Thesis submitted in fulfilment of the requirements for the degree
Magister Technologiae: Mechanical Engineering
in the Faculty of Engineering
at the Cape Peninsula University of Technology
2008 / The increasing requirement for light weight constructions and the unsatisfactory performances of
traditional metals and conventional engineering materials, especially in their failure to positively
respond to environmental stimuli, in a demanding environment have made the search for the
development of alternative materials inevitable. Such alternative materials being sought, which
are the so-called adaptive, multifunctional, smart or intelligent composites would facilitate the
realization of some engineering applications that are simply difficult to achieve with the existing
conventional materials.
Composite materials have found increasing applications in construction, aerospace and
automotive industries due to their good characteristics of light weight, improved strength,
corrosion resistance, controlled anisotropic properties, and reduced manufacturing and
maintenance costs. However, there is a growing demand to improve on composite materials to
have “smart" capabilities so as to be able to sense, actuate and respond to the surrounding
environment.
Shape memory alloys (SMAs) are metallic alloys that can undergo martensitic phase
transformations as a result of applied thermomechanical loads and are capable of recovering
permanent strains when heated above a certain transformation temperature. SMAs possess
sensing and actuating functions and have the potential to control the mechanical properties and
responses of their hosts due to their inherent unique characteristics: shape memory effect (SME)
and pseudoelasticity. When integrated into structural components, they perform sensing,
diagnosing, actuating and repair or healing functions, thereby enhancing improved performance
characteristics of their hosts. Amongst the commercially available SMAs, NiTi (Nickel-Titanium)
alloys in forms of wires, ribbons, bars, particles and porous bulks are the most widely used
because of their excellent mechanical properties and superior material characteristics.
Embedding SMAs into composite materials can create smart or intelligent hybridized
composites.
This thesis details an investigation of the mechanical properties and behaviour of the hybridized
composites formed by embedding NiTi SMA wires into 60D polyurethane. The composites were
produced by the vacuum process of manufacturing. The properties of the implanted SMA wires
were enhanced by ageing and pre-straining. Uniaxial tensile and four point bending tests were
conducted to ascertain the significance of embedding SMA wires into the polyurethane host
matrix. It was found that the embedded SMA results in an increasing in elastic modulus, tensile
strength and bending stiffness. It was found that these improvements in the properties can not
be sustained at high temperature owing to degradation of interfacial strength between the SMA
and polyurethane as a result of the high recovery stress generated by the SMA upon activation.
Some measures that can ameliorate the interfacial breakdown were suggested.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:cput/oai:localhost:20.500.11838/1241 |
| Date | January 2008 |
| Creators | Ayodele, Olukayode Lawrence |
| Publisher | Cape Peninsula University of Technology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | http://creativecommons.org/licenses/by-nc-sa/3.0/za/ |
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