(65) |

where , and are material model parameters and is yield value, originally assumed in the following form of hardening/softening law [17]

with . The hardening/softening law (66) is shown in fig.(5). Note that the curved diagram is a continuous relation. The energy under the load-displacement diagram can be related to a ``compressive fracture energy''. The original hardening law (66.1) exhibits indefinite slope for , which can cause the problems with numerical implementation. This has been overcomed by replacing this hardening law with parabolic equation given by

(67) |

An associated flow and strain hardening hypothesis are being considered. This yields

(68) |

The model parameters are summarized in Tab. 17. There is one algorithmic issue, that follows from the model formulation. Since the cap mode hardening/softening is not coupled to hardening/softening of shear and tension modes the it may happen that when the cap and shear modes are activated, the return directions become parallel for both surfaces. This should be avoided by adjusting the input parameters accordingly (one can modify dilatancy angle, for example).

2018-01-02