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Adrian Catangiu, Dan Nicolae Ungureanu and Veronica Despa

Abstract

The strength of materials is a complex function which involve two main components, material nature and the presence of defects. Usually glasses exhibit a fragile behavior due to a numerous flaws and the effect is a large range of data scattering in tensile strength measurement. The Weibull probability density function was applied to describe the scatter of experimental data in tensile test, which emphasize a difference between variance in case of tensile strength of three stainless steel grades and glass epoxy composite. The main goal is mathematical modeling of those distributions and finding of equations which predict the probability of failure for a sample subjected to a specific stress.

Open access

Ivona Petre, Aurora Anca Poinescu, Adrian Catangiu and Simona Mihai

Abstract

With the development of industry have made efforts to improve the performance of braking systems of motor vehicles on public roads. The choice of materials used for coupling brake system involved the development of new materials that meet safety requirements in circulation. During braking of any vehicle, due to the friction created between the disk and pad, temperature rise occurs with negative effects on the process of slowing down the vehicle. Mechanical and thermal stress being put on the brakes is very high. Due to overheating, brake discs and pads may warp or crack, and the material they are made may their change its structure. These defects give rise to vibrations and noise during braking, to reduce the coefficient of friction, reduce the effectiveness of the braking mechanism. This paper proposes a study regarding the thermal stresses effects of brake mechanism on the disc material of a car Dacia Logan. It proposes a theoretical model to calculate the temperature that occurred during the operation of the braking system and experimental analysis on the influence of temperature on the brake disc material.

Open access

Dan Nicolae Ungureanu, Daniela Avram, Nicolae Angelescu, Adrian Catangiu, Florina Violeta Anghelina and Veronica Despa

Abstract

In this paper is presented a comparative study regarding the synthesis of hydroxyapatite powders. The chosen method of synthesis of this biomaterial was chemical co-precipitation. The structure, size and morphology of the obtained powders were analyzed by X-ray diffraction, infrared spectroscopy - FTIR, dynamic light diffusion DLS tehnique and scanning electron microscopy-SEM. The results obtained were compared with those obtained on a commercial hydroxyapatite powder. Investigation methods have confirmed the synthesis of a high purity hydroxyapatite with a optimal degree of crystallization and crystallinity for the reconstruction and regeneration of hard tissue.