Weight reduction is a hot topic in automotive industry. Both the applications of tube hydroforming technique and magnesium alloys offer a large potential for reducing the weight of automotive components. In this research, the relationship between forming pressure and bulge height, the maximum forming pressure and the forming limit during the tube hydraulic bulging process are first analysed. A self-designed warm hydraulic bulge forming equipment and the seamlessly extruted magnesium alloy AZ61 tubes, are used for carrying out a series of warm hydraulic bulge tests, and discussing the formalibility of the magnesium tubes at various temperatures. Furthermore, the flow stress curves are determined by the mathematical model in this paper with the bulge forming test results. Then the validity of the analytical model is verified by comparing the forming pressure and bulge height between analytical and experimental values.

The growing cost of energy combined with the increasing energy demand has driven the need for more efficient energy use. Air-to-air energy recovery in buildings has been shown to provide substantial energy savings in many cases. A new type of air-to-air energy recovery system, known as a run-around energy exchanger (RAEE), and which has excellent potential for the retrofit market, has been proposed and numerically modelled for heat and moisture exchange by Fan et al. (2006). This thesis focuses on the material properties of semi-permeable membranes required for each RAEE exchanger core.<p>Two commercially available membranes are considered in this thesis: a spunbonded polyolefin manufactured by DuPont with the trade name Tyvek®, and a two layer polypropylene laminate material manufactured by the 3M Company with the trade name Propore.<p>The moisture transfer effectiveness of the RAEE system depends mostly on the ability of its membrane to transfer water vapour. This effectiveness is investigated by measuring the vapour diffusion resistance of Tyvek® and Propore using a dynamic moisture permeation cell (DMPC). For Tyvek®, the average vapour diffusion resistance is 440 s/m, which corresponds to an expected typical RAEE energy recovery effectiveness of 52%. For Propore, the average vapour diffusion resistance is 140 s/m, which corresponds to an RAEE effectiveness of 62% in the same exchanger system.<p>The air permeability is also measured using the DMPC with Tyvek® having a Darcy air flow resistance of 27 nm-1 and Propore having a Darcy air flow resistance of 111 nm-1. The lower air flow resistance of Tyvek® is undesirable since air transfer is undesirable in the RAEE system. <p>The liquid penetration pressure is determined using a modified standard method that resembles the geometry of a membrane in the RAEE exchanger. It is found that the Propore has a liquid penetration pressure beyond the measurement capabilities of the apparatus (276 kPa); while the Tyvek® membrane has a liquid penetration pressure of 18 kPa which agrees well with published values. <p>The elastic moduli of the membranes are required to predict the membrane deflection under typical operating pressures and to properly size a support screen. The elastic modulus is determined using two tensile standards and a bulge test. The bulge test results are used in the design since the geometry of the bulge test better represents the situation of a pressurized membrane in the RAEE. The elastic modulus of Propore is found to be 20 ± 3 MPa and the elastic modulus of Tyvek® is found to be 300 ± 45 MPa. The values are used in subsequent calculations for sizing the square screen, where it is found that a screen with square openings of 12.7 mm (0.5 in.) is required to support the membrane. <p>The degradation of Tyvek® and Propore with UVC exposure is also investigated. It is found that both materials deteriorate when exposed to UVC radiation, and that the degradation is primarily a function of the exposure time and not the exposure intensity. <p>Considering all material properties tested, it is concluded that the Propore membrane is a better membrane choice for the RAEE than the Tyvek® membrane.

The growing cost of energy combined with the increasing energy demand has driven the need for more efficient energy use. Air-to-air energy recovery in buildings has been shown to provide substantial energy savings in many cases. A new type of air-to-air energy recovery system, known as a run-around energy exchanger (RAEE), and which has excellent potential for the retrofit market, has been proposed and numerically modelled for heat and moisture exchange by Fan et al. (2006). This thesis focuses on the material properties of semi-permeable membranes required for each RAEE exchanger core.<p>Two commercially available membranes are considered in this thesis: a spunbonded polyolefin manufactured by DuPont with the trade name Tyvek®, and a two layer polypropylene laminate material manufactured by the 3M Company with the trade name Propore.<p>The moisture transfer effectiveness of the RAEE system depends mostly on the ability of its membrane to transfer water vapour. This effectiveness is investigated by measuring the vapour diffusion resistance of Tyvek® and Propore using a dynamic moisture permeation cell (DMPC). For Tyvek®, the average vapour diffusion resistance is 440 s/m, which corresponds to an expected typical RAEE energy recovery effectiveness of 52%. For Propore, the average vapour diffusion resistance is 140 s/m, which corresponds to an RAEE effectiveness of 62% in the same exchanger system.<p>The air permeability is also measured using the DMPC with Tyvek® having a Darcy air flow resistance of 27 nm-1 and Propore having a Darcy air flow resistance of 111 nm-1. The lower air flow resistance of Tyvek® is undesirable since air transfer is undesirable in the RAEE system. <p>The liquid penetration pressure is determined using a modified standard method that resembles the geometry of a membrane in the RAEE exchanger. It is found that the Propore has a liquid penetration pressure beyond the measurement capabilities of the apparatus (276 kPa); while the Tyvek® membrane has a liquid penetration pressure of 18 kPa which agrees well with published values. <p>The elastic moduli of the membranes are required to predict the membrane deflection under typical operating pressures and to properly size a support screen. The elastic modulus is determined using two tensile standards and a bulge test. The bulge test results are used in the design since the geometry of the bulge test better represents the situation of a pressurized membrane in the RAEE. The elastic modulus of Propore is found to be 20 ± 3 MPa and the elastic modulus of Tyvek® is found to be 300 ± 45 MPa. The values are used in subsequent calculations for sizing the square screen, where it is found that a screen with square openings of 12.7 mm (0.5 in.) is required to support the membrane. <p>The degradation of Tyvek® and Propore with UVC exposure is also investigated. It is found that both materials deteriorate when exposed to UVC radiation, and that the degradation is primarily a function of the exposure time and not the exposure intensity. <p>Considering all material properties tested, it is concluded that the Propore membrane is a better membrane choice for the RAEE than the Tyvek® membrane.

The bulge test is a commonly used experiment to establish the material stress-strain response at the highest possible strain levels. It consists of a metal sheet placed in a die with a circular opening. It is clamped in place and inflated with hydraulic pressure. In this thesis, a bulge testing apparatus was designed, fabricated, calibrated and used to measure the stress-strain response of an aluminum sheet metal and establish its onset of failure. The custom design incorporates a draw-bead for clamping the plate. A closed loop controlled servohydraulic pressurization system consisting of a pressure booster is used to pressurize the specimens. Deformations of the bulge are monitored with a 3D digital image correlation (DIC) system. Bulging experiments on 0.040 in thick Al-2024-T3 sheets were successfully performed. The 3D nature of the DIC enables simultaneous estimates of local strains as well as the local radius of curvature. The successful performance of the tests required careful design of the draw-bead clamping arrangement. Experiments on four plates are presented, three of which burst in the test section as expected. Finite deformation isotropic plasticity was used to extract the true equivalent stress-strain responses from each specimen. The bulge test results correlated well with the uniaxial results as they tended to fall between tensile test results in the rolling and transverse directions. The bulge tests results extended the stress-strain response to strain levels of the order of 40%, as opposed to failure strains of the order of 10% for the tensile tests. Three-dimensional shell and solid models were used to investigate the onset of localization that precedes failure. In both models, the calculated pressure-deformation responses were found to be in reasonable agreement with the measured ones. The solid element model was shown to better capture the localization and its evolution. The corresponding pressure maximum was shown to be imperfection sensitive. / text

Les tubes métalliques de précision sont largement utilisés pour des applications biomédicales. De tels tubes sont fabriqués par étirage à froid car ce procédé garanti le meilleur aspect de surface, le plus grand contrôle des dimensions du tube et le contrôle des propriétés mécaniques. L'objet de cette étude est de modéliser le procédé d'étirage de tube sur mandrin afin d'en améliorer la compréhension et de construire un outil permettant l'optimisation du procédé et de prédire la rupture des tubes en étirage. La construction du modèle élément finis s'appuie sur la réalisation d'essais expérimentaux afin de caractériser les propriétés mécaniques des matériaux et le frottement entre le tube et les outils d'étirage (mandrin, filière). Le comportement mécanique des alliages est caractérisé par des essais de traction sur tube, des essais de traction sur des éprouvettes découpées dans différentes orientations dans un tube déplié et des essais de gonflement de tube. Pour ces derniers, une machine et un outillage de gonflement de tubes ont été développés spécifiquement. Par le biais de ces essais différents aspects ont été étudiés : la viscoplasticité, l'anisotropie plastique, l'hétérogénéité des propriétés dans l'épaisseur du tube, la thermomécanique. Les coefficients de frottements ont été identifiés par analyse inverse sur des essais d'étirage instrumentés par des cellules d'effort. Des essais d'étirage ont été spécifiquement conçus en modifiant la géométrie du mandrin afin de conduire à la rupture des tubes lors de l'étirage. L'objectif de tels essais étant d'identifier la limite de formabilité des tubes. L'approche choisie pour prédire de la rupture a été d'utiliser des critères de ruptures qui pouvaient être calibrés sur des essais de traction uniquement. Les critères ont été calculés au cours de la simulation numérique de l'étirage sur mandrin et ils ont été évalués par rapport à leur capacité à prédire les réductions de section et d'épaisseur maximales. Enfin, des méthodes analytiques de calcul d'effort d'étirage ont été développées et comparées à la modélisation éléments finis. / Precision metallic tubes are widely used for biomedical applications. The requirements of such tubes in term of surface quality, precise dimensions and mechanical properties can be achieved by cold tube drawing only. The purpose of this study is to model the mandrel tube drawing in order improve the process understanding and to build a tool both for process optimisation and for failure prediction during drawing. Building the finite element modelling requires to perform a series of experimental tests in order to characterise the material mechanical behaviour and the friction between the tube and the forming tools (mandrel, die). The materials mechanical behaviour is characterized by means of tube tensile tests, tensile tests of oriented samples cut in different directions from flattened tubes and tube bulge test. For the latter, a tube bulge test device was specifically designed. Different aspects were covered by these tests: viscoplasticity, plastic anisotropy, materials properties heterogeneity in the tube thickness, thermomechanics. Friction coefficients were identified by inverse analysis on instrumented tube drawing tests. A specific drawing test was designed in order to identify the tube fracture during drawing by modifying the mandrel geometry. The goal of such test was to identify the tube formability limit. Among the different techniques available to predict tube failure, the approach of failure criterion was chosen. Different failure criteria that could be calibrated on tensile test were selected. Failure criteria were computed during the simulation of the mandrel tube drawing and they were evaluated in term of predictability of the maximum section and thickness reductions before fracture. Finally, analytical methods that enable to compute the drawing force were developed and compared with the finite element modelling.

The diploma thesis is focused on the analysis of the behavior of the thin-walled tubular test specimen during the technological test of the liquid draining of the tubes. The test specimen ‘in the form a tube was made of austenitic stainless steel 17 240 (1.4301, X5CrNi18-10). During the experiment, the radial expanding tool was quasi-statically charged by the internal fluid pressure. In the introductory part, the thesis focuses on the stress-strain description of the method of tube bulging and possible ways of detecting the strain of material during forming. The experimental part is primarily focused on the analysis of the test sample that was obtained from the experiment. Theoretical approaches were used to analyze the real test sample to detect strain and stress in material, numerical simulation of the bulge process and 3D ATOS scanning device, which helped clarify behavior tube during bulging process. At the end of the thesis is proposed possible design of the tool. This modification should contribute in the future to the full functionality of the radial expanding tool, or the bulging of the tube by liquid.

Main objective of this diploma thesis is to finish a construction of the Bulge test apparatus for measurement of thin films, perform first tests on commercially available Si3N4 membranes and bilayer membrane with aluminium. First part of the thesis is focused mainly on literature review of current knowledge regarding this topic and other methods of thin films testing. Experimental part deals with construction of apparatus, methodology of data evaluation and results of the measurement. The thin films of interest are fabricated as amorphous silicon nitride or bilayer of mentioned nitride and either aluminium, titanium or Ta-B-C layer. The apparatus has been built in house in collaboration with Institute of Scientific Instruments of CAS. Both reliability and repeatability of this method has been tested on over 160 measurements of commercially available membrane. The results of measurements are compared with literature and nanoindentation test. More detailed data analysis is currently under development with colleagues at Institute of Physics of Materials. It has been proven beyond doubt that Bulge test method and constructed apparatus are suitable for the measurement of several mechanical properties of thin films.

No description available.

Determination of mechanical properties of very thin films is rather difficult task as all of currently using testing techniques have some weakness. This master’s thesis deals with microcompressive test and bulge test. Finite element simulations of the two methods were carried out in order to better understanding of experimental record. Microcompression combines the sample preparation with the use of focused ion beam (FIB) with a compression test carried out using nanoindenter. Cylindrical specimens (pillars) were prepared from Al film deposited on Si substrate using FIB. Experimentally measured data on pillars needs correction to obtain undistorted material properties of Al thin film. A necessary correction using FE modeling is suggested in the thesis. Second part of the work is focused on modeling of bulge test. Pressure is applied on freestanding SiNx film while deflection of the film is measured. Stress state in the film is biaxial making determination of mechanical properties of the film more complicated. The goal is to present how to model the whole problem. In addition, preparation of the specimens was simulated to estimate residual stress in the film. The paper contributes to a better characterization of very thin surface layers and determination of their mechanical properties.

<p>The functionalization of nonwoven electrospun polymeric fibers with metallic nanostructures has enabled the design of novel nanocomposite materials used in a wide range of applications. In particular, designs based on incorporating established antimicrobial species such as copper and silver have potential applications as antimicrobial filtration membranes, leveraging on the convoluted fiber assembly and high surface area–to–volume ratios of the constitutive fibers. Electroless deposition based on spontaneous electrochemical reactions offers a facile and tunable methodology for surface–confined growth of metallic nanostructures on the non–planar substrate architectures presented by nonwoven electrospun fibers. </p> <p>Firstly, this work explores, in a broad sense, the effects of two different seed catalyst chemistries, palladium and silver, on the evolution of copper nanoparticles on electrospun polyacrylonitrile fibers. Copper nanoparticle coverage and conformity; deposition kinetics; modifications in the surface chemistry of the PAN fibers; and thermal stability of the resultant nanocomposites were examined. Secondly, qualitative and quantitative assessment of the interfacial adhesion between the copper nanostructures and PAN fibers were undertaken by exploiting the elastic mismatch between both phases during tensile deformation. For copper nanocubes on nanofibers, the adhesion energy is estimated to be between 0.48 J/m² and 1.0 J/m² using strain and growth based adhesion models.</p> <p>Macroscopically, the compliant nature of the nonwoven fiber mats makes them susceptible to out-of-plane deformation during water filtration processes which may alter their size exclusion configuration for effective filtration. A bulge testing device is built and implemented to simulate and characterize hydraulic flow – induced deformation in the electrospun PAN fiber mats. The pressure–deflection relationships of the mats show a sub-linear dependence in contrast to classical continuum materials. The macroscopic mat behavior was governed by the properties of the constituent fibers, with an apparent mat bending rigidity dependent on the fiber diameters.</p> <p> Lastly, the nonwoven fiber mats functionalized with copper nanoparticles were evaluated for use as potential antimicrobial microfiltration membranes. The fiber mats displayed high water flux and high separation efficiency for model 3 μm particles, with separation factors reaching above 99%.</p>