Applied Mechanics and Materials Vols. 752-753

Abstract: Micromechanical changes in the surface layer of glass-filled PA-6 modified by beta radiation were measured by instrumented test of microhardness. The specimens were prepared by injection technology and subjected to radiation doses of 0, 66, 99, 132 kGy. Measurements of microhardness showed considerable changes of behavior of surface layer in middle as well as high radiation doses with higher values of indentation hardness and stiffness.

Abstract: This paper describes an interesting approach aimed at analysis of material properties. This work is based on simulated measurements of transmission coefficients of multi-layered materials. These measurements (in a waveguide) are taken as a product of a certain situation, therefore there is an inverse problem in which we try to estimate the original properties of the layers. This study employs analysis of closed-form solutions and numerical multi-parameter optimization.

Abstract: Radiation processing of polymers is a well-established and economical commercial method of precisely modifying the properties of polymers, especially thermo-mechanical properties. The thermo-mechanical properties and the tensile behaviour of modified LDPE samples by radiation cross-linking were measured at the ambient temperature and after temperature load. The tested samples showed significant changes of tensile behaviour before and after temperature load. From this point of view, new applications could also be seen in areas with service temperatures higher than their former melting point.

Abstract: In this study there was found that ionizing beta radiation increased the strength of bonded joints and improved the adhesion properties of polycarbonate (PC). Bonded joints at elevated temperature (60 °C) were tested. Generally, for the formation of quality bonded joint it is important to wet the adhesive bonding surface well. Wettability is characterized by the contact angle of wetting. The liquid has to have a lower surface energy than the solid in order to be able to wet the solid substance. The measurement results indicated that ionizing beta radiation was a very effective tool for improvement of adhesive properties and increased the strength of bonded joints of PC at elevated temperature (60 °C). Bonded surfaces with ionizing beta radiation doses of 0, 33, 66, 99, 132, 165 and 198 kGy were irradiated. The best results were achieved by irradiation at doses of 66 kGy by which the highest surface energy and the highest strength of bonded joints of PC were achieved. The strength of bonded joints after irradiation was increased up to 10 % and surface energy up to 30 % compared to untreated material.

Abstract: A study of the effect of material gradient on the performance of a functionally graded endodontic prefabricated parallel post (FGEPPP) is the main goal of the current study. Elastic modulus (E) of FGEPPP is considered to vary continuously from lower to upper surfaces. This variation is performed according the volume fraction. Based on a modified sigmoid function, the volume fraction will be defined in the present work. The primary goal of the current investigation is to analyze the difference between the performance of a homogeneous endodontic prefabricated parallel post (EPPP) and a FGEPPP through finite element analysis (FEA). In the current investigation, von Mises stress, and shear stress in FGEPPP case with a modified sigmoid function and in homogeneous EPPP case are carried out. After that, the effect of material gradient on the performance of an EPPP made of FGM was carried out through FEA in the current investigation. The simulation cases shown that, the maximum values of von Mises stress, and shear stress increase when increasing the value of “D”, and decrease when increasing the value of “w”.

Abstract: Natural products have attracted much attention in recent years as a useful substance used in medicine and dental products. Propolis is a lipophilic resinous mixture collected from various plant sources by honeybees. It has been known for many biological activities including antimicrobial properties. Objective: To evaluate the in vitro antimicrobial activity of propolis against caries-associated microorganisms, Streptococcus mutans, Lactobacillus casei and Candida albicans. Materials and methods: The antimicrobial activity was initially screened using agar disc diffusion and then the minimum lethal concentrations (MLCs) were determined using broth dilution technique. Chlorhexidine (0.2%) and dimethyl sulfoxide (5%) were used as positive and negative controls, respectively. Results: Propolis exhibits the zones of inhibition ranged from 15 to 18 mm for S. mutans, and from 10 to 12 mm for L. casei, but presented no activity against C. albicans. The MLC against S. mutans was 2.86 mg/mL and those against L. casei were 11.44 mg/mL and 12.87 mg/mL. Conclusion: Propolis shows a potent antimicrobial effect against S. mutans and L. casei. This could provide a scientific basis to its application of usage in oral care products for the prevention of dental caries. However, further studies are necessary to evaluate other biological activities and molecular mechanisms of action as well as its cytotoxic effect.

Abstract: The Joule-Thomson (JT) effect will occur when the gas flows through the components of filters, valves, orifices and end faces in the system of the dry gas seal, which may cause the temperature of the seal gas to decrease, and even the emergence of liquid condensation. Generally, the Joule-Thomson effect is reflected by the Joule-Thomson coefficient. As to the hydrogen, nitrogen, carbon dioxide and air, which are often met in the dry gas seal, the corresponding Joule-Thomson (JT) coefficients were calculated by four classical equations of state (EOS) of VDW, RK, SRK and PR, which are compared with the experimental data in the literature. The results show that the JT coefficients calculated by RK equation are most close to the experimental data in the literature, whose relative error is lowest and less than 4%. When the JT effect of real gas in the dry gas seal is analyzed, the RK equation of state is recommend.

Abstract: In this paper the Halbach array with different segments per pole are modeled. The dimensions of magnets among segments are different with different magnetization direction. The unified harmonic model for the magnetic flux density distribution of the Halbach array with different segments per pole is derived by using Fourier series and magnetic scalar potential. Then the Halbach array with different segments per pole can be analytically analyzed and compared by the unified harmonic model.

Abstract: The effect of surface defects formation in grinding on two compositions of silicon nitride have been studied experimentally. The influence of composition of nitride ceramics, diamond wheels characteristics and grinding regimes on the grinding forces, final strength of samples and the degree of structure imperfection of their surfaces after grinding has been understood as a result of undertaken series of grinding tests.

Abstract: This experiment analyzes the relation between rubber power asphalt mixture and Marshall Test results under the action of the temperature and salt corrosion, by using matrix asphalt mixture and 80 mesh 10% rubber power. It carries out 18 test, considering two factors of NaCl solution solubility and soak time. The test result indicated that immersed in the NaCl solution of the matrix asphalt mixture and the rubber power asphalt mixture stability is trending downward, with the increase of immersion time; Rubber power can improve the ability of asphalt mixture for resistance temperature and salinity. According to SEM micro-analysis, NaCl solution of salt corrosion can contribute to the further damage of asphalt mixture. Keywords. Temperature; Chlorine Salt Corrosion; Rubber Powder; Asphalt Mixture