Open Access Open Access  Restricted Access Subscription or Fee Access

A Comparison Between Ultrasonic Testing and Lockin Thermography in Nondestructive Evaluation of Porous CFRP Plates



The introduction of composite materials in the aeronautical industry, as substitute to metals, for fabrication of primary and secondary structural parts, has fulfilled two main requirements. In fact, on one side, composites supply a response to the increasing need of favorable stiffness to weight ratio and, on the other side, they represent the best solution to the requirements of producing even more complex structural parts by starting from the design of the row material. As a main drawback, composites, and specifically carbon fibers reinforced polymers (CFRP), are strongly heterogeneous being made by long carbon fibers kept together by a polymeric matrix. So, they are characterized by directional mechanical properties and, due to the complex production processes, they are vulnerable to the formation of specific defects since their fabrication. Among the main manufacturing defects, porosity is one of the most difficult to be taken under control, while it has detrimental effects on the mechanical properties of the final component. On the other hand, its evaluation is rather difficult. In this work, the extreme case of a delaminated CFRP plate affected also by porosity is addressed. To this end, several groups of coupons are manufactured with induced in each group a different amount of porosity within their structure, and with also an artificial inclusion interleaved in the lamination sequence to simulate a local delamination. Then, the aim of the present work is to compare the effectiveness of two techniques: Ultrasonic Testing (UT) and Lock-In Thermography (LT) in the detection of delamination in such a difficult environment. The obtained data highlight a different capability of the two techniques to detect defects, also in the light of a data fusion.

Full Text: