bluuebunny/crossref_metadata_2025 huggingface dataset:
Le marigot médiatique africain. Approches d'une information à rebours (2010-1960)
Authors: Bat Jean-Pierre
Published: August 2011

Résumé Le « marigot africain » des espions a traditionnellement été dévoilé par la loupe des enquêtes journalistiques depuis les indépendances. Loin d’opérer comme une épiphanie neutre de la vérité contre le monde opaque des polices secrètes africaines, ces processus de révélation participent en réalité d’un équilibre complexe entre droit de regard sur l’univers clos des Services et manipulation de la parole à des fins plus délicates à identifier. À travers une plongée dans les mécanismes de dévoilement des Services dans l’histoire contemporaine de l’Afrique, il s’agit donc de revisiter la construction de l’opinion publique comme outil potentiel des tactiques de renseignement.
La France, une grande puissance ? Le tardif réveil de l'espion français au cinéma
Authors: Dehée Yannick
Published: August 2011

Résumé Des années 1970 à nos jours, le film d’espionnage à la française reste un genre peu productif qui met en scène une France terrain d’affrontement de la CIA et du KGB, peu gênés par un contre-espionnage français aux moyens limités (années 1970). Les séquelles du terrorisme d’extrême gauche font leur apparition dans les intrigues des années 1980. Les années 1990-2000 marquent un renouveau du genre, axé sur les nouveaux dangers de l’après-guerre froide, esquissant une fragile affirmation des services français sur la scène internationale.
La Vie des autres (2006): espion de la Stasi ou héros ordinaire ?
Authors: Moine Caroline
Published: August 2011

Résumé La Vie des Autres de Florian Henckel von Donnersmarck, sorti en 2006 en Allemagne, connut un très grand succès international. L’histoire de la relation complexe qui se noue au cours des années 1980 entre un espion de la Stasi, la police politique de la RDA, et le dramaturge qu’il est chargé de surveiller, a ainsi conquis des millions de spectateurs dans le monde entier. Présenté par l’efficace campagne de communication qui accompagna sa sortie comme le premier film de fiction rendant véritablement compte de la réalité de la vie quotidienne en RDA à cette époque, La Vie des Autres n’en fut pas moins vivement critiqué par plusieurs spécialistes de la question. Il s’avère donc intéressant de revenir sur les arguments des uns et des autres pour tenter de mesurer le caractère crédible ou non de la représentation fictionnelle du système de surveillance et de répression de la Stasi, et de la conversion d’un espion, d’un persécuteur, en homme bon. Au-delà de la question de l’authenticité ou non du film d’un point de vue d’historien/ne, se pose en fait, à travers le succès du film, celle de la place, plus problématique, tenue par la Stasi de nos jours dans l’imaginaire collectif et dans la mémoire de la RDA.
Becoming part of the network: French scientists and the use of English at conferences
Authors: Banks David
Published: August 2011

Dans le domaine de l’anglais de spécialité, il semble y avoir une tendance à attribuer, sans véritable fondement, des opinions et des attitudes aux scientifiques. La présente contribution présente les résultats d’un questionnaire qui tente de rectifier cette situation en ce qui concerne l’usage de l’anglais dans les congrès. Elle démontre, malgré la confirmation de beaucoup d’idées reçues, que l’importance de certains types de présentation est sous-estimée, et que la participation aux débats et aux discussions pose des problèmes particuliers. Il faut prendre en compte ces données dans la formation des scientifiques et dans les structures de services linguistiques mises en place pour les aider.
Characterisation and Modelling of a Melt-Extruded LDPE Closed Cell Foam
Authors: Jebur Qusai Hatem , Harrrison Philip , Guo Zao Yang , Schubert Gerlind , Navez Vincent
Published: August 2011

This paper describes uniaxial compression tests on a melt-extruded closed-cell Low-Density Polyethylene (LDPE) foam. The stress-strain response shows the mechanical behaviour of the foam is predominantly transversely isotropic viscoelastic and compressible. Images analysis is used to estimate the Poisson’s ratio under large strains. When the deformation is less than 5 percent, the kinematics and mechanical response of the polymer foam can be well-described by a linear compressible transversely isotropic elastic model. For large strain, a method of manipulating experimental data obtained from testing in the principal and transverse directions (stress vs strain and Poisson’s ratio) in order to estimate the uniaxial compression response of the foam at any arbitrary orientation is proposed. An isotropic compressible hyperfoam model is then used to implement this behaviour in a finite element code.
Verification of a Finite Element Simulation of the Progressive Collapse of Micro Lattice Structures
Authors: Mines Robert A.W. , Tsopanos Sozohn , McKown S.T.
Published: August 2011

Stainless steel micro lattice structures, manufactured by selective laser melting, have the potential to be used as core materials in twin skinned structures. The configuration considered here is body centred cubic. One of the major structural performance requirements for such twin skinned structures is foreign object impact. The paper describes the series of steps taken to simulate (using DYNA) and validate the low velocity foreign object impact behaviour of twin skinned panels with micro lattice cores. This includes the validation of a three beam model for each micro strut, the modelling of node behaviour, and the modelling and validation of compressed micro lattice blocks, and of full foreign object impact panel behaviour.
Model Updating for a Welded Structure Made from Thin Steel Sheets
Authors: Abdul Rani M. N. , Stancioiu D. , Yunus M.A. , Ouyang Hua Jiang , Deng H. , James S.
Published: August 2011

Dynamic behaviour of a welded structure made from thin metal sheets which has a large flat surface and has been assembled together by a number of scattered spot welds is investigated. An impact hammer and roving accelerometers are used in the modal tests to provide data to update the FE model. NASTRAN Solution 103 is used to compute natural frequencies and modes of interest. The large error of the initial FE model is largely reduced mainly by adjusting a crucial parameter of the bending moment of inertia ratio, 12I/T**3.
Validation of Welding Simulations Using Thermal Strains Measured with DIC
Authors: De Strycker Maarten , Lava Pascal , van Paepegem Wim , Schueremans Luc , Debruyne Dimitri
Published: August 2011

Residual stresses can affect the performance of steel tubes in many ways and as a result their magnitude and distribution is of particular interest to many applications. Residual stresses in cold-rolled steel tubes mainly originate from the rolling of a flat plate into a circular cross section (involving plastic deformations) and the weld bead that closes the cross section (involving non-uniform heating and cooling). Focus in this contribution is on the longitudinal weld bead that closes the cross section. To reveal the residual stresses in the tubes under consideration, a finite element analysis (FEA) of the welding step in the production process is made. The FEA of the welding process is validated with the temperature evolution of the thermal simulation and the strain evolution for the mechanical part of the analysis. Several methods for measuring the strain evolution are available and in this contribution it is investigated if the Digital Image Correlation (DIC) technique can record the strain evolution during welding. It is shown that the strain evolution obtained with DIC is in agreement with that found by electrical resistance strain gauges. The results of these experimental measuring methods are compared with numerical results from a FEA of the welding process.
Understanding Crack Tip Plasticity – a Multi-Experimental Approach
Authors: Tomlinson Rachel A , Du Ying , Patterson Eann A
Published: August 2011

Crack tip plasticity has been investigated using thermoelastic stress analysis (TSA) and digital image correlation (DIC). The plastic zone size at the tip of a propagating fatigue crack was measured using both techniques. At longer crack lengths, the results compared well with Dugdale’s and Irwin’s models for crack tip yielding. The TSA methodology requires careful observation of the adiabatic assumption.
Experimental and Theoretical Study of Fracture Paths in Brittle Cracked Materials Subjected to Pure Mode II Loading
Authors: Aliha M.R.M. , Rezaei Mahdi
Published: August 2011

Crack growth path was investigated experimentally, numerically and theoretically using two test specimens subjected to pure mode II loading. The specimens were (a) the center cracked circular disc (CCCD) specimen subjected to diametral compression often called the Brazilian disc and (b) the diagonally loaded square plate (DLSP) specimen containing inclined center crack and subjected to pin loading. A few CCCD and DLSP specimens made of two brittle materials (i.e. marble rock and PMMA) were tested under pure mode II conditions. It was observed that the fracture initiation directions and the fracture paths for the tested specimens differed significantly and grew in two different trajectories. However, it was shown that the experimentally observed fracture paths for both specimens can be predicted theoretically very well by using the incremental crack growth method. Several finite element analyses were performed to simulate the whole fracture trajectories of the tested CCCD and DLSP specimens. At each increment, the direction of fracture initiation for the tip of growing crack was determined using the fracture parameters (i.e. stress intensity factors and T-stress) based on the modified maximum tangential stress (MMTS) criterion. The main difference in the fracture trajectory was found to be related to the magnitude and sign of the fracture parameters (which depend strongly on the specimen geometry and loading configuration) and also the type of tensile or compressive loading in the CCCD and DLSP samples.
Assessment of Measuring Errors in Strain Fields Obtained via DIC on Planar Sheet Metal Specimens with a Non-Perpendicular Camera Alignment
Authors: Lava Pascal , Coppieters Sam , Wang Yue Qi , van Houtte Paul , Debruyne Dimitri
Published: August 2011

The determination of strain fields based on displacement components obtained via 2D-DIC is subject to several errors that originate from various sources. In this contribution, we study the impact of a non-perpendicular camera alignment to a planar sheet metal specimen’s surface subject to biaxial loading conditions. The errors are estimated in a numerical experiment. To this purpose, deformed images - that were obtained by imposing finite element (FE) displacement fields on an undeformed image - are numerically rotated for various Euler angles. It is shown that a 3D-DIC stereo configuration induces a substantial compensation for the introduced image-plane displacement gradients. However, higher strain accuracy and precision are obtained - up to the level of a perfect perpendicular alignment - in a proposed ”rectified” 2D-DIC setup. This compensating technique gains benefit from both 2D-DIC (single camera view, basic amount of correlation runs, no cross-camera matching nor triangulation) and 3D-DIC (oblique angle compensation).
Error Estimation of DIC for Heterogeneous Strain States
Authors: Wang Yue Qi , Lava Pascal , Debruyne Dimitri , van Houtte Paul
Published: August 2011

Digital image correlation (DIC) involves certain errors during correlation, which are highly influenced by factors, e.g. image qualities, DIC parameters, and furthermore, degrees of deformation or strain states. In this contribution, attention is paid to the influence of strain states on the uncertainty of DIC, including the magnitude and the heterogeneity of the strains. A series of 2D-DIC numerical experiments are carried out on tensile specimens associated with finite element analysis (FEA). The specimens are made of 3 materials, i.e. steel DC06, steel DX54D+Z, and aluminium alloy Al6016, and cut into 3 different geometries, i.e. standard and 2 complex designs. Initial images were taken from these real specimens, which were all painted manually with random speckle patterns. Deformed images were obtained by imposing FE displacement fields on these undeformed initial images. Consequently, the errors source from imaging system are avoided, and only intrinsic errors of DIC itself are taken into account. The hardening behaviours of those materials in 3 different orientations were introduced to FEA for simulation, namely rolling direction (RD), transverse direction (TD) and 45o w.r.t. RD (45o). In FEA, homogeneous and heterogeneous strain states are achieved through applying uniaxial tension on two ends of the standard and complex specimens, respectively. The strain states are characterized by different material properties and geometries of specimens. DIC calculation are performed at various load steps to investigate the influence of the magnitude of the strain. Errors of the fields are compared among the different specimens to study the influence of the heterogeneity. In this contribution, the qualities of the speckle patterns are considered, since different patterns are applied to each experiment.
Experimentation of Steel Fiber Reinforced Concrete Tri-Axial Split Strength under Quasi-Static Loading and High Strain-Rate
Authors: Qu Jia , Zou Guang Ping , Xia Pei Xiu
Published: August 2011

A split tensile test methodology has been established for the concrete spheriform specimens with the principal stress ratio of σ1:σ2:σ3=0.24:0.24:-1 in order to study the tensile-tensile-compressive tri-axial strength. Using a Universal Material Testing Machine and Split Hopkinson Pressure Bar, the quasi-static and dynamic spliting tensile tests have been conducted for the concrete spheriform specimens consisting of 1% steel fiber. In the quasi-static test, the average strain rate of the steel fiber reinforced concrete specimens was 8.3×10-5s-1 and the split tensile strength was found to be 0.77MPa, which is consistent with the existing literature. In the high strain rate tests, the average strain rate was 170s-1 and the split tensile strength was found to be 1.01MPa. When compared with the quasi-static testing results, it is seen that the split tensile strength of the steel fiber reinforced concrete increases with increasing strain rate. The split tensile test methodology established in the present paper is simple and inexpensive, while the strength obtained located on the meridian plane of tension and compression, has practical significance.
Dynamic Behavior of Advanced Ti Alloy under Impact Loading: Experimental and Numerical Analysis
Authors: Demiral Murat , Roy Anish , Silberschmidt Vadim V.
Published: August 2011

Industrial applications of Ti-based alloys, especially in aerospace, marine and offshore industries, have grown significantly over the years primarily due to their high strength, light weight as well as good fatigue and corrosion-resistance properties. A combination of experimental and numerical studies is necessary to predict a material behavior of such alloys under high strain-rate conditions characterized also by a high level of strains accompanied by high temperatures. A Split Hopkinson Pressure Bar (SHPB) technique is a commonly used experimental method to characterize a dynamic stress-strain response of materials at high strain rates. In a SHPB test, the striker bar is shot against the free end of the incident stress bar, which on impact generates a stress pulse propagating in the incident bar towards the specimen sandwiched between the incident and transmitted bars. An experimental study and a numerical analysis based on a three-dimensional finite element model of the SHPB experiment are performed in this study to assess various features of the underlying mechanics of deformation processes of the alloy tested at high-strain and -strain-rate regimes.
Investigation of the Friction Variation with Sliding which is Commonly Observed in Individual Fretting Test Cycles
Authors: Mulvihill Daniel M. , Kartal Mehmet E. , Nowell David , Hills Dawid A.
Published: August 2011

Many researchers that have carried out fretting wear tests have presented results which show a variation (usually an increase) in the friction force during the sliding phase of individual cycles. This phenomenon is contrary to the Amontons/Coulomb model of friction which predicts a constant friction force as sliding proceeds. An in-line fretting test involving an abrupt increase in amplitude was used to show that the effect is a result of wear scar interaction effects. A pair of rotational fretting tests were then carried out to determine whether these interaction effects originate from interaction of the wear scar ends, or whether such interaction occurs throughout the nominal contact area. A new experimental rig designed to adapt conventional in-line test machines for rotational fretting was designed and built for this purpose. Results show that the friction variation occurs whether or not wear scar ends are present. After testing, the worn surface topography of each fretting pair was scanned using a focus variation microscope, and these surface images revealed the existence (and size) of many distributed local peaks and troughs distributed throughout the contact area. In conclusion, the friction variation commonly observed in the literature arises predominantly from the interaction of local wear scar features distributed over the contact region.
Effect of Indenter Geometries on Material Properties: A Finite Element Simulation
Authors: Kang J.J. , Becker A.A. , Sun W.
Published: August 2011

In this study, numerical indentation tests are carried out to examine the sensitivity of FE solutions with respect to different types of substrate models. Axisymmetric, 3D-quarter and 3D-half geometry substrates with a perfectly sharp indenter are modelled. Numerical evaluations of three different indenters, namely Berkovich, Vickers and conical indenters with perfectly sharp tips are investigated. From the FE simulations, the loading-unloading curves can be obtained. From the slope of the unloading curve, the hardness and elastic modulus can be calculated by using the Oliver-Pharr method. The results are compared to investigate the effects of using different indenter geometries. The equivalent plastic strains and the effects of different face angles of the indenters are analysed.
3D/4D Strain Mapping Using In Situ X-Ray Microtomography
Authors: Toda Hiroyuki , Uesugi Kentaro , Suzuki Yoshio , Kobayashi Masakazu
Published: August 2011

X-ray microtomography (XMT) has been utilized for the in-situ observation of various structural materials under external disturbance such as loading. In-situ XMT provides a unique possibility to access the three-dimensional (3D) character of internal microstructure and its time evolution behaviours non-destructively, thereby enabling advanced techniques for measuring local strain distribution. Local strain mapping is readily enabled by processing such high-resolution tomographic images either by the particle tracking technique or the digital image correlation technique. Procedures for tracking microstructural features which have been developed by the authors, have been applied to analyse localised deformation and damage evolution in a material. Typically several tens of thousands of microstructural features, such as particles and pores, are tracked in a tomographic specimen (0.2 - 0.3 mm3 in volume). When a sufficient number of microstructural features is dispersed in 3D space, the Delaunay tessellation algorithm is used to obtain local strain distribution. With these techniques, 3D strain fields can be measured with reasonable accuracy. Even local crack driving forces, such as local variations in the stress intensity factor, crack tip opening displacement and J integral along a crack front line, can be measured from discrete crack tip displacement fields.
Stroboscopic Fringe Projection Method for 3D Dynamic Displacement Measurement
Authors: He Xiao Yuan , Zhu Fei Peng , Wang Cheng Fei , Xu Ying Jun
Published: August 2011

The determination of dynamic characteristics of microelectromechanical system (MEMS) devices is of great importance. Currently, vibrometer techniques using a Laser-Doppler Vibrometer (LDV) are used for dynamic measurement of MEMS, utilizing an interferometer based on a stroboscope and high-speed cine photomicrography are used for MEMS. But, these methods can’t be used for 3D dynamic displacement measurement simultaneously because of their limitations. In this paper, an optical system for 3D dynamic displacement measurement of micro-components is presented using stroboscopic fringe projection and digital image correlation (DIC), which can measure both in-plane and out-of-plane motions simultaneously. In the system, stroboscopic fringe patterns are projected onto the surface of a vibrating specimen by a phase-shifting projector and stroboscopic illumination supplied with a pulsed laser diode. Synchronization between the stroboscopic laser and the driving signal for the specimen vibrating is achieved by the stroboscopic controller. For a certain vibration state, four deformed phase-shifting fringe patterns are captured by a high-resolution CMOS camera with a long working distance microscope. The images are processed by a phase-shifting technique to obtain the phase distribution. The surface pattern of the specimen without fringes could be obtained by certain phase-shifting algorithms. When stroboscopic pulses are delayed, the stroboscopic phase is changed and another vibrating status could be captured in the same way. Comparing the phase distributions of these two states, the out-of-plane displacement is achieved, which is the displacement of the specimen between these two states. The in-plane displacement could be obtained from the surface pattern without fringes by DIC. Adjusting the phase delay of illumination by stroboscopic controller, the motions of the specimen in the whole vibration period can be obtained.
Measurement of Residual Stresses within a PWR Swaged Heater Tube
Authors: Goudar D.M. , Kingston Ed J. , Smith Mike C. , Hossain Sayeed
Published: August 2011

Frequent failures of the pressuriser heater tubes used in Pressurised Water Reactors (PWRs) have been found. Axial cracks initiating from the tube outer diameter have been detected in some tubes as well as the resulting electrical problems. Replacement of the heater tubes requires an undesirably prolonged plant shutdown. In order to better understand these failures a series of residual stress measurements were carried out to obtain the near surface and through-thickness residual stress profiles in a stainless steel pressuriser heater tube. Three different residual stress measurement techniques were employed namely, Deep-Hole Drilling (DHD), Incremental Centre Hole Drilling (ICHD) and Sachs’ Boring (SB) to measure the through thickness residual stress distribution in the heater tubes. Results showed that the hoop stresses measured using all three techniques were predominantly tensile at all locations, while the axial stresses were found to be tensile at the surface and both tensile and compressive as they reduce to small magnitudes within the tube. The magnitude of the in-plane shear stresses was small at all measurement depths at all locations. The various measurement methods were found to complement each other well. All the measurements revealed a characteristic profile for the through-thickness residual stress distribution.
The Validation of Weld Residual Stresses for Use in Structural Integrity Assessment
Authors: Bate Steve K. , Bouchard P. John
Published: August 2011

The continued safe and reliable operation of plant invariably has to consider the assessment of defects in welded structural components. This requires some estimate of the residual stresses that have developed during the welding fabrication process. For as-welded structures these stresses can be of yield magnitude. Engineering critical assessment procedures such as R6, BS 7910, FITNET and API 579-1 provide simplified estimates, bounding profiles or advice on detailed analysis or measurement which can be applied to provide conservative estimates of the remaining life of plant. The use of finite element analysis (FEA) is being applied more frequently to predict residual stresses in welded components for assessment purposes. This calculation involves complex non-linear analyses with many assumptions. As a consequence, the accuracy and reliability of solutions is variable. In order to improve the consistency of weld modelling, and hence the accuracy and confidence in their use, a set of Guidelines covering the calculation of residual stresses have been developed. The residual stress calculations need to be validated before the results can be used in assessments and guidance on how to demonstrate the required standard of validation proof is provided with these Guidelines. The level of validation required, depends on the problem being solved and the sensitivity of the assessment to the presence of residual stress. For example a high level of validation may be required for assessments of safety critical plant. To support these calculations, measurements are required and a series of ‘Weld Residual Stress Benchmarks’, describing welded mock-ups which have been measured using various measurement techniques, are being collated which the users can then refer to when validating their finite element modelling techniques and thus provide a greater confidence in the predicted results.
Analysis of Forces in Vibro-Impact and Hot Vibro-Impact Turning of Advanced Alloys
Authors: Muhammad Riaz , Maurotto Agostino , Roy Anish , Silberschmidt Vadim V.
Published: August 2011

Analysis of the cutting process in machining of advanced alloys, which are typically difficult-to-machine materials, is a challenge that needs to be addressed. In a machining operation, cutting forces causes severe deformations in the proximity of the cutting edge, producing high stresses, strain, strain-rates and temperatures in the workpiece that ultimately affect the quality of the machined surface. In the present work, cutting forces generated in a vibro-impact and hot vibro-impact machining process of Ti-based alloy, using an in-house Ultrasonically Assisted Turning (UAT) setup, are studied. A three-dimensional, thermo-mechanically coupled, finite element model was developed to study the thermal and mechanical processes in the cutting zone for the various machining processes. Several advantages of ultrasonically assisted turning and hot ultrasonically assisted turning are demonstrated when compared to conventional turning.
Measurement of Tangential Contact Stiffness in Frictional Contacts: The Effect of Normal Pressure
Authors: Kartal Mehmet E. , Mulvihill Daniel M. , Nowell David , Hills Dawid A.
Published: August 2011

The tangential contact stiffness of frictional interfaces affects both the vibration response and structural integrity of structures comprising frictional joints. Vibration and structural response of monolithic structures can be predicted very accurately; however, when assemblies of components involve frictional interfaces, additional damping and compliance are present due to these interfaces. These features make it more challenging to predict the vibration characteristics of assemblies with the same degree of accuracy as can be achieved for single components. If these interface properties can be determined, it should then be possible to significantly enhance current models of the vibration of engineering assemblies. Measurements of both force and displacement in the tangential direction are obtained from a series of in-line fretting tests involving flat pads with rounded corners clamped against the flat surface of a specimen which is oscillated by a hydraulic tensile testing machine. In order to measure the local displacement field very close to the contact interface, the digital image correlation (DIC) method is employed. The effect of normal contact pressure on tangential contact stiffness is investigated. Multiple experiments with the same parameters show good repeatability given the number of variables involved.
Synchronization between Driving and Illumination Signals in a High Frequency Stroboscopic Imaging System
Authors: Wang Cheng Fei , Xu Ying Jun , Zhu Fei Peng , He Xiao Yuan
Published: August 2011

In a stroboscopic imaging system, in order to make images to be correctly captured the synchronization must be strictly satisfied. Direct digital synthesizer (DDS) is a new frequency synthesizing technique used for creating arbitrary waveforms from a single, fixed-frequency reference clock. It has many advantages such as fast frequency conversion, high resolution of frequency and keeping phase continuous while frequency switches. By applying the DDS technique, this paper presents a method to generate the illumination signal of light source and the drive signal of device, and more attention is paid to how to perform the precise synchronization between the two signals. By adjusting the relative delay of the illumination and the drive signals, the phase can be changed. Allowing a sequence of images depicting the motion over the interval studied to be captured, which yields a complete picture of the vibration of a specimen or the surface structure of a MEMS device. Experimental results show that the high frequency of a signal could be up to 120 MHz with frequency resolution 4μHz. The phase resolution of 2-16 can be achieved by the proposed method. The relative phase error between illumination and driven signals could be down to 2-16. It is relatively easy to a synchronization illumination signal of light source and drive signal of MEMS accurately. However, as the two signals' transmission paths are different, their transmission delays are different also. Accordingly, a phase error would be caused and it would change as the signal frequency changes. Moreover, if the drive signal of external objects is used, the phase error, which is introduced via inaccuracy synchronizing the frequency of signal, would be superposed, indeed. These phase errors would affect the quality of imaging and the accuracy of measurement. In this paper, an effective method to adjust the errors is proposed. By means of specially designed hardware circuit, the error of phase and frequency synchronization between illumination signal of light source and drive signal of MEMS can be adjusted automatically. The proposed method improves the accuracy in synchronism and reduces the impact of the error of signal synchronization in the system. It is proved that the minimum relative phase error between illumination signal of light source and drive signal of MEMS can be reduced by more than 10 times using this method.
Vibratory Analysis of Turning Process
Authors: Serra Roger
Published: August 2011

The aim of the paper is to analyse the vibrations during a turning manufacturing process in terms of the Machine-Tool-Part unit having particularly complex dynamic characteristics. The vibratory phenomenon is influenced by many parameters like workpiece, tool overhang, cutting speed, depth of cut and feed rate. This phenomenon is not completely known yet, so the aim was to highlight its origins using two complementary approaches: numerical and experimental. Finite element calculations were carried out, in order to identify parameters which characterize vibrations in machining like structural parameters (lathe, tool holder, cutting tool, workpiece, tailstock, tool overhang ...). A design for an experiment of process parameters (depth of cut, feed and cutting speed) was used and one series of turning tests was performed. Results have shown a significant effect between these parameters on the resulting surface roughness, consumed power, cutting time and tool vibrations and a best comprehension of the process.
A Strategy for Delivering High Torsionality in Longitudinal-Torsional Ultrasonic Devices
Authors: Al-Budairi Hassan , Harkness Patrick , Lucas Margaret
Published: August 2011

A composite longitudinal-torsional vibration mode has applications in ultrasonic motors, ultrasonic welding and ultrasonic drilling. There are two ways to obtain this vibration behaviour using a single transducer, namely (i) coupling of a longitudinal and a torsional mode, which is known to be difficult; and (ii) degenerating a longitudinal mode to deliver longitudinal-torsional behaviour at the horn tip. A mode-degenerating horn is achieved by incorporating helical or diagonal slits in an otherwise traditional exponential horn driven by a Langevin transducer. However, it is often difficult with this configuration to avoid coupling of unwanted bending modes, low responsiveness, and loss of ultrasonic energy due to boundaries between tuned components. Therefore, in this study the mode-degenerating characteristics are achieved by incorporating the helical slits and exponential geometry features in the front mass of the transducer itself. Finite element analysis and vibration experimental analysis show that this strategy prevents coupling of bending modes, increases responsiveness, and reduces energy losses. Most importantly the transducer delivers a very high torsionality.
Validation of Micro-Slip in Interference Fitted Shafts Subject to Complex Loading Regimes
Authors: McMillan Martin , Booker Julian D. , Smith David John
Published: August 2011

The intention of the present work reported is to provide a detailed characterisation of the factors that contribute to failure of interference fitted joints under combined axial and torsional loading conditions and to provide analytical and finite element based simulations of the slip propagation and interfacial stresses leading to a failure envelope indicating the limits of each loading component in service to avoid premature failure. Small scale tests are conducted to examine failure torque and failure load separately before combined loading regimes are applied. The experimental tests are used to validate each stage of model development and the key parameters such as interference are measured under test conditions for use in the simulation models. The measured probabilistic variation in manufactured specimens will allow parametric studies to be carried out using finite element analysis and ultimately, provide a more comprehensive, validated approach for interference fit design.
Acoustic Emission Source Characterisation in Large-Scale Composite Structures
Authors: Eaton Mark J. , Pullin Rhys , Featherston C.A. , Holford Karen M.
Published: August 2011

Damage detection and location in aerospace composites is currently of great interest in the research community and is being driven by the need to reduce weight of commercial aircrafts and hence make substantial environmental improvements. The increased use of composites as safety critical components has led to the need for development of structural health monitoring (SHM) systems. Acoustic Emission (AE) offers an excellent potential for delivering the necessary information of damage detection to maintenance engineers in terms of location however there are currently no methodologies that can use AE signals to characterise damage sources. This paper explores a methodology for damage characterisation based on measuring the amplitude ratio (MAR) of the two primary plate wave modes, to allow identification of in-plane (matrix cracking) and out-of-plane sources (delamination). Results from a large-scale buckling test show good correlation between signal characterization and observed damage mechanisms.
Dynamic Properties of Cortical Bone Tissue: Impact Tests and Numerical Study
Authors: Abdel-Wahab Adel A. , Silberschmidt Vadim V.
Published: August 2011

Bone is the principal structural component of a skeleton: it assists the load-bearing framework of a living body. Structural integrity of this component is important; understanding of its mechanical behaviour up to failure is necessary for prevention and diagnostic of trauma. Bone fractures occur in both low-energy trauma, such as falls and sports injury, and high-energy trauma, such as car crash and cycling accidents. By developing adequate numerical models to predict and describe the deformation and fracture behaviour up to fracture of a cortical bone tissue, a detailed study of reasons for, and ways to prevent or treatment methods of, bone fracture could be implemented. This study deals with both experimental analysis and numerical simulations of this tissue and its response to impact dynamic loading. Two areas are covered: Izod tests for quantifying a bone’s behaviour under impact loading, and a 3D finite-element model simulating these tests. In the first part, properties of cortical bone tissue were investigated under impact loading condition. In the second part, a 3D numerical model for the Izod test was developed using the Abaqus/Explicit finite-element software. Bone has time-dependent properties – viscoelastic – that were assigned to the specimen to simulate the short term event, impact. The developed numerical model was capable of capturing the behaviour of the hammer-specimen interaction correctly. A good agreement between the experimental and numerical data was found.
Coupled Thermo Mechanical Characterisation of Polymers Based on Inverse Analyses and IR Measurements
Authors: Maurel-Pantel Aurelien , Baquet E. , Bikard Jerome , Billon Noelle
Published: August 2011

Heat dissipation during mechanical testing can disturb experimental characterisation of polymers. In this work it is demonstrated that these effects are not limited to extreme loading conditions such as impacts. A visco-hyperelastic, visco-plastic constitutive model is proposed that accounts for thermo mechanical coupling in a fully 3D thermodynamics approach. Strain-rate and temperature dependencies are coupled using a concept close to the well known time-temperature superposition principle. Constitutive and coupling parameters are identified at the same time using an inverse analysis protocol. An experimental data base is generated for mechanical measurements at different temperatures and strain rates but also for temperatures during tests measured using IR technology. Such a protocol allows investigation on the strain-rate sensitivity in a much more relevant manner than classical one and the value of the so-called Taylor-Quinney coupling parameter is discussed.
Experimental and Numerical Analysis of Thermal Deformation in Thermoelectric Coolers
Authors: Wang Wei Chung , Wu Ting Ying
Published: August 2011

In this paper, the electronic speckle pattern interferometry (ESPI) and the finite element method (FEM) were used to obtain the thermal deformation induced in a centrally supported thermoelectric cooler (TEC). The results of ESPI and FEM are in good agreement and show that the warpage varies linearly with respect to the temperature difference between the two ceramic plates inside the TEC.
Analysis of Creep Behavior of Polypropylene Fibers
Authors: Sabuncuoglu Baris , Acar Memiş , Silberschmidt Vadim V.
Published: August 2011

Time and stress-dependent viscoelastic properties of polypropylene fibers are determined by means of a series of creep tests and data analysis technique. Relaxation tests are carried out to verify and update the suggested model. The tests are performed for single polypropylene fibers that form a thermally bonded low-density nonwoven. The obtained properties are implemented into the finite element analysis software MSC. Marc - Mentat. Tensile tests and simulations are performed in order to demonstrate suitability of the developed creep model. The obtained results are discussed and further recommendations are given.
Experimental Investigation of the Deformation of Built-up Members of Cold-Formed Steel Profiles
Authors: Georgieva Iveta , Schueremans Luc , De Roeck Guido , Pyl Lincy
Published: August 2011

Built-up members of cold-formed steel (CFS) profiles were tested in 4-point bending. CFS profiles (generally thin-walled) deform considerably under load, and the deformed configuration is a result of the superposition of different buckling mode shapes. Local buckling propagates through the profile walls; during distortional buckling parts of the cross-section rotate around a web-flange juncture. Alongside the buckling effects, the overall deformation of the member is considerable. To study these slender and relatively long members, a sufficient number of measuring positions on the specimens is needed. Often, this is not feasible with the conventional measuring techniques. An optical measuring device was used to record the movement of a large number of points per specimen. The obtained results are placed in a 3D coordinate system and can be exported for further data processing. The goal of the measurement campaign was to calibrate a Finite Element model that will simulate the tests. The model will be used for the analysis of composed frame members of CFS profiles, whose design is not entirely covered by the European Standard [1]. After calibration, the FEA predicts the performance of these built-up members well.
Experimental Study on Stress Field Parameters of an Interface Crack in Aluminum/ Epoxy
Authors: Lei Zhen Kun , Li Xing Min
Published: August 2011

Standard experimental tests including photoelasticity in the evaluation of stress intensity factors in crack tip has been regarded widely. A least-squares method is used to determine the stress field parameters of interface crack in Aluminum/ epoxy bimaterial and its evolvement. Based on multi-parameter stress field equations and the least-squares principle, a set of over-determined nonlinear equations is established by fitting the isochromatic phase field obtained by digital phase-shifting photoelasticity in this paper. An iterative procedure based on Newton-Raphson method is utilized to estimate the unknown stress field parameters. Interface crack experiments reveal that the modulus of combined stress intensity factor increases with the applied loads and however its phase angle holds the line on the condition of same loading direction. On the other hand, the modulus of combined stress intensity factor increases with the loading direction from 30o to 75o under the same applied load, however, its absolute phase angle decreases and is independent of the loads.
Effects of Ray Bending in Scattered Light Photoelasticity for Tempered and Annealed Glass Plates
Authors: Hödemann Siim , Kikas Jaak , Aben Hillar , Anton Johan , Errapart Andrei
Published: August 2011

Residual stresses in tempered glass plates can be measured with the scattered light method. Usually a rectilinear propagation of light is assumed. However, due to the gradients of the refractive index, the light rays curve. We have experimentally demonstrated this for tempered (surface stress 120 MPa and more) and annealed glass plates. For a laser beam of finite width this also results in broadening and loss of photoelastic modulation. While some features of the experimental picture (dependence of the period of modulation on depth), can be captured in the simple model of rectilinear propagation, the other observations need development of more elaborated models.
Application of High Speed Image Correlation for Measurement of Mode Shapes of a Car Bonnet
Authors: Siebert Thorsten , Wang Wei Zhuo , Mottershead John E. , Pipino Andrea
Published: August 2011

For the analysis of vibrations and mode shape extraction in particular the use of optical full-field measurement techniques has grown during the last years. Beside techniques like Digital Speckle Pattern Interferometry, Moiré, Thermography or Photoelasticity the Digital Image Correlation techniques have already been successfully proven to be an accurate displacement analysis tool for a wide range of applications.
Spectroscopic Birefringence Mapping by Channeled Spectrum
Authors: Wakayama Toshitaka , Yoshizawa Toru , Otani Yukitoshi
Published: August 2011

Birefringence mapping of objects has attracted great interest in the fields of material technology and biomedical science. This paper describes spectroscopic birefringence mapping using a channeled spectrum. To perform spectroscopic birefringence mapping using a microscope, an acousto-optical tunable filter (AOTF) was employed as a spectrometer. The AOTF can select a specific wavelength from a white light source. The optical arrangement consists of a white light source, the AOTF, a polarizer, two retarders with high-order retardance, two objective lenses, an analyzer, and a CCD camera. The polarizer and the first retarder can modulate the polarization state and they function as polarizing optics, while the second retarder and the analyzer can analyze the polarization state and they function as analyzing optics. A sample is inserted between the polarizing and analyzing optics. Images obtained at a specific wavelength generate 128 data points at visible wavelengths. A channeled spectrum (i.e., the intensity distribution) can be generated from the images obtained. A Fourier spectrum can be obtained by the fast Fourier transform (FFT) method. The birefringence properties of the sample can be derived by calculating the inverse FFT. We used this technique to measure the polarization properties of a nematic liquid crystal droplet.
The Effect of Plastic Deformation on the Thermoelastic Constant and the Potential to Evaluate Residual Stress
Authors: Robinson A. F. , Dulieu-Barton Janice M. , Quinn S. , Burguete R. L.
Published: August 2011

In some metals it has been shown that the introduction of plastic deformation or strain modifies the thermoelastic constant, K. If it was possible to define the magnitude of the change in thermoelastic constant over a range of plastic strain, then the plastic strain that a material has experienced could be established based on a measured change in the thermoelastic constant. This variation of the thermoelastic constant and the ability to estimate the plastic strain that has been experienced, has potential to form the basis of a novel non-destructive, non-contact, full-field technique for residual stress assessment using thermoelastic stress analysis (TSA). Recent research has suggested that the change in thermoelastic constant is related to the material dislocation that occurs during strain hardening, and thus the change in K for a material that does not strain harden would be significantly less than for a material that does. In the work described in this paper, the change in thermoelastic constant for three materials (316L stainless steel, AA2024 and AA7085) with different strain hardening characteristics is investigated. As the change in thermoelastic response due to plastic strain is small, and metallic specimens require a paint coating for TSA, the effects of the paint coating and other test factors on the thermoelastic response have been considered.
The Application of Thermoelastic Stress Analysis to Evaluate Debond Damage in Composite Sandwich Structures
Authors: Fruehmann R.K. , Wang W , Dulieu-Barton Janice M. , Quinn S.
Published: August 2011

The work described in the paper investigates the stresses in the vicinity of a debond between the face sheet and core in a foam core / composite sandwich beam. Experiments were conducted in which the damaged side of the beam was loaded in compression in a four point bend test. Thermoelastic stress analysis (TSA) was used to obtain a measure of the stress field in the central part of the beam to evaluate its potential for damage detection and assessment. It is shown that TSA is capable of both identifying the damage and assessing its severity in terms of the remnant load carrying capacity of the beam. Fatigue tests were also performed, which showed that the cyclic load applied as a necessity for TSA did not cause the damage to grow, thereby demonstrating the potential of TSA as a non-destructive method for inspecting sandwich structures.
Non-Destructive 3-D Determination of Interior Stresses
Authors: Lin S.J. , Quinn S. , Boyce B.R. , Rowlands R.E.
Published: August 2011

Thermoelastic stress analysis and grey-field photoelasticity are combined with the Laplace and Beltrami-Michell equations to non-destructively evaluate the individual internal components of stress in a loaded 3-D aluminium member. Experimental results agree with those predicted numerically by the finite element and finite difference techniques.