Investigation of wear conditions of a composite material based on an anti-friction alloy AO20-1 reinforced with Ti particles

Сomposite material samples were obtained by the method of reaction casting by mixing titanium particles to obtain intermetallic phases Al3Ti. Dry sliding wear tests were carried out using a fixed sleeve (steel 45) against a rotating disk (sample) at sliding speeds from 0.25 to 0.75 m/s and loads from 0.5 to 3.5 MPa.There were constructed maps of wear rate, which determine the friction modes during testing. There were shown boundaries and conditions of changing wear modes.

Effect of brushing on colour stability of nanohybrid composite after immersion in brewed beverages – an in vitro study

Background and aims. In today’s world, everyone is mindful of one’s appearance and appreciates aesthetics. Of the various restorative materials available, composites are considered as the most aesthetic with good color stability. This study aims at finding the effect of brushing on the color stability of nanohybrid composite after being immersed in various beverages. Methods. Thirty disk specimens were prepared for each staining solution (N=30), with a total of 90 specimens. The disk specimens for each staining solution were then sub divided into 2 groups (N=15): brushing and non-brushing. After preparation, the specimens were soaked in distilled water for 24 hours in separate containers. Baseline color of the samples was evaluated using spectrophotometer. The samples were then immersed in tea, coffee or water. The groups of samples to be brushed were held in the mold and 20 strokes of brushing using an electronically powered toothbrush were done on each side of the disk sample. The color was re-evaluated after a period of 14 days. Results. When comparing among the three beverages, tea showed the highest ΔE*ab indicating greatest discoloration when compared to coffee and water. This can be graded as tea > coffee > water. However, statistically there was no significant difference between tea and coffee. When compared within tea, coffee, or water specimens the non - brushed specimens showed greater discoloration compared to the brushed specimens both clinically and statistically. Conclusion. When immersing the specimens in the solutions, tea showed more color change compared to coffee, making the specimens clinically unacceptable. However, brushing the specimens reduced the discoloration when compared to non–brushing, making the coffee specimens clinically acceptable.

INSTALLATION AND ME TION AND METHODOLOGY FOR DE OGY FOR DETERMINING OF TERMINING OF ANTIFRICTIONAL PROPER AL PROPERTIES OF AN TIES OF ANTISTATIC-HEA TIC-HEATCONDUCTING COMPOSI TING COMPOSITE POLYMERIC M YMERIC MATERIALS INTERACTING WI TING WITH FIBROUS M TH FIBROUS MASS (CO ASS (COTTON-RAW)

The paper Presents a disk tribometer installation and allows to determine the antifriction properties of machine-building composite antistatic-heat-conducting polymer materials working in interaction with the fibrous mass (raw cotton). A method for determining the friction force, temperature and electrostatic charge values arising in the friction zone is developed. The friction of the fibrous material is carried out on the flat surface of the rotating disk sample from the material under study at specified clamping pressures and sliding speeds. Values of friction forces, temperatures and values of electrostatic charges of the tested sample in a zone of friction with cotton-raw are measured by means of sensors.

DEVIATION FROM CLASSICAL ELASTICITY IN THE ACOUSTIC RESPONSE OF AUXETIC FOAMS

ABSTRACT Acoustic properties of an auxetic foam were measured to validate a previously proposed lower bound for Poisson's ratio, ν ≥ 1/5, inferred from classical two-parameter elasticity theory. This limit differs from the commonly reported lower limit of −1 for isotropic materials in the linear elastic range. For a foam measured to have a value of ν > 0.2, agreement was found between the measured flexural resonance frequency of a disk sample and the theoretical value. On the other hand, for an auxetic sample (ν < 0), the prediction from the two-parameter theory was significantly in error. Thus, for materials having ν < 1/5 (auxetic foams, as well as very hard solids such as diamond, germanium, and fused quartz), the equations of classical elasticity are invalid.

COMPARATIVE RADIOGRAPHIC ASSESSMENT OF A NEW BIOCERAMIC-BASED ROOT CANAL SEALER

Background and aims. The aim of this study was to assess the radiopacity of two bioceramic-based root canal sealers, the conventional TotalFill BC sealer (FKG Dentaire Switzerland) and a new experimental filling material developed in collaboration with 'Raluca Ripan' Institute for Research in Chemistry, Cluj-Napoca. Methods. Five disc samples were prepared using both materials (10 mm diameter x 1 mm thickness), being subjected to digital radiography together with aluminum step wedges (1 to 12 mm in thickness), in accordance with ISO 6876: 2012. Radiopacity was determined by the computer analysis of the images obtained. Four different areas were selected for each sample, corresponding to a disk-sample quadrant. Statistical analysis was performed using ANOVA.Results. Both materials showed a radiopacity that was 3 mm greater than the equivalent thickness of aluminum. Total Fill BC showed greater radiopacity than the experimental material, but the differences were not statistically significant. Conclusions. Both materials comply with ISO 6876: 2012 recommendations on minimum radiopacity.

Development of a Technique for the Calibration of HPGe Detector to Estimate Radionuclides Present in Steel Samples

The quantitative assay of radionuclides present in steel samples is required for the environmental safety as well as in the process control and quality control of the finished products. The standard sources should also be prepared in the required size and shape as that of the sample, for the efficiency calibration of the HPGe detector system. A method was developed and tested to use 152Eu point source for the determination of efficiency of an extended steel disk source using HPGe detector system. Standard point sources of 152Eu were prepared by transferring known amount of 152Eu activity by weight. Standard steel disk sources of required dimensions were also prepared by distributing uniformly the standard activity of 152Eu on both sides of the inactive steel disk. The extrapolated efficiency of the steel disk sample was determined using the efficiency of the 152Eu point source and it was compared with the efficiency determined using the standard sources of 152Eu prepared on the steel disks. The two efficiency calibration curves matched very well within the experimental limits. Using this efficiency calibration, a few steel samples were analyzed for the radionuclides present in them. The detections limits for most of the nuclides were much less than the specified limits. The method can further be extended for other types of geometries with suitable modifications for the changes in thickness and attenuation corrections.

Carbide Particle-Reinforced Tungsten Composites in Extreme Hazard Environments

The ablation as well as the associated thermal shock resistance of tungsten composites reinforced by TiC and ZrC particles is investigated with an oxyacetylene equipment. 30TiC/W (30TiC stands for 30 vol. % TiC particle content in tungsten, the same below) and 40TiC/W fail to withstand the thermal shock of 2000ºC/s during heating. In contrast, 30ZrC/W and 40ZrC/W withstand the thermal shock. Additionally, ZrC/W composites exhibit better ablation resistance than TiC/W composites. The thermal stress fields of the composite at both macro-/micro-scales induced by thermal shock at the early stage of the ablation are analyzed using finite element method. The calculated results of the damage mode of the composites show that crack initiates at the disk sample peripheral zone and then propagates to the sample center, which is consistent with the experimental observation.

Wear Resistance of Aluminized Steel Plates

Wear Resistance of Aluminized Steel Plates The results of the abrasion resistance measurements of aluminized steel strips are presented in the hereby paper. Steel strips of DX52D+AS120 grade, before and after a heat treatment at temperatures of 200-1000°C for 1 - 5760 minutes, were tested. Tests of the abrasion resistance were carried on in a specially built device: rotating disk - sample performing a plane-rotary motion, with an application of a lubricating medium. Examinations of the abrasion resistance were also performed by means of the block-on-ring tester. Estimations of a coating mass loss, roughness and thickness changes were carried on. The obtained results are illustrated by diagrams and macro- and micro-observations. Phase analysis investigations were also performed on samples selected after the abrasibility testing. The range of the heat treatment parameters - after which the Al-Si coating increased its abrasion resistance - was estimated.