The non-destructive assessment of porosity in composite repairs

Composite materials are increasingly used in aerospace applications and, if they are damaged, it is frequently attractive to repair them rather than to undertake complete replacement. Non-destructive techniques to assess the quality of repairs are therefore required. Porosity is a very common problem in repairs, and this paper discusses possible techniques for measurement of the degree of porosity present in the repaired area and in the bondline between the repair and the parent structure. It has been shown that ultrasonic attenuation measurements obtained from the amplitude of the echo returning from the back wall of the structure provide a satisfactory technique for use in the field, where immersion testing is not possible. Tests have been carried out on a variety of both good and poor quality repairs and it has been shown that satisfactory measurements can be obtained using commercially available equipment that is well suited for field use.