Date of Award

2016

Document Type

Open Access Dissertation

Department

Mechanical Engineering

Sub-Department

College of Engineering and Computing

First Advisor

Addis Kidane

Abstract

The focus in the present work is to explore and characterize the underlying deformation and failure mechanisms in multifunctional materials including woven composites and polymeric foams, using full-field measurements. Attention has been especially drawn towards the challenges associated with characterizing these materials at extreme length and time scales, and investigating the advantages of full-field measurements to resolve the existing limitations. Accordingly, the current limitations in the study of dynamic deformation response of low-impedance materials are identified. An approach based on the general stress equilibrium is presented and successfully implemented to include the concurrent effects of inertia and material compressibility into the analysis of direct impact response of various low impedance rigid closed-cell foams. The approach takes advantage of full-field measurement based on stereovision digital image correlation (3D-DIC) to measure the full-field acceleration and material density, later used to determine the distribution of inertia stresses developed in the material. The inertia stress is superimposed with the boundary-measured stress to give the local variation of stress in the dynamically deformed specimen.

The rest of the work is dedicated to the characterization of orthogonally woven fiber reinforced composites, with emphasis on exploring the origin of deformation nonlinearity and orientation dependence of these materials when subjected to far-field loads. Attempts have been made to quantify the local deformations over fiber bundles and matrix-rich areas in woven composites with different reinforcements (glass fiber and carbon fiber) and different yarn dimensions. The full-field deformation captured through the use of 2D and 3D DIC at sub-millimeter scales is utilized to reveal the underlying load-bearing mechanisms, dominant failure modes and the origin of non-linearity in the global stress-strain response of the material subjected to in-plane axial tensile load. Results obtained through the application of full-field measurements are validated using post-mortem fracture surface study in the composites.

Rights

© 2016, Behrad Koohbor

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