Crack path selection in microstructurally tailored inhomogeneous polymers

Gonzalez, Joseph

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https://hdl.handle.net/2142/29485 Copy

Description

Title

Crack path selection in microstructurally tailored inhomogeneous polymers

Author(s)

Gonzalez, Joseph

Issue Date

2012-02-01T00:48:49Z

Director of Research (if dissertation) or Advisor (if thesis)

Lambros, John

Department of Study

Aerospace Engineering

Discipline

Aerospace Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• polyethylene
• digital image correlation
• microstructure
• material degradation
• material tailoring

Abstract

In this work, the wide range of properties of a photodegradable polymer are exploited to generate a host of different inhomogeneous arrangements that can help us experimentally study crack path selection problems. The model material which we are using is a polyethylene co-polymer, ECO, whose photosensitive behavior allows alterations in its mechanical properties when subjected to ultraviolet (UV) irradiation. It is seen that ECO becomes stiffer but more brittle upon UV irradiation. Material degradation in such polymers enables their use as an environmentally friendly material that can be broken into smaller nontoxic parts under small forces such as wind and light. This model material is then used to generate microstructures that possess either discrete or distributed local inhomogeneities similar to granular materials, i.e.,metals. The first part of this literature describes the experimental work done on the three microstructures developed. The microstructures all exhibited the same grain properties but possessed varying grain boundary properties. Each microstructure was loaded in a single edge notch tension (SENT) configuration, and the resulting strain fields were recorded using digital image correlation (DIC). Depending on the applied load and the local microstructure, different crack paths occur, such as the main crack simply extending, or a main crack arresting and a host of secondary cracks appearing at critical locations. Additionally, different types of failure occur within the granular inhomogeneous model displaying intergranular and/or transgranular failure for specific hours of UV irradiation. The DIC results, correlated with global load-displacement measurements, shed light on the conditions under which local crack nucleation and growth can occur. In the second part of this work, the global load-displacement results are compared with a finite element model using ABAQUS. Two different models, interface and interphase, are created to assist in validating the experimental results. Through comparison of the global load-displacement results with the experimental and numerical study, the different developed models can be seen to represent a particular microstructure. A failure criteria is also considered using numerical analysis by analyzing areas of high stress levels using the von Mises and Tresca yield criteria. These criteria illustrate areas in which high magnitudes of stress occur and these results are compared with the experimental failure initiation sites.

Graduation Semester

2011-12

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http://hdl.handle.net/2142/29485

Copyright and License Information

Copyright 2011 Joseph Gonzalez

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