Detection of surface flaws by means of visual inspection

Kompozitni materijali veoma su pogodni za korištenje u zrakoplovnoj industriji zato što imaju visoku specifičnu čvrstoću i otpornost na oštećenja uzrokovana zamorom materijala, te otpornost na koroziju, a uz to su zbog male gustoće puno lakši od konvencionalnih materijala korištenih u strojarstvu. Navedene karakteristike nude velik potencijal za štednju goriva i manju potrebu održavanja, ali nagli porast korištenja kompozitnih matrijala u zrakoplovstvu, stvara dodatni izazov pri uporabi specifičnih metoda ispitivanja nepravilnosti. U ovom završnom radu, naglasak je stavljen na detekciju površinskih nepravilnosti u obliku ogrebotina, delaminacija, udarnih oštećenja itd. Prvi dio rada zamišljen je kao općeniti pregled, odnosno prikaz nerazornih metoda ispitivanja (NDT) koje bi bilo moguće iskoristiti u svrhu izvođenja inspekcija površinskih nepravilnosti. Te metode uključuju vizualni pregled, infracrvenu termografiju, 3D laserske skenere, metodu ultraljubičaste slikovne dijagnostike i terahertz metodu. Drugi dio rada odnosi se na opis provedenog praktičnog dijela ispitivanja. Budući da smo vizualnu metodu smatrali najpogodnijom za provedbu ovog ispitivanja po kriteriju dostupnosti opreme i znatiželje za rezultatima dobivenim vizualnom metodom, osmišljen je postav za provođenje ispitivanja, koji će biti detaljnije opisan u drugom dijelu rada.Composites have many advantages as structural aircraft materials — among them, high specific strength and stiffness and resistance to damage by fatigue loading, coupled with corrosion resistance and low weight. These factors offer great potential for economic savings associated with reduced maintenance and fuel consumption. But the rapidly increasing use of composites in primary structure has brought with it the challenge of making sure damage inspection can keep pace. Accurate nondestructive inspection (NDI) methods are a necessity to ensure aircraft airworthiness and passenger safety. In this particular final thesis work, the focus is put on the specific type of flaws – surface flaws (scratches, delaminations, impact damage etc.) . The first part of the work is made with the idea of giving the general overview of some interesting NDT methods which could be possibly used for the purpose of detecting surface flaws in composite materials including visual testing (VT), 3D laser scanning, infrared thermography, ultraviolet photography and terahertz methods. The second part of this final thesis is the description of non-destructive inspection conducted in cooperation with my mentor prof.dr. Damir Markučić. As we found visual inspection the most appropriate method for this research considering the factors of availability of technical instruments and our curiosity for the results, we came up with the idea of the setup that was necessary to conduct this non-destructive testing inspection on the aircraft interior honeycomb composite panel, which will be briefly described later in the text