Wykrywanie wewnętrznych uszkodzeń w lekkich pancerzach kompozytowych metodami termografii w podczerwieni

W artykule przedstawiono problematykę związaną z wykrywaniem podpowierzchniowych uszkodzeń powstałych w wyniku badań niszczących lekkich pancerzy kompozytowych stanowiących struktury wielowarstwowe wykonane z włókien aramidowych lub szklanych. Jako metodę nieniszczącą wykrywania strefy uszkodzenia zastosowano aktywną metodę termograficzną lock-in. Określenie wielkości strefy wewnętrznych uszkodzeń umożliwia porównywanie pancerzy wykonanych z różnych materiałów. Na podstawie przeprowadzonych badań stwierdzono, że strefa pod-powierzchniowych uszkodzeń materiału od strony uderzenia przez pocisk symulujący odłamek może być 3-krotnie większa od kalibru pocisku i 15 krotnie większa od strony przeciwnej dla lekkich pancerzy wykonanych na bazie włókna aramidowego lub szklanego.

Light composite armour is a preferred solution against military and paramilitary sources of present threats as the reducing mass of battle vehicles provides a possibility of their quick air-transport. The light armours of these vehicles should be resistant against: common and rifle bullets, grenades, anti-personal mines, IED - improvised explosive devices. Recently, NATO countries have initiated an intensive investigation process to introduce modern composite materials into protection systems of armored vehicles and infantry fighting vehicles. The composites reinforced by fibres are used in structural elements of vehicle trunks. Materials of composite armours include graphite epoxy, glass epoxy and aramid fiber composites. The composites that have been examined can include a variety of defects, such as ballistic impacts, embedded defects, manufacturing defects, thermal damage, moisture ingress and other induced defects. Methods for testing ballistic protection of light armours are known and used. First of all, they consist of checking armours resistance against the bullets where the bullet velocity is known. Moreover, the V50 velocity is defined during the test. In this method the V50 velocity of a round or standard fragment is defined (according to STANAG 2920) as a velocity at which armour is penetrated with the probability of 50% (Fig. 2). The distribution of points hit by bullets or fragments on the surface of an armour is also important. In fact, only correct distribution of these points provides a guaranty for an impartial assessment of tested designs. After hitting by a bullet, shape and size of an area of damage in composite armours depends on the type and design of armour, so type of reinforcing material is particularly important. Knowledge of damage characteristics allows arranging the hitting points to avoid overlapping of damaged areas. Considering quality and protection ability of armour, the extent of internal damage should be kept in mind besides the direct ability to stop bullets and fragments. The Military Institute of Armament Technology in cooperation with the Military Institute of Armour & Automotive Technology carried out a project on using nondestructive testing method in order to evaluate destruction zones in light ballistic armour which appear as a result of impact of bullets and fragments. Nondestructive testing by using active IR thermography methods is very useful for evaluation of internal defects. In the paper there is presented the dependence between the energy of fragments/or bullets and the dimension of internal defects (Figs. 8 and 11).