COMPARATIVE ULTRASONIC ANALYSIS OF DAMAGE IN CFRP UNDER STATIC INDENTATION AND LOW-VELOCITY IMPACT

Non-destructive testing plays an important role in analyzing composite damage by supplying useful information on damage initiation and propagation. However, for the scientist, the main problem to be solved is the choice of how best to detect the damage. For impact damage to carbon/epoxy plates, widespread methods such as X-ray inspection are not easy to use because the damage does not always penetrate completely through the thickness. The choice of an ultrasonic facility designed to dimension the damage correctly and give access to interface delaminations has thus proved to be necessary. The ultrasonic method has been applied here for a comparative analysis of the damage detected after static indentation and after low-velocity impact on a composite with quasi-isotropic lay-up and a comparative analysis of the damage caused by static indentation for two different lay-ups (quasi-isotropic and cross-ply) on T300/914 material. The results show the damage process. A crack initiation threshold, crack propagation, delamination initiation threshold and delamination propagation are observed. The propagation of the delaminated area is similar for static and impact damage versus the maxi-mum load. Similarly, propagation of the delaminated areas obtained in through-transmission mode is similar for the two lay-ups analyzed. By using a ply-by-ply ultrasonic analysis the authors observed a slightly different internal delamination process comparing cross-ply and quasi-isotropic laminates under static indentations. Two other methods, fractography and accelerometry, were used in association with the ultrasonics to complete the results. The influence of parameters, such as the indenter diameter and the velocity and form of loading, was also evaluated under local bending loads.