Thesis
Investigate the use of strain gauge technology for the determination of the mechanical characteristics of polypropylene ankle-foot orthoses
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2008
- Thesis identifier
- T12170
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- Ankle-Foot Orthoses (AFOs) are devices applied to the foot and lower leg when ankle joint stability has been lost, commonly through, upper and lower motor neuron lesions resulting in gait abnormalities. Conventional leather and metal AFOs have been largely superseded by plastic devices in recent years, especially made from polypropylene (PP). To date the design of AFOs is mainly based on empirical studies. A survey of the literature indicates that there is a dearth of experimental investigations in this area. Consequently, more research should be conducted on the mechanical characteristics of AFOs and their interaction with the limb in order to improve design criteria, performances and prescription of the orthoses. The objective of this project was to assess the performance of strain gauges attached to polypropylene (PP) with the perspective of using them to determine orthotic loads and stresses generated in polypropylene AFOs during patient’s activity. Initially PP samples with an extensometer attached on them were tested following as far as possible the British Standard BS 527-1, with two different tensile test protocols on an Instron machine with the aim of investigating the material’s viscoelastic nature. Strain gauged samples were tested in tension at low (0.158 mm/min) and high strain rates (2.43 mm/min), in a stress range between 0-2 MPa. Investigation of two different bonding methods used for gauge foils installation on polypropylene was, thus, carried out to verify the most preferable technique. This was achieved by comparing strains measured by the strain gauges and the extensometer, attached to the side of the sample. Results obtained by strain gauge testing showed that a better accuracy was achieved in polypropylene UV light pre-treated samples where strain gauges were attached with cyanoacrylate adhesive (10% difference at slow rate) rather than in samples in which M-Bond AE-10 adhesive was used (19% difference). The accuracy was found to be reduced at fast strain rate. Higher values of strains were measured by strain gauges than by the extensometer. Reasons for this unexpected result require more detailed investigations on viscoelastic properties of the adhesive and its interaction both with the sample and strain gauge backing foil, gauge lengths, and sample shape. A custom-made polypropylene AFO was strain gauged using UV light treatment and cyanoacrylate adhesive. Moments in the sagittal plane generated in the orthosis were calculated from strain gauge voltage outputs during one walking trial of a normal subject donned with the instrumented orthosis. The moment pattern obtained followed the expected plantar and dorsiflexion pattern for a normal subject during walking. More walking trials, however, should be conducted to provide repeatability in the results.
- Advisor / supervisor
- Solomonidis, Stephan
- Spence, Bill
- Resource Type
- DOI
- Funder
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