Non-destructive measurement of coating adhesion

Adhesive coating failure arises when various internal or external forces overcome the resistance provided by work of adhesion and other energy dissipation mechanisms. Typical examples include blistering and slow or fast delamination (eg flaking and impact damage). Furthermore a loss of adhesion under wet conditions can be the precursor to corrosion. Tests used by the coatings industry are often relatively crude, such as simple tape and cross hatch tests. The tests may distort the results and are usually destructive. Not only is this inconvenient but it raises questions of relevance if the destructive process is outside the normal operating parameters, or introduces testing artefacts such as an additional bonded surface. A range of non-destructive techniques (eg thermography, ultrasonics, acoustic emission and laser shearography) is reviewed against their potential for meeting the criteria for different end-use applications in such areas as quality control, product development, fault diagnosis and service life prediction.