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.
The effect of specimen roughness and indenter tip geometry on the determination accuracy of thin hard coatings stress–strain laws by nanoindentation
Abstract Nanoindentation, conducted using devices with enhanced accuracy and capabilities, contributes to the reliable characterization of coatings and other material mechanical properties. Herein there are many parameters that significantly affect measurement reliability and thus may lead to errors in the evaluation of results. Such parameters include specimen roughness and geometrical deviations (due to manufacturing tolerances) in the indenter tip form. In earlier investigations, the actual tip geometries of various indenter types were approached with the aid of a continuous simulation of the nanoindentation using finite element method modeling techniques that enable the determination of material stress–strain characteristics. In the present paper, the application of this method—further improved to define the constitutive laws of thin hard coatings—is described, wherein the effect of specimen roughness on the accuracy of the indentation results is taken into account. Furthermore, the results introduced show that the defined material elastoplastic deformation characteristics, based on the nanoindentation test results, are independent of the indenter type (Vickers or Berkovich) when deviations in the indenter tip geometry from the ideal are considered.
Mechanical behaviour and durability of high volume fly ash cementitious composites
The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles. KEYWORDS. Cementitious matrix; Raw fly ash; Second layer particles; Third layer particles.