Applied Mechanics and Materials Vols. 325-326

Abstract: PEEK based composites have been increasingly employed as biomaterials due to its excellent biological characteristics. In this paper, the biocompatibility, bioactivity, bio-tribology and biomechanics of PEEK composites were investigated. The results showed that PEEK possesses excellent cellular and blood compatibility. The bioactivity of PEEK could be improved by various techniques such as plasma treatment, surface grafting, surface deposition and addition of bioactive glass ceramic in the PEEK matrix. The results of bio-tribology showed that the biotribological properties of PEEK based composites could be comparable with that of traditional artificial joint materials such as UHMWPE. It is even superior to UHMWPE under certain conditions. The biomechanical properties of PEEK composites showed that they can improve the initial stability, reduce the stress shielding and improve bonding strength between bone and implant after replacement, while they are compared with traditional implants such as stainless steel, titanium alloy and Co-Cr-Mo alloy.

Abstract: This paper presents the concept of a compact hybrid sound absorber, based on a combined approach for sound absorption. A flexible micro-perforated panel (MPP) is used as the passive sound absorber for mid and high frequencies and a piezoelectric patch as the active control actuator for low frequency. The volume of this new absorber is highly reduced compare to conventional hybrid systems which employ porous layer as passive part and loudspeaker as active part. The vibration effect of the MPP in the hybrid system is also considered. Theoretical and experimental results show that the flexible MPP has the potential to dissipate more energy and can be utilized to improve absorption performance of the hybrid system by appropriately selecting its parameters.

Abstract: To extend the stable combustion range of micro-combustor, a heat-recirculating-type planar micro-combustor fitted with a bluff-body was proposed in the present work. Numerical simulation on CH₄/air premixed combustion in this combustor was performed and the stable combustion range was determined, which showed that the blow-off limit increases with the equivalence ratio and the lower flammability limit was extended. Effect of the equivalence ratio and inlet velocity on combustion efficiency and maximum temperature were investigated. The numerical results showed that combustion efficiencies were higher than 99%, and the maximum temperatures were larger than the corresponding adiabatic flame temperature due to the excess enthalpy combustion effect. However, flashback emerged when the inlet velocity was too small and the equivalence ratio is relatively high.

Abstract: Magnesium alloys exhibit poor formability at room temperature because of their hexagonal close packed (hcp) structure. The grain refinement can improve its ductility and formability. Friction stir processing (FSP) is an emerging solid state surface modification technique that can produce homogeneous microstructure with fine-grains in a single pass. The effect of friction stir processing variables that can affect tensile strength and formability of magnesium AZ 31B alloy are studied. The formability of friction stir processed sheet was studied by limiting dome height (LDH) test in plane-strain deformation condition. The results indicate that the tensile properties and formability are improved by friction stir processing. The objective of the present work is to establish randomisation of texture to increase work hardening exponent by favourably orienting a large number of grains (texture) in AZ31 alloy to improve its stretch formability by promoting additional straining in thickness direction. Keywords: Friction stir processing, LDH, Formability, etc.

Abstract: In this theoretical study, based on Trescas yield criterion and its associated flow rule, the elastic deformation of a centrally heated compound cylinder with fixed ends is investigated analytically by taking into consideration not only the geometrical but also the material parameters such as yield strength, modulus of elasticity, Poissons ratio, thermal conductivity and coefficient of thermal expansion. These material parameters are assumed to be independent of the temperature. The compound cylinder is assumed to be very long such that axisymmetric condition exists. Both of the constituent materials of the two layers are supposed to be elastic-perfectly plastic materials. There is heat generation in the interior solid cylinder but no heat generation in the outer hollow cylinder. Both of the cylinders are assumed to be bounded perfectly at the interface. Elastic stress analysis is performed to prevent yield in the compound cylinder. Keywords: Compound cylinder, elastic stress analysis, thermal stress, yield strength.

Abstract: Composite in aircraft structures has become increasingly important and should represent approximately 50% in mass till 2012. During the structure assembly, in aerospace centres of production there are used pneumatic positive feed units (also called automatic drilling units). They are manually positioned on specific grids to drill the panels of structure (assemblies of composite materials, aluminium and titanium). This article compares vibration-assisted drilling and non-vibratory drilling and presents the advantages of using vibrations in the process. The conclusions will show the results obtained and the developments to be carried out in an immediate future. Keywords: multi-layer material, vibration assisted drilling, Campbell diagram.

Abstract: Polymer matrix composites, particularly carbon fiber reinforced polymers (CFRPs) are widely used in various high technology industries, including aerospace, automotive and wind energy. Normally, when CFRPs are cured to near net shape, finishing operations such as trimming, milling or drilling are used to remove excess materials. The quality of these finishing operations is highly crucial at the level of final assembly. The present research aims to study the effect of cutting tool wear on the resulting quality for the trimming process of high performance CFRP laminates, in the aerospace field. In terms of quality parameters, the study focuses on surface roughness and material integrity (uncut fibers, fiber pull-out, delamination or thermal damage of the matrix), which could jeopardize the mechanical performance of the components. In this study, a 3/8 inch diameter CVD diamond coated carbide tool with six straight flutes was used to trim 24-ply carbon fiber laminates. Cutting speeds ranging from 200 m/min to 400 m/min and feed rates ranging from 1524 mm/min to 4064 mm/min were used in the experiments. The results obtained using a scanning electron microscope (SEM) showed increasing defect rates with increased tool wear. The worst surface integrity, including matrix cracking, fiber pull-out and empty holes, was also observed for plies oriented at -45 degrees. For the surface finish, it was observed that for the studied cutting length ranges, an increase in tool wear resulted in a decrease in surface roughness. Regarding tool wear, a lower rate was observed at lower feed rates and higher cutting speeds, while a higher tool wear rate was observed at intermediate values of our feed rate and cutting speed ranges.

Abstract: TiN coating as an interlayer in Ti/TiN/PbO₂ electrode and PbO₂ catalytic layer were fabricated by reactive plasma spray and electro-deposition, respectively. It is shown that because of good effect of the TiN interlayer, the Ti/TiN/PbO₂ electrode exhibits a higher oxygen evolution potential and much improved accelerated life compared with the Ti/PbO₂ electrode.

Abstract: In this paper nanotube TiO₂ coating as an interlayer was produced on Ti substrate and the performances of the Ti/nanotube TiO₂/Sb-SnO₂ electrodes were investigated. It is shown that the microstructure of the nanotubes changes with the anodic oxidation voltage and time, and the introduction of the nanotube TiO₂ in the electrodes gives rise to both the oxygen evolution potential and the accelerated life of the electrodes.