Advanced Materials Research Vols. 41-42

Abstract: YAG nanopowders were synthesized by a co-precipitation method using ammonium hydrocarbonate and ammonia water as the precipitants respectively. The influences of precipitants on chemical compositions, phase transformation and sinterability of the prepared powders, and transmittance of the vacuum-sintered YAG ceramics were studied. The sinterability of powders synthesized using ammonium hydrocarbonate as precipitant is better than that with ammonia water. Pure YAG phase can be obtained by calcining the hydrate precursor at 1200°C, while some impurity phases exist when calcining the carbonate precursor at the same temperature. Transparent YAG ceramics were fabricated by vacuum sintering at 1700°C for 5 h using the YAG nanopowders, and their in-line transmittance is about 60% in the visible light range.

Abstract: Knowledge of the tension softening process of concrete is essential to understand fracture mechanism, further to analyze fracture behaviour, and further to evaluate properties of concrete. For the last eight years, many different tests on uniaxial tension with elimination of secondary flexure were performed in Tohoku Institute of Technology. The paper is dedicated to predict tension softening curve of concrete by using artificial neural networks (ANNs) based on experimental data of five different mixtures of concrete (including High Performance Concrete). It is an advantage to predict a proper tension softening curve without performing uniaxial tension tests. Several artificial neural networks with different architectures (with various hidden neurons and layers) were studied using software - Statistica Neural Network. In order to evaluate the prediction accuracy, tension softening curve and other fracture parameters were predicted for each mix from the other four mixes and compared with the omitted data of the relevant mix. High accuracy was obtained in the all predicted tension softening curves and the fracture parameters were also well predicted.

Abstract: Pattern competition and selection of strain localization were observed in rocks under uniaxial compression. The localization may be the trigger mechanism and an effective precursor of eventual rupture in brittle media. It is found that usually two high strain zones form before the eventual rupture. The rapidly increasing strain and strain rate within one of the high strain zones will lead to the eventual rupture of the specimen, and in the meantime, the strain and strain rate in the other high strain zone decrease rapidly. The digital speckle correlation method (DSCM) was used to measure the surface deformation fields.

Abstract: The microstructural heterogeneity and stress fluctuation play important roles in the failure process of brittle materials. In this paper, a generalized driven nonlinear threshold model with stress fluctuation is presented to study the effects of microstructural heterogeneity on continuum damage evolution. As an illustration, the failure process of cement material under explosive loading is analyzed using the model. The result agrees well with the experimental one, which proves the efficiency of the model.

Abstract: We describe the design and construction about the Ultrasonic method to determine the defects in concrete structure. The wave velocity and its energy are different when it transfers in the concrete material with various defects. The defects can then be detected according to the relative wave velocity and energy variations in concrete material. In the present paper, two methods contain both the wavelet analysis and the nerve network used to determine the relative wave energy change in concrete, and then we will evaluate the defects in material by energy change. The result shows that the present method can give an accurate measurement for the defects in concrete structure.

Abstract: In this study the creep behaviour and adhesion characteristics of hybrid sol-gel silica-based coatings on copper substrates was examined. Sol-gel technology was used to synthesize the organically modified silanes using mixtures of tetraethoxysilane and glycidoxypropyltrimethoxysilane precursors. The creep properties and adhesion behaviour of the coatings were assessed using nanoindentation and microtensile testing, respectively. The link between film structure and creep behaviour was explored. It is shown that the creep response of the coatings is influenced dramatically by the introduction and quantity of the organic substituent.

Abstract: Natural fiber reinforced polypropylene composites (NF/PP) have attracted a lot of attention because of their light weight, good mechanical properties, recyclable and environmental friendly features. This work has successfully fabricated ramie fiber reinforced polypropylene composites (RF/PP) with a hybrid method of melt-blending and injection molding. Different RF/PP eco-materials have been fabricated by varying the fiber length, fiber content and way of fiber pre-treatment. This paper studied the mechanical properties of the fabricated RF/PP composites in depth by investigating the mechanical behaviors of RF/PP and microstructures of the ruptured surfaces. The results show that the increases of fiber length and fiber content can improve the tensile strength, flexural strength and compression strength apparently, but result in negative influences on the impact strength and elongation behaviors of RF/PP composites. The optimal addition amount of ramie fiber is around 20 wt%. The pre-treatment of ramie fiber in 10%~15% NaOH is good to the mechanical properties of RF/PP. The fiber length can be varied in the range of 3-8 mm. It is expected that the fabricated RF/PP composites can be applied to automobile industry as environmental friendly eco-materials.

Abstract: Epoxy composites reinforced with recycled cellulose fibre (RCF) have been synthesized and characterized. The reinforcement by RCF has resulted in a significant increase in the strain at break, fracture toughness and impact toughness but moderate increase in flexural strength and flexural modulus. The effect of seawater soaking on the flexural and impact properties has also been investigated. The micromechanisms of toughening and crack-tip failure processes are identified and discussed in the light of observed microstructures from in-situ and ex-situ fracture.

Abstract: The microstructure (i.e., fibre volume fraction, void content, and fibre misalignment) of unidirectional carbon fibre-reinforced polymer (CFRP) composites was optimised by controlling several parameters during manufacture, namely: (i) compressive pressure (0.25~1.25 MPa, in steps of 0.25 MPa), (ii) vacuum pressure (−0.15, −0.20, −0.30, −0.45, and −0.65 MPa), and (iii) holding temperature (100~140 oC, in steps of 10 oC), applied during autoclave curing with the holding time being 30 minutes for all specimens. Optical micrographs captured from cross-sectional, through-the thickness areas, and in-plane areas of the resulting composites were evaluated and analysed in order to describe their microstructural characteristics.

Abstract: The hardness, wear rates, phase structure and morphologies of DC(direct current) and PC(pulse current )electrodeposited Ni-W-P-SiC, RE-Ni-W-P-SiC, RE-Ni-W-P-SiC-MoS2 and RENi- W-P-SiC-PTFE composite coatings are studied. The results indicate that the hardness of pulse composite coatings is higher than that of DC composite coatings, but the hardness of RE-Ni-W-PSiC- PTFE composite coating is lower. The hardness of the four kinds of composite coatings increases with the rise of heat treatment temperature and reaches the highest value at 400°C, thereafter, the hardness begins to decrease. The hardness of RE-Ni-W-P-SiC composite coating is the highest when duty cycle is at 0.6 and 0.8 and pulse frequency is at 50Hz and the hardness of RE-Ni-W-P-SiC composite coatings at 0.8 is higher than that at 0.6; the wear rates of Ni-W-P-SiC, RE-Ni-W-P-SiC, and RE-Ni-W-P-SiC-PTFE pulse composite coatings are lower than that of DC composite coatings and the wear rates of RE-Ni-W-P-SiC-MoS2 and RE-Ni-W-P-SiC-PTFE composite coatings are the lowest. Ni-W-P-SiC and RE-Ni-W-P-SiC pulse composite coatings are amorphous, and RE-Ni-W-P-SiC-MoS2 pulse composite coating is mixture, but the RE-Ni-W-PSiC- PTFE composite coating is crystal as–deposited. The crystalline grain size of PC composite coatings is smaller than that of DC composite coatings, and the addition of rare earth into the coatings can make crystalline grains become fine, all kinds of grains in the coatings distribute equably and there are not cracks on the surface and in the sections.