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Open access

Florina Violeta Anghelina and Dan Nicolae Ungureanu

Abstract

The structural transformations occurring at tempering for some high-speed steels are a subject of research for which have been dedicated numerous studies. More complex compositions of the high-speed steels were direct consequence of the complexity of structural transformations which occur during heat treatment. On the other hand, current tendency in energy requires maximum efficiency and rational use of heating sources used in industry. Thus, only a precise knowledge of the kinetics of transformations occurring at tempering can be a basis for optimizing this treatment. Although cobalt is used for a long time as an alloying element, though relatively recently it was considered important to the properties of rapid steel. These circumstances, combined with the lack of quantitative information on the kinetics transformation at tempering operation treatment for some steel has led to this paper. The thickness of the studied samples is 5 mm and was taken from the annealed steel bars. These samples were subjected to hardening and tempering treatment in salts bath. Heating for hardening was performed in two steps, at 5500C and 8300C. Austenitizing was done at 12000C, during 120 seconds. The cooling was done up to 5300C in salts bath, with a keeping of 15 seconds, and then air cooling was done. On these samples were carried out, HRC Rockwell hardness measurements, and X-ray diffraction analysis.

Open access

Nicolae Angelescu, Dan Nicolae Ungureanu and Vasile Bratu

Abstract

The current work is intended to explain the role of some organic admixtures on the hardened structure of refractory concretes with aluminous cement. The influences on the mechanical-structural properties in the normal hardening but in the heating conditions at different temperatures are emphasized, also. These are due to the influence on the hydration process (i.e. the kind of the neoformations and degree of hydration) and implicitly on the size and distribution of structural pores.

Open access

Daniela Avram, Dan Ungureanu, Nicolae Angelescu and José Barroso de Aguiar

Abstract

Phosphocalcic glasses, based on ternary system SiO2 - CaO- P2O5 and those doped with copper (SiO2 – CaO - P2O5 - Cu2O) can be obtained by the traditional method of sub-cooling melts or modern methods such as process that uses mechanical energy, neutrons action, deposition in thin layers or by sol-gel technique. This paper shows the experimental results of three compositional phosphocalcic glasses: 50% SiO2 - 43% CaO - 7% P2O5, 50% SiO2 - 38% CaO - 7% P2O5 - 5% Cu2O obtained through sol-gel method and 45% SiO2 - 22.5% CaO - 22.5 Na2O - 5% P2O5 - 5% Cu2O obtained by melting. In order to study their bioactivity, the three compositions were structural analyzed by X-ray diffraction method. In this case the apatite formation was highlighted after soaked in simulated body fluid, but also other compounds (CaCO3 and CuO) resulting from the same process were observed. In case of the melting glass apatite formation has not been highlighted. The functional groups present in the structure of glasses before and after soaking (PO4 3−, CO3 2− and HO) were highlighted by the Fourier Transform Infrared Spectroscopy (FTIR). The elemental chemical composition was confirmed by elemental analysis WD-XRF. The morphology of sol-gel glass powders was revealed by SEM analysis. All glass compositions were tested in terms of antibacterial activity in vitro.

Open access

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

Elena Valentina Stoian, Vasile Bratu, Cristiana Maria Enescu and Dan Nicolae Ungureanu

Abstract

Aim of the study is to present the technological process of obtaining cast iron with lamellar graphite for use in the manufacture of cylinder liners, and to identify the main alloying elements and track their influence on the mechanical properties of cast iron with lamellar graphite.

Also paper presents analysis of 20 batches of cast iron with lamellar graphite, which are made of cylinder liners, in terms of chemical composition and the mechanical properties.

After the analysis of the 20 castings of cast iron Fc 250 it is observed that: the increase in the carbon content shows a decrease of the tensile strength and hardness of the gray cast iron; the increase in silicon content shows a decrease in hardness and tensile strength. Decreasing the amount of graphite and especially the alloy of silicon iron lead to hardness increase 1% Si increases hardness by 50 HB). A statistical analysis has been performed on the data obtained that accounts for changes in alloying additions. A modeling and optimization of mechanical properties (tensile strength and hardness) was performed according to the percentages of carbon, silicon and manganese. Mathematical modeling found that the hardness and traction resistance of the cast iron decreased with the increase in carbon, silicon and manganese content.

Open access

Nicolae Angelescu, Vasile Bratu, Elena Valentina Stoian, Dan Nicolae Ungureanu and Ana-Maria Gurban

Abstract

Calcium-phosphate cements is one of the most popular types of biomaterials, both due to their specific properties of self - setting and of their superior biocompatibility.

Although in general the phosphocalcic cements, which are the subject of the present paper, have somewhat lower mechanical properties than other biomaterials based on calcium and phosphorus, or even other dental cements of the same nature. The ceramic compositions presented in the present paper constitute a special category of biomaterials due to other notable advantages that characterize them. Thus, this category of materials is defined by a near-perfect adaptation to the surface of the biological tissue, as well as by a convenient resorption rate, processes followed by the generation of optimal bone formation. In this paper are presented principles of realization of the calcium-phosphate cements (raw materials and conditions of production), as well as the properties of these biomaterials, insisting, in particular, on the chemistry of the setting reactions. At the same time, informations regarding the possibilities of clinical use, such as implants are presented.

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.

Open access

Florina Violeta Anghelina, Dan Nicolae Ungureanu, Carmen Popa, Elena Valentina Stoian, Ileana Nicoleta Popescu, Cristiana Maria Enescu and Constantin C. Anghelina

Abstract

In this presentation are evidenced instrumental characterization by Electronic Scanning Microscopy (SEM) equipped with EDS / WDS of aluminum alloys such 2024 alloy with multiple synergistic purposes as: acquisition of new knowledge, increase the amount of information obtainable about the material, increasing the efficiency and the quality of the tests, characterization of special destination alloys and assessing their conformity with the specified requirements. In this direction, it requires both the knowledge the test methods (theoretical basis, test method, procedure relating to the method, quality assurance testing) as well material characteristics investigated. These aspects are necessary for test system design, and preliminary interpretation of experimental results.

Open access

Ivona Camelia Petre, Adrian Catangiu, Ileana Nicoleta Popescu, Dan Nicolae Ungureanu, Alexis Daniel Negrea, Aurora Anca Poinescu, Maria Cristiana Enescu, Elena Valentin Stoian and Veronica Despa

Abstract

The aim of the paper was to develop a device (“pin-on-disc” type) for the measurement of friction in plane friction couplings with sliding movement. On tribometric device (made in our laboratory) we can measure the friction force, friction coefficient and wear, for different loading conditions, speeds, time and material coupling.

For the measurement of the frictional force as well as of the coefficients of friction, mainly the method with a resistive tensiometric transducer is used. With a DataQ DI 245 data acquisition board it is possible to record up to 2 kHz frequencies in the range of -10 ÷ +10 mV with a resolution of 13 bits. To test the functionality of the device, a preliminary test was carried out for a steel pin- on- cast iron disc, for different values of the normal pushing force. The device was calibrated and the measurement results were recorded and processed on the computer.