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J. Holzweber, Z. Major
CHARACTERIZATION OF THE FATIGUE BEHAVIOR OF TPUS

The fatigue behavior of different thermoplastic polyurethanes is discussed and compared to a cross-linked thermoset H-NBR elastomer. The characterization of the fatigue behavior is of great interest for long-term properties under cyclic loading. There is hardly any fatigue data available for these new classes of materials. There are two common ways to describe the lifetime of an elastomer fatigue behavior. One method is the classic fatigue test to generate the Wöhler curve. The other approach is focused on fatigue crack growth using the Tearing Energy or J-Integral concept. Displacement controlled cyclic test were performed and local strain based Wöhler curves were determined in this paper.

D. Gubencu, C. Sosdean, E. Szücs
COMPUTER ASSISTED STAND FOR SIMULATING AND STUDYING WIND ENERGY CONVERSION INTO ELECTRICITY

Actual global challenges, like the depletion of conventional resources and global warming forced the society to adopt sustainable development policies, which implies achieving growth without compromising the chances of next generations. Among the objectives of sustainable development, one of the most important is referring to the limitation of climate changes and its negative effects on environment and society, by implementing green energy solutions. Wind energy is one of the renewable energy powers which accomplished a rapid growth during the last decade. Consequently, promoting and enhancing knowledge related to wind energy systems became a priority. So, a computer assisted experimental stand was designed and realized, to simulate and study the wind energy conversion, suitable for both academic research and teaching activities. The device has all major components of a real wind system and two distinctly different configurations - horizontal and vertical axis - available for the turbine design. Experimental tests designed and carried out using the stand allowed the modelling of the influence factors constructive parameters of wind turbines and wind characteristics - action on the electrical power generated. The paper also presents the response surfaces and the contour plots of this objective function. The results obtained enable the understanding of the influence of different factors on the performance of the wind energy conversion process into electricity.

N. Golinelli, A. Spaggiari
EXPERIMENTAL DYNAMIC CHARACTERIZATION OF MAGNETORHEOLOGICAL SILLY PUTTY

In the present study the dynamic behavior of a commercial silicon based magnetorheological elastomer was investigated. This material presents a non-newtonian characteristics whose response depends on the rate at which it is stressed. The damping properties under dynamic load of these materials have been studied in technical literature, while the influence of the magnetic field on the dynamic shear modulus is unknown. Hence, the aim of this paper is to test the change in dynamic shear modulus under a sinusoidal strain with amplitude of 2 and 4 mm, cyclic frequency of 4, 8 and 12 Hz and magnetic flux density of 0 and 0.2 T. The approach adopted in this work was based on a design of experiment technique in order to evaluate the influence of the three variables involved and their interactions. The results highlights a strong dependence of the dynamic shear modulus on the strain rate while the influence of the magnetic field is weak, especially at the higher frequencies.

T. Fila, P. Zlámal, D. Kytýr, P. Koudelka, T. Doktor, O. Jirousek
ON THE X-RAY MICRO-TOMOGRAPHY MEASUREMENTS OF BIOLOGICAL SAMPLES UNDER COMPRESSIVE LOADING

In this paper, compact loading device for micro-CT measurements under applied load was used in a series of instrumented compressive test of bone sample. Tested bone samples were loaded in several deformation steps and micro-CT scanning was carried out in each step. Reconstructed three-dimensional data of intact bone sample were used to develop 3D model of the specimen. Data from each deformation step were processed by DVC method for identification of displacement and strain fields and thus for evaluation of deformation response of human trabecular bone sample.

K. Fellner, P. F. Fuchs, G. Pinter
SIMULATION OF THE ”SINGLE VIA THERMAL CYCLE TEST” FINITE ELEMENT MODELLING OF PCBS UNDER THERMAL LOADS

The “Single Via Thermal Cycle Test” (SVTCT) is a thermal cycle test used for life time assessment of Printed Circuit Boards (PCBs) under cyclic thermal loads. During the SVTCT, the electrical conductivities of the interconnections (vias) of the tested PCB are monitored by resistance measurements. Hence, by a decrease of electrical conductivity, failure can be detected. A single via in a PCB is modeled using an axisymmetric simulation model. The simulations are conducted decoupled. One model for computing the temperature field in the PCB and another model to compute the stress and strain distribution are generated. The calculated stress and strain distributions are opposed to microsections of vias in PCBs, which have been subjected to the SVTCT. All cracks occurred at locations, which are highly stressed according to the simulations. This research work is part of the Master’s Thesis “Simulation of the ‘Single Via Thermal Cycle Test’ - modelling and determination of the material input parameters”.

R. da S. Correa, F. T. Stumpf
DESIGN AND CONSTRUCTION OF AN APPARATUS TO PERFORM HYDROLYSIS TESTS IN POLYMERIC YARNS AND MOORING ROPES

Throughout the extent of its life, a mooring line used in an offshore oil platform working in deep and ultra-deepwater is subjected to the environmental conditions present at seabed. Along with low water temperature, high salinity, and acidity, the materials capacity of absorbing water plays an important role when it comes to its mechanical behavior in service conditions.
Previous studies have shown that the longer a synthetic rope is in contact with seawater, both its force-elongation behavior and its ultimate strength are affected. The phenomenon of the materials water absorption is known as Hydrolysis, and typically this type of experiment can take several months to a few years until observable results can be noticed. One way to speed-up the hydrolysis process is to subject the samples to high temperature water, and then stipulate a correlation factor between the results of the experiment time at high temperature and the real time at low temperature. This way one can have an accurate prediction of how long it will take until a material loses a certain percentage of its ultimate strength at a low temperature water, having the samples tested on a shorter period of time at higher temperature water.
The aim of this paper is to propose the development of an apparatus specially designed to perform hydrolysis tests on synthetic fiber ropes and yarns. Variables such as water temperature, along with its composition, acidity and salinity will be monitored and controlled, so that different combinations of these factors and their influence on the mechanical behavior of those materials can be studied.

F. M. Clain, O. C. Nogueira
DESIGN AND CONSTRUCTION OF AN APPARATUS TO PERFORM TENSILE TESTS AT LOW TEMPERATURES IN MOORING ROPES

Mooring ropes used in offshore oil platforms are exposed to a set of environmental conditions that can be crucial to their behavior in service. When one is talking of synthetic fiber ropes, such as Nylon, PET or HMPE, for instance, of all these peculiar conditions, the water temperature at the seabed can be pointed out as the one that affects the ropes mechanical response the most. For this specific reason, sometimes there can be a significant discrepancy between data collected at room temperature during tensile test in these components and their actual behavior in service. Seeking to acquire more accurate data during tensile tests and, consequently, better simulate mooring ropes behavior in service, the aim of this paper is to design and construct an apparatus to be attached to an existing 300 ton tensile/fatigue testing machine of ropes and sub-ropes in order to allow the application of different water temperatures to the samples. As boundary conditions for this project, the device shall be capable of admitting both ropes and sub-ropes types of samples and it also has to be thermally efficient. Mechanical, structural and thermal projects will be detailed, as well as the specification of a commercial chiller capable of maintaining the water at steady temperature throughout an entire test.h projects, to discuss due questions and problems and to promote the co-operation between individuals as well as between institutions. Therefore in the symposium discussions will play a highly significant role.

C. Casavola, A. Cazzato, V. Moramarco
THERMOGRAPHICAL ANALYSIS OF FRICTION STIR WELDING AND LASER ASSISTED FRICTION STIR WELDING

Friction Stir Welding (FSW), developed at The Welding Institute (TWI) in 1991, is a new solid-state welding process. In this technique, the material does not reach the fusion but the joint is the consequence of the plasticization resulting from the generation of heat by friction and the stirring action of the pin on the material due to the rotation and the displacement of a non-consumable tool. Thus, the FSW reaches temperatures lower than those reached by conventional fusion welds. Laser Assisted Friction Stir Welding (LAFSW) is a combined welding technique in which the FSW is assisted, during the weld, by the pre-heating of a de-focalized laser. This technique leads higher welding speeds, lower clamping force and it has some benefits for tool wear. Nevertheless the control of the temperature field is fundamental to guarantee a high quality joint. In this work FSW and LAFSW bead on plate tests were conducted on 6 mm thick 5754 H111 aluminum alloy plates with constant tool rotation and welding speed. Thermographic images were acquired to compare the effect on the temperature field of laser source distance from the tool and laser power.

C. Barile, C. Casavola, G. Pappalettera, C. Pappalettere
CONSIDERATIONS ON TEMPERATURE FIELDS AND INTERNAL RADIUS OF ANALYSIS IN HDM + ESPI RESIDUAL STRESS MEASUREMENTS

Hole drilling is the most widespread method for measuring residual stress. This method is based on the principle that drilling a hole in a material causes stress relaxation; by measuring the resulting strain it is possible to calculate the initial residual stress. Recently optical systems were introduced to replace strain gage rosette since they can provide full field measurements with high sensitivity. When using ESPI technique, the analysis area, that is to say, the portion of the image which must be used for measuring strain is defined by the operator. Proper choice of this area can be affected by many factors. In this paper, in particular, the influence of drilling rotation speed is investigated. To this scope measurements at three different speeds were carried out and for each speed the temperature field around the hole was measured by using a thermocamera.

M. Bajgrowicz
CFD MODEL OF BLOOD FLOW THROUGH ARTIFICIAL HEART VALVES

Artificial valve replacement is a common procedure in case of heart valve disorders treatment. The main task of this prosthesis is to generate blood flow similar to flow generated by natural, human valve. Velocity distribution depends mainly on the geometry of the valve. That is why it should be analysed and modified in case to obtain the best results. The objective of this study was to numerically investigate how geometry of valve (the maximal opening angle) influences velocity distribution behind a valve in terms of potential negative effect on blood components. For this purpose seven 2D models of artificial heart valves (AHV) with different maximal opening angle were created in Gambit. The blood flow was simulated in Ansys Fluent. This paper demonstrates the effectiveness of CFD method in artificial heart valves design process. Using Ansys Fluent, it is possible to simulate flow thorough AHV and analyze blood distribution in a region close to the valve, where physical measurements are very difficult to conduct.

Page 401 of 977 Results 4001 - 4010 of 9762