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Modelling rate dependent behaviour of orthotropic metals

Mohd Nor , Mohd Khir (2012) Modelling rate dependent behaviour of orthotropic metals. PhD thesis, Cranfield University.


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A finite strain constitutive model for orthotropic metals was developed within a consistent thermodynamic framework of irreversible process in this research project. The important features of this material model are the multiplicative decomposition of the deformation gradient and a new Mandel stress tensor combined with the new stress tensor decomposition. The elastic free energy function and the yield function are defined within an invariant theory by means of the introduction of the structural tensors. The formulation was limited to small elastic deformation. The Hill’s yield criterion was adopted to characterise plastic orthotropy, and the thermally micromechanical-based model, Mechanical Threshold Model (MTS) was used as a referential curve to control the yield surface expansion using an isotropic plastic hardening assumption. The complexity was further extended by coupling the formulation with the equation of state (EOS). This ‘micro-macro’ material model was developed and integrated in the isoclinic intermediate configuration in the new deviatoric plane. The proposed formulation which is the key novelty of this work was implemented into the LLNL-DYNA3D code by the modification of several subroutines in the code. This material model and its implementation were then validated in the final phase of this project. The process started with the validation of the new stress tensor decomposition itself, and continued with the validation of elastic isotropic behaviour, the validation of orthotropic elastic behaviour and the validation of orthotropic elastic-plastic behaviour which include strain rate and temperature sensitivity tests. The final part of this process was a comparison of the results generated by the proposed material model against the available experimental data from both the Plate Impact test and Taylor Cylinder Impact test. A good agreement between experimental and simulation was obtained in each test to fulfil the objectives of this research project. This achievement is a good indication for more appropriate orthotropic material models in future to help towards a better understanding of the complexity of material orthotropy impacted with high strain rates loading.

Item Type: Thesis (PhD)
Subjects: T Technology > TA Engineering (General). Civil engineering (General) > TA401-492 Materials of engineering and construction. Mechanics of materials
Depositing User: Normajihan Abd. Rahman
Date Deposited: 27 Dec 2013 08:06
Last Modified: 27 Dec 2013 08:06
URI: http://eprints.uthm.edu.my/id/eprint/4647
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