Performance of Hooked-End Superelastic Shape Memory Alloy and Steel Fibre Reinforced Concrete and Stiffness of Ankle Foot Orthosis With Superelastic Shape Memory Alloy Hinges
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Authors
Menna, Demewoz
Date
Type
thesis
Language
eng
Keyword
Shape memory alloy fibre reinforced concrete , Fibre reinforced concrete , Hooked end fibres , Steel fibre , Ankle foot orthoses , AFO stiffness
Alternative Title
Abstract
Civil engineering structures are vulnerable to damage from aging and hazards such as earthquakes and fire. Engineers are therefore seeking innovative materials that can adapt to environmental changes, function in harsh environments, and extend the service life of the structure. Superelastic shape memory alloys (SMA) and steel fibre reinforced concrete (FRC) have recently emerged as viable materials.
A novel superelastic SMA fibre production method was proposed. The fibres were fabricated from heavily cold worked SMA wire followed by heat treatment, with the goal of enhancing fibre pullout performance and simplifying the fibre production process. The heat treatment conditions significantly affected the pullout load, re-centering ratio, and average and equivalent bond strength values.
The cyclic flexural responses of hooked-end superelastic SMA and steel fibre reinforced concrete prisms were examined. The superelastic fibres were fabricated from a heavily cold worked, 1 mm diameter NiTi alloy, followed by a 40-minute heat treatment at 350ºC. For fibre volume fractions ranging from 0.25% to 1.00%, the increased volumetric ratio of the fibres increased the ductility, tensile strength, flexural stress, and cumulative energy dissipation characteristics of the FRC. The SMA FRC exhibited significantly better performance than that of its steel FRC counterpart.
To investigate the potential application of FRCs in retrofitting existing structures, the punching shear response of concrete slabs strengthened with a thin layer of ultra high-performance FRC (UHPFRC) was studied using finite element methods. The model was verified by analyzing previously tested slab-column connections from literature. Parametric studies showed that the punching shear capacity of the retrofitted slab increased with an increase in the thickness of the UHPFRC layer.
Applications of superelastic SMA in ankle foot orthoses (AFO) were examined in Chapters Six and Seven of this thesis. AFOs are orthotic devices used by patients who have an abnormal gait caused by conditions such as foot drop syndrome. A systematic review was conducted and the mechanical characterization of AFOs equipped with SMA hinges was investigated experimentally. The results indicate that producing AFO hinges from heavily cold worked superelastic SMA followed by an optimum heat treatment could be an effective alternative to existing AFOs.
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ProQuest PhD and Master's Theses International Dissemination Agreement
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Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.
Attribution-NonCommercial-NoDerivs 3.0 United States