Phenol–formaldehyde resins modified by copper nanoparticles

Abstract

Phenol–formaldehyde (PF) resins modified by copper nanoparticles were synthesised by in situ polymerisation process. X-ray diffraction (XRD), transmission electron microscopy (TEM) revealed that nanosized copper particles were well dispersed in the resulting PF resins. The thermal properties of the prepared PF resins were investigated by thermogravimetric analysis (TGA). It was indicated that copper nanoparticles remarkably improved the thermal stability of the PF resins at lower temperature. However, the copper nanoparticles increased the rate of the degradation of the PF resins at the elevated temperature. The toughness and the tribological properties of the friction materials based on the prepared PF resins were also studied. The results showed that copper nanoparticles obviously improved the brittleness and the tribological performances of the friction materials.     

Influence of nano–micrometre powder blends on microstructure and mechanical properties of silicon nitride

Abstract

A well known route to making tough silicon nitride compositions is to control the grain size and aspect ratio distributions. This is usually done by choosing the appropriate powder characteristics, sintering conditions, as well as sintering additives. The effect of hot pressing a blend of nano and micrometre scale silicon nitride powder is explored here. Microstructures and mechanical properties are determined for these hot pressed ceramics and are compared with a reference silicon nitride. Hardness and fracture toughness are determined at room temperature using hardness indents produced by a macro Vickers hardness indenter. Grain size and aspect ratio distributions and their impact on mechanical properties are presented. Blending of nano and micrometre scale powder is shown to result in a refined microstructure with an increase in the area/volume fraction of finer grains. Rising R curves are established for these ceramics demonstrating toughening behaviour. Crack bridging and crack path deviation are identified as possible toughening mechanisms.     

Vibration weld strength data for a poly(phenylene oxide)/polyamide blend

The weldability of a commercial, impact-modified blend of poly(phenylene oxide) and polyamide 6,6 is assessed through 120 Hz vibration welds. Relative weld strengths on the order of 100%, with very high strains to failure, have been demonstrated.     

Transverse Low-Speed Impact Behavior of Adhesively Bonded Similar and Dissimilar Clamped Plates

This study concentrates on the transverse low-speed impact behavior of adhesively bonded similar and dissimilar clamped plates using the three-dimensional explicit finite element method. The contact force and plastic dissipation histories of the adhesively bonded dissimilar plates, such as aluminum–aluminum (Al–Al), aluminum–steel (Al–St), steel–aluminum (St–Al) and steel–steel (St–St) layered structures, were studied for different values of the impactor mass, radius and velocity (impact energies). The residual plastic strains in both adhesive layer and plates increased with increasing impact energies. The impactor radius had only a minor effect on the contact force histories for all configurations. The peak transverse deflection in the impact region was maximal in Al–Al, decreased in Al–St, St–Al plates and became minimal in St–St bonded plates. Impact effect was evident in the back plates of all four configurations. Al–Al plates dissipated impact energy as much as the adhesive layer, whereas the adhesive layer rather than plates absorbed the impact energy in Al–St, St–Al and St–St bonded plates and this state became evident in the St–St bonded plates. The number and locations of the steel plates considerably affected impact force history, impact time as well as the plastic dissipation level; thus, the contact force increased, the contact time shortened and the dissipated energy decreased. As the impact energy was increased the impact period got longer. Damage areas in the adhesive layer were minimal in Al–Al bonded plates but maximal in St–St bonded plates.     

Fabrication of Novel Superhydrophobic Surfaces and Droplet Bouncing Behavior — Part 2: Water Droplet Impact Experiment on Superhydrophobic Surfaces Constructed Using ZnO Nanoparticles

When a liquid droplet impacts a solid surface, it spreads up to a point and the kinetic energy is dissipated by viscosity, collision and surface energy during the process. The droplet can retract if the energy dissipation during the impact process which is only partly governed by surface properties is not too large. Otherwise, the droplet would stick to the surface or break into smaller droplets. In this second part, we introduced contact angle hysteresis (CAH) and studied the impact behavior between a water droplet and a superhydrophobic surface both theoretically and experimentally. On our superhydrophobic surface, the contact angle is about 155° , so the kinetic energy of the droplet can be largely transferred to surface energy. Thus, under certain conditions, the droplet can fully bounce. The impact behavior of normal impact was analyzed theoretically. The critical falling heights for rebound (CFHR) were investigated on constructed ZnO–PDMS superhydrophobic surface in both normal and oblique impact conditions, and CFHR was found to increase with the increase of tilt angle. This shows that the normal Weber number (We _n ) is the major factor governing the rebound, while the tangential Weber number (We _t ) also has effect on the phenomenon. Compared to the energy dissipated by collision and viscosity, the influence of surface properties is relatively small. The adhesion number (N _a ) is the parameter determining the energy dissipated by surface tension and N _a has direct relation with contact angle (CA) and CAH.     

Changes in toughness at low oxygen concentrations in steel weld metals

Abstract

Oxides in steel weld metals can initiate fracture or can improve toughness by influencing the development of beneficial microstructures. In this work, the authors conducted experiments in which the oxygen concentration was varied from 20 to 560 ppmw (parts per million by weight) in weld metals with tensile strength in the range 580–780 MPa. It is demonstrated that low and medium strength weld metals benefit from oxides up to a concentration of ～200 ppmw as consistent with previous research, because acicular ferrite is stimulated in the microstructure. By contrast, oxides are detrimental to the toughness of high strength weld deposits at low oxygen concentrations under 140 ppmw, because the microstructure remains a predominantly martensite and the oxides simply serve to nucleate fracture. In high strength weld metal, therefore, good toughness is achieved even at low oxygen concentration of 20 ppmw O.     

Superconducting Bi(2223) thick film on Ba2HoNbO6: a new perovskite ceramic substrate

Abstract

Barium holmium niobate Ba₂HoNbO₆ (BHNO) has been developed as a new substrate for (Bi,Pb)₂Sr₂Ca₂Cu₃O_x (Bi(2223)) superconductor film. Ba₂HoNbO₆ has a cubic perovskite structure with lattice constant a = 8·26 Å. The dielectric constant and loss factor of this material are in a range suitable for its use as a substrate for microwave applications. The Bi(2223) superconductor shows no detectable chemical reaction with BHNO, even under extreme processing conditions. Dip coated Bi(2223) thick film on Ba₂HoNbO₆ substrate had T _c(0) of 109 K and current density of around 4 × 10³ A cm ^{- 2} at 77 K and in zero magnetic field.     

Thermal shock behaviour of mullite–cordierite refractory materials

Abstract

The characterisation of thermal shock damage in cordierite–mullite refractory plates used as substrates in fast firing of porcelain whiteware has been investigated. Two different refractory compositions (termed REFO and CONC), characterised by different silica to alumina ratios, were studied. Thermal shock damage was induced in as received samples by water quenching tests from 1250°C. Thermal and mechanical properties were measured at room temperature by means of standard techniques and then the thermal shock resistance parameter R was calculated. The fracture toughness of selected samples was measured before and after thermal shock by the chevron notched specimen technique. The reliability of this technique for evaluation of small differences in fracture toughness after a given number of thermal shock cycles was investigated. The suitability of K _Ic measurements by the chevron notched specimen technique to characterise the development of thermal shock damage in refractory materials was proved in this investigation.     

Impact properties of sintered and wrought 17–4 PH stainless steel

Abstract

Charpy V notch (CVN) impact testing was conducted on full size and subsize specimens of sintered and wrought 17–4 PH stainless steel (17–4 PH SS) in the as sintered and H900 heat treated conditions. Test geometries correspond to the American Society for Testing and Materials (ASTM) and Metal Powder Industries Federation (MPIF) impact testing standards. Merits of a notched specimen compared with an unnotched specimen were analysed for both the wrought and sintered materials. The notched ASTM standard bars had a lower coefficient of variance for impact energy than the unnotched MPIF standard bars and displayed greater toughness. Porosity and grain size have a detrimental synergistic effect on impact toughness for the sintered material. Following a discussion about the differences in the wrought and sintered microstructures, it is recommended that impact testing of the injection moulded and sintered specimens should be evaluated according to the ASTM test specifications.     

Mode I quasi–static and fatigue delamination characterisation of polymer composites for wind turbine blade applications

Abstract

Ambitious electricity generation targets from renewable sources set by many governments have lead to the rapid growth of the wind energy industry over the last two decades. The need for larger wind turbine blades for increasing energy generation has considerably increased the demand and use of high performance composites in wind turbine applications, mainly in blades. A common type of failure in composite materials is delamination of adjacent layers, which can occur either due to manufacturing inconsistencies or due to in service loads. Understanding and characterising delamination is very important in order to implement damage tolerant design methodologies. The present research work focuses on the assessment of the delamination behaviour of composites for wind turbine applications. Several composite systems were tested and their fracture toughness and fatigue delamination propagation behaviour under mode I (peeling) loading conditions were evaluated. Quasi–static tests were performed and delamination initiation values were evaluated. Fatigue delamination growth rate curves (da/dN versus G _Imax) were also produced. The carbon/epoxy and glass/epoxy material systems tested were compared in terms of resin type, fibre type and interfacial characteristics.