DETERMINATION OF EPOXY RESIN ’ S MECHANICAL PROPERTIES BY EXPERIMENTAL-COMPUTATIONAL PROCEDURES IN TENSION Assist . Prof . VLDILV
The use of epoxy resins in metal structures for adhesive reasons is getting wider. Epoxy resins possess enhanced mechanical, chemical and physical properties, i.e. increased shear and compression strength, resistance in solvents, as well as at high temperatures. Tensile tests were carried out with standard aluminium tension specimens glued with epoxy resins. The thickness of the glue and the acting crosssection area were variable. The specimens were cemented under constant temperature and humidity conditions. The experimental results were simulated with the aid of FEM-based procedures, while the stress–strain curves of the epoxy resins, as obtained by nanoindentations and corresponding FEM-supported algorithm, were taken into account. The obtained results allow the determination of the epoxy resins’ strength versus its thickness and the occupying cross-section area.
Actual indenter tip geometries, material elastoplastic deformation laws and universal hardness
The precise knowledge of materials mechanical properties is always a core issue in every technical application. Through a developed finite elements method (FEM) continuous simulation of the nanoindentation, the applied force course versus the penetration depth is adequately simulated during the loading and unloading phases of this test, and the corresponding material stress ‐ strain curves, as well as the universal hardness, are stepwise defined. Furthermore, the actual tip geometries of various indenters are approached and through equivalent magnitudes described. The results show that the defined material elastoplastic deformation characteristics are independent of the indenter type, as Vickers or Berkovich, since the existing indenter tip form deviations from their ideal geometry are considered. Furthermore, using the developed FEM-based nanoindentation simulation, the influence of the indenter tip geometry on the defined constitutive laws and the universal hardness is sufficiently elucidated. Various materials stress ‐ strain curves and universal hardness courses versus the indentation depth, determined by means of the developed procedure, are presented.
Influence of grit blasting pre-treatment on the adhesion strength of plasma sprayed coatings: fractal analysis of roughness
Abstract Since the adhesive strength of ceramic coatings by plasma spraying is fairly low, serious efforts have been made to improve it. In order to improve the adhesiveness of coatings, the substrate surfaces were roughened by blasting, sometimes by angled blasting as a pre-treatment. The measured adhesive strength showed the maximum value at blasting angle 75°. Average surface roughness of the substrates remains almost constant with respect to the blasting angle. Introducing fractal analysis to evaluating the surface topography of substrates, the fractal dimension was evaluated for the roughened surfaces. It showed a maximum fractal dimension at 75° where the adhesive strength reaches approximately its maximum value. It is concluded that fractal dimension is a better measure than average surface roughness for the evaluation of adhesive strength of ceramic coatings.