Morphing blades with embedded SMA strips: An experimental investigation

This paper focuses on the development and experimental testing of a composite blade for an automotive axial fan. A novel concept of morphing blade is proposed with the aim of replacing the conventional actuator systems. The structure is made up of a polymeric matrix equipped with NiTi shape memory alloy strips as active elements. The morphing blade changes its shape as the phase transformations of the strips are thermally activated by airflow. To study the morphing capability of the blade, together with the recovery behavior of the NiTi strips, four different polymeric compounds have been compared. Digital image analysis techniques have been performed to quantitatively analyze the blade deflections and to evaluate the most suitable polymeric matrix for the intended application. Finally, the blade shape modifications, which occur along the blade span during the activation cycles, have been reconstructed by three-dimensional non-contact surface detection. Results from the comparison between these two reverse engineering methods could provide a powerful support for the assessment of the aerodynamic performance of the morphing blade.     

An efficient decision-making framework for hybrid metamodelling

In engineering design optimization, the usage of hybrid metamodels (HMs) can take full advantage of the individual metamodels, and improve robustness of the predictions by reducing the impact of a poor metamodel. When there are plenty of candidates, it is difficult to make decisions on which metamodels to choose before building an HM. The decisions should simultaneously take into account of the number, accuracy and diversity of the selected metamodels. To address this problem, this research developed an efficient decision-making framework based on partial least squares for metamodel screening. A new significance index is firstly derived from the view of fitting error in a regression model. Then, a desirable metamodel combination which consist of only the significant ones is subsequently configured for further constructing the final HM. The effectiveness of the proposed framework is demonstrated through several benchmark problems.     

Simulation and optimization of pulsating heat pipe flat-plate solar collectors using neural networks and genetic algorithm: a semi-experimental investigation

Clean Technologies and Environmental Policy - This research study presents an investigation on the behavior of a Pulsating Heat Pipe Flat-Plate Solar Collector (PHPFPSC) by artificial neural...     

An intelligent pressure sensor using neural networks

In this paper, we propose a scheme of an intelligent capacitive pressure sensor (CPS) using an artificial neural network (ANN). A switched-capacitor circuit (SCC) converts the change in capacitance of the pressure-sensor into an equivalent voltage. The effect of change in environmental conditions on the CPS and subsequently upon the output of the SCC is nonlinear in nature. Especially, change in ambient temperature causes response characteristics of the CPS to become highly nonlinear, and complex signal processing may be required to obtain correct readout. The proposed ANN-based scheme incorporates intelligence into the sensor. It is revealed from the simulation studies that this CPS model can provide correct pressure readout within ±1% error (full scale) over a range of temperature variations from -20°C to 70°C. Two ANN schemes, direct modeling and inverse modeling of a CPS, are reported. The former modeling technique enables an estimate of the nonlinear sensor characteristics, whereas the latter technique estimates the applied pressure which is used for direct digital readout. When there is a change in ambient temperature, the ANN automatically compensates for this change based on the distributive information stored in its weights     

Flexibility and manufacturing system design: An experimental investigation

Manufacturing industries today are faced with steady and unrelenting changes to the environment in which they operate. In order to survive and profit, manufacturing facilities must be designed such that they exhibit desirable system-level flexibility characteristics. The relationships between flexibility and manufacturing system design, however, remain largely unexplored. This paper investigates the effects of manufacturing system design on product, mix, production, and volume flexibilities, and on trade-offs between these flexibility types, for different product environments. Of particular concern is the determination of whether or not flexibility trade-offs can be avoided, and if so, how. Simulation experiments are performed to determine flexibility values for 16 different manufacturing system design 'approaches' and two levels of part processing flexibility. A total of 800 different manufacturing system/product set combinations are investigated. The results indicate that the effects of manufacturing system design on flexibility are not always intuitive, and that they can change depending upon the level of part processing flexibility present. In addition, however, they show that flexibility trade-offs are not inevitable: multiple flexibility types can be increased in value simultaneously through proper selection of the design approach.     

An experimental investigation of mixed-mode fracture

In this paper, mixed-mode fracture is investigated experimentally. In the first part, critical conditions for initiation of crack growth are explored. The method of caustics was used in conjunction with a high speed video system to determine critical stress intensity factors at initiation of crack growth. It was found that the maximum tangential stress criterion originally proposed by Erdogan and Sih [1] was the best criterion in terms of predictive capability. Polymethylmethacrylate and Homalite-100 were used in the experiments and Homalite-100 was found to exhibit significant rate dependence. In the second part, crack growth initiated under mixed-mode loading is addressed. It is shown that subsequent slow crack growth in PMMA is under pure mode-I conditions.

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Résumé On étudie par voie expérimentale les ruptures selon un mode mixte. On explore, dans une première partie, les conditions d'amorçage de la croissance d'une fissure. En utilisant la méthode des caustiques en association avec un système vidéo à grande vitesse, on détermine les facteurs critiques d'intensité de contraintes correspondant à l'amorçage de la fissure. On trouve que le critère de contrainte maximum tangentielle, proposé à l'origine par Erdogan et Sih, est le meilleur en termes de capacité de prédiction. Pour les essais, on a utilisé du plyméthylméthacrylate et de l'Homalite-100, et on a trouvé que ce dernier matériau faisait état d'une sensibilité importante à la vitesse. La deuxième partie du travail est consacrée à la croissance d'une fissure sous un mode de sollicitations mixte. On montre que la propagation lente de la fissure dans le PMMA se produit sous des conditions de pur Mode I.

     

An analysis of the equilibria of neural networks with linear interconnections

In this paper, we analyse the equilibria of neural networks which consist of a set of sigmoid nonlinearities with linear interconnections,without assuming that the interconnections are symmetric or that there are no self-interactions. By eliminating these assumptions, we are able to study the effects of imperfect implementation on the behaviour of Hopfield networks. If one views the neural network as evolving on the openn-dimensional hypercubeH = (0, 1) ⁿ , we have the following conclusions as the neural characteristics become steeper and steeper: (i) There is at most one equilibrium in any compact subset ofH, and under mild assumptions this equilibrium is unstable. In fact, the dimension of the stable manifold of this equilibrium is the same as the number of eigenvalues of the interconnection matrix with negative real parts. (ii) There might be some equilibria in the faces ofH, and under mild conditions these are always unstable. Moreover, it is easy to compute the dimension of the stable manifold of each such equilibrium. (iii) A systematic procedure is given for determining which corners of the hypercubeH contain equilibria, and it is shown that all equilibria in the corners ofH are asymptotically stable.     

Design of manufacturing systems by a hybrid approach with neural network metamodelling and stochastic local search

Metamodels are models of simulation models. Metamodels are able to estimate the simulation responses corresponding to a given combination of input variables. A simulation metamodel is easier to manage and provides more insights than simulation alone. Traditionally, the multiple regression analysis is utilized to develop the metamodel from a set of simulation experiments. Simulation can consequentially benefit from the metamodelling in post-simulation analysis. A backpropagation (BP) neural network is a proven tool in providing excellent response predictions in many application areas and it outperforms regression analysis for a wide array of applications. In this paper, a BP neural network is used to generate metamodels for simulated manufacturing systems. For the purpose of optimal manufacturing systems design, mathematical models can be formulated by using the mapping functions generated from the neural network metamodels. The optimization model is then solved by a stochastic local search approach, simulated annealing (SA), to obtain an optimal configuration with respect to the objective of the systems design. Instead of triggering the detailed simulation programs, the SA-based optimization procedure evaluates the simulation outputs by the neural network metamodels. By using the SA-based optimization algorithm, the solution space of the studied problem is extensively exploited to escape the entrapment of local optima while the number of time consuming simulation runs is reduced. The proposed methodology is illustrated to be both effective and efficient in solving a manufacturing systems design problem through an example.     

An experimental investigation of wave energy trapping

The type of motions under consideration are surface waves over shallow-water regions bordered by an area of deeper water (although we shall consider this deeper water sufficiently shallow, compared with wavelength, to be amenable to shallow-water theory). It is now well known that oscillations of this type can be trapped by the bottom contours. We discuss two different bottom topographies and compare the theoretical and experimental results. In both cases good agreement is reached.     

Enhancing the performance of household refrigerators with latent heat storage: An experimental investigation

This paper presents the results of experimental tests carried out to investigate the performance of a household refrigerator using a phase change material (PCM). The PCM is located on the back side of the evaporator in order to improve its efficiency and to provide a storage capacity allowing several hours of refrigeration without power supply. The system has been tested with water and with a eutectic mixture (freezing point ?3 °C) and for a range of operating conditions (PCM thickness, ambient temperature, thermal load). The analysis of the results shows a significant improvement of the performance compared to a conventional system.     

An experimental investigation of dynamic crack propagation

The dynamic fracture behavior of polymethylmethacrylate (bdPMMA) has been investigated. The specimens were in the form of rectangular sheets with sharp notches. The elastodynamic crack tip stress field and the crack velocity were determined by the use of resistance strain gauges. An analytic expression for the dynamic crack tip stress field was used to evaluate the dynamic stress intensity factors, and the dynamic arrest toughness was also determined.The dynamic response of the stresses at the notch tip at varying loading rates was considered and some “hysteresis” fracture phenomena were observed.     

An experimental investigation of carbon-fiber/aluminium laminates with double-edge cracks

The mechanical behavior in the damage zones around crack-tips in carbon-fiber/aluminium hybrid composite laminates (CALL) have been studied by moiré interferometry. The strain distributions in the zones around the double-edge crack-tips in longitudinal and transverse specimens were obtained under tensile loading. The morphology of the damaged sections was observed by the use of scanning electron microscopy and the damage characteristics were analyzed for these specimens.     

Shock response of 3D woven composites: An experimental investigation

A modified shock tube was used to determine the effect of shock wave loading on 3D woven composite panels. The shock wave, which produces a short duration steeply rising pressure pulse when impacting the panel, was used to load the panels. The out of plane deformation response was measured using a full field Digital Image Correlation (DIC) technique. The results allow for measurements of full field displacements and strains in the samples. Three distinct textile composite architectures, corresponding to different amounts of Z-fiber (fiber tows that bind the different textile layers together) were investigated. Two separate shock intensities were used. Matrix micro-cracking was observed to be the mechanism by which failure is initiated, and this micro-cracking was found to occur closest to the center of the panel where the outer-surface straining is highest. Fiber tow failure was absent in the shock strengths studied in the present work. The results suggest that the 6% Z-fiber architecture provided the largest panel stiffness and the least amount of damage. This result suggests that this may be the optimal architecture and density for orthogonally woven Z-fiber reinforced composites, however due to the complex nature of the problem the same architecture with a different tow (and fiber) volume fraction may yield different results.     

Propene/isobutane mixtures in heat pumps: An experimental investigation

Zeotropic mixtures in heat pumps, based on thermodynamic analysis, should lead to higher coefficients of performance (COP) due to the temperature glide which decreases exergy losses in the heat exchangers. However, fluid mixtures influence every component of a plant and the total system performance. In addition to the various theoretical studies in this field, a laboratory scale vapour compression heat pump test rig was designed and set up. In the present experimental investigations, the operating performance for the pure fluids isobutane and propene, and their mixtures are systematically investigated. COPs and exergetic efficiencies as a function of evaporation temperature, compressor speed and composition of the mixture are presented and compared with a theoretical approach. Contrary to theoretical expectations, the experimental results show only a slight increase of the COP for the mixture, compared to the better pure fluid, because heat exchanger pressure drops reduce the temperature glide.     

An experimental investigation into dynamic fracture: II. Microstructural aspects

This is the second of a series of four papers in which problems of dynamic crack propagation are examined experimentally in large, thin sheets of Homalite 100 simulating crack growth in an unbounded plate. In the first paper crack initiation resulting from stress wave loading to the crack tip and crack arrest were investigated. It was found that for increasing rates of loading in the micro second range, the stress intensity required for initiation rises markedly. Crack arrest occurs abruptly without any deceleration phase at a stress intensity below that value which causes initiation under quasi-static loading.In this paper we investigate the microscopic processes that control the process of dynamic fracture. Through post-mortem examination of the fracture surfaces it is established that microcracks are nucleated and grown ahead of a propagating crack. A measure of the size of the fracture process zone in which these microcracks are activated is obtained. Real time high speed photomicrography is used to capture the evolution of crack growth and crack branching. Under conditions of low stress intensity the crack front exhibits thumbnail curvature similar to the crack front profiles associated with quasi-static fracture processes. At increasing stress intensity the crack front straightens out and is identifiable as a front of multiple microfractures.The third contribution establishes the hitherto unreported occurrence that cracks can propagate rapidly with constant velocity even though the stress intensity factor varies considerably during this propagation. This velocity is determined by the initial stress wave loading on the crack tip and is changed, within limits, only by stress pulses of sufficient magnitude and brevity of rise time.The final paper in the series deals with the effect of stress waves on the behavior of running cracks, in particular with the influence of stress waves on the branching phenomenon. Also, crack curving under transient stress waves is examined. These results are believed to apply to brittle materials other than Homalite 100 and the reasons for this belief are discussed briefly in the first paper of this series.

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Résumé Le présent mémoire est le deuxième d'une série de quatre, consacrés à l'examen des problèmes de propagation dynamique d'une fissure par voie expérimentale dans des feuillards minces d'Homalite 100 destinés à simuler la croissance d'une fissure dans une tôle non limitée. Dans le premier mémoire, l'amorçage de la fissure qui résulte d'une sollicitation par contrainte ondulée à l'extrémité de cette fissure, ainsi que les problèmes d'arrét de fissure ont été étudiés. On a trouvé que, lorsque la vitesse de mise en charge s'accélère dans la gamme de la microseconde, l'intensité de contrainte requise pour l'amor¢age s'accroit de manière significative. L'arrêt de fissure se produit brutalement sans la moindre phase de décélération à une intensité de contrainte inférieure à la valeur qui provoque l'amor¢age sous des sollicitations quasi-statique.Dans le présent mémoire, on examine le processus microscopique qui régit la rupture dynamique. Grâce à l'examen post-mortem des surfaces de rupture, on établit que des micro-fissures sont créées et croissent en avant d'une fissure en cours de propagation. On obtient une mesure de la taille de la zone concernée par le processus de rupture dans laquelle ces micro-fissures se trouvent activées. L'utilisation est faite de la photo-micrographie à haute vitesse et à temps réel en vue de capter l'évolution de croissance de la fissure ainsi que son arborescence. Sous des conditions de faible intensité de contrainte, le front de fissuration fait état d'une courbure en ongle similaire au profil de front de fissure associé avec un processus de rupture quasi-statique. Lorsque s'accroit l'intensité de contrainte, le front de fissure tend à devenir droit et est identifiable à un front de micro-ruptures multiples.La troisième contribution de cette série rapporte le phénomène jusqu'ici non publié selon lequel des fissures peuvent se propager rapidement avec une vitesse constante même si le facteur d'intensité de contrainte évolve considérablement au course de cette propagation. Cette vitesse est déterminée par la charge ondulante initiale à l'extrémité de la fissure et ne se modifie, du moins dans certaines limites, que par des pulsations de contrainte d'une amplitude suffisante et d'une soudaineté d'apparition.Le dernier des documents de cette série est relatif à l'effet des ondes de contrainte sur le comportement de fissure en cours de propagation en particulier en tenant compte de l'influence des ondes de contraintes sur le phénomène d'arborescence. On examine également la courbure que peut prendre une fissure sous l'effet d'ondes de contrainte transitoire. On pense que ces résultats s'appliquent a des materiaux fragiles autres que l'Homalite 100 et l'on discute brièvement dans le premier document de cette série les raisons de cet avis.

     

Variations in unsaturated flow with flow direction in resin transfer molding: An experimental investigation

The dual-scale nature of fiber preforms due to the presence of large continuous gaps between fiber tows gives rise to the unsaturated flow in resin transfer molding (RTM) process which is characterized by a droop in the injection pressure history due to the delayed absorption of fiber tows (the ‘sink’ effect). In this study, we experimentally investigate the effect of change in flow direction on the unsaturated flow in three anisotropic dual-scale fiber mats. A series of 1-D mold-filling experiments involving a constant flow rate were conducted for a unidirectional woven fiber-mat, a biaxial stitched mat, and a triaxial stitched fiber-mat along with a reference single-scale random mat. In the case of the unidirectional mats, the droop in the inlet-pressure history, signifying the strength of the sink effect, is found to be strongest for flow along the micro-channels aligned with fiber tows. The droop, and hence the sink effect, is observed to weaken progressively for flow-directions at 45° and 90° to this principal direction. In the case of the biaxial and triaxial mats, the situation is more complex due to the multi-layer construction of such mats: maximum droop is found when mats are oriented at a 45° angle with respect to the fiber-mat coordinate, and it weakens in the 0° and 90° directions. The unsaturated flow effect is also quantified by measuring percentage deviation in the area under the experimental curve from that of the predicted curve. A clear correlation between the droop (through the percentage deviation) and the permeability along a flow direction in the unidirectional mats is observable, though such a relationship eludes the triaxial mat. The effect of unsaturated flow on liquid-front progress during the 1-D experiment was also studied. In contrast to the reference single-scale random mat where the observed front progress closely follow the prediction based on the single-scale physics, a small difference was observed between the observed and predicted front progress for the three dual-scale mats considered. However the difference was too small to yield any significant correlation with the flow direction.     

Impact loading of plates — An experimental investigation

The impact of projectiles at sub-ordnance velocities against mild steel, stainless steel and aluminium plates, has been studied in a series of experiments. The projectile mass, nose shape and hardness have been shown to have an important effect on penetration as does the target rigidity and support condition. All materials exhibit a clear ‘kink’ effect related to a change from energy absorption by plastic deformation to perforation with well-defined shear bands and no appreciable bulging.     

An experimental investigation on flash butt welded rails

In this paper, experimental studies performed for flash butt welded rails used in Turkish railways network having 49E1 and 60E1 rail sections are presented. These studies comprise of full-scale laboratory tests such as four point bending fatigue and three-point slow bending tests, as well as related instrumentation of test specimens and data measurement. Fatigue and bending tests are prepared and carried out in accordance with EN 14587-2 standard. The fracture surfaces of the welded samples are examined to identify the associated failure modes. The fatigue test results are superimposed on a S–N diagram derived from earlier results reported as a part of the European Commission steel rails research project. A best fit curve following an exponential function is derived to describe the load deflection behavior of the weld under the slow bend testing conditions. It is shown that a single component of the equation defining the best fit curve is the factor controlling the scattering in the non-linear part of the load deflection curve, and hence control of this parameter can also be used to impart consistency to the welding process.     

An experimental and numerical investigation on tyre impact

A key issue in the design of tyres is their capability to sustain intense impact loads. Hence, the development of a reliable experimental data basis is important, against which numerical models can be compared. Experimental data on tyre impact in the open literature is somewhat rare. In this article, a specially design rig was developed for tyre impact tests. It holds the test piece in a given position, allowing a drop mass with a round indenter to hit pressurised tyres with different impact energies. A high-speed camera and a laser velocimeter were used to track the impact event. From the laser measurement it was possible to obtain the impact force and the local indentation. A finite element study was then conducted using material properties from the open literature. By comparing the experimental measurements with the numerical results, it became evident that the model was capable of predicting the major features of the impact of a mass on a tyre. This model is therefore of value for the assessment of the performance of a tyre in extreme cases of mass impact.