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Title: Novel experimental characterisation of hyperelastic materials
Author: Ahmed, Shakeel
ISNI:       0000 0004 7967 0110
Awarding Body: Sheffield Hallam University
Current Institution: Sheffield Hallam University
Date of Award: 2018
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A History Channel modern marvels broadcast aired in 2004 opened with this statement 'Our four most important natural resources are air, water, petroleum, and rubber'. In this list, the last element surprised everyone. No wonder the natural rubber latex is an essential material in today's modern world. An important application of natural rubber is medical gloves. Reducing thickness of gloves to match the natural feel of human hands is always a challenge while maintaining structural integrity. A simple testing methodology is required to understand the mechanical behaviour of the thin latex sheets. A uniaxial test and a bulge test with circular and rectan-gular bulge windows is a simple combination to characterize the mechanical be-haviour of this polymer sheet. Poisson's ratio is directly measured from simple tensile test using Digital Image Correlation (DIC). The value of Poisson's ratio is used to critique the bulge test results and under-lying assumptions of bulge test analytical models. A bulge test with a sufficiently long rectangular bulge window creates a plane-strain condition, which simplifies the analytical treatments, and an analytical model of bulge pressure and maxi-mum bulge height gives plane-strain modulus. Similarly, a circular bulge window creates a state of equibiaxial strain and a similar analytical model gives biaxial modulus. Both analytical models of the bulge test also give residual stress. Material samples from gloves (thickness 125 μm) have been characterized with biaxial modulus of 1.863±0.11 MPa, plane-strain modulus of 1.171 ± 0.24 MPa and a biaxial residual stress of 0.292 ± 0.052 MPa. The value of Poisson's ratio a mean value of 0.385 ± 0.003. Tensile test samples have been cut along three different directions and tensile data shows that the material is isotropic and an interesting relationship between biaxial data and plane-strain data is developed to calculate the anisotropy. Finally, stress-strain data from these three tests is used to calibrate hyperelastic material models in ANSYS.
Supervisor: Asquith, David Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available