Key Engineering Materials Vols. 334-335

Abstract: Stringer-stiffened plate-like structure is a typical engineering structure and its structural integrity is critical. A guided Lamb wave-based damage identification scheme and an online structural health monitoring (SHM) system with an integrated PZT-sensor network were developed. In the previous studies, the specimens were relatively simple. In this paper, the abovementioned method was extended to the stiffened plate-like structure—a flat plate reinforced by stringer. FE dynamic simulation was applied to investigate the Lamb wave propagation characteristics due to the existence of stringer with the consideration of its material and geometric configurations.

Abstract: Interfacial stress distribution of bonded quarter planes subjected a concentrated force was re-investigated based on Bogy’s solution [1]. It’s found that the characteristic length of the singularity of interface end (δ), varies with the index of stress singularity at interface end from millimeter to nanometer. This is a unique characteristic of stress singularity at interface end. How the characteristic length of the singularity of interface end (δ) influences the initial de-bonding of the interface end is a new question worth to pay attention. It’s found in the photoelasticity experiments that usually the debonding initiated at the interface end with singularity, but as the index of stress singularity, as well as the characteristic length of singularity of interface end, decrease to some extent, the initial debonding moves to an inner point near the interface end. This phenomenon clearly shows the index of stress singularity has obvious influence on the debonding of interface end.

Abstract: Highly-ordered titania nanotube array has been fabricated by a potentiostatic anodization process in acidic fluoride electrolyte. Calcination at high temperature is followed to achieve crystallization from amorphous to anatase phase. The approach of embedding bioactive enzymes inside titania tubule channels has been applied for bioactivation modification of titania/titanium. The electropolymerization process is applied by using conductive pyrrole monomer to achieve surface immobilization of enzymes to improve interfacial connection. Characterizations including field emission scanning electron microscopy, nano-indentation and linear sweep voltammetry measurements have been performed to fully evaluate the surface morphology, nanomechanical and electrochemical properties of this composite. Molecule detection application has been investigated by applying such an enzyme-titania/titanium composite.

Abstract: The effects of component concentrations and addition order of the components, on the final properties of ternary nanocomposites composed of amorphous poly (ethylene terephthalate) matrix, organically modified clay, and an ethylene / methyl acrylate / glycidyl methacrylate (E-MAGMA) terpolymer were studied. All formulations were prepared by melt compounding of the components with a two-step mixing procedure in a corotating twin-screw extruder. Considering the X-Ray Diffraction, SEM, impact and strain at break results, the best sequence of component addition was the one in which PET was first compounded with E-MA-GMA, later this mixture was compounded with the organoclay in a subsequent run. In this mixing order, the polymer-impact modifier matrix mixture prepared in the first extrusion run has higher melt viscosity than pure PET, thus this matrix can apply high shear stresses on the clay particles and delaminate the clay layers resulting in the best mechanical properties.

Abstract: Nano-yttria powder can be synthesized by yttrium citrate-urea precursor, combusted at 600°C in air. The CVD SiC coated on graphite (CVD SiC/Graphite) infiltrated by the yttrium citrate-urea precursor, combusted at of 600°C, and then sintered at 1450°C, the thin yttria film can be achieved. The SEM morphology and EDS result of the thin yttria film show a mass of needle-shaped pining into the CVD SiC layer, which improves the combination of CVD SiC layer and wash yttria coating. Therefore, it is an effective transition layer between CVD SiC coating and wash yttria layer.

Abstract: A number of micromechanical investigations have been performed to predict behaviour of composite interfaces, showing that the detailed behaviour of the material at these interfaces frequently dominates the behaviour of the composite as a whole. The interfacial interaction is an extremely complex process due to continuous evolution of interfacial zones during deformation and this is particularly true for carbon nanotubes since the interfacial interaction is confined to the discrete molecular level. The atomic strain concept based upon Voronoi tessellation allows analysing the molecular structure atom by atom, which may give a unique insight into deformation phenomena operative at molecular level such as interface behaviour in nanocomposites.

Abstract: Mechanical properties of nanoclay/epoxy composites (NC) have been studied by various experimental setups in bulk form recently. Creep mechanism of the NC is an important manufacturing criterion for the aircraft industry. In this paper, nanoindentation was employed to investigate the nano-mechanical creep effects on different wt. % of nanoclay contents in epoxy matrix. Creep behaviors of the nanoclay/epoxy composites with different wt. % of nanoclay contents were modeled by the power-law creep equation. Neglecting the temperature effects on creep, the stress exponents of tested composites were estimated.