Applied Mechanics and Materials Vol. 430

Abstract: The forced vibrations of railway vehicles are caused by excitations that appear during the rolling process , especially by the wheel-rail contact forces, which have a random distribution . Another example is represented by the internal forces that appear not only because of the force equipments inside the system or vehicle, which are not fully balanced for centrifugal forces, but also because of the gear boxes. The running stability of the rail-car is analyzed based on the proposed mechanical model and the general Lagrange equation. The amplitude amplification factor and the delay of oscillations are firstly analyzed theoretically, then graphically plotted in function of the non-dimensional normal pulsation for different values of the relative damping factor, both of the rail car suspension and the railroad. The possibility of improving the buffers for both coaches and trucks is analyzed in function of the non-dimensional normal pulsation for different transits of the rail cars through the resonance zone.It leads to several important practical conclusions for the rail car designers and manufacturers.

Abstract: The paper presents a comparative study of the kinematic parameters of the upper limbs of one healthy subject and one patient with lateral distal humerus implant. This study aims to identify the movement patterns of the upper limb joints, having a particular interest in elbow joint, due to the patients pathology. Both subjects have been recorded in identical conditions, performing the same exercise what simulates one of the common daily activities. The kinematic parameters which have been analyzed were flexion-extension and abduction-adduction in shoulder joint and flexion-extension of the elbow joint. The joint angles have been averaged per each valid trial and exercise. The comparison of the joint angle variation was performed in terms of normalized time. Standard deviation was computed to evaluate the variability of joint angles. Movement symmetry between left and right arms was evaluated by computing the p-values of the averaged series.

Abstract: The paper proposes a protocol used for data processing, designed to handling the foot pressure data recorded in human walking. This protocol represents a stage of a global protocol that deals with identification of some biomechanical parameters used in diagnosis and prediction. In order to validate the functionality of the data processing protocol, a lot of 10 patients suffering of Hallux Valgus deformity were recorded both before and after the surgery. The patients were divided into three age groups: 20-30, 40-50, 51-60. The measurements consist in recording of plantar pressure data in both dynamic (gait) and static way. This is an additional investigation to the clinical usual examinations in hallux valgus patients. The recorded data were averaged per each subject and then per whole lot. Based on determining the ground reaction force (GRF) variation in time and observing the foot pressures on static measurements, we can conclude that the static approach of evaluation of Hallux Valgus condition is no very reliable.

Abstract: The internal fixator principle is a novel, minimally invasive approach to epiphyseal fractures of the long bones. It has been advocated to provide a stable fixation of fracture fragments with the preservation of the osseous blood supply due to the lack of periosteal decortication. The aim of this minimally invasive technique is to allow for early rehabilitation, so in theory patients that went trough minimally invasive internal fixation osteosynthesis should have better clinical results with higher scores than patients that had classic ORIF technique. We investigated a number of 18 tibial plateau fractures in 18 patients that were matched by fracture classification and patient sex and age, 9 were treated by conventional plating techniques and the other 9 were treated by using an internal fixator. The patients were evaluated pre and postoperatively by conventional radiographic means and by CT scanning with 3D reconstruction, they were evaluated with the KOOS score at 3 and 6 months postoperative. Gait analysis was performed in the lab using a Zebris FDM System and a Zebris CMS 10 3D Movement Analysis System. Gait analysis was performed based on patient availability as soon as ambulation was possible and permitted without auxiliary support (crutches). KOOS scores increased from 3 to 6 months, the initial evaluation showed a mean value of 27,5 (19,7 to 39,4) for the ORIF group and a value of 33,9 (24,1 to 42,4) for the internal fixator group at 3 months, and increased to 64,8 (55,3 to 73,1) for the ORIF group and 69,8 (59,7 to 82,7) for the internal fixator group. The difference between stance and swing times, knee flexion angles and was found not to be statistically significant (p<0.05) at either 3 or 6 months postoperatively. The data shows no clear advantage in using an internal fixator over the classic plating methods at 6 months postoperatively. The minimally invasive technique provided for faster wound healing with better KOOS scores at 3 months but there was no statistically significant difference at 6 months postoperative. Limitations of the current study are the relatively small number of matched patients and the heterogeneity in patient physical characteristics such as patient weight and height and the level of preoperative fitness.

Abstract: Many of the studies in the biomechanics of the human body made globally focused primarily on hand-arm. This segment of the human body is considered a "gateway" of vibrations to other parts of the body or to internal organs. A long-term exposure to these mechanical vibration (caused by vibrating hand equipment: drill, grinder, etc.) affects the soft tissues and may lead to a dangerous syndrome, that is particularly vibration white finger (VWF), which is narrowing of blood vessels, a phenomenon that in time and untreated can even cause gangrene. This article focuses on a dynamic model with three degrees of freedom of the human finger. Some dynamic characteristics, such as centre of gravity, stiffness and damping, using both a rigid body structure system and computer simulations can be determined after measuring the vibrations.

Abstract: Hydroxyapatite is a biomaterial, more exactly a bioceramic, from a category of materials frequently used in bone implants. In order to improve mechanical properties, hydroxyapatite is doped with different chemical substitutes, among which the most used are: Mg^2*, Zn ^2*, La^3*, Y^3*, In^3* Bi^3* CO₃^2-, Si and Mn. In the paper are presented the modality of obtaining hydroxyapatite doped with magnesium through wet precipitation method and also the determination of its main mechanical characteristics. There is also an analysis on the effects of magnesium on the following mechanical properties: density, hardness, longitudinal modulus of elasticity, conductibility and thermal stability.

Abstract: The dynamic analysis of the lower limb prosthesis is necessary mainly for defining the joint mechanical specifications. This paper presents two models of lower limb prosthesis. Both models have two active joints (ankle and knee) and the same overall dimensions. The main difference between the two models consists in the joints mechanical parameters. The prosthesis elements are modeled according to the human anatomy, taking into account the weight of the amputated limb. Based on this preliminary data the two models were developed using the Solid Edge V20 software. The dynamic analysis was developed in Dynamic Designer Motion Professional module which is a subset of Motion Professional software. The gait cycle time was set to 2 seconds. There were studied two main stages during the gait cycle: extension (from hyper-flexion to hyper-extension), and flexion (vice versa), respectively. The input data are: geometrical model, material properties of the prosthesis elements, gravity force, joint laws of motions and ground reaction forces. Based on this input data the software calculates the path, velocity and acceleration of the prosthesis elements and reaction forces and torques in each joint.

Abstract: Application of the prediction models for railway noise indicators calculation, which was already developed by other countries, represents a major challenge in Serbia. Prediction model "Schall 03" was developed in line with technical and technological characteristics of the rolling stock and infrastructure of German Railways. Prior to its application at the national level, due to different technical-technological characteristics of railway stock and railway infrastructure it is necessary to perform its validation and, depending on the needs, the calibration in accordance with local conditions. This will assure accuracy and precision of the calculations of noise indicators, as well as confidence in the results obtained by prediction model "Schall 03". This paper presents the analysis of the possibilities to apply German prediction model "Schall 03" on the Serbian railway network, more precisely railway section from Belgrade to Romanian border. Calculated values of noise indicators were compared with the results of measurements of noise indicators within measuring interval, which correspond to the referent time intervals for different day periods.

Abstract: The great majority of cities in the world have resolved problem of acoustic zoning in the urban part of the city. Two approaches are usually applied in acoustic zoning: acoustic zoning of the territory in accordance with land-use where the allowed values of noise indicator are defined and acoustic zoning by preparing noise maps around dominant sources of noise in urban areas and defining land-use in relation to calculated isofonic lines. As international standard and internationally recognized methodology for preparation of acoustic zoning does not exist, the authors of this paper initiated preparation of methodology for acoustic zoning. The concept of methodology is demonstrated in this paperwork. The methodology has been applied on the City of Nis example starting from the specificity of Nis urban area as well as requests and goals that have been set and defined during sustainable planning of Nis City development. Based on defined acoustic zones and noise measurement results for five years period on the territory of Nis City, the evaluation of the condition of noise level has been done and this paperwork presents results obtained.

Abstract: nside the industrial halls one can find different noisy machines and equipments. During their work these ones generate noise and vibrations which affect human beings inside or outside the hall. In this paper we present the results obtained in the investigation of the acoustic field generated by sources within an industrial hall emphasizing the frequency spectra, characteristic parameters, propagation way and some effects generated. A description of measurements is included together with an analysis of obtained results as well as the establishment of noise mitigation methods consisting in acoustical arrangement of the hall in order to eliminate the unpleasant effects.