Applied Mechanics and Materials Vols. 809-810

Abstract: The concepts which go out from the design activity are based on high knowledge [1], rules of designing [2] and previous experience. Until the product is closer to the series and after in the final customer environment, many processes have to be followed. In the development phase (the phase which contains the concept ideas), considering that a separate plastic connector assembled with Aluminum housing has more advantages [4], the current topic which is handled in this paper is to change the material to plastic and establish how the PCB is mounted and positioned inside the housing. More said which the optimal process for this application is. And this is the most challenging step, of choosing the optimal technology for the assembly (in this case 2 assemblies are considered: the PCB with the housing, which is the PCB mounting/ fixation, and the PCB holes with the connector pins, which is the PCB positioning). The material was changed due to higher properties of plastic which in automotive field brings strong added value. As known, in automotive field there are several processes for the mounting of PCB inside the housing like, snapping-on, clamping, screwing and press-fit. To position and to interconnect the PCB holes with the pins, processes like press-fit, spring contact and wave soldering. The selection of the proper process is made by implementing each of the processes requirements into the shape design of the connector, pins and housing.

Abstract: The paper presents a design methodology for a slider assembly from tools used in laminating process of decorative parts with big curvature and negative draft. In usual cases are used a single active part to laminate parts. For laminating process of this surface are designed a slider assembly with three active parts. All these three active parts have their own heating-cooling systems. That means a good temperature control in each point on surface. The results are a laminating process without scratches, signs or imperfections. In the paper are also presented the working method of slider assembly and all the main steps in design from concept direction to clash analysis.

Abstract: Presented in this article are the properties of flame sprayed ceramic coatings using oxide ceramic materials consisting of a powdered zirconium oxide (ZrO₂) matrix with 30% calcium oxide (CaO) applied to unalloyed S235JR grade structural steel. A primer consisting of a metallic Ni-Al-Mo based powder has been applied to plates with dimensions of 5x200x300 mm and front surfaces of ø 40x50 mm cylinders. Flame spraying of primer coating was conducted using a RotoTec 80 torch, and an external surface was coated with a CastoDyn DS 8000 torch. Evaluation of the coating properties was conducted using metallographic testing, phase composition research, measurement of microhardness, abrasive wear resistance (acc. to ASTM G65 standard) and erosion wear resistance (acc. to ASTM G76-95 standard).

Abstract: In this article, the authors have analysed the influence of quenching temperature (T_Q) on the microstructure of a dual-phase steel with a low carbon and manganese content (0,094 % C and 0,53 % Mn). The ferrite-martensite structures, typical of the dual-phase steels, has been obtained by intercritical quenching that consisted of heating at temperatures (T_Q) ranging between 750 ^°C and 830 ^°C, maintaining for 30 minutes and cooling in water. After carrying out intercritical heat treatments, samples have been subjected to metallographic analysis through which the volume fraction of martensite (V_M), the volume fraction of ferrite (V_F), the carbon content of the martensite (C_M), the morphology and distribution of these phases have been determined, and then, the influence of quenching temperature (T_Q) has been established.

Abstract: The major goal of our research work is to develop an effective and efficient procedure to prepare surfaces with an average surface roughness R_a of 1...2,5 μm and a proper surface topography, as the morphology of dental implant surface is of extreme importance in the process of implant osseointegration. The aim of present research was to elucidate the effect of surface preparation and passivation treatment on topography of Ti6Al4V surfaces for dental implants, and to perform an efficient procedure, in terms of process time. Thirty samples were prepared, some samples were subjected to sand blasting, all samples were acid etched using a dual bath of H₂SO₄ 1n and HCl 1n (1:1) at different temperatures (60°C, 80°C, and 100°C) using different process durations (1 h, 3 h, 6 h, 12 h, and 24 h). After acid etching procedure some samples were passivated in 30% HNO₃ at room temperature, for 15 min. Scanning electron microscopy was performed in order to characterize the topography of the surfaces. We found that sand blasting and passivation treatment promotes the formation of a proper surface topography with large, smooth valleys (∼50 μm), different size large peaks (∼30 μm), and micropores (<10 μm) opened on the surface of valleys and peaks, required by a good osseointegration. We showed that the same proper morphology can be achieved by acid etching at different temperatures, using different process duration. The most efficient procedure takes place at 100°C, with process times of 1...3 hours.

Abstract: Published literature is rich with investigations of mechanical properties of composites, but fewer publications are focused on thermal properties. Several publications addressing different theoretical approaches for predicting thermal conductivity of composite materials have been noted. However, one of the publications has discussed both transverse and axial thermal conductivity of a carbon fiber composite. A non-linear increase in the thermal conductivity was reported with the increase of fiber volume fraction of plain weaves and no theoretical models are able to predict this non-linearity. The result of literature search even further identified the necessity and importance of carrying out further investigations on thermal behavior of composites materials. Thermal conductivity of composites is anisotropic in nature and data about thermal conductivity of resin is known to reduce stresses related to shrinkage of composites during cure and mismatch in thermal expansion coefficients. Before conducting experiments to determine thermal conductivity of various composites, knowledge about effect of different parameters influencing thermal conductivity is essential. This paper deals with an analytical study on few nanocomposites behavior at heating.

Abstract: An innovative way of improving the thermal conductivities of fluids is to suspend small solid particles in the fluids. Various types of powders such as metallic, non-metallic and polymeric particles can be added into fluids to form slurries. The thermal conductivities of fluids with suspended particles are expected to be higher than that of common fluids. Application of nanoparticles provides an effective way of improving heat transfer characteristics of fluids. By suspending nanophase particles in heating or cooling fluids, the heat transfer performance of the fluid can be significantly improved. Moreover, the thermal conductivity of nanofluid is strongly dependent on the nanoparticle volume fraction. So far it has been an unsolved problem to develop a sophisticated theory to predict thermal conductivity of nanofluids, although there are some semi empirical correlations to calculate the apparent conductivity of two-phase mixture. In this article few correlations were considered and differences were noted between different theories. In conclusion, a lot of uncertainties in determining thermal conductivity were noticed.

Abstract: Mechanical behaviour law for thermoplastic polymers was established on the basis of phenomenological models. This work is intended to examine whether a constitutive equation used for thermoplastic polymers could be applied in case of their composites. G’Sell-Jonas model gave good results when used for the prediction of stress-strain characteristics at high strain rate, for semi-crystalline polymers subjected to mechanical tests. Data obtained through compressive test of polyphenylene sulphide (PPS) composites were processed by a numerical algorithm based on G’Sell-Jonas constitutive equations. Besides, a comparative analysis of experimental results and numerical model was done. The study showed clearly a good agreement between experimental and numerical results.

Abstract: Armored steel sheets have various uses in civil and military industry. For the last one, especially in aeronautics, a better determination of the lifetime for the fatigue and shock loaded parts, is a major challenge. Several methods for fatigue calculus are known: safe-life, fail-safe, crack propagation method. All of this methods are not considering in any way the shocks that can accidentally occur, so in the calculation of lifetime, the role of impact multiplier is null. The authors propose a corrected formula for the calculus of the lifetime for 2P armor steel, based on the internal energy developed into the test specimens, through the impact multiplier.

Abstract: A shape memory composite plate has been produced by adding a shape memory interlayer between two carbon-fibre epoxy-matrix prepregs. A Small plate has been obtained which was used for testing under bending at different rates up to the final failure. The first test was performed at low rate and final damage was recovered by heating. A second bending test was performed on the self-repaired plate at high rate. As a result, a good shape recovery after damaging has been observed and a fairly good residual stiffness was measured. The residual stiffness after shape recovery was about 80% and the composite plate was able to withstand a second test at higher rate (with a residual strength about 40%). Results show that it is possible to combine shape recovery of shape memory polymers with structural properties of composite materials: the goal is producing composite structural