Abstract:
The Finite Element Method is a powerful tool that can be used to test, improve or better
understand an industrially relevant problem. There are numerous Finite Element
Analysis (FEA) software packages that operate either in the commercial, open source or
research space. Di erent application speci c codes also have specialised model formulations.
Most software packages have a comprehensive list of material models already
implemented. If a di erent material model is required, some form of user material can
often be implemented and linked to the software package.
In some cases the e ective implementation and testing of a user implemented material
requires knowledge on the e ect and handling of strain formulations, element
technologies and the desired material behaviour. With sophisticated material models
available in the research space, this thesis focuses on the identi cation and implementation of existing computational plasticity models for use within FEA.
The e ect of di erent strain formulation choices is rst illustrated and discussed
using di erent sample problems. Three di erent FEA software packages are also compared
before discussion and implementation of a general numerical framework for corotated
hypo-elastoplasticity in isotropic and combined hardening. The numerical framework
allows expansion to include di erent, more sophisticated hardening behaviour by
simply altering the scalar equation used to update the von Mises yield surface.
The Mechanical Threshold Stress (MTS) material model is implemented within the
hypo-elastoplastic numerical framework. Material parameter identi cation is investigated
using linear regression on data followed by numerical optimisation. The MTS
model is a rate and temperature dependent state variable based material model. The
model is tuned to t imperfect cemented carbide data in compression, where material
test frame compliance or some eccentricity caused inhomogeneous deformation through
the test section of the specimen. The characterised model is then used on a sample
problem to investigate the plastic deformation in the cemented carbide anvils during
the High Pressure, High Temperature (HPHT) synthesis of diamond.
Further extensions, built on the dislocation density based modelling theory of the
MTS model, are investigated by selecting an alternate form of the state dependent
variable. A dislocation density ratio is used instead of the original stress like variable
in the MTS model. The evolution of this internal state variable is altered, along with
additional state dependent variables, to include additional deformation and thermal
mechanisms. The model extensions in the case of rate and temperature dependent
cyclic deformation as well as multiple waves of recrystallisation are discussed and implemented.
The recrystallisation and through thickness microstructural variation of a
High Strength, Low Alloy (HSLA) steel are nally investigated during the process of
industrial hot rolling or roughing simulations.
