Test method Nondestructive damage assessment in fiber reinforced composites with the pulsed ultrasonic polar scan Mathias Kersemans a, * , Ives De Baere a , Joris Degrieck a , Koen Van Den Abeele b , Lincy Pyl c , Filip Zastavnik c , Hugo Sol c , Wim Van Paepegem a a Department of Materials Science and Engineering, Ghent university, Technologiepark-Zwijnaarde 903, 9052 Zwijnaarde, Belgium b Department of Physics, Catholic University of Leuven – KULAK, Etienne-Sabbelaan 52, 8500 Kortrijk, Belgium c Department Mechanics of Materials and Constructions, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium article info Article history: Received 7 November 2013 Accepted 3 January 2014 Keywords: Pulsed ultrasonic polar scan Fiber reinforced plastics Damage characterization NDT abstract This study investigates the use of both amplitude and time-of-flight based pulsed ultra- sonic polar scan (P-UPS) as a sophisticated non-destructive damage sensor for fiber reinforced composites. Focus is put on stiffness related damage phenomena, which are in general difficult to monitor nondestructively, and their associated signature in the P-UPS image. Various composite samples, with different damage states, have been inspected at multiple material spots with the P-UPS technique. The results demonstrate the capability of the P-UPS method to obtain a unique signature of the local material damage charac- teristics. Several indicators in the acquired P-UPS images have been identified from which the type and level of material degradation can be obtained. The P-UPS extracted charac- teristics are fully supported by simulations, conventional tests as well as visual inspection. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Fiber reinforced composite materials have gained great popularity in a wide range of high-tech applications because of their excellent high-strength-to-low-mass ratio. By simply arranging the fiber reinforcements along specific directions in the matrix, the elasticity of the resulting structure can be tuned in order to meet a design functionality. The mechanical nature of these materials then becomes anisotropic, making the inspection and characterization of components a difficult but critical task [1,2]. Considering furthermore that in-service components are subjected to a variety of loading conditions, which include tensile, shear, fatigue and impact, a reliable in- spection method to ascertain the integrity of the compo- nent during its lifetime is of crucial importance. Although several non-destructive testing techniques are already present in literature [3–16], in which ultrasonics can be considered to be the largest class, none of them are fully capable of detecting, identifying and following up different types of damage, especially when considering that microscopic damage in composites often manifests itself in a macroscopic reduction of mechanical properties [17,18]. Furthermore, considering that disassembling a component is often difficult, if not impossible, most of the inspection methods already fail on this point. In short, an in-situ non-destructive inspection technique, capable of quantifying various types of composite degradation, is needed. The pulsed ultrasonic polar scan (P-UPS) technique [19] has already been demonstrated to be a promising means for NDT and material research. Basically, the method in- terrogates a material spot with pulsed ultrasound from every possible angle of incidence j(4,q), with 4 the azimuthal angle, further called the polar angle, and q the angle with the normal on the surface, further called the incident angle (see Fig. 1a), hence making it highly appro- priate to map different features of anisotropic materials like fiber reinforced composites [20,21]. To enhance the * Corresponding author. E-mail addresses: Mathias.Kersemans@UGent.be, MathiasKersemans@ hotmail.com (M. Kersemans). Contents lists available at ScienceDirect Polymer Testing journal homepage: www.elsevier.com/locate/polytest 0142-9418/$ – see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.polymertesting.2014.01.001 Polymer Testing 34 (2014) 85–96