Applied Mechanics and Materials Vol. 732

Abstract: Characteristics cushions from PU foam together with coat determine comfort automobile seats. Frame of car seat with cushion from PU foam and cover serve like body rest. Also perform safety rules, that are demanded on car seat. Cushion in car seat is basically manufactured from PU foam. Experimental testing their property investigate correlation between their characteristic and comfort. One type of experiment is combination static and dynamic loading in medium term time interval . Subject research and content hereof article is recognition transmission characteristics and contact pressures cushions from PU foams in time interval two o'clock in turns static and dynamically weight constant loading.

Abstract: In this paper, the authors draw attention to biomechanics connected with the possibilities of treatment of complicated bone fractures. They present information about their own design, laboratory tests and numerical solutions (i.e. strength analyses and reliability assessments) of the various types of external fixators applied in traumatology and orthopaedics (i.e. intended for fractures of limbs and pelvis and its acetabulum). The new design of external fixators is based on the development of Ilizarov and other techniques and satisfies new demands of science.

Abstract: The effects of the polyvinyl alcohol (PVA) concentration on mechanical properties of hydrogels based on blends of native or denatured collagen / PVA were examined. Blends of PVA with collagen were obtained by mixing the solutions in different ratios, using glycerol as a plasticizer. The solutions were cast on polystyrene plates and the solvent was allowed to evaporate at room temperature. Uniaxial tensile tests were performed in order to obtain the initial modulus of elasticity (up to deformation 0.1), the ultimate tensile stress and the deformation at failure of the material in the water-saturated hydrogel form. It was found that the material was elastic and the addition of PVA helped to enhance both the ultimate tensile stress and modulus of elasticity of the films. Samples prepared from denaturated collagen showed the higher ultimate tensile stress and the deformation at failure in comparison with those prepared from native collagen. The results suggest that we could expect successful application of the collagen/PVA biomaterial for tissue engineering.

Abstract: This article deals with a study and optimization of technology for a production of low-diameter biodegradable vascular grafts using modified electrospinning device. This production method allows preparation of grafts with diameter under 6 mm, which serve as carriers of tissue cells. Also their production and establishing of a simulation model, which describes their behaviour under internal pressure. For this purpose spinning device was created with a rotary collector, which allows obtaining the desired fiber orientation that is perpendicular to the axis of rotation. This orientation is necessary for the efficient proliferation of cells and future mechanical properties of artificial blood vessels. Formations created in this way were subjected to mechanical testing. Based on obtained data a suitable material model and FEM model of artificial vessels was established. These vessels were loaded with internal pressure corresponding with standard blood pressure in human body (120/80 mmHg). The results allow assessing the behaviour of the blood vessels during cultivation and proliferation of the cells in bioreactor. This is very important, because in bioreactor a medium, which pulsed under some pressure, is applied. Based on the obtained results were recommended optimization of production process, which led to suitable vessel properties.

Abstract: The paper contains results of a study aimed at exploring possibilities of use of direct current potential drop (DCPD) method for evaluation of depth and profile of cracks occurred under or near press fitted hubs in a full-scale axle during severe rotating bending loading. DCPD method was applied on section of an axle after fatigue by a specific way and potentials were measured in several circumferential areas of the axle section, when direct current passed longitudinally. Results are analysed and discussed. It was indicated that unlike previous use of the method for crack measurement of different components, even large and complicated, described in the literature, when potentials corresponded to ratio of cracked and uncracked area, in this case of approximately circumferential crack, measured potentials correspond better to relative crack depth in the relevant point of the circumference.

Abstract: Safety assessment of railway axles is based on fatigue strength design. During the design overall lifetime, railway axles undergo a very high number of loading cycles under rotating bending. Due to safety and reliability reasons, fatigue strength design has to be very carefully evaluated. Both theoretical modelling and extensive experimental fatigue testing including full scale tests have to be performed, whereas such tests have to be performed correctly with a high precision. In the paper, problems of dynamic forces during fatigue tests of railway axles are pointed out. Though static calibration can be carried out with a very high precision, dynamic forces can cause a significant redistribution of static stresses along the axle. An example is given and discussed.

Abstract: The contribution deals with the investigation of the influence of facet size and smoothing on the results obtained by low-speed digital image correlation (DIC) system by strain analysis performed on specimen with a small hole loaded by tension loading. In conclusion the obtained results are verified by a numerical solution using finite element method.

Abstract: Paper deals with the identification of coupled mode shapes by experimental modal analysis. Main attention is focused on the using of Complex Mode Indicator Function that is based on singular value decomposition of frequency response function matrix and allows to separate coupled and also closed modes. In the paper there is described experimental modal analysis at which digital image correlation method is used to measure responses of a circular plate. The measurement was evaluated in program Modan 3D that is being developed by the authors.

Abstract: Steam turbines are complex rotating machines working at high pressure and high temperature levels. Their high-pressure parts, which are subjected to the highest steam parameters, are most affected by these conditions and may suffer from creep deformation. Permanent changes in geometry become visible in high-pressure turbine casings when they are disassembled after certain time in operation.

Abstract: The paper shows a possibility of the tuning mechanical system by means of two pneumatic springs in a differential configuration connected with a throttle valve. The springs are inserted into the lead mechanism and connected to its parts, and to its supporting platform. The vibrations, transferred from the kinematic excitation of the base, are intended to be minimized. The vibration isolation by means of pneumatic springs is available in many technical systems, e.g. in supports of heavy machinery as well as in systems characterized by the human interaction, such as driver seats, ambulance couchettes, etc. The pneumatic springs provide the option of adaption of the stiffness, and herewith the adaption of the natural frequency of the system according to the exciting frequency. In cases of application of the object vibration isolation, they can change the load characteristics in a relative large range. In the studied case of the differential spring configuration, the springs are connected with an air pipe to the throttle valve. The air being exchanged during the motion period comes through the valve, the cross-section of which determines the time delay of the pneumatic sub-system thus creating a hysteresis of load characteristic of the spring support. This brings an additional, controllable damping to such a system that is profitable in most vibration isolation cases.