Hollow glass microspheres have been used extensively in the automotive and marine industries as an additive for reducing weight and saving material costs. They are also added to paints and other materials for their reflective properties. They have shown promise for weight critical applications, but have thus far resulted in materials with low fracture toughness and impact resistance when combined with thermosetting resins in syntactic foam. The advent of commercially available microspheres with a wide range of crushing strengths, densities and adhesive properties has given new impetus to research into syntactic foam with better fracture behaviour. Current research suggests that the beneficial effects on fracture and impact resistance gained by the addition of solid reinforcements such as rubber and ceramic particles are not seen with the addition of hollow glass microspheres. The research presented in this paper has examined the mechanisms for fracture resistance in glass microsphere filled epoxy (GMFE) syntactic foams, as well as determined the effect microsphere crushing strength and adhesion strength has on the material???s fracture toughness. The flexural properties of various GMFE have also been determined. GMFE were manufactured with varying microsphere volume fraction up to 50%, and with variances in microsphere crushing strength and adhesion. The specimens were tested for Mode I fracture toughness in a three point single edge notched bending setup as described in ASTM D5045 as well as a three point flexural setup as described in ASTM D790-3. Fracture surfaces were inspected using scanning electron microscope imaging to identify the fracture mechanisms in the presence of microspheres. Results indicate a positive effect on fracture toughness resulting from new fracture areas created as tails in the wake of the microspheres in the fracture plane. Results also indicate a negative effect on fracture toughness resulting from weak microspheres or from interfacial disbonding at the fracture plane. These two effects combine to show an increase in GMFE fracture toughness as the volume fraction of microspheres is increased to between 10 ??? 20% volume fraction (where the positive effect dominates), with a reduction in fracture toughness as microspheres are added further (where the negative effect dominates).
| Identifer | oai:union.ndltd.org:ADTP/257865 |
| Date | January 2008 |
| Creators | Young, Peter, Aerospace, Civil & Mechanical Engineering, Australian Defence Force Academy, UNSW |
| Publisher | Awarded by:University of New South Wales - Australian Defence Force Academy. School of Aerospace, Civil and Mechanical Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Peter Young, http://unsworks.unsw.edu.au/copyright |
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