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Biblioteca Digital do IPB (53.442 recursos)

A Biblioteca Digital do IPB, tem por objectivo divulgar e permitir o livre acesso à produção científica produzida pela comunidade académica, promovendo a integração, partilha e a visibilidade da informação científica e garantindo a preservação da memória intelectual do Instituto Politécnico de Bragança.

DMA - Comunicações em Encontros Científicos Indexadas ao ISI

Mostrando recursos 1 - 20 de 21

  1. Evaluation of the cortical bone thickness in lumbar vertebra using CT and RP experimental techniques

    Fonseca, E.M.M.; Barreira, Luísa; Teixiera, M.C.
    The main objective of this paper was to assess the cortical bone thickness of human lumbar vertebra, through Computed Tomography (CT) images by using radiology reading software (iQ-VIEW), image processing software (ScanIP) and the rapid prototyping (RP) experimental methodology. The study here presented focus sixteen postmenopausal patients from the North of Portugal, with age between 50 and 85 years, collected from May to June 2011. All clinical data were obtained in a Medical Centre of Radiology and Imaging, in Porto. Results regarding the cortical bone thickness and the biomechanical resistance of human lumbar vertebra are presented in this work. The acquirement of accurate values, concerning cortical bone thickness,...

  2. The assessment of the thermal necrosis due a drilling dental process with or without irrigation

    Fonseca, E.M.M.; Magalhães, Kelly; Fernandes, M.G.A.; Sousa, Gerdal; Barbosa, Marcos Pinotti
    The main objective of this work is to present a methodology to assess the thermal necrosis in a dental model due a drilling process with and without water irrigation. An experimental methodology, using an infrared thermography camera, was used to measure the rate of temperature change during the drilling in a pig mandible. The finite element method is used with the Ansys program to compare the results with the experimental model. A simplified model was analyzed in a transient thermal process. Using appropriated boundary conditions, successful numerical results could be used as an alternative to the in-vivo models.

  3. The assessment of the thermal necrosis due a drilling dental process with or without irrigation

    Fonseca, E.M.M.; Magalhães, Kelly; Fernandes, M.G.A.; Sousa, Gerdal; Barbosa, Marcos Pinotti
    Main goal of this work is to present a numerical model to study the thermal necrosis due a dental drilling process, with and without water irrigation. Also an experimental methodology is used to measure the thermal occurrence in a pig mandible.

  4. Pushover analyses of a R/C frame by distinct software

    Pereira, V.G.; Barros, R.C.; Braz-César, M.T.
    A series of pushover analyses on two-dimensional RC frames, part of an office building, are performed. They constitute a detailed parametric study, varying the number of stories and its height, and also the bay width. Regarding the stated objective, several commercial packages universally used in the design of civil engineering structures were used, namely SAP 2000, SeismoStruct and MIDAS. To represent the influence of the masonry infill panels, the equivalent tie method is used considering several values for the tie width. The influence of other parameters, on the structural behavior of the RC frame through a pushover analysis, is also analyzed: the confinement of the structural...

  5. Cyclic experimental response of reinforced concrete frames: validation methodology

    Braz-César, M.T.; Oliveira, Daniel V.; Barros, R.C.
    This article validates numerically the experimental behavior of a reinforced concrete frame subject to cyclical loads, resorting to a commercial program using finite element analysis. The experimental results were obtained in the National Laboratory of Civil Engineering (LNEC). In the numerical simulation several constitutive models were used, with different degrees of complexity, based on the concept of local plastification in critical zones (plastic hinges) of the elements that constitute the frame as well as on fiber models.

  6. Unwrapping techniques for speckle phase maps: study and comparison of the performance of principal methods

    Lopes, H.; Ribeiro, J.E.; Vaz, M.A.P.; Gomes, J.F. Silva
    Holographic interferometry (HI) techniques are powerful tools for experimental mechanics which can be used to assess displacement fields on a loaded object surface. Used with no contact and high resolution HI can be combined with image methods for data analysis. Nevertheless, the speckle should be fully resolved by the image detector to digitally record an interferogram. This leads to a noisy recording which difficult it’s post-processing. Each measurement with HI ends normally in a phase map computation representing the object displacement. Phase calculation algorithms are based on spatial or temporal phase modulation and lead to wrapped phase maps. To obtain the continuous phase distribution several solutions have been...

  7. Semi-active vibration control of a three degree-of-freedom scaled frame with a magneto-rheological damper

    Braz-César, M.T.; Barros, R.C.
    The present work describes part of the R&D on using a semi-active structural control technique in a civil engineering experimental model frame equipped with a MR damper, developed within COVICOCEPAD project approved in the framework of Eurocores program S3T. Some results are provided associated with the calibration of a MR damper at FEUP as well as on the experimental modal identification of the dynamic properties of a small-scale metallic frame, without and with inclusion of a specific MR device. Some numerical results of the controlled frame under simulated earthquakes are given, to be compared with the experimental results of such frame installed in a Quanser shaking table.

  8. Experimental behaviour of standardised European end plate beam-to-column stel joints under arbitrary cyclic loading

    Nogueiro, Pedro; Silva, Luís Simões da; Bento, Rita; Simões, Rui
    This work presents the results of the study of the six experimental tests of standardised end-plate beam-to-column steel joints under arbitrary cyclic loading. The experimental programme is divided into two groups, varying the column section size. Each group has the first monotonic test and two more cyclic tests with arbitrary loading. The results are presented in terms of M-Ø curves, main mechanical joint properties and same relevant illustrations are presented. Finally, some conclusions can be drawn.

  9. Interferometric techniques in structural damage identification

    Lopes, H.; Ribeiro, J.E.; Santos, J.V. Araújo dos
    This paper describes several interferometric techniques and their applications in structural damage identification. With that objective in mind, damaged aluminium beams with clamped-free and free-free boundary conditions are analyzed. Different damages cases are inflicted by creating small cuts perpendicular to the beams longitudinal axis, being the damage, therefore, characterized by the dimensions of these cuts. The out–of–plane displacement field of modal response is measured with an electronic speckle pattern interferometric system. The measurement of the static and dynamic rotation fields, defined as the spatial derivative of the displacement field, are measured with two different speckle shearography systems. Second and third...

  10. Damage localisation in beams using the ritz method and speckle shear interferometry

    Santos, J.V. Araújo dos; Lopes, H.; Ribeiro, J.E.; Maia, N.M.M.; Vaz, M.A.P.
    A novel numerical-experimental technique is developed in order to minimise some of the difficulties exhibited by others damage localisation approaches. The present technique relies on the computation of undamaged rotation fields using the Ritz method and the Timoshenko beam theory, while the measurement of damaged rotation fields is performed by speckle shear interferometry. Two damage localisation indicators are also presented, which, instead of being based on the second derivative of displacement fields, are based on the first spatial derivative of rotation fields. These damage localisation indicators, the modified curvature difference (MCD) and the modified damage index (MDI), were applied successfully in the localisation of damage in two clamped-clamped aluminium...

  11. Flow of physiological fluids in microchannels: the sedimentation effect

    Garcia, Valdemar; Correia, Teresa Montenegro; Dias, Ricardo P.; Lima, R.
    Microfluidic devices are becoming one of the most promising new tools for diagnostic applications and treatment of several chronic diseases. Hence, it is increasingly important to investigate the rheological behaviour of physiological fluids in microchannels. The main purpose of the present experimental work is to investigate the flow of two different physiological fluids frequently used in microfluidic devices. The working fluids were physiological saline (PS) and dextran 40 (Dx40) containing about 6% of sheep red blood cells (RBCs), respectively. The capillaries were placed horizontally on a slide glass and the flow rate of the working fluids was kept constant by using a syringe pump. By means of a camera the images were...

  12. The effect of residual stresses in the lateral-torsional buckling of steel I-beams at elevated temperatures

    Vila Real, P.M.M.; Cazeli, R.; Silva, L.S.; Santiago, Aldina; Piloto, P.A.G.
    When a beam is bent about its major axis it may twist and move laterally, before it reaches in bending. Although the problem, of lateral-torsional buckling of steel beams at room temperature has a well established solution, the same problem at elevated temperature has not. A numerical investigation of the laleral-torsional of buckling of steel I-beams subjected to a temperature variation from room temperature up to 700 °C, with the aim of assessing the effects of the residual stresses in this mechanism of failure, is presented in this page. To this purpose, a geometrically and materially non-linear finite element program, has...

  13. Numerical and experimental evaluation of lateral torsional buckling of beams at elevated temperatures

    Piloto, P.A.G.; Vila Real, P.M.M.; Franssen, J.-Marc
    When a beam is bent about its greatest flexural resistance axis it may twist and move laterally, before it reaches its strength limit. Although this problem of lateral torsional buckling of steel beams at room temperature is well known, the same problem at elevated temperature is not. This paper summarises the results obtained iii the scope of a research project entitled “Lateral buckling of steel I beams under fire conditions”, where a set of 120 experimental and numerical tests were performed on IPEIOO beams, submitted to temperature varying from 20 °C to 600 GC, to validate a new proposal for the...

  14. Temperature evaluation in steel fire protected elements with intumescent coating

    Mesquita, L.M.R.; Piloto, P.A.G.; Vaz, M.A.P.
    The heat transfer analysis plays an important role in the temperature prediction of insulated steel members exposed to fire conditions. Based on the results of a previous experimental work, made in intumescent-coated protected elements, the intumescent effective thermal conductivity temperature variation was estimated. An analytical approach, based on the one-dimensional heat transfer parabolic partial differential equation through the insulation, considering a nonhomogeneous (time-varying) boundary condition at fire interface and a lumped capacitance at the insulation-steel interface, is presented. Solutions are established with temperature independent thermal properties and then extended to temperature dependent thermal properties. These solutions are compared with numerical results performed by finite element method using Matlab for different values...

  15. Numerical modelling of internal voids in fire exposed structures

    Fonseca, E.M.M.; Oliveira, C.A.M de
    The study of steel structures at elevated temperatures needs the characterisation of the thermal action and the material thermal properties variation with temperature as well as the thermal conduction problem solution in a domain with well know boundary conditions. Structures may have internal voids (figure 1) filled with air (hollow columns, profile sections thermally insulated, steel pipes,…). In the presence of internal voids, the internal air temperature will be determined with some simplified formulas deduced from heat transfer equations

  16. A new finite element for generalized in-plane pipe loading. Experimental and numerical comparison

    Fonseca, E.M.M.; Oliveira, C.A.M de; Melo, F.J.M.Q. de; Piloto, P.A.G.
    In structural engineering, the geometry of a large number of structural details may involve the combination of straight and curved parts in order to meet requirements of functionality and/or attractive design. Piping systems are structural elements used in the chemical industry, aeronautical and aerospace engineering, conventional and nuclear power plants and fluid transport in general-purpose process equipment. This paper presents a new finite element pipe with 19 degrees of freedom, where shape functions are set-up from the displacement field parallel to a local reference system. A displacement-based formulation was developed with Fourier series for increasing the structural element distortion capabilities. A finite element pipe may be considered as a part...

  17. Steel mechanical properties evaluated at room temperature after being submitted at fire conditions

    Piloto, P.A.G.; Vila Real, P.M.M.; Mesquita, L.M.R.; Vaz, M.A.P.
    Several researchers have already studied the effect of temperature increase in steel structures regarding load-bearing capacity and some material models have been developed in fire conditions, based on experimental results. The mechanical properties of a S275 JR steel construction material has been tested at elevated temperatures after a natural and forced cooling. The major focus has been made on yield and ultimate strength behavior, hardness material and residual stress relief. Experimental results will be presented for each temperature level, dwell time and cooling rate. Test results were compared with the normal room temperature condition. The material specimens were cutted from...

  18. Metal ceramic fixed partial denture: fracture resistance

    Piloto, P.A.G.; Alves, Ana; Correia, A.; Campos, J.C. Reis; Fernandes, J.C. Sampaio; Vaz, M.A.P.; Viriato, Nuno
    Partially encased beam is a steel-concrete composite structure, made-up with a hot rolled profile and filled with concrete between flanges. Such structural element improves load-bearing capacity at elevated temperatures. Metal ceramic Fixed Partial Dentures (FPD) are suitable to increase fracture resistance presenting higher clinical longevity. This type of prosthesis is mainly used when a great number of teeth replacements are needed. The FPD under analysis is defined by a metallic infrastructure (titanium) and by a ceramic coating. The advantages of hybrid FPI) lie in their predictable biomechanical behavior versatility and cost. The main disadvantage is related to aesthetic functionality. Karlsson (1986),...

  19. The flexibility of steel hollow tubular sections subjected to thermal and mechanical loads

    Fonseca, E.M.M.; Melo, F.J.M.Q. de; Valente, R.A.F.
    Numerical analysis of hollow tubular sections is used as a starting tool to establish the reliability assessment of these elements when mechanically or thermally loaded. To quantify the material deformation behaviour of these elements resulting from ground motion, crack propagation, effects from high temperatures, theoretical and experiments analyses can be used for testing a service reliable guarantee. Structural hollow sections have excellent static properties, not only with regard to buckling and torsion, but also in the overall design of members. They can offer economic advantages compared to open sections. It is possible to change the strength by varying the wall thickness or filling the section with other material without...

  20. Charring rate determination of wood pine profiles submitted to high temperatures

    Fonseca, E.M.M.; Barreira, Luísa
    The wood material presents an increasing use for structural engineering applications in buildings and other specials engineering production. To assess safety rules, this type of elements should have sufficient mechanical resistance to guarantee the design loads. Wood is a natural material and is submitted to many constantly changing influences. The high wood vulnerability, due accidental conditions, requires rigorous thermal and mechanical assessment. The combustion and the chemical phenomena occurred in wood during an accidental situation of elevated temperature is a complex study issue. When wood structures are exposed to high temperatures, the burned wood becomes a char layer which loses all strength but insulating temperature rise in the core...

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