Optimization Methods for Minimizing Induced Stress During Tensile Testing of Prosthetic Composite Materials

Optimization Methods for Minimizing Induced Stress During Tensile Testing of Prosthetic Composite Materials

Kwame Anane-Fenin (University of Johannesburg, South Africa), Esther Titilayo Akinlabi (University of Johannesburg, South Africa) and Nicolas Perry (Bordeaux University, France)
DOI: 10.4018/978-1-5225-8235-9.ch008

Abstract

The application of composite materials for prosthetic applications is the norm in recent times. Accurately characterizing the principal stresses during tensile testing is therefore essential. The low transverse compressive strength of most composite materials limits high clamping forces during tensile testing. Tabs are consequently critical for cushioning against grip pressure and surface damage. However, tabs tend to introduce induced stress concentrations. In this chapter, the induced stress concentrations are minimized via the optimization of tab design configurations. Stress concentration obtained via finite element analysis were used to develop a full factorial design for statistical analysis and compared with a Taguchi, Taguchi-multi response and Taguchi-genetic algorithm optimizations. It was established that to minimize the stress concentrations, low values of tab stiffness, thickness, and taper angle were required while the adhesive thickness was increased. The Taguchi and hybrid approaches were efficient and reduced the number of simulations from 32 to 8 (75% reduction).
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Introduction

In the past decade, fibre reinforced composites have become the most notable materials for applications in orthotics and prosthetics. These composites are preferred due to their Lightweight, flexibility, corrosion resistance, fatigue resistance, energy storage, release properties ease of manufacture and aesthetics (Berry, 1987; Kadhim Oleiwi & Namah Hadi, 2016). Glass fibre over the years has consistently become the material of choice for prosthetic applications. Some of these applications include the manufacture of flexible composite keels, prosthetic limbs, prosthetic sockets and dental prosthesis. Recently Freedom Innovations introduced the Maverick™ Comfort AT, an all-terrain, fibreglass foot with an innovative Keel design which combines durability with flexibility (News Medical Life Science, 2017). Ali et al. (2016) also engineered a prosthetic limb for lower-limb amputees from glass fibre reinforced polymer composite and observed relatively good tensile and compressive properties.

Prosthetic sockets are designed to transfer a patient’s weight to the ground by providing a structural interface between the human body and prosthetic part (Gerschutz, Haynes, Nixon, & Colvin, 2012). In industry, the standard procedure for fabrication of laminated prosthetic socket involves the application of acrylic polymer matrix to layers of a combination of conventional materials such glass fibre, carbon fibre, cotton or nylon around a mould (Campbell et al., 2012; Ganzert, 2012; Gerschutz et al., 2012; Phillips & Craelius, 2005; Slocumb, 2014). In accordance with industry standards, glass fibre is consistently regarded as suitable in relations to tensile strength (Campbell et al., 2012; Me, Ibrahim, & Tahir, 2012; Phillips & Craelius, 2005).

In dentistry, the most favourable reinforcement for resin composites are long continuous fibres placed on the tensile side of prosthetic components with the loading applied perpendicular to the fibre strands (Dyer, Lassila, Jokinen, & Vallittu, 2004; van Heumen, Kreulen, Bronkhorst, Lesaffre, & Creugers, 2008). Carbon fibre provides superior mechanical properties, however, the black appearance poses an esthetical disadvantage and therefore not favoured in the dental sector (Maruo, Nishigawa, Irie, Yoshihara, & Minagi, 2015). Glass fibre, on the other hand, provides not only enhanced mechanical properties but excellent biocompatibility, aesthetics and design flexibility for dental clinic or laboratory applications (Anusavis, 2013; Kanie, Fujii, Arikawa, & Inoue, 2000; Meriç, Dahl, & Ruyter, 2005; Vallittu, 2007). For the above reasons, Fibreglass is the most extensively utilized reinforcement in dental prosthesis.

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