engleski

Method of Caustics in Fracture Mechanics of Mechanically Anisotropic Materials

This contribution deals with the application of the reflection method of caustics to the fracture mechanics problem of non transparent mechanically anisotropic materials containing a crack, such as fiber reinforced composites. By using the analogy of geometrical assumptions for mechanically isotropic materials, the theoretical basis and complete procedure for determining stress intensity factor is originally developed and here described in general. The solution leads to the singular caustic curve surrounding a dark spot. The shape of the curve depends extremely upon the mechanical properties of the material and the position of the crack-tip, while its size depends upon the optical conditions and load intensity applied to the specimen. The necessity of the numerical simulations of the optical effect for the material treated for each situation separately (position of the crack, mixed-mode crack opening ratio) is explained by reasons of proper evaluation of experimental results. The experimentation is presented for the representative type of carbon fiber-reinforced composite material. The experimental determination of the stress intensity factors K , e. g. KI and KII , is simultaneously performed by measuring the maximum dark spot diameters and by using the advanced multi-point over-deterministic data reduction method, using the experimental equipment that makes possible the filtering of the image and better recognition of the dark zone boundary.

fracture mechanics; caustics; anisotropic materials; stress intensity factor

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