Melin Sahin

Stress Distribution of Post-Core Applications in Maxillary Central Incisors

The purpose of this study was to evaluate the stress distribution in a maxillary central incisor restored with various post–core applications. The study used a three-dimensional finite element method. The tooth was assumed to be endodontically treated with a porcelain crown. Two different sizes of Flexi-post, Cera-post, and Composipost were compared for 200 N palatal and incisal loads. It was determined that, purely from the point of view of strength considerations, core material was determined to be of greater importance than post material or size. Higher elastic moduli of the posts resulted in lower stresses throughout the tooth.

Vibration-based damage identification in beam-like composite laminates by using artificial neural networks

Abstract This paper investigates the effectiveness of the combination of global (changes in natural frequencies) and local (curvature mode shapes) vibration-based analysis data as input for artificial neural networks (ANNs) for location and severity prediction of damage in fibre-reinforced plastic laminates. A finite element analysis tool has been used to obtain the dynamic characteristics of intact and damaged cantilever composite beams for the first three natural modes. Different damage scenarios have been introduced by reducing the local stiffness of the selected elements at different locations along the finite element model of the beam structure. After performing the sensitivity analyses aimed at finding the necessary parameters for the damage detection, different input-output sets have been introduced to various ANNs. In order to check the robustness of the input used in the analysis, random noise has been generated numerically and added to noise-free data during the training of the ANNs. Finally, trained feedforward back-propagation ANNs have been tested using new damage cases and checks have been made for severity and location prediction of the damage.

Deformation and strain measurement techniques for the inspection of damage in works of art

Abstract The engineering techniques used for inspecting structural damage are not widely known in the conservation sector. Techniques are available based on deformation or strain measurement that have the ability to provide quantitative data. This paper reviews currently available techniques, covering point-strain measurements using resistance strain gauges and fibre-optic sensors, as well as full-field optical measurement approaches such as holography, electronic speckle pattern interferometry, photoelastic stress analysis and photogrammetry. The underlying technology of each of the techniques is described for the non-specialist. The relevance of each technique is established from a conservation perspective through accounts of usage. The application of the techniques to a wide range of artwork, including panel paintings, statues, murals and mosaics is described and the results critically reviewed. The paper also provides an insight into possible future applications of the techniques and identifies areas for further investigation.

Assessing the Feasibility of Monitoring the Condition of Historic Tapestries Using Engineering Techniques

The findings of a year-long programme carried out by a multidisciplinary engineering/conservation team are described. A mass-produced textile material that can be used to represent tapestries is identified and mechanical tests are detailed which demonstrate it behaves in a similar way to tapestry. The feasibility of using optical fibre sensors, full-field optical strain measurement techniques and thermography for monitoring tapestry degradation is assessed. The results of preliminary findings are presented and a rationale is developed for in-situ quantitative strain monitoring of tapestries.

Performance evaluation of piezoelectric sensor/actuator on active vibration control of a smart beam

In this paper the performance of a piezoelectric sensor/actuator pair and self-sensing piezoelectric actuator on the investigation of vibration characteristics and active vibration control of a smart beam are presented. The performance of piezoelectric patches on actuation and sensing is evaluated by investigating the vibration characteristics of the smart beam via various excitation mechanisms and transduction systems. For active vibration suppression of the smart beam, robust controllers are designed and experimentally implemented by using a piezoelectric sensor/actuator pair and self-sensing piezoelectric actuator. Finally, experimental results for active control of free and the first-resonance forced vibration of the smart beam are presented.

A Hybrid Morphing Trailing Edge Designed for Camber Change of the Control Surface

In this study, the design and analyses of a novel morphing trailing edge control surface is presented. The developed control surface is intended to be utilized on an Unmanned Aerial Vehicle (UAV). The morphing features of the control surface was obtained by using different compliant materials, which are able to undergo large in-plane deformations. The design also includes the utilization of the composite materials together with conventional aluminum material hence the design is called a hybrid one. The actuation was applied by using various number of small servo actuators located inside the control surface at different locations. During the design, CATIA V5-6R2012 package program was utilized and the structural analyses were conducted with Finite Element Method by using ANSYS® WorkbenchTM v14.0 package program. First, the design and analyses were done for in-vacuo condition and the relevant aerodynamic loading was later considered. The required aerodynamic loads, which were representing the flight conditions of the UAV, were calculated by Computational Fluid Dynamics analyses. The aerodynamic mesh used was generated by Pointwise® V17.2 R2 package program. The SU2 (Stanford University Unstructured) V3.2.1 open source software was also used in the study as the flow solver. The UAV had a baseline wing with NACA6510 airfoil. The required camber and de-camber characteristics were tried to be achieved for various NACA airfoil targets. By conducting a non-linear Finite Element Analysis it was shown that the control surface can successfully undergo both camber and de-camber morphing, both in-vacuo condition and under aerodynamic loading.

Damage detection in a sandwich composite beam using wavelet transforms

There is a growing interest in developing non-destructive damage detection methods for damage assessment of composite structures, especially in the aerospace and marine industries. Although damage detection of composite laminates has been widely investigated, little work has been carried out on sandwich composite configurations. A technique using the Lipschitz exponent, which is estimated by wavelet transforms, as a damage sensitive signal feature is outlined here to identify damage in sandwich composites. It is based on the fact that damage causes singularities to appear in the structure’s dynamic response which can be identified, and its severity estimated, using the Lipschitz exponent. In order to demonstrate this technique, damage in cantilevered fibre reinforced plastic (FRP) sandwich beams is investigated both numerically and experimentally.

Verification of a Finite Element Model of an Unmanned Aerial Vehicle Wing Torque Box via Experimental Modal Testing

In this stud y, the detailed finite element model (FEM) of an unmanned aerial vehicle wing torque box was verified by the experimental modal testing. During the computational studies the free-free boundary conditions were used and the natural frequencies and mode-shapes of the structure were obtained by using the MSC ® Software. The results were then compared with the experimentally obtained resonance frequencies and modeshapes. It was observed that the frequencies were in close agreement having an error within the range of 1.5-3.6%. NOMENCLATURE

Active Vibration Control of a Smart Beam by Using a Spatial Approach

The vibration control is an important and rapidly developing field for lightweight flexible aerospace structures. Those structures may be damaged or become ineffective under the undesired vibrational loads they constantly experience. Hence, they require effective control mechanism to attenuate the vibration levels in order to preserve the structural integrity. The usage of smart materials, as actuators and/or sensors, has become promising research and application area that gives the opportunity to accomplish the reduction of vibration of flexible structures and proves to be an effective active control mechanism.

Design optimization, control and experimental characterization of flapper mechanism with amplified piezo actuator

T alpha (α)-hematite (Fe2O3) nanomaterial is attractive due to its band gap, chemical robustness, availability in the nature and excellent photoelectrochemical (PEC) properties to split water into oxygen and hydrogen. However, the α-Fe2O3 suffers from low conductivity, slow surface kinetic, low carrier diffusion and greater electron-hole combination. The electronic properties such as carrier mobility and diffusion of α-Fe2O3 can be improved through doping, synthesis of composite material or formation of structured films. Recently, 2D-molybdenum disulfide (MoS2) has shown interesting photocatalytic activity due to its bonding, chemical composition, doping and nanoparticles grown on other 2D-film. Recently, our group has studied photoelectrochemical properties of hybrid film of regioregular poly (3-hexylthiophene-2, 5-diyl) (P3HT) with nanodiamond as well as P3HT-MoS2. In the present study, we have studied photoelectrochemical properties of polyhexylthiophene (RRPHTh)-nanodiamond (ND) and α-Fe2O3-MoS2 nanocomposite based electrodes films. The photoelectrochemical properties of α-Fe2O3-MoS2 as n-type and ND-RRPHTh as p-type electrodes in photoelectrochemical cell in various electrodes have been studied. We have obtained 3 to 4 times higher photocurrent and energy conversion efficiencies than the parent electrode based photoelectrochemical cell. We have synthesized nanocomposite α-Fe2O3MoS2 using sol-gel technique. The nanocomposite α-Fe2O3-MoS2 as well as ND-RRPHTh films were characterized using SEM, X-ray diffraction, UV-vis, FTIR and Raman techniques. The electrochemical techniques were used to understand the photocurrent in electrode/electrolyte interface of α-Fe2O3-MoS2 as well as ND-RRPHTh films in both acid base based electrolyte. The α-Fe2O3-MoS2 and ND-RRPHTh electrodes reveal improved production of hydrogen compared to α-Fe2O3 and aluminum doped α-Fe2O3 and MoS2 doped α-Fe2O3 nanostructured films. The band structure has been used to understand the mechanism of photoelectrochemical water splitting in p-n types based photoelectrochemical cell.Thermal degradation of two tung oil based reactive diluents, linseed oil alkyd and different amounts of two reactive diluents having paint formulations were investigated using TGA and DSC under non-isothermal conditions and dynamic nitrogen atmosphere and air. Activation energies were obtanied from Freidman method and Freeman-Carroll method and subsequently the preexponential factor, A, and reaction order,n,for reactive diluents and alkyd were also determined according to general rate equation. From kinetic analysis of the thermal degradation of using TGA, it was founded that thermal degradation of two diluents and alkyd has taken place in one stage but thermal degradation of all paint formulations have taken place in more than two stages. As shown from Freidman method and Freeman-Carroll method, the chemical composition and atmosphere of reactive diluents influenced the thermal degradation. Increasing reactive diluents decreased slightly the thermal stability of linseed oil alkyd.