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DISSERTATION ABSTRACT CONSTITUTIVE MODELING OF JOINING MATERIALS Manu Dube, Ph.D. Advisor: Prof. T. Kundu Modeling simplifications for complex material behavior may lead to
unanticipated errors under generalized loading conditions, which are
difficult to detect in finite element analyses. This work analyzes
existing models under simple loading conditions where the nature of the
results is known a priori, and proposes new models to overcome the
limitations detected. Elastic and elastoplastic formulations for loading
dependent material parameters are generalized, and limitations of the
rate dependent elastoplastic simulation and the Perzyna viscoplastic
formulation are discussed. A yield function that provides continuous
yielding irrespective of the direction of loading and does not generate
spurious plastic strain increments under temperature change is
developed. A thermomechanical model based on the concept of
superposition of asymptotic phases is also proposed, with generalized
stress-strain-temperature relationships that intrinsically predict the
variation of the coefficient of thermal expansion and elastic constants
with temperature. These are validated for aluminum, lead, tin and
solder. A plastic yield criterion shown to be in general agreement with
hardening based on dislocation density and a preliminary empirical creep
equation for lead tin eutectic solder are developed as part of the
thermomechanical model. Finally an approximate dissipated work based
formulation for the Disturbed State Concept of Desai (2001) is developed
and limitations of DSC assumptions are discussed. Validations are
conducted for the eutectic lead tin data of Wang et al. (2001), with
prior parameters being shown to require recomputation.
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