The mechanisms of fatigue crack propagation are breifly reviewed in relation to Professor McClintock's contributions to the early development of the field. The most securely established understanding has been obtained for those mechanisms of propagation involving plasticity-inducedgeometrical changes to the crack tip during tensile and compressive straining (the plastic blunting process). The roles of more complex factors in controlling the kinetics of crack propagation,which cause the magnitude of the Paris exponent to exceed 2, remain to be elucidated. Recentlyobtained results revealing the interconnection between the slip behaviour at the crack tip, theplastic blunting process and the dislocation structures present in the material before the crackencounters them are reported.
By using EPR and magnetic susceptibility measurements, the Cr ion distribution in the xCr2O3.(1-x)[70TeO2·25B2O3·5PbO] glasses with 03 mol%, the Cr3+ ions participate in superexchange interactions and are predominantly antiferromagnetically coupled.
Three commercially available phenolic resins are assessed for compatibility with a fibreglass wovenroving reinforcement. Compatibility assessment is based on laminate physical properties f flexuralstrength and modulus in three and four point bending, interlaminar shear strength, and tensilestrength and modulus. The physical properties are also used for assessment of hand laminatedglass/phenolic systems
Low and medium carbon steels were aluminized by the pack aluminizing technique using halideactivated pure-Al and Fe-Al packs. The effect of mixture composition, aluminizing temperatureand time and C content of the steel substrate on the structure and thickness of the aluminidelayer, and on the oxidation resistance was investigated. The optimum oxidation resistance canbe achieved with a low carbon steel substrate when the intermetallic phases Fe3Al and FeAlform the surface of the aluminide layer. In this case, the Al concentration at the surface of thealuminide coating is at least ≥15 wt pct. Formation of high Al concentration phases (FeAl3 andFe2Al5) during aluminizing should be avoided as they tend to embrittle the aluminide layer andreduce its oxidation resistance.
Acrylonitrile-butadiene-Styrene (ABS), with and without calcium carbonate (calcite) particles,was used as the matrix for reinforcement with as-received short-glass fibres (were originallytreated by the manufacturer) and sized short-glass fibres with two amino-silane coupling agents.The calcite particle content is 0, 11.7 and 23.5 vol. pct for the matrices. The glass fiber contentis 0, 10 and 15 vol. pct. The matrix materials and corresponding composites were compoundedusing a twin screw extruder and dumbbell-shaped tensile bars were prepared with an injectionmolding process. The tensile and flexural properties as well as the unnotched and notchedCharpy impact energies of short glass fibre/calcite/ABS composites were studied in this paper.The effects of fibres, fibre surface treatments and particles on these mechanical properties ofthe composites were discussed in detail. An importarit information was obtained, which is thatthe tensile and flexural strengths of hybrid SGF/calcite/ABS composites are the same as thoseof corresponding fibre composites when the ratio of the interfacial adhesion strength betweenparticles and matrix to that between fibres and matrix is higher than certain value. otherwise theformer are lower than the latter.
Two obvious emissions are observed from the ZnS clusters encapsulated in zeolite-Y. The emissionaround 355 nm is sharp and weak, locating at the onset of the absorption edge. The bandaround 535 nm is broad. Strong and Stokes-shifted. Both the two emissions shift to blue andtheir intensities firstly increase then decrease as the loading of ZnS in zeolite-Y or clusters sizedecreases. Through investigation, the former is attributed to the excitonic fluorescence, andthe latter to the trapped luminescence from surface States. The cluster size-dependence of theluminescence may be explained qualitatively by considering both the carrier recombination andthe nonradiative recombination rates. Four peaks appearing in the excitation spectra are assignedto the transitions of 1S-1S, 1S-1P, 1S-1D and sudsce state, respectively. The excitation spectraof the clusters do not coincide with their absorption spectra. The states splitted by quantum-sizeconfinement are detected in the excitation spectra, but could not be differentiated in the opticalabsorption spectra due to inhomogeneous broadening. The size-dependence of the excitationspectra is similar to that of the absorption spectra. Both the excitation spectra of excitonicand of trapped emissions are similar, but change in relative intensity and shift in position areobserved.
The mechanism of LiCo1-xNixO2(x=0, 0.5, 1) synthesis from carbonates or hydrates was studied by thermogravimetric analysis and X-ray diffraction to identify the medium and final products. The synthesis process from carbonates can be divided into two steps. Below 300℃cobalt carbonate and/or nickel carbonate decompose forming oxides. Over 300℃ Li2CO3 decomposes and reacts with Co and/or Ni oxides gradually, as a result Co++ and/or Ni++ areoxidized to Co+++ and/or Ni+++, finally LiCo1-xNixO2 forms. The proportion of cobalt tonickel in the starting mixture and atmosphere during synthesis affects the structure of products.LiCo1-xNixO2(x≤0.5) can be synthesized in air or oxygen and characterized by solid solutionof LiCoO2 and LiNiO2. LiNiO2 can be obtained only from hydrates and in oxygen atmosphere.LiNiOz and LiCo0.5Ni0.5O2 have higher first charge capacity than that of LiCoO2. Their discharge capacity reaches a level with that of LiCoO2 and has reasonable reversibility.
In order to reveal the wear mechanism of ceramic cutting tools in real cutting process, a simulationtest was carried out on a block-on-ring tribometer. The investigation was conducted at ambienttemperature to determine the wear behaviour of ceramic/metal tribo-systems under boundarylubrication of water and oil. In this test, the boundary lubrication conditions were provided bydropping oil or water into contact area at a rate of 5 drops per minute (about 0.1 ml/min). Thetested materials are Al2O3-Ti(CN) composite ceramic, Al(purity>99.5 wt pct), Fe(C<0.04 wtpct) and a stainless steel (ASTM 302), which combined into three ceramic/metat frictional pairs.The test results indicate that wear loss of the materials increases with load and speed. Comparedwith unlubricated conditions, the boundary lubrication condition made the materials wear moreserious, which show that lubricating method is very important to a tribo system, and unsuitablelubricating method could increase the wear of materials instead of reducing it. The sudeces ofthe ceramic and the metallic samples were analysed by using a scanning electron microscopewith energy-dispersive X-ray attachment, which indicate that material transfer occurred betweenthe ceramic and metallic materials. The wear mechanism was discussed.
We have theoretically analysed the perimeter-area relation and simulated its application to measuring the fractal dimension of fracture surfaces. It is proved that the fractal dimension Dobtained by slit island method (SIM) is related to the dependence of measured area A(δ) ofthe slit island on yardstick δ. So in some cases, the dimension D obtained by SIM is dependenton yardstick and in other cases independent on yardstick δ. But in all cases, when δ→0 thedimension D obtained by SIM approaches the real fractal dimension (similar dimension) of coastline' of the island. We analysed some experimental data and found some new and interestingcharacteristics of crack propagation in steels.
The hydrolysis rate of Co-bearing ferrous chloride at elevated temperature and the conditionsof separation of Co from Fe have been investigated. The hydrolysis process is comprised of theinterfacial chemical reaction and the intra-grain diffusion. At the stage under the control of theinterfacial chemical reaction, the apparent rate constant k equals to 198.79exp(-80.57/RT). Theeffects of the temperature, the partial pressure ratio of water vapor and the reaction time on theCo recovery and the separation of Co from Fe are examined. The optimum hydrolysis conditionsare determined.
The soft magnetic properties are reported for newly-developed nanocrystalline Fe72.7Cu1Nb1.8-Mo2Si13B9.5 and Fe73Cu1Nb1.5Mo2Si13B9.5. The high frequency core losses of the new alloys are as follows: P3/100K=473 kW·m-3, P2/200K=750 kW·m-3, P2/500K=3400 kW·m-3,P0.5/1000K=680 kW·m-3, which are clearly lower than those of the early-developed Fe-Cu-Nb-Si-B nanocrystalline alloys and the superior power MnZn ferrite H7.4. The dependences ofcore loss on frequency and amplitude magnetic flux density have been analysed. The temperature relations of initial susceptibility have been examined for as-quenched and different annealedFe72.7Cu1Nb1.8Mo2Si13B9.5 alloy and interpreted by using the phenomenological theory.
A modified Miedema model and pattern recognition technique are used to establish the criteriafor the formation of continuous solid solutions in alloy systems, and to study the occurrence ofthe melting temperature minimum of continuous solid solutions.
Porous Al2O3 host/NiO nanocomposites have been prepared by pyrolysis of Ni2(OH)2CO3 inthe nanostructured Al2O3 hosts. Diffuse reflection spectra in the wavelength range of 200 to800 nm were measured. Results show that (1) in each spectrum exist several absorption bandsof nano-NiO. With increasing the pyrolysis temperature from 550 to 1000℃, the numbers ofabsorption bands of NiO increase from 2 to 6 (P1-P6), (2) comparing with optical absorptionbands of single crystal NiO, for porous nanocomposites the P1, P2 and P4 present "blue shift"and the P3, P5 and P6 exhibit "red shift"; (3) when the pyrolysis temperature, Tp, is 550℃, theabsorption bands become so weak that only two bands (P1 and P6) can be observed and inverselywhen Tp=1000℃ all six absorption bands of NiO are strong, (4) for porous Al2O3/NiOnanocomposites prepared by pyrolysis at 1000℃ the PF+ caused by the F+ centers in theAl2O3 host moves towards the short wavelength at first with increasing the doping amount ofNiO from 5 to 50 wt pct and then shifts to the long wavelength with further increasing NiO. Inthis paper, the above phenomena and mechanism of the absorption bands of NiO are discussedin detail.
ER fluid is one of the popular materials used in smart materials and structures (SMS). In thispaper, several ER fluids were synthesized. The static and dynamic mechanic characteristics weremeasured and discussed. The application of ER fluid on a sandwich beam featuring ER fluidapplied to vibration control was investigated.
The behaviour of hydrogen permeation and diffusion in amorphous alloy Ni68Cr7Si8B14Fe3 hasbeen investigated by an ultrahigh vacuum gas permeation technique. A comparison experimentwas carried out between the as-quenched and annealed States (400℃/2h) of the amorphousalloy. The results show that, for both states of the amorphous alloy in the temperature rangeof 200~350℃, the diffusivity and permeability of hydrogen are in agreement with Arrheniusrelationship, there does not exist H-trapping effect, and the activation energies of diffusion andpermeation almost keep the same.
Thermodynamic analysis of the main reactions in the process of thermal decomposition ofAl(OH)3 was made using Temkin-Schwarzman's method and by means of regression analysis.
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