Methodology Based on the State Transition Concept for Simple Constitutive Modeling of Smart Materials
Varela Jiménez, Manuel I.
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Smart materials have the capability to sense and respond to environmental stimuli in a predictable and useful manner. Its existence has transformed the paradigm that materials can be used only for structural purposes into the concept that these can also be the basis for actuators or sensors, generating new possibilities for design of devices. However, development of these materials also creates necessity of proposition of new theories and concepts that allow understanding its behavior. This dissertation focuses on development of a general constitutive model for describing response of several smart materials by considering that a microstructural change is stimulated in them, such a state transition that follows a sigmoidal behavior and can be modeled by a proposed expression that describes transition induced by an external factor. Such expression results flexible and able to adapt to take several kinds of external variable as the main parameter that induces transformation. A methodology for purposing a state transition in smart materials and modeling its response to some stimulus through a common mathematical expression relating the effect of microstructural changes on some variable associated to the material is proposed and evaluated. This way, there were studied; 1) effect of twinned martensite - detwinned martensite - austenite strain/temperature induced phase transformation on stress of Nicke l - Titanium shape memory alloy, 2) effect of glassy - active temperature induced state transition on stress of shape memory polymers, 3) effect o f magnetic field induced arrangement of iron particles on shear yield stress of magnetorheological fluid and 4) effect o f electric field induced arrangement of ions on the bending of a thin film of electroactive polymer. A constitutive model is proposed for each material resulting in promising results due to good fitting with experimental data and comparison with some other models, although it has some limitations such as being unidimensional, considering only one way behavior of the materials or have been fitted for specific geometries or chemical composition and stills needs to be generalized. However, it can be considered as an initial approach for a general model for smart materials regardless of their atomic structure, chemical bonds or physical domain, that could be applied for design of materials and simulation of its behavior through numerical methods.