7. Kissing Defects

Initial work focuses on the use of the model, developed in Chap. ‎6, to identify the thickness of the minimum detectable air gap. Results showed it would be possible to identify a very thin air gap, therefore, a means of opening such defects was then considered. Kissing defects were experimentally simulated via the addition of silicon grease to the bond line. Initially work focussed on the use of the bending moment created through loading single lap joints to open experimentally simulated kissing defects. Thermoelastic stress analysis (TSA) was also carried out during these tests to give information about the stress state in the lap joints to assess the effect the defects were having when joints were loaded. Comparison of TSA and pulse phase thermography (PPT) defect detection was undertaken. While the addition of load using a test machine was found to enable defect detection using PPT it was not practical for onsite use. However the findings of this chapter enabled the development of a portable device, described in Chap. 8.