Key Engineering Materials Vols. 345-346

Abstract: The bending property and failure mechanism of sandwich beams were investigated. The multi-walled carbon nanotubes (MWNTs) were used as the reinforcement in the MWNTs/polymer nanocomposites and the epoxy and phenolic resins were used as the matrix. The MWNTs/polymer nanocomposites were used as the core materials of sandwich beams, which had faces made by graphite/epoxy laminates. In experiment, the hot press method was applied to fabricate the MWNTs/polymer nanocomposites and graphite/epoxy laminates. The weight percentage of MWNTs in core materials and the fiber orientation of face laminates were varied to assess their effects on the bending properties of the sandwich beams. The failure mechanism of sandwich beams with two kinds of polymer core materials was investigated. In analysis, the finite element method was used to obtain the bending behavior of the sandwich beams. The numerical results were in good agreement with the experimental ones.

Abstract: Stents are special metallic or polymer endoprostheses of meshed structure and tube shape. Their function is to prevent restenosis in the arteries. Stents can be coated or uncoated. In the expanded part of the artery the chance of restenosis is bigger even without a stent so it is practical to coat the stents. The aim of this work is to present the results of the coating experiments made on the coronary stents. Three types of commercially available polyurethanes were used for these experiments. The coatings were produced by a dipping method. Electro-polished and non-electro-polished metallic sheets and stents were used for these experiments. Contact angle measurements were done to examine the wetting properties of the three different polyurethane coatings. The quality and the changing of the coatings were examined by different methods (stereomicroscope, scanning electron microscope and energy dispersive spectrometry).

Abstract: The reinforcement of high voltage electric power cables is a promising application field of the composite wires. The temperature of the power cables can reach 200-300 °C due to an over-loaded electrical grid. The composite wires have to stand these high temperatures for a long time in the power cables. Long term heat treatments have been done to examine the eligibility of the composite wires. After heat treatment impact test was applied to measure the changes of the mechanical properties of composite wires. With the instrumented impact tester the process of the failure was examined. In this paper the continuous production method of ceramic fibre reinforced metal matrix composite wires and their properties are shown.

Abstract: General thermometers pose difficulty in measuring the actual surface temperature of a micro-area, especially in electronic devices. In the present study, an approach to direct measurement of surface temperature is described, which utilizes the potential of melting point of different chemical reagents. The present technique exhibits a temperature resolution of about 5○C and the measurable maximum temperature of about 200○C. A short comment on the application of the technique to determine the actual surface temperature of small areas in some engineering applications
is also stated.

Abstract: In the present paper we summarize some of our results obtained in the field of magnetic testing of thermal shock fatigue testing of power plant steels. In this work 15Mo3 type ferritic heat resistant steel was investigated. This steel and several similar grades are commonly used in power plants boilers as the material of reheating steam pipelines and pressure vessels. Their typical application temperature is about 500-550 °C. It is commonly accepted that a combined form of mechanical, thermal fatigue and the creep processes causes the long term deterioration of this structural steels. The applied thermal shock fatigue test can model the material degradation due to long term service in high temperature environment. A parallel motion vibrating sample magnetometer, an AC permeameter and a magnetic Barkhausen noise measuring device was used for testing the magnetic properties of the samples and several different magnetic properties were measured to characterize the microstructural processes of the deterioration.

Abstract: The thickness dependency of the temperature image obtained by an infrared thermography was investigated using specimens with three kinds of metal materials of different heat conduction and four kinds of thickness of the specimens. Then, the infrared hybrid method was developed to separate each stress components. However, it contains the influence of heat conduction in the infrared stress measurement method. Therefore, heat conduction error will arise in the infrared hybrid analysis. Then, the new system which corrects the error by an heat conduction inverse analysis was developed. Thereby, the accuracy of the stress intensity factor was able to be raised using heat conduction inverse analysis. Furthermore, the accuracy of hybrid method taking heat conduction into consideration was discussed in comparison with 3-D finite-element analysis and the 2-D infrared hybrid method.

Abstract: In reinforced concrete, when slits take places, the problem arises to control the growth of it. If the critical limit is exceeded due to further load increases, the final strength relies on the integrity of the tight rods. The ability of finding possible defects in these rods and in controlling the relevant growth is therefore of great importance in structural safety at the ultimate stage. In particular, thin reinforced concrete structures draw researchers attention to such a point that several theoretical models have been developed with the aim to reproduce with adequate reliability the real behaviour, taking into consideration the actual deformability, the rising and spreading of fissuring, together with the mechanisms and the loads leading to collapsing. In this work, an experimentation is carried out on a deflect less reinforced concrete specimen, which underwent to rising traction up to the fissuring. The employed investigation technique is an application of the well-known eddy current-based methodology. The magnetic fields maps which were got by this way constitute an electromagnetic representation of the tensional condition of the specimen at the different values of the applied traction, using the above mentioned experimental database, concerns the extraction of inferences to predict and assess the growth of defects in reinforced concrete elements similar to the employed specimen.

Abstract: The leakage of the pipes is a major issue for the safety of industrial structures. However, in many cases, because of their geometrical complexity and inaccessibility, it is difficult to inspect them by the conventional NDE method. A long-range guided wave inspection, thus, is an option to inspect them. A torsional vibration mode, T(0,1) shows many advantages in a long-range guided wave examination of a pipe, such as no dispersion characteristic, no radial displacement and low attenuation. However, it is not easy to fabricate a transducer with an array of piezoelectric elements for generation of torsional vibration mode and even expensive. Recently a magnetostrictive metal strip sensor was used for a generation of the torsional vibration modes in a pipe and this technique has shown several advantages for practical applications. This study investigated the applicability of a long-rang guided ultrasonic method to the detection of artificial notches even in the presence of various foreign objects.

Abstract: Combining vibration testing and numerical method is a potential inverse technique for determining elastic constants of materials because of its nondestructive characteristic, single test, and producing average properties. In order to simplify the modeling processes and to reduce complicated derivation in the numerical method, the combination of finite element analysis and optimum design is adopted in this work. A finite element package, ANSYS, is used to do the modal analysis of the composite plate. A hybrid genetic algorithm, in which a simulated annealing mutation process and adaptive mechanisms are added to the real-parameter genetic algorithm, is used to search the possible elastic constants. After obtaining the natural frequencies of the composite plates from vibration testing, this inverse technique could predict the elastic constants of the composite plate. The inverse technique is verified by comparing with other methods and by determining the elastic constants of aluminum plates, and the excellence of including the hybrid genetic algorithm is proved. The results also indicate that the present technique could obtain very accurate elastic constants of composite plates.

Abstract: A fault diagnosis method based on wavelet and adaptive interference canceling is presented for the identification of a damaged gear tooth. A damaged tooth of a certain gear chain generates impulsive signals that could be informative to fault detections. Many publications are available not only for the impulsive vibration signal analysis but the application of signal processing techniques to the impulsive signal detections. However, most of the studies about the gear fault detection using the impulsive vibration signals of a driving gear chain are limited to the verification of damage existence on a gear pair. Requirements for more advanced method locating damaged tooth in a driving gear chain should be a motivation of further studies. In this work an adaptive interference canceling combined with wavelet method is used for a successful identification of the damaged tooth location. An application of the wavelet technique provides a superior resolution for the damage detection to the traditional frequency spectrum based methods. An analysis and experiment with three pair gear chain show the feasibility of this study yielding a precise location of the damaged gear tooth.