Key Engineering Materials Vols. 353-358

Abstract: We have developed a novel atomic force microscope (AFM) probe as a highly sensitive sensor and an application of the probe into various mechanical tests for characterizing micro/nanostructures. Using MEMS fabrication technique, we have designed and fabricated rhombus-shaped symmetric AFM probe. Adhesion forces between silicon tip and artificial nano-hair structures of cyclic olefin copolymer (COC) and polypropylene (PP) were measured using the probe with a flat tip. The results exhibited the usual characteristics of force-displacement curves of COC and PP nano-hair structures, in which a pull-off force was detected at the point of unloading. The average adhesion forces of the COC and PP hair structures are about 9.48 μN and 10.67 μN, respectively.

Abstract: The cyclic peptides can self-assemble into β-sheet like antiparallel tubular ensembles through intermolecular hydrogen-bonding interaction. Under the self-assembling effects of the dimer subunits, various aggregate properties may alter with the change of the structure. The relationship between the property and structure of ensembles is extremely important for designing new nanostructures. Molecular mechanics (MM) and molecular dynamics (MD) were employed to investigate the structure and property of single dimer and dimer-ensemble from cyclo-[D-Phe-(1R, 3S)-γ-Acc]3. Results reveal that the single dimer cannot adsorb CHCl3 molecule into its cavity, while the two-dimer ensemble can do. It suggests that the self-assembled cyclic peptide nanotube from the dimer-ensemble may act as the transport channel of CHCl3 molecules.

Abstract: The present study investigates the effect of nitrogen implantation on the surface of pure titanium on the bonding strength of porcelain and titanium. A series of pure titanium specimens are cut and divided into nitrogen implantation group. The TiN is found in the implantation layer. The bending strength of porcelain-titanium is reinforced after titanium is nitrided.

Abstract: In this paper, an overview on nanoindentation and its combination with AFM is presented with regard to current instrument technology and applications on dental and bony tissues. Nanoindentation has been a widely used technique to determine the mechanical properties such as nanohardness and Young’s modulus for nanostructured materials. Especially, atomic force microscopy (AFM) combined with nanoindentation, with the pit positions controlled accurately, become a powerful technique used to measure mechanical properties of materials on the nanoscale, and has been applied to the study of biological hard tissues, such as bone and tooth. Examples will be shown that significantly different nanohardness and modulus in the isolated domains within single enamel, the prisms, interprisms, the surrounding sheaths and the different parts of skeletal bone, could been distinguished, while such information was unable to be obtained by traditional methods of mechanical measurements.

Abstract: Hydroxyapatite (HAP)-forming calcium phosphate cement (CPC), due to the high biocompatibility, easy-to-shape characteristic, and the capacity to self-setting under ambient conditions, has been widely used for the repair of hard tissue defects. To satisfy the different clinical need, some modified CPC, including porous CPC, fast-biodegradable CPC, injectable CPC, water-resistant CPC, and rhBMP-2/CPC, have been designed and fabricated in recent years. This paper attempts to give an overview of different types of CPC that have being developed at the present time. Meanwhile, the application perspective of these modified CPC is also explored.

Abstract: The alternative current field measurement (ACFM) technique is a new non-destructive testing (NDT) method to evaluate the surface flaws, and in contract to other methods it has advantages of non-contacting and non-calibrating. Precise locating and crack length measurement can be easily achieved. But it is rather difficult to measure the crack depth with the complicated mathematic model. Its application is thus limited. On this ground, the swept frequency method is introduced to make up of this shortage. The penetration depth of eddy current that is theoretically different for different operational frequencies is the principle of crack depth measurement of the swept frequency method. By means of measuring the switching-frequency of the characteristic curve, the information of flaw depth is achieved by sweeping frequency. The paper introduced the physical model of ACFM and assayed the errors of measurement. Some methods were introduced to decrease the errors. The crack depth is proportional to the interval of the switching-frequency of flaw and of no-flaw, which is detected at the position of minimum value of Bz.

Abstract: During plant operation, high temperature and high pressure water and steam are flowing at high velocity inside these piping systems. In pipes of power plants, local wall thinning may result from erosion/corrosion(E/C). Therefore, it is important to evaluate the nondestructive characteristics for corroded pipes to maintain the integrity of the secondary piping systems. In this study, the pressure vessel piping with corrosion used during long terms were investigated from the timefrequency analysis method. The damage of piping could be evaluated by ultrasonic parameters such as center frequency and echo waveform. Based on NDE analysis by time-frequency analysis method, it should also be possible to evaluate from various damages and defects in piping members.

Abstract: The bending moment test used by the specimens with partial and circumferential wall thinning was carried out to obtain the AE signal. The time-frequency analysis method for the investigation of the frequency characteristics of the AE signal was applied. The results of the wavelet analysis were compared with those of the bending moment test for the structural integrity of tube. The result of the frequency characteristics by applying wavelet analysis method and dropping ball test was presented similarly to those of bending moment test. It is considered that this simple method with combination of dropping ball test and wavelet analysis is very useful scheme for investigating the structural integrity.

Abstract: Triangular cantilevers are usually used as small force sensors in the transverse direction. Analyzing the effect of a crack on transverse vibration of a triangular cantilever will be of value to users and designers of cantilever deflection force sensors. We present a method for prediction of location and size of a crack in a triangular cantilever beam based on measurement of the natural frequencies in this paper. The crack is modeled as a rotational spring. The beam is treated as two triangular beams connected by a rotational spring at the crack location. Formulae for representing the relation between natural frequencies and the crack details are presented. To detect crack details from experiment results, the plots of the crack stiffness versus its location for any three natural modes can be obtained through the relation equation, and the point of intersection of the three curves gives the crack location. The crack size is then calculated using the relation between its stiffness and size. An example to demonstrate the validity and accuracy of the method is presented.

Abstract: Structural damage often happens in rotating machinery such as steam engines, aircraft engines, and compressors due to the high-speed rotating of the shaft. The most common structural damages in rotating machinery are rotor shaft crack, rotor to stator rub, and bolts looseness and so on. In the present paper, the model based identification method is used to detect single structural damage such as crack, rotor to stator rub, pedestal looseness, and also, coupling fault such as rotor to stator rub and crack, crack and pedestal looseness. Utilizing the characteristic that equivalent loads of rub forces are internal forces, and the equivalent loads of the crack are external moments, the coupling faults of crack and rub-impact and crack and pedestal looseness are analyzed and exampled. The merit of the method is that it is an online diagnosis method, which provides early warning of machine failure. Theoretical simulation and laboratory testing are conducted to validate the method.