Characterization and sensitivity analysis of hyperelastic materials in biaxial tension

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Title: Characterization and sensitivity analysis of hyperelastic materials in biaxial tension
Author: Smoger, Lowell
Abstract: The focus of this study was to improve characterization of hyperelastic materials in biaxial tension through improved design and validation of an existing test fixture and specimen geometry. Additionally, a sensitivity analysis of the material properties to variations in selected test parameters was conducted to better understand material response. Misalignment and binding in the original tensile test fixture resulted in non-equibiaxial loading and inaccurate stress-strain data. Analysis and modification were required to improve accuracy and repeatability. Vector analysis of the link system and the Minimum Constraint Design method were used to achieve this aim. Based on a proposed set of criteria, a FE analysis was conducted on several biaxial specimen geometries to determine the best shape and scale for obtaining stress and strain data. A stress decay factor (SDF) is proposed to predict internal stresses from measurable data. A test method has been designed around the use of the SDF and was ultimately applied to a cruciform specimen geometry. In addition to the ideal equibiaxial case, numerical simulations have been perturbed in two ways. The first variation involved a specimen gripped clamps offset by up to half the width of the clamp. The second variation involved non-equibiaxial load ratios ranging from 0.85 to 1.15. The goal was to quantify the change in stress-strain response to slight deviations from ideal loading conditions. Binding has been eliminated from the test fixture and a 1:1 load ratio has been achieved. The new specimen experiences less stress decay while achieving greater experimental strain. A high sensitivity to non-equibiaxial load ratios and low sensitivity to clamp offset are seen in the test parameter analysis. Finally, results from the SDF correction material characterization method is compared with results from an inflated boiling flask geometry.
Record URI: http://hdl.handle.net/1850/13160
Date: 2010-10-08

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