Thermodynamic Compatibility of the HystereticPoly Uniaxial Material Implemented in OpenSees

The fulfillment of the Drucker postulate applied to a phenomenological hysteretic constitutive model is hereby investigated. Such a material is defined in terms of analytical functions so that it is capable of determining the response and its tangent operator in closed form and does not require any iterative algorithm. Hence, the constitutive model is very appealing for several applications, including structural analysis and homogenization techniques. Within this context, the thermodynamic compatibility implied by the Drucker’s postulate aims to ensure that the model does not provide responses associated with negative values of the dissipated energy, this in order to fulfill the 2nd law of thermodynamics. In particular, the research is focused on two peculiar phenomena associated with non-consisten energy dissipations: the negative softening and the hysteretic crossing paths. It is shown that the thermodynamic compatibility may be violated because of negative softening although it is possible to determine a displacement range for which the material preserves its physical significance. On the contrary, it is proved that the analytical formulation of the investigated model avoids the crossing path phenomenon thus ensuring the fulfillment of the Drucker’s postulate.