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Thermomechanical modeling of a shape memory polymerGhosh, Pritha B. 15 May 2009 (has links)
The aim of this work is to demonstrate a Helmholtz potential based approach for
the development of the constitutive equations for a shape memory polymer undergoing
a thermomechanical cycle. The approach is motivated by the use of a simple spring-dashpot
type analogy and the resulting equations are classified as state-equations
and suitable kinetic equations for the recoverable-energy elements and the dissipative
elements in the model respectively. These elements have mechanical properties which
vary with temperature. The governing equations of the model are developed starting
from the basic conservation laws together with the laws of thermodynamics. The
entire set of equations are written in a state-evolution form as a set of ordinary
differential equations to be solved using Matlab. It is shown that the results of the
simulation in Matlab are in qualitative and quantitative agreement with experiments
performed on polyurethane. Subsequently, we study the dependence of the yield-stress
on temperature to be similar and different functions of heating or cooling processes.
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Synchronized assessment ofcompression of corrugatedboard : Mechanics and visualizationBürger, Johan January 2023 (has links)
Flexographic printing involves driving a paper substrate through the gap between two cylinders, where one of the cylinders has a print form layer covered in ink. The ink transfer from the print form to the paper is dependent on the pressure between the paper substrate and the cylinders. Knowledge about how the paper substrate reacts to compression is therefore important when aiming for high quality flexography printing. In this project the paper substrate in focus is corrugated board consisting of a top liner, a bottom liner and a fluted paper material in between the liners. To gain knowledge about the compression dynamics of the boards they are subjected to compression experiments with and without print form. The compression experiments are filmed and the videos are then analyzed using thresholding and tracking methods. The developed thresholding method is able to measure the thickness of each material separately in each frame while the developed tracking method is able to track the movement of the top and bottom metal blocks compressing the materials. The strains calculated from the image analysis measurements are then used as input values to the Maxwell spring-dashpot model with the intention of modelling the stress. Analysis of the compression experiment videos shows that the material properties of thecorrugated board may not be constant for the duration of the compression. This is because the fluting changes its shape when being compressed. Comparing the modelled stress to the stress measured by the press used in the experiments shows that the Maxwell spring-dashpot model is not able to model the stress accurately when the corrugated board goes through multiple stages of compression. The model works better for compression where the shape of the fluting is not significantly changed.
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