engleski

The Optical Method of Caustics Applied to Composites

Cracks in different types of structures occur as a consequence of manufacturing process or due to static and dynamic loading during the exploitation, therefore all the new constructions have to be designed and produced according to regulations which eliminate all possible risk situations. If the crack is anyway detected, it can be estimated from the point of view of safety and stability according the principles of fracture mechanics. One of the important indicators is stress intensity factor, that can be determined on real structures or their models by several possible methods of experimental mechanics under real loading conditions. Comparison of estimated or exactly determined stress intensity factor K and critical value Kc of the related factor as a material property, leads to the decision whether the structure is still safe enough for future exploitation period or whether the cracked part has to be reconstructed. Particularly, mode I crack opening has to be examined through KI factor, as the most important for brittle cracking. The experimental determination of the stress intensity factors K by the optical method of caustics is commonly in use for the mechanically isotropic materials either in transparent or non transparent light arrangement [1]. The general solution for the shape of caustic curve for mode I crack opening is of the same epicyclical form for any kind of isotropic material. The determination of KI is performed by measuring the maximum dark spot diameter on the real or image referent plane. The size of a caustic curve for non transparent materials depends upon the optical conditions, mechanical characteristics and load intensity applied to the specimen.

fracture mechanics; stress intensity factor; method of caustics; composites

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