| Intumescent mat material is used to support substrates in catalytic converters and is known to be critical to the durability. The material is highly compressible, rate dependent and expands dramatically due to irreversible vermiculite expansion as temperature increases beyond a critical point.; In this study, several tests are performed to characterize thermo-mechanical properties of the intumescent mat material. Thermo-mechanical properties tested mainly focused on several issues, such as, relation in each stress versus mechanical strain curve at different temperature, permanent vermiculite expansion, rate effects and plastic deformation under different loading and unloading processes. Assumptions are made to simplify mat material property. A constitutive model is developed based on simple isotropic hyper-elastic theory. The theory is extended to include visco-plastic material behavior. A one dimensional plasticity theory in the thickness direction is developed by assuming a special form of the plastic deformation gradient tensor and yield criteria, based on experimental observations. To consider the temperature effect in the constitutive model, the irreversible strain due to vermiculite expansion is defined as a chemical strain. Mechanical property change due to temperature is implemented by the proposed softening model. A stress function is derived from the 2 nd law of thermodynamics to consider material softening. A simple relationship among mechanical, thermal and chemical strain is established by an assumed strain decomposition. Finally, the thermo-mechanical constitutive modeling is implemented by employing the concept of a master curve and strain shift function, derived from the softening model and strain decomposition. The complete spatial elasticity tensor for a new constitutive model is derived for implicit finite element code and implemented in the ABAQUS™ user subroutine called UMAT.; The proposed theory is verified by solving simple boundary value problems and by comparing with measured data. An example field application is discussed for incompressible anisotropic hyperelastic material under thermo-mechanical loading as a part of the theory extension. Also, a catalytic converter is analyzed for the canning, heating, and cooling process. The numerical results are compared with measured data. |
