Key Engineering Materials Vols. 334-335

Abstract: This paper describes the effective electromechanical properties of hydroxyapatite-BaTiO3 0-3 composites as a potential bone substitute material. The permittivity, d3j and g3j piezoelectric coefficients are calculated for composites at a range of compositions and connectivities to understand the relationships between composite composition and piezoelectric and dielectric properties. The properties of the composites can be tailored by adjusting the volume fraction and aspect ratio of the BaTiO3 particles and the shape and level of porosity in the hydroxyapatite matrix.

Abstract: A piezoelectric microactuator for minimally invasive surgery procedures was developed using the piezoelectric tube actuator. The tube was fabricated by electrophoretic deposition of a doped PZT powders on the graphite rod substrate and co-sintering. The obtained tube shows maximum strain 0.045% in 31 mode and coercive field 1.5 kV/mm under static condition. Under dynamic condition, bending and longitudinal vibration modes can be identified from impedance spectrum and simulation. Theoretical analysis indicates that the displacement of the two modes depends on the geometry, material property, driving condition and damping conditions. The developed device uses bending mode to create rotation mechanical motion, and longitudinal mode to produce ultrasonic energy to soften and break up the target into fragments.

Abstract: Giant magnetostrictive composites have attracted a great deal of attention by supplementing shortcomings of monolithic Terfenol-D such as brittleness, eddy current loss and formability. Recently, infiltrated Terfenol-D/Epoxy composite has been developed as an alternative composite. This composite was fabricated by an unidirectional solidification of Terfenol-D followed by an infiltration of epoxy. The iron content in composite has been changed in order to control volume fraction of RFe2 phase producing magnetostriction on Terfenol-D/Epoxy composite. The magnetostriction of both as-grown and infiltrated Terfenol-D/Epoxy composite was measured to confirm the effects of eutectic phase and heat treatment on magnetostriction. The enhancement of magnetostriction of Terfenol-D/Epoxy composite was mostly contributed by the eutectic phase through the hindering of movement and rotation of domain walls. The magnetostriction modelling of Terfenol-D/Epoxy composite was suggested, based on the change of texture and elastic modulus. The suggested model was in good agreements with the experimental results on the measurement of magnetostriction of Terfenol-D/Epoxy composite.

Abstract: Micromagnetic simulation was carried out to investigate the behavior of ferromagnetic materials at a very small length scale, at which the materials usually exhibit different properties compared with those of the corresponding bulk materials. By solving the time and spatial dependent Landau-Lifshitz-Gilbert (LLG) equation in reciprocal space using fast Fourier transformation (FFT) technique, the equilibrium magnetization state was, thus, achieved. The hysteresis loops were also simulated, from which the relation of coercivity and characteristic length was established. Besides, the effect of external stress on coercivity was also taken into consideration. The results showed that at such length scales the external stress strongly affected the magnetic behavior of ferromagnetic materials.

Abstract: Most structural materials existing in nature take the form of composite. After centuries’ evolution, these materials gain highly optimized microstructures and performances. In this work, a kind of natural biomaterial, shinbone, is observed with a scanning electron microscope (SEM). The observation result shows that the bone is a bioceramic composite consisting of hydroxyapatite layers and collagen matrix. The observation also shows that the hydroxyapatite layers are composed of hydroxyapatite sheets. The hydroxyapatite sheets are of thin and long shape and parallel distribution along the orientation of the maximum main stress of the bone. The shape and distribution of the hydroxyapatite sheets may endow the bone with favorable fracture toughness, which is analyzed and illuminated based a representational model of the hydroxyapatite sheets and the idea of maximum pullout force.

Abstract: A comparative study was presented to demonstrate the clear influence of the different buffer layer (TiN and TiO2) on the HA film. In this study, magnetron sputtering was applied for different film deposition. Nano-indentation was used to examine the mechanical properties of the HA film on both TiN and TiO2 buffer layers. It is found that HA film on TiN buffer layer is harder and the HA film on TiO2 buffers is more rigid. Further more, the simulated body fluid (SBF) soaking test was selected to investigate the properties of the HA/TiN and HA/TiO2 films in the physiological media. The obvious delamination was observed on the surface of HA film on TiN buffer layer, while the surface morphology of HA film on TiO2 buffer layer remained nearly unchanged. The result indicated that TiO2 buffer layer shows a better interfacial bonding to the HA film.

Abstract: The authors developed a damage detection system that generates ultrasonic waves with a piezo-ceramic actuator and receives them by a fiber Bragg grating (FBG) sensor. In this research, this system was applied to evaluate debonding progress in CFRP skin/stringer bonded structures. FBG sensors were bonded on the stringer or embedded in the adhesive layer. Then, ultrasonic wave at 300kHz was propagated through the debonded region, and the wavelet transform was applied to the received waveform. After that, a new damage index
and a correlation coefficient were calculated from the distribution of the wavelet transform coefficient. As a result, the damage index increased and the correlation coefficient decreased with an increase in the debonded area. Hence the length of the debonding between the skin and the stringer could be well evaluated.

Abstract: A series of digital frequency filters (DFFs) were designed to screen diverse noises and the spectrographic analysis was conducted to isolate complex boundary reflection, which obscures the damage-induced signals. The scale-averaged wavelet power (SAP) technique was applied to enhance the measurement accuracy of Time of Flight (TOF). As an example, the propagation characteristics of elastic wave in a structural beam of square cross-section were analyzed using such an approach and verified experimentally and numerically, with the consideration of the complicated wave scatter caused by the non-ignorable section dimensions.

Abstract: Fine nickel powders have been prepared by chemical reduction between nickel acetate and alcohol under solvothermal conditions. The effect of adding surfactant and varying solvent on the particle size of the as-synthesized nickel powders have been explored. SEM, XRD and TG were employed to characterize the size, morphology, crystalline structure and the thermal stability of the as-synthesized nickel powders. It is revealed that the FCC-structured nickel powders are of uniform spherical shape with good crystallinity and thermal stability. Typically, nickel powders with an average size of 300 nm were obtained at 200°C for 8 h using 0.04 mol/L solution of Ni(CH3COO)2·4H2O in n-butyl alcohol under solvothermal conditions.

Abstract: A method based on entropy-based criteria is present to choose the optimal decomposition of Wavelet Packets Analysis (WPA) for damage detection in composite materials. The structural damage indexes constructed based on energy spectrum variation of the structural vibration responses decomposed using WPA before and after the occurrence of structural damage usually generate a complete binary tree to calculate its elements. Date mining is carried out in this paper by adoption entropy as the criteria to choose the optimal decomposition tree. In the decomposition process, only the sub-signals which contain main information of the original signal are decomposed to generate next level sub-signals. New damage index is constructed based on the optimal decomposition. Then the dimension of the damage index is reduced while still keeping its sensitive to damage. Whether Artificial Neural Network (ANN) or genetic algorithm (GA) is used in the further process of telling structural damage status from damage index, this reduction will make remarkable time saving.