R. E. Knasmillner

Bio: R. E. Knasmillner is an academic researcher from University of Vienna. The author has contributed to research in topics: Caustic (optics). The author has an hindex of 1, co-authored 1 publications receiving 10 citations.

Crack-tip Caustics in Mechanically Anisotropic Materials

Abstract: This contribution focuses on the theoretical development of the method of caustics and its applicability to anisotropic materials. The method displays its full power when employed in conjunction with interactive numerical data reduction and evaluation procedures. For the analysis the selection of data points along the experimentally recorded caustic curve is done automatically, the selected points are marked on the screen and if necessary interactive correction of the positions is possible. Final proof of the correctness of the result of the automatic data point selection is achieved by comparing for acceptable coincidence the numerically generated caustic determined on the basis of the results of the data-reduction technique with the experimentally recorded caustic.

Experimental analysis and computational modelling of damage and fracture

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Experimental caustics analysis in fracture mechanics of anisotropic materials

Abstract: The originally developed reflection method of caustics is presented for application to cracks in mechanically anisotropic materials such as fiber-reinforced composites. The derived solutions for the combination of crack-opening modes I and II show that the size of the dark spot depends on the load intensity, whereas its shape depends strongly on the mechanical properties of the material, the orientation of the crack tip and the mixed-mode mixture. The evaluation of optical effects is possible using the diameter-measuring method or the advanced multipoint overdeterministic data reduction method. To find the exact position of caustics, the experimental images are analyzed by the simple boundary value method and a more sophisticated differential method, which is accomplished by shifting the real image onto the gradient image. The standard experimental testing procedure is performed for cracks oriented 0 deg, 45 deg and 90 deg to the material axes in carbon-fiber-reinforced polymer composites.

Smooth elastic contact of cylinders by caustics: the contact length in the Brazilian disc test

Abstract: The smooth contact of two elastic cylinders compressed against each other along a common generatrix is studied analytically and experimentally. The main objective is the quantification of the length of the contact arc. For the analytic study, the complex potentials method is employed while experimentally the contact arc’s length is determined by extending the reflected caustics technique. A series of experiments are then carried out using the device suggested by the International Society for Rock Mechanics for the standardized implementation of the Brazilian test and the typical set-up of the reflected caustics method. The experimental results are compared to the analytically determined ones. The agreement is satisfactory especially for low load levels, ensuring validity of the linear elasticity assumption.