Division of Information Technology, Engineering and the Environment
School of Advanced Manufacturing and Mechanical Engineering
School of Advanced Manufacturing and Mechanical Engineering
Thesis Abstract
Structural adhesives have been used for over fifty years to enable the bolding of materials which are subjected to high loads and dissimilar conditions. The natural forms of adhesive are chosen because of (a) desirable mechanical properties such has high strength and resistance to creep, (b) High resistance to chemicals such as oil and solvents, and (c) excellent resistance to creep when subjected to high service temperatures.
However, most structural adhesives have very poor fracture toughness which makes them prone to catastrophic brittle failure under static or cyclic loading. Due to their desirable properties such as high strength, research has been continually done on adhesive materials to improve the fracture toughness without compromising these thermo-mechanical properties. A method of improving the fracture toughness of an adhesive is by the addition of a second phase. This second phase can be in many different forms, and varying results have been achieved throughout research. The most common method for modifying a structural adhesive is to add addictives. There is evidence to show that an optimum size of particle exists which will achieve the optimum fracture toughness in the modified material. Much research has been done on micro-sized rubber particles and there is an agreement that fracture toughness is improved, although with a slight loss in mechanical properties such as strength. However, some research demonstrates that particles on nano dimensions are more efficient in improving fracture toughness without compromising other desirable properties.
Double cantilever beam (DCB) method for adhesive toughness measurement was improved by the incorporation of a sufficiently sharp crack made by wedge tapping. A known route to producing cracks by loading–unloading cycles was proved unreliable because the cycles produced plastic deformation to the adhesive where new cracks propagated. Abnormally high toughness values with large standard deviations were obtained with cracks made by embedding a non-sticky paper. Only instantly propagated cracks made by tapping were sufficiently sharp to produce reproducible, accurate toughness. Toughened resin was insensitive to crack sharpness. A crack length to adherend length ratio 0.2–0.5 was recommended.
