Advanced Engineering Forum Vol. 34

Abstract: The composite materials for self-regulating heaters are conductive composites based on a polymer matrix and a dispersed conductive filler consisting in either carbon black or another carbon material, such as graphite or nanotubes. Similar materials are suitable for sensors and current limitations. As these materials used in heating applications work usually at elevated temperatures in presence of air, the ageing processes would be an important limiting factor of their lifetime. Therefore, thermal oxidation processes and crystallinity changes during the service of these products are of major interest in durability studies. The potential interference of carbon-based materials with the oxidation and ageing of polymer matrix shall be known in order to correctly estimate the durability of such materials. The effect of radiation exposure is studied taking into account the potential use of such materials in radiation environments. In this work, the activation energies of some initial, unaged and aged products at elevated temperatures are compared in order to characterize the effect of thermo-oxidative ageing and hence to evaluate their durability. The effect of some antioxidants is also discussed. The crystallinity, calculated from DSC was used for evaluation of the physical changes induced within the aged materials, following the procedures described in previous work. FTIR-ATR technique was used for characterization of chemical changes induced by ageing.

Abstract: Recent developments in the field of tissue engineering recommend the 3D printing to obtain the complex shape of the final alloplastic grafts (for soft or hard tissues). The medium pressure injection moulding (MEDPIM) technology could be a cost-effective alternative to 3D printing. This paper presents the first studies for the MEDPIM applicability in the case of some alloplastic bone grafts manufacturing. Two biocomposite feedstocks have been researched in order to obtain the injected parts (herein after named green parts). The Ti6Al4V respectively TiH₂, both as powder particles, were mixed with hydroxyapatite (HAP) powders in the W 50 EHT measuring mixer. Both powder mixtures contain NaCl as foaming agent as well as some wax-based binders. The MEDPIM process is developed in the laboratory-scale device, designed and manufactured in the frame of the research project BONY. This device replicates, at lab-scale, the MEDPIM process developed by the Goceram MEDPIMOULD equipment, able to work at mass-production scale. The injection moulding tests were performed at the temperature range of 50…110°C, respectively at 30-45 MPa as injection pressure. The green parts quality was evaluated by means of the physical characteristics (dimensional and density measurements) as well as macroscopic evaluation using the stereomicroscope NIKON SMZ 745T. The influence of the biocomposite feedstock type as well as the injection temperature on the green pats quality is studied in this research.

Abstract: In this paper, obtaining by PM of aluminum based materials, characterization of them and Finite Element Analysis (FEA) of compaction were investigated. Sintered aluminum alloys (Al-Cu and Al-Mg-Si) were tested from physical and mechanical point of view and the obtained experimental results were compared with those of sintered bronze powder materials. We studied the compressibility and densification mechanism of Al-Cu mixed powders and for prediction of compaction behavior we used FEA. The data was obtained on the stress distribution in the compacted material and on the deformations occurring throughout the mixed metal powder of the compacted samples. The results of FEA were compared with those obtained experimentally

Abstract: The paperwork presents the way the reliability logic schemes could be used for modeling the reliability of the systems in the conditions the reliability models for their components are known. There is presented an application for a complex system of the vehicle, the breaking system, based on the normal or exponential identified models for the components reliability. The achieved results confirm the applicability of the proposed working method and highlight that this approach easily allows the forecast in an analytical way of the reliability of the complex systems.

Abstract: The reliability evaluation of an equipment is made through its functionality analysis in specific conditions. When these conditions are various, the accomplishment of functional requirements could be partial, not integral. In these cases, the reliability evaluation is realised through methods specific to systems with many stages, those based on the fuzzy logic being one of them. In this paperwork there are presented the most used algorithms for evaluation.

Abstract: The appearance of quick wear of rolling paths and rolling elements (balls) through contact fatigue phenomena and through surface defects lead to a decrease in the life of ball bearings in service. One of the causes is the interruption of the lubricating film between surfaces with relative motion under load conditions and high speeds, which leads to plastic micro-deformations and micro-welding between contact surfaces. Diagnosing defects by visual observation involves disassemble of the bearing and is an ineffective method of investigation in serial production. In this context, the necessity of: (i) comparative study of the stresses to which two types (100Cr6 steel and 100CrMnSi6-4 steel type) of radial ball bearings are subjected, (ii) the influence of contact between the ball and the inner ring during rotation, and (iii) the analysis with Finite Element Method (FEM) of the deformations occurring at the application of radial bearing forces. FEM is a current approach to real phenomena in mechanical assemblies, which allows a validation of study assumptions; the results of FEM can lead to the detection of tribological causes of increased bearing wear at inner ring to bearing balls contact. In this paper, FE simulation of radial loading deformations was performed in SolidWorks software using the Simulation module and the stresses and deformations in the bearing rings for the two materials were obtained. It has been found that the stresses that appear during simulations are similar for both materials and do not exceed the limits allowed for heavy duty steel bearings.

Abstract: In this paper we were looking for the production of a physical car body part (the left side fender of a Peugeot 206) made from composite materials based on epoxy resin and reinforced carbon fiber and kevlar woven. On the newly created fender model, a modal analysis has been made in order to determine its own frequencies on a certain direction, and an harmonic analysis with Finite Element Method.

Abstract: The paper includes the stability study of some dynamical systems given by systems of differential equations. The paper examines the stability of three dynamic systems using the Leapunov function method. The originality of the paper consists of how we choose the Leapunov function. We apply the stability theorems given by Leapunov for autonomous systems. Stability is an important property of a dynamic system that has applications in the technique.

Abstract: Although aircraft carriers operating in the seas have developed considerably from a constructive point of view, naval aviation continues to face significant challenges due to short runways, often in motion or unpredictable weather conditions, as a rule. This paper aims to analyze the concept of aircraft's rapid deceleration to landing, as well as to study the dynamic behavior of the aircraft restraint system used by aircraft carriers.

Abstract: To study the vibrations of a Multiparker lift lift model, use various models for the lifting mechanism. Calculate the first pulsation using the Dunkerley method. Behavior of the elevator to the action of an explosive task. We intend to evaluate the own pulsations in case of free vibrations of a lifting mechanism at an elevator within a multiparker parking lot. IT is absolutely necessary that the wave pulsation is different from the own pulsation of the studied system so as to avoid the resonance phenomenon leading to the system’s destruction. We shall establish a work algorithm using several models of the system as following: the model of the system with an autonomy degree; the calculation of the first own pulsations is used by the Dunkerley method; the model of the continuous system.A model is executed for the lifting mechanism of the Multiparker parking lot, considered as being composed of a continuous and homogeneous bar, embedded at the base, becoming a common unit with the mass M of the elevator. The own pulsations are determined in case of free vibrations for this bar.