scholarly journals Buckling of Imperfect Thin Cylindrical Shell under Lateral Pressure

2008 ◽  
Vol 2008 ◽  
pp. 1-8 ◽  
Author(s):  
R. Lo Frano ◽  
G. Forasassi
Keyword(s):  
Lateral Pressure ◽  
Numerical Models ◽  
External Pressure ◽  
Thin Cylindrical Shell ◽  
Research Activity ◽  
Load Bearing Capacity ◽  
Different Types ◽  
Engineering Significance ◽  
Set Up ◽  
Good Agreement

The strength of thin shells, under external pressure, is highly dependent by the nature of imperfection. This paper investigates buckling behaviour of imperfect thin cylindrical shells with analytical, numerical, and experimental methods in conditions for which, at present, a complete theoretical analysis was not found in literature. In general, collapse is initiated by yielding, but interaction with geometrical instabilities is meaningful, in that imperfections reduce the load bearing capacity by an amount of engineering significance also when thickness is considerable. The aim of this study was to conduct experiments that are representative of buckling, in the context of NPP applications as, for instance, the IRIS (international reactor innovative and secure) and LWR steam generator (SG) tubes. At Pisa University, a research activity is being carried out on the buckling of thin walled metal specimen, with a test equipment (and the necessary data acquisition facility) as well as numerical models were set up by means FEM code. The experiments were conducted on A-316 test specimens, tubes with and without longitudinal welding. The numerical and experimental results comparison highlighted the influence of different types of imperfections on the buckling loads with a good agreement between the finite-element predictions and the experimental data.

scholarly journals An Enhanced Method to Evaluate Tensile Yield Stress by Small Punch Tests Using Deflection Curves

Materials ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 2840
Author(s):  
Betül Gülçimen Çakan ◽  
Peter Hähner ◽  
Celal Soyarslan ◽  
Swantje Bargmann
Keyword(s):  
Present Method ◽  
High Strength ◽  
Maximum Error ◽  
Deflection Curve ◽  
Small Punch ◽  
Different Types ◽  
Single Force ◽  
Set Up ◽  
Force Displacement ◽  
Good Agreement

While force–displacement curves are often preferred in Small Punch (SP) tests due to the ease of the experimental set-up, they encompass significant uncertainties arising from frame compliance. In this work, a methodology is presented to predict yield stresses from the force vs. deflection curves. The present method relies on determining different force levels from the initial part of the force–deflection curve to reflect both the slope and the curvature instead of using a single force level only. The predicted yield stresses for different types of materials, that is, low- and high-strength alloys, are found to be in good agreement with the actual proof stresses with a maximum error of 16%.

Development and Experimental Validation of a Simulation Tool for a Fuel Cell Based Power System

Volume 1 ◽  
2004 ◽  
Author(s):  
Luca Andreassi ◽  
Stefano Cordiner ◽  
Massimo Feola ◽  
Fabio Romanelli
Keyword(s):  
Experimental Data ◽  
Fuel Cell ◽  
Proton Exchange Membrane ◽  
Numerical Models ◽  
Critical Issue ◽  
Proton Exchange ◽  
Design Parameters ◽  
Operating Pressure ◽  
Research Activity ◽  
Set Up

Fuel cells (FC) technology applied to energy production could represent an effective solution to face greenhouse gas emissions and to differentiate energy sources. However, real performances of FC systems still represent a critical issue in the definition of an assessed and economically competitive technology. In fact, FC performances depend on many variables such as temperature, pressure, current, membrane humidification, stoichiometry of the reactant gas, etc.; additionally, many of these influencing parameters depend one on the other, further complicating the analysis. Numerical simulation could greatly contribute to a better understanding of the influence of design parameters. Nevertheless, the availability of experimental data to validate and to verify the numerical models is an imperative issue. The primary target of the research activity described in this paper is the set up of an experimental test bench for Proton Exchange Membrane Fuel Cell (PEM FC) at the Department of Mechanical Engineer of the University of Roma Tor Vergata aiming to completely test 8 cells 0.1 kW stack: the measured data are fundamental to validate the numerical models which have been developed by the Authors following different hierarchical levels (both semi-empirical and dimensional analytical approach) with different predictive capabilities. This apparatus allows the control of the reactant gas mass flow rates, stack pressure, humidity, current, temperature and voltage. In this way it is possible to assess a mixed experimental-numerical methodology allowing a tuning procedure for the developed models making a wide use of dedicated experimental data. The preliminary results in terms of comparisons between experimental and computational data show a good agreement even by varying some of the most performance-affecting parameters such as operating pressure and temperature.

An Impulsive Method for the Analysis of Piezoelectric Energy Harvesters for Intelligent Tires

2016 ◽  
Author(s):  
Alberto Doria ◽  
Federico Moro ◽  
Daniele Desideri ◽  
Alvise Maschio ◽  
Zhifeng Zhang
Keyword(s):  
Numerical Models ◽  
Low Cost ◽  
Performance Comparison ◽  
Electrical Performance ◽  
Design Development ◽  
Energy Harvesters ◽  
Piezoelectric Energy ◽  
Input Acceleration ◽  
Set Up ◽  
Good Agreement

Piezoelectric harvesters used for feeding the sensors of intelligent tires experience impulse excitation when the harvester enters the contact patch of the tire. The design, development and set up of advanced harvesters characterized by new materials, optimized shape and specific solutions for tuning require the possibility of testing prototypes in the laboratory simulating the actual working conditions and in particular impulsive events. The aims of tests are manifold: verification of mechanical and electrical performance, comparison with numerical models and updating, identification of parameters of the harvester that are difficult to measure directly. In this paper a testing method based on hammer excitation of an harvester mounted on a specific testing rig is presented. The testing rig is simple and low cost. It makes possible the measurement of the frequency response function (FRF) between output voltage and input acceleration. Design requirements for the testing rig are reported and a validation of the realized system is presented. A multimodal mathematical model is developed in MATLAB to simulate the impulse response of the harvester and in particular to stress the effect of higher order modes. Results show the dominance of the fundamental mode in the response of the tested harvesters. Calculated and experimental results are in good agreement.

Chemical and physical characterization of C(N)-doped W–S sputtered films

2004 ◽  
Vol 19 (8) ◽  
pp. 2356-2365 ◽  
Author(s):  
A. Nossa ◽  
A. Cavaleiro
Keyword(s):  
Photoelectron Spectroscopy ◽  
Amorphous Structure ◽  
X Ray Diffraction ◽  
Load Bearing Capacity ◽  
X Ray ◽  
Sputtered Films ◽  
Different Types ◽  
N Compounds ◽  
Good Agreement

The load-bearing capacity of self-lubricating W–S films can be improved by doping with nitrogen or carbon. In this study, the chemical composition, the atomic bonding, the structure, and the surface and cross section morphologies of sputtered W–S–C(N) films were analyzed. The addition of the doping element leads to a progressive broadening of the x-ray diffraction (XRD) peaks indicating a loss of crystallinity. In W–S–N films, amorphous structure could be obtained. In W–S–C films, W–C compounds were detected in conjunction with the hexagonal WS2 phase. For the highest C contents, a nanocomposite structure, including those phases and graphite, was suggested for the film. X-ray photoelectron spectroscopy results showed different types of bonds in the W4f peak in good agreement with the XRD results, i.e., when W–C(N) compounds were indexed W–S, W–C, and W–N bonds are present in the W4f peak. For the highest C content film, the detection of C–C bond in the C1s peak confirmed the formation of graphite.

Numerical-Analytical Prediction of the Collapse of Flexible Pipes Under Bending and External Pressure

2012 ◽  
Author(s):  
Walter C. Loureiro ◽  
Ilson P. Pasqualino
Keyword(s):  
Numerical Models ◽  
External Pressure ◽  
Analytical Prediction ◽  
Collapse Pressure ◽  
Analytical Formulation ◽  
Collapse Strength ◽  
Industry Standards ◽  
Flexible Pipes ◽  
Analytical Approaches ◽  
Good Agreement

This work gathers the phenomena indicated through the available literature and industry standards as determinant in the evaluation of the collapse of flexible pipes under combined bending and external pressure. It also proposes a complete analytical formulation to assess the collapse strength. The effects of dimensional variations and added ovalization due to bending are combined to evaluate the final collapse pressure. Numerical models are generated for comparison purposes and experimental results are used to validate the formulation proposed. The good agreement obtained between numerical and analytical predictions show that is possible to determine the curve collapse of flexible pipes through analytical approaches.

scholarly journals Experimental and numerical investigation of thermal improvement of window frames

2020 ◽  
pp. 189-189
Author(s):  
Milan Gojak ◽  
Aleksandar Kijanovic ◽  
Nedzad Rudonja ◽  
Ruzica Todorovic
Keyword(s):  
Thermal Conductivity ◽  
Numerical Models ◽  
Wooden Frame ◽  
Thermal Transmittance ◽  
Different Types ◽  
Thermal Improvement ◽  
Air Cavities ◽  
Glass Unit ◽  
Good Agreement ◽  
Window Frames

In this article are presented experimental and numerical determinations of thermal transmittance performed on three different types of window frames (vinyl, aluminium and wooden) within the same insulated glass unit. Good agreement between experimental and numerical results was attained. Using the numerical models, thermal improvement techniques of the frames and their influence on thermal transmittance of frames were studied. The first thermal improvement technique was using the insulation materials inserted inside large air cavities. By filling the cavity of vinyl frame with the polyurethane foam, thermal transmittance of vinyl frame was lowered by 10%. The second technique was based on repeating the procedure with materials installed inside frames with the materials that have lower thermal conductivity. This technique can be applied on thermal breaks and on steel profiles inside cavities. The result of this thermal improvement (attained by replacing thermal break material with material that has lower thermal conductivity) was certain reduction of the thermal transmittance of frames, by 9%. Using stainless steel instead of the oxidized steel was reduction of the thermal transmittance of vinyl frame by 3%. For the case of wooden frames was analysed the influence of shifting glazing unit deeper into profile upon the thermal transmittance of the frame. Installing the glass unit by 5 mm deeper into the wooden frame reduced glass thermal transmittance by 5%.

Pipe Response Under Concentrated Lateral Loads and External Pressure

2006 ◽  
Author(s):  
Kyros P. Andreadakis ◽  
Spyros A. Karamanos
Keyword(s):  
Finite Element ◽  
Internal Pressure ◽  
Three Dimensional ◽  
External Pressure ◽  
Pressure Effects ◽  
Lateral Loads ◽  
End Conditions ◽  
Different Types ◽  
Different Levels ◽  
Good Agreement

The paper focuses on the denting the response of pipeline segments subjected to lateral quasi-static wedge loading, in the presence of internal pressure. Nonlinear finite element models of pipeline segments, which are in good agreement with denting test data from internally pressurized pipes, are employed to obtain load-deflection curves for different levels of pressure, for various wedge shapes and for different types of boundary conditions. It is found that the presence of internal pressure increases significantly the denting resistance. The present study gives special emphasis on the development of a simplified three-dimensional analytical model, which yields closed-form expressions for the denting force and the corresponding denting length in terms of the corresponding denting displacement. The model, introduced elsewhere for non-pressurized tubes, is enhanced to include the pressure effects, accounting for different types of pipe end conditions. The analytical solution compares very well with the finite element results, and illustrates tube denting response in a clear and elegant manner.

scholarly journals Laboratory Measurements of Light Scattering by Dust Particles

1996 ◽  
Vol 150 ◽  
pp. 409-413
Author(s):  
Patrick P. Combet ◽  
Philippe L. Lamy
Keyword(s):  
Light Scattering ◽  
Laser Beam ◽  
Mie Theory ◽  
Spherical Particles ◽  
Dust Particles ◽  
Laboratory Measurements ◽  
Scattering Function ◽  
Hene Laser ◽  
Set Up ◽  
Good Agreement

AbstractWe have set up an experimental device to optically study the scattering properties of dust particles. Measurements over the 8 — 174° interval of scattering angles are performed on a continuously flowing dust loaded jet illuminated by a polarized red HeNe laser beam. The scattering is averaged over the population of the dust particles in the jet, which can be determined independently, and give the “volume scattering function” for the two directions of polarization directly. While results for spherical particles are in good agreement with Mie theory, those for arbitrary particles show conspicuous deviations.

scholarly journals Constitutive Modeling of the Densification Behavior in Open-Porous Cellular Solids

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2731
Author(s):  
Ameya Rege
Keyword(s):  
Constitutive Model ◽  
Cell Walls ◽  
Compressive Strain ◽  
Pore Collapse ◽  
Compressive Response ◽  
Linear Elastic ◽  
Nonlinear Springs ◽  
Different Types ◽  
Point Of Intersection ◽  
Good Agreement

The macroscopic mechanical behavior of open-porous cellular materials is dictated by the geometric and material properties of their microscopic cell walls. The overall compressive response of such materials is divided into three regimes, namely, the linear elastic, plateau and densification. In this paper, a constitutive model is presented, which captures not only the linear elastic regime and the subsequent pore-collapse, but is also shown to be capable of capturing the hardening upon the densification of the network. Here, the network is considered to be made up of idealized square-shaped cells, whose cell walls undergo bending and buckling under compression. Depending on the choice of damage criterion, viz. elastic buckling or irreversible bending, the cell walls collapse. These collapsed cells are then assumed to behave as nonlinear springs, acting as a foundation to the elastic network of active open cells. To this end, the network is decomposed into an active network and a collapsed one. The compressive strain at the onset of densification is then shown to be quantified by the point of intersection of the two network stress-strain curves. A parameter sensitivity analysis is presented to demonstrate the range of different material characteristics that the model is capable of capturing. The proposed constitutive model is further validated against two different types of nanoporous materials and shows good agreement.

Immunological Determined Plasminogen Groups And Its Possible Biological Relevance

1981 ◽  
Author(s):  
V Sachs ◽  
R Dörner ◽  
E Szirmai
Keyword(s):  
Human Plasma ◽  
Type I ◽  
Type Ii ◽  
Precipitation Line ◽  
Gene Frequencies ◽  
Type Iii ◽  
Different Types ◽  
Human Plasminogen ◽  
Gel Diffusion ◽  
Good Agreement

Anti human plasminogen sera of the rabbit precipitate human plasma in the agar gel diffusion test by means of intra-basin absorption with plasminogenfree human plasma with three different types: type I is represented by one strong precipitation line, type II by two lines, a big one and a small one, and type III by three slight but distinct lines. The following frequencies of the different types have been observed in a sample of 516 human plasmas: type I 65%, type II 33% and type III 2%. Suppose the types are phenotypical groups of a diallelic system where the types I and III represent the homozygous genotypes and the type II the heterozygous the estimated gene frequencies are in good agreement with the expected values. There is also a good agreement of the distribution of plasminogen groups determined by electrofocussing from RAUM et al. and HOBART. The plasminogen groups possibly may have also a biological meaning because the plasmas of type III always have a lesser fibrinolytic activity than the plasmas of the other types.

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