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.
Optimization of the cutting edge radius of PVD coated inserts in milling considering film fatigue failure mechanisms
The fatigue and wear behavior of PVD coatings on cemented carbide substrates in milling are investigated experimentally and analytically through Finite Elements Method (FEM) simulation of the cutting process. Cutting inserts with different cutting edge radii and at various feedrates were examined. The initiation and progress of the tool failure is depicted through Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray microspectral investigations of the used cutting edges. The FEM simulation of the contact between the tool and the workpiece enables a quantitative description of the influence of mechanical stress components on the coating fatigue failure. Hereby critical coating fatigue stresses determined by means of the impact test were considered. The experimental and computational results exhibit quantitatively the effect of tool radius and feed rate on the coating fatigue failure as well as on the overall cutting performance for various substrates and film structures. In order to utilize the superior characteristics of coatings towards improving the cutting performance, it is highly recommended to optimize the cutting insert wedge radius, as well as the cutting conditions. Herewith a premature coating failure and a consequent rapid wear development can be prevented.