Materials selection in mechanical design

A novel materials-selection procedure has been developed and implemented in software. The procedure makes use of Materials Selection Charts: a new way of displaying material property data; and performance indices: combinations of material properties which govern performance. Optimization methods are employed for simultaneous selection of both material and shape.

Comprehensive Property Retrieval and Measurement of Concrete Spalling Using Machine Vision for Post-Earthquake Safety Assessments

Active vibration control (AVC) is a relatively new technology for the mitigation of annoying human-induced vibrations in floors. However, recent technological developments have demonstrated its great potential application in this field. Despite this, when a floor is found to have problematic floor vibrations after construction the unfamiliar technology of AVC is usually avoided in favour of more common techniques, such as Tuned Mass Dampers (TMDs) which have a proven track record of successful application, particularly for footbridges and staircases. This study aims to investigate the advantages and disadvantages that AVC has, when compared with TMDs, for the application of mitigation of pedestrian-induced floor vibrations in offices. Simulations are performed using the results from a finite element model of a typical office layout that has a high vibration response level. The vibration problems on this floor are then alleviated through the use of both AVC and TMDs and the results of each mitigation configuration compared. The results of this study will enable a more informed decision to be made by building owners and structural engineers regarding suitable technologies for reducing floor vibrations.

Mechanical properties of hierarchical lattices

This paper focuses on the stiffness and strength of lattices with multiple hierarchical levels. We examine two-dimensional and three-dimensional lattices with up to three levels of structural hierarchy. At each level, the topology and the orientation of the lattice are prescribed, while the relative density is varied over a defined range. The properties of selected hierarchical lattices are obtained via a multiscale approach applied iteratively at each hierarchical level. The results help to quantify the effect that multiple orders of structural hierarchy produces on stretching and bending dominated lattices. Material charts for the macroscopic stiffness and strength illustrate how the property range of the lattices can expand as subsequent levels of hierarchy are added. The charts help to gain insight into the structural benefit that multiple hierarchies can impart to the macroscopic performance of a lattice. © 2013 Elsevier Ltd. All rights reserved.

Improvement of morphology, structure, and optical properties of GaAs nanowires grown on Si substrates

We investigate vertical and defect-free growth of GaAs nanowires on Si (111) substrates via a vapor-liquid-solid (VLS) growth mechanism with Au catalysts by metal-organic chemical vapor deposition (MOCVD). By using annealed thin GaAs buffer layers on the surface of Si substrates, most nanowires are grown on the substrates straight, following (111) direction; by using two temperature growth, the nanowires were grown free from structural defects, such as twin defects and stacking faults. Systematic experiments about buffer layers indicate that V/III ratio of precursor and growth temperature can affect the morphology and quality of the buffer layers. Especially, heterostructural buffer layers grown with different V/III ratios and temperatures and in-situ post-annealing step are very helpful to grow well arranged, vertical GaAs nanowires on Si substrates. The initial nanowires having some structural defects can be defect-free by two-temperature growth mode with improved optical property, which shows us positive possibility for optoelectronic device application. ©2010 IEEE.

MEMS-based mechanical AGC for oscillator circuits

This paper investigates a nonlinear amplitude saturation behavior in an electrostatically transduced, silicon MEMS disk resonator operating in its secondary elliptical bulk-mode (SEBM) at 3.932 MHz towards its implementation as an all-mechanical automatic gain control (AGC) element. The nonlinear vibration behavior of the SEBM mode is experimentally observed in open-loop testing such that above a threshold small signal drive voltage at a given polarization voltage, the vibration amplitude of the SEBM mode saturates. We also study this nonlinearity in an oscillator circuit designed such that the driving power level at the resonator input can be manually tuned as the circuit operates. The measurements of the voltage amplitudes show a clear transition from the linear to the nonlinear saturation region as the driving power is increased. Short-term frequency stability measurements were also conducted for different v ac and the resulting Allan deviation plots show an improvement in the short-term stability from 1.4 ppb in the linear region to 0.4 ppb in the amplitude saturation region. © 2013 IEEE.

An Improvement on 2× 2 Silicon-on-Insulator Mach-Zehnder Thermo-Optical Switch

An improved 2 ×2 silicon-on-insulator Mach-Zehnder thermo-optical switch is designed and fabricated, which is based on strongly guided multimode interference couplers and single- mode phase-shifting arms. The multimode interference couplers and input/output waveguides are deeply etched to improve coupler performances and coupler-waveguide coupling efficiencies. However, shallow etching is used in the phase-shifting arms to guarantee single-mode property. The strongly guided coupler presents an attractive uniformity about 0. 03 dB and a low propagation loss of -0.6 dB. The 2× 2 switch shows an insertion loss as low as -6.8 dB, where the fiber-waveguide coupling loss of -4.3 dB is included, and the response-time is measured as short as 6.8 μs, which are much better than our previous results.

Improvement of Pt catalyst for soot oxidation using mixed oxide as a support

Catalytic activity of Pt catalysts for soot oxidation was studied using temperature programmed reactions. The activity of Pt loaded over TiO2-SiO2 (Pt/TiO2-SiO2) showed higher activity than other Pt/MOx systems (MOx = TiO2, ZrO2, SiO2, Al2O3. TiO2-ZrO2. TiO2-Al2O3, ZrO2-SiO2, ZrO2-Al2O3, SiO2-Al2O3). The activity was highest when the molar ratio of TiO2/(TiO2 + SiO2) ranged from 0.4 to 0.7. The effect of pretreatment with a gas containing low SO2 concentrations on the activity was compared for Pt/SiO2, Pt/TiO2 and Pt/TiO2-SiO2. In the case of Pt/TiO2-SiO2, the activity was markedly promoted by the pretreatment whereas no variation in the activity was observed for Pt/SiO2. The difference in the behavior towards the SO, pretreatment was attributed to property difference in the supports for sulfate accumulation. The high activity of Pt/TiO2-SiO2 was also confirmed under practical conditions with a diesel engine exhaust using a catalyst-supported diesel particulate filter (DPF). (C) 2003 Elsevier Science B.V. All rights reserved.

Rheology, morphology and mechanical properties of compatibilized poly(vinylidene fluoride) (PVDF)/thermoplastic polyurethane (TPU) blends

Compatibilized blends of poly(vinylidene fluoride) (PVDF) and thermoplastic polyurethane (TPU) were developed using maleated PVDF (PVDF-g-MA). Excellent compatibilization between PVDF and TPU was demonstrated by theological, morphological, and mechanical measurements. The introduction of PVDF-g-MA into the PVDF/TPU blends caused an increase in viscosity and storage modulus. Much finer morphology was clearly observed by SEM. The tensile tests showed that the tensile strength and ultimate elongation achieved a significant improvement with addition of PVDF-g-MA.

Thermal and mechanical properties of poly(butylene terephthalate)/epoxy blends

In this study, melt blends of poly(butylene terephthalate) (PBT) with epoxy resin were characterized by dynamic mechanical analysis, differential scanning calorimetry, tensile testing, Fourier transform infrared spectroscopy, and wide-angle X-ray diffraction. The results indicate that the presence of epoxy resin influenced either the mechanical properties of the PBT/epoxy blends or the crystallization of PBT. The epoxy resin was completely miscible with the PBT matrix. This was beneficial to the improvement of the impact performance of the PBT/epoxy blends.

Structure and mechanical properties of extruded Mg-Gd based alloy sheet

The Mg-8Gd-2Y-1Nd-0.3Zn-0.6Zr (wt.%) alloy sheet was prepared by hot extrusion technique, and the structure and mechanical properties of the extruded alloy were investigated. The results show that the alloy in different states is mainly composed of alpha-Mg solid solution and secondary phases of Mg5RE and Mg24RE5 (RE = Gd, Y and Nd). At aging temperatures from 200 degrees C to 300 degrees C the alloy exhibits obvious age-hardening response. Great improvement of mechanical properties is observed in the peak-aged state alloy (aged at 200 degrees C for 60 h), the ultimate tensile strength (sigma(b)), tensile yield strength (sigma(0.2)) and elongation (epsilon) are 376 MPa, 270 MPa and 14.2% at room temperature (RT), and 206 MPa. 153 MPa and 25.4% at 300 degrees C, respectively, the alloy exhibits high thermal stability.

Facile Synthesis and Assemblies of Flowerlike SnS2 and In3+-Doped SnS2: Hierarchical Structures and Their Enhanced Photocatalytic Property

Novel flowerlike SnS2 and In3+-doped SnS2 hierarchical structures have been successfully synthesized by a simple hydrothermal route using biomolecular L-Cysteine-assisted methods. The L-cysteine plays an important role both as assistant and as sulfur source. Experiments with various parameters indicate that the pH values have a strong effect on the morphology of the assembly. Based on the experiments, a growth mechanical process was proposed. The synthetic samples were characterized by XRD, SEM, TEM (HRTEM), BET measurement, TGA, and XPS in detail.

Influence of Annealing on Microstructure and Mechanical Properties of Isotactic Polypropylene with beta-Phase Nucleating Agent

The microstructure and mechanical properties of beta-nucleated iPP before and after being annealed at different temperatures (90-160 degrees C) have been analyzed, Annealing induced different degrees of variation in fracture toughness of beta-nucleated iPP samples. namely, slight enhancement at relatively low annealing temperatures (< 110 degrees C) and great improvement at moderate temperatures (120-130 degrees C), whereas dramatic deterioration at relatively high temperatures ( > 140 degrees C) has been observed. The variation of fracture toughness of beta-nucleated iPP is observed to be dependent on the content of beta-NA. Experiments, including scanning electronic microscope (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and dynamic mechanical analysis (DMA), are performed to study the variations of microstructures as well as the toughening mechanism of the beta-nucleated iPP after being annealed.

Effect of yttrium-rich misch metal on the microstructures, mechanical properties and corrosion behavior of die cast AZ91 alloy

Die cast AZ91-xYmm (x = 0-0.8 wt.%) magnesium alloys with excellent tensile properties and corrosion resistance behavior were successfully prepared by a simple addition of yttrium-rich misch metal (Ymm) to AZ91. Influences of Ymm on the microstructure, mechanical properties and corrosion behavior of AZ91 were investigated. The results showed that addition of Ymm to die cast AZ91 alloy could re. ne the microstructure including primary alpha-Mg and eutectic beta-Mg17Al12. When the content of Ymm reached 0.8 wt.% a small quantity of Al2Y phase would form. The tensile properties were improved greatly with addition of Ymm to AZ91. The creep rate of the AZ91-Ymm alloys, tested at 150 degrees C/50MPa, was one order of magnitude lower than that of AZ91. When addition of Ymm was more than 0.3 wt.%, the salt-spray corrosion resistance of AZ91-Ymm alloys could be 30-40 times of that of AZ91. The improvement of corrosion resistance with addition of Ymm was confirmed by the results of electrochemical polarization experiments. Mechanism of the improvement of mechanical properties and corrosion behavior caused by Ymm was also discussed.

Effect of substituting cerium-rich mischmetal with lanthanum on microstructure and mechanical properties of die-cast Mg-Al-RE alloys

Die-cast Mg-4Al-4RE-0.4Mn (RE = Ce-rich mischmetal) and Mg-4Al-4La-0.4Mn magnesium alloys were prepared successfully and their microstructure, tensile and creep properties have been investigated. The results show that two binary Al-RE phases, Al11RE3 and Al2RE, are formed along grain boundaries in Mg-4Al-4RE-0.4Mn alloy, while the phase compositions of Mg-4Al-4La-0.4Mn alloy mainly consist of alpha-Mg phase and Al11La3 phase. And in Mg-4Al-4La-0.4Mn alloy the Al11La3 phase occupies a large grain boundary area and grows with complicated morphologies, which is characterized by scanning electron microscopy in detail. Changing the rare earth content of the alloy from Ce-rich mischmetal to lanthanum gives a further improvement in the tensile and creep properties, and the later could be attributed to the better thermal stability of Al11La3 phase in Mg-4Al-4La-0.4Mn alloy than that of Al11RE3 phase in Mg-4Al-4RE-0.4Mn alloy.

Influence of Zn content on the microstructure and mechanical properties of extruded Mg-5Y-4Gd-0.4Zr alloy

Microstructures and mechanical properties of the Mg-5Y-4Gd-xZn-0.4Zr alloys have been investigated. These results show that the Mg-5Y-4Gd-0.5Zn-0.4Zr alloy in the peak-aged condition exhibits the highest tensile strength, and the values of the ultimate tensile strength and yield tensile strength are 370 and 300 MPa, respectively. It is suggested that addition of 0.5% Zn has a great effect on age hardening response. The long periodic stacking structure has been found in these Zn-containing alloys, and the volume fraction of this phase increases with increasing Zn addition. This phase plays an important role in improvement of the mechanical properties, especially for the elongations. The beta' phase precipitates during the ageing process are responsible for the improvement of the mechanical properties of the alloys in the peak-aged condition.