Developments of interfaces containing auxetic constituents

Chirima, G T. (2013) Developments of interfaces containing auxetic constituents. PhD thesis, University of Bolton.

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Auxetic materials display a negative Poisson’s ratio. Such materials have a host of potential benefits that could be exploited such as high shear resistance, fracture toughness, and high indentation resistance amongst others. The inclusion of auxetic materials within positive Poisson’s ratio materials is investigated in an attempt to improve the effective mechanical properties. The project focuses on the modification of mechanical properties of an adhesive, or interface, system via the addition of either auxetic and/or conventional constituents. The objective is achieved via two main approaches: a multi-layer adhesive/film interface and auxetic particulate filled adhesives. Multi-layer film/adhesive interfaces are modelled for Constant Interface Thickness (CIT) and Constant Constituent Layer Thickness (CCLT) systems using Finite Element Modelling (FEM), analytical expressions from averaging techniques for the effective elastic properties of a composite (the Ramirez approach) and a modified (weighted) Rule of Mixtures approach developed by the author. High and low modulus adhesives relative to the films are considered. In the second approach, FEM of particulate filled systems is performed for high and low modulus auxetic fillers relative to the matrix. The results are compared to existing analytical theories such as the Self-Consistent Field theory, Hashin Shtrikman and the bounding techniques of elasticity. Auxetic materials are predicted by the models to give rise to improvements in the effective mechanical properties (Young’s modulus and shear modulus) of both the multi-layer film/adhesive and particulate filled composite interfaces. Experimental work in support of the model predictions includes 3 and 4 point bending tests of multi-layer film adhesive interfaces comprising polypropylene films and polyolefin adhesive, and tensile testing of auxetic silica particulate (high modulus filler) and short chopped auxetic polypropylene fibre (low modulus filler) filled epoxy matrix composites. The multi-layer film adhesive approach requires an understanding of the production of auxetic polypropylene films. A parametric study of the melt extrusion process for the production of auxetic and conventional films has, therefore, been undertaken and has included producing, for the first time, auxetic PP films at significantly higher processing temperatures than those previously established in the vicinity of the melt onset temperature.

Item Type: Thesis (PhD)
Additional Information: A thesis submitted in partial fulfillment of the requirements of the University of Bolton for the degree of Doctor of Philosophy
Divisions: University of Bolton Research Centres > Institute for Materials Research and Innovation
University of Bolton Theses > Engineering and Sciences
Depositing User: Tracey Gill
Date Deposited: 01 Oct 2015 14:51
Last Modified: 01 Oct 2015 14:51

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