Identifier

etd-11052009-182059

Degree

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Document Type

Dissertation

Abstract

Syntactic foams are composite materials synthesized by dispersing microballoons in a polymeric, ceramic or metallic matrix. In the past three decades, syntactic foams have gained immense importance as a lightweight and damage-tolerant material when used in foam-cored sandwich structures. Because of the structural-length scale damages by low velocity impact such as tool drops, runway debris etc., sandwich structures usually have a very low residual structural capacity. Unfortunately, macro-length scale damage, in particular internal damage such as impact damage, is very difficult to repair. Therefore, there is a genuine need to develop impact-tolerant and self-healing syntactic foams which can be used as a core in sandwich structures. In this study, a new shape memory polymer (SMP) based syntactic foam was proposed, fabricated, characterized, and tested using DSC, TEM, SEM, and stress-controlled programming and free shape recovery by association with the foam cored sandwich. A micromechanics based model was employed to clearly visualize the microstructure and to quantify the geometrical and mechanical properties of the smart foam composite in the linear elastic region. An orthogrid stiffened SMP based syntactic foam cored sandwich was then fabricated, programmed, impacted, healed (sealed), and compression tested, for the purposes of sealing impact damage. Two impact energy levels (30J and 53J), two prestrain levels (3% and 20%), and two confinement conditions (2-D confined and 3-D confined) were used in the low velocity impact test, strain-controlled programming and constrained shape recovery, respectively. C-scan and visual observation were also conducted to visualize impact damage and evaluate the degree of sealing achieved. It is found that the shape memory functionality of the SMP based syntactic foam can be utilized for the purpose of sealing impact damage with the developed programming and shape recovery. The developed foam and the hybrid sandwich structure are able to heal (or seal) structural-length scale damage (here impact damage) repeatedly (up to 7 rounds of impact-healing cycles), efficiently (with a healing efficiency over 100%); and almost autonomously (the only human intervention is by heating). This study lays a solid foundation for the next generation of smart self-healing composite structures in engineering applications.

Date

2009

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Li, Guoqiang

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