Investigation of deformation and shape memory characteristics of thermoplastic polymers

Yiğitbaşı, Cihan
Algorithmic implementation of constitutive models for shape memory polymers into commercial software packages through user material interfaces is the subject of this thesis. The effect of temperature change on the behaviors of these materials has been examined. The formulation of the generated material model has been constructed in the logarithmic strain space. Material model structure consists of three main steps. (i) In the geometric pre-processing step, using current and plastic metric, total and plastic logarithmic strain measures were defined, respectively. (ii) In the material model step, constitutive equations for (an)isotropic elasto viscoplasticity in the logarithmic strain space were identified in a structure analogous to geometrically linear theory. (iii) In geometric post-processor step, the objects obtained in logarithmic strain space were mapped back to their nominal, Eulerian or Lagrangian counterparts. After these three main stages, the 8-chain model with the double kink theory was used to define the flow rule for plastic strain in logarithmic strain space. All the material information that was theoretically defined was written as a FORTRAN code. A new term has been added to the tangent moduli calculations in order to run this code in ABAQUS. The obtained material model was verified by comparing with the test data in the literature. Finally, the shape memory effect of thermoplastic materials on a tube geometry is investigated in ABAQUS. The results suggest significant shape memory effect for plexiglass.


Numerical Modelling and Experimental Analysis of Vibratory and Acoustics Behaviours of a Special Design Squirrel-Cage Three-Phase Asynchronous Machine
Ionescu, R. M.; Negoita, A.; N'Diaye, A.; Torregrossa, D.; Djerdir, A.; Miraoui, A.; Scutaru, Gh. (2011-09-10)
The paper presents a comparison between the obtained results from testing a special design 5 kW squirrel-cage three-phase asynchronous machine and the numerical model of the same machine, simulated under the FLUX2D Finite Element Software. The aim is to validate the numerical model in the loaded and unloaded cases. The resulting model will be used for further research into the vibratory behaviour and noise of the motor. In this paper, an experimental approach is used to show the influence of load on motor v...
Evaluation of effective elastic properties of honeycomb sandwich structures by optimization involving modal behavior
Çınar, Okan; Erdal Erdoğmuş, Merve; Kayran, Altan; Department of Mechanical Engineering (2014)
This thesis aims to develop an alternative approach which estimates the effective elastic properties of 2D orthotropic equivalent model of the honeycomb core material. For this purpose, 3D detailed finite element (FE) model of honeycomb structure, with the actual cell geometry and the face sheets, is used as the reference structure. Effective elastic properties of the equivalent 2D orthotropic model, representing the honeycomb core, are determined by means optimization. The objective function of the optimiz...
Application of Continuum Damage Mechanics in discontinuous crack formation: Forward extrusion chevron
Soyarslan, Celal; TEKKAYA, AHMET ERMAN; Akyüz, Uğurhan (2008-06-01)
Materializing Continuum Damage Mechanics (CDM), numerical modeling of discrete internal cracks, namely central bursts, in direct forward extrusion process is presented. Accordingly, in a thermodynamically consistent setting, a local Lemaitre variant damage model with quasi-unilateral evolution is coupled with hyperelastic-plasticity. The formulations are constructed in the principal axes where simultaneous local integration schemes are efficiently developed. To this end, the framework is implemented as ABAQ...
Investigation of effect of design and operating parameters on acoustophoretic particle separation via 3D device-level simulations
Sahin, Mehmet Akif; ÇETİN, BARBAROS; Özer, Mehmet Bülent (Springer Science and Business Media LLC, 2019-12-16)
In the present study, a 3D device-level numerical model is implemented via finite element method to assess the effects of design and operating parameters on the separation performance of a microscale acoustofluidic device. Elastodynamic equations together with electromechanical coupling at the piezoelectric actuators for the stress field within the solid parts, Helmholtz equation for the acoustic field within fluid, and Navier-Stokes equations for the fluid flow are coupled for the simulations. Once the zer...
Computational Modeling of Myocardial Infarction
Berberoglu, Ezgi; Göktepe, Serdar (2014-07-19)
Recent developments in computer technology and mathematical modeling have lead to a remarkable improvement in the computational modeling of the cardiovascular system. The virtual heart models have huge potential to understand the electrophysiological and mechanical response of the heart in the healthy and pathological cases. The simulation of physidogical behavior of the heart depends on the usage of physiologically sound constitutive models besides the incorporation of the efficient, robust, and stable num...
Citation Formats
C. Yiğitbaşı, “Investigation of deformation and shape memory characteristics of thermoplastic polymers,” M.S. - Master of Science, Middle East Technical University, 2018.