A depth sensing indentation study of the hardness and modulus of adhesives

The depth sensing indentation (DSI) technique has been used to investigate the distribution of mechanical properties through the bondline for several adhesive joints and to compare this with the mechanical properties measured from bulk adhesive samples used for conventional uniaxial testing. Comparison is also made between adhesive joints manufactured by secondary-bonding (SB) and co-bonding (CB). It is found that the elastic modulus derived from DSI is approximately 5-20% higher than that derived from uniaxial tests. It is seen that the mechanical properties of the adhesive are essentially uniform across its thickness and unaffected by the addition of carrier fibres, by SB or CB, or by the elastic modulus of the adherend.