions can be implemented independently or coupled, depending on the application. For the coupled case, the radial‐return algorithm is no longer sufficient, so that the local iteration is calculated with the Fischer–Burmeister residual. Due to the lack of rotational symmetry in the experimental results, it is not possible to compute in two dimensions; instead, a 3D model is used for the simulation.