Key Engineering Materials Vol. 633

Abstract: The deformation performance of concrete with steel slag aggregate and scrap tire particles was reviewed. The addition of steel slag makes the volume of concrete present expansion effect which can improve the early-age plastic cracking performance of concrete. The expansion of steel slag concrete and shrinkage of concrete by partially substitution of rubber colloidal particles showed obvious decrease. So the scrap tire particles modified steel slag concrete with satisfactory volume deformation, the theory is that the stress relaxation in shrinkage process of the concrete with scrap tire particles. The exploration of steel slag concrete with scrap tire particles expansion inhibition and deformation micromechanics mechanism is important for the research and application of concrete with steel slag and scrap tire particles.

Abstract: In order to improve the corrosion resistance and bioactivity of magnesium alloy coated by ultrasound micro-arc oxidation (UMAO), different content of n-TiO₂ was added into silicate electrolyte. Electrochemical corrosion and simulated body fluid (SBF) soaking were conducted, and the surface morphology, phase structure and composition also were analyzed. The results indicated that Ecorr and Icorr of UMAO biocoatings with n-TiO₂ increased and decreased an order of magnitude with increase of n-TiO₂, respectively. The corrosion resistance of coatings with adding 4.8g/L n-TiO₂ into electrolyte was the best. After soaking in SBF, the samples increased loose weight firstly and then increased weight to form Mg₃Ca (CO₃)₄, Mg1₀Cl (OH)₁₈·5H₂O and Na₄Mg₂(PO₄) ·2H₂O new phases and Mg, MgO, MgSiO₃ were still exit, which showed that good bioactivity of the UMAO coatings with n-TiO₂.

Abstract: SrO–BaO–Nb₂O₅–B₂O₃ system glass-ceramics with Gd₂O₃/BaF₂ addition have been prepared by controlled crystallization method. The effect of Gd₂O₃/BaF₂ addition on the phase evolution, dielectric properties and energy storage properties has been investigated. The addition of Gd₂O₃/BaF₂ to the glass-ceramics changes the dielectric property and energy storage density. The glass-ceramics with 0.5 mol% Gd₂O₃ and 4.5mol% BaF₂ heat treated at 850°C/3h possesses a dielectric constant of 125, a breakdown strength of 1055 kV/mm and energy storage density of 6.16J/cm³, which are promising materials for high energy storage density dielectrics.

Abstract: For study the damage characteristic of the mullite heat storage ceramic under thermal shock condition, mechanical properties of mullite have been investigated. Under the different cooling mediums (room temperature water, boiling water, air), single and five cycles thermal shock conditions, The article studied the variation of flexural strength and fracture toughness along with temperature. The result show that with the increase of heat transfer coefficient of cooling medium, the bending strength of ceramic decreased. In the 600°C,the ceramic have a maximum bending strength and a minimum fracture toughness. The fracture toughness of precrack specimen is lower than that of non-precrack specimen on the whole. Both Precrack ceramic and non-precrack ceramic have a maximum fracture toughness at 400°C. The study of this paper provides a theoretical basis for the better predicting fracture damage and service life of heat storage ceramic.

Abstract: The development of concrete deformation is determined by the time depended distribution of temperature and humidity in concrete resulting form the variation of temperature and humidity and also their coupling effect, which also greatly influences the durability and service life of concrete. Therefore, the coupling effect of temperature-humidity variation must be considered when study the volume deformation of concrete. The studies related to the hygro-thermal deformation of concrete were reviewed and summarized, which included the research status of concrete deformation resulting from temperature and humidity, the coupled heat and moisture transfer model and the numerical simulation method. The research status and existing problems of hygro-thermal deformation of concrete were also analyzed in detail for promoting the investigation on the mechanism of volume deformation cracking and the durability of concrete material, which will benefit to the deformation prediction and crack control technology of engineering structure. Periodically variation of environmental temperature and humidity can be used to describe the seasonal or diurnal temperature-humidity changing of concrete materials and structures in the construction and service period of concrete structure. Consideration should also be given to "fatigue effect of heat and moisture stress" when study the deformation evolution and the damage mechanism of concrete crack.

Abstract: The plane surface energy of the mullite crystals (001), (010), (100) and (-100) is comparative calculated by using first-principles plane-wave pseudopotential method and the open hydrothermal system preparing mullite phase crystal test conditions. Also the plane growth habits can be predicted according to the results. The result shows that: the descending order of the mullite crystal surface energy is: E₍₀₀₁₎ > E₍₀₁₀₎ > E_(-100) > E₍₁₀₀₎. On the basis of Cune-Woolf principle, the surface energy of mullite crystals (001) surface is the maximum and growth rate is the fastest. Thus the (001) crystal face is growth surface habits of mullite phase crystal. Crystal growth morphology mostly extends in one direction.

Abstract: This paper studied the problems met in the quantitative analysis of synthetic Mullite phase,which was based on the analysis of various typical Mullite composite scheme. A method of quantitative analysis of Mullite phase (excluding amorphous phase SiO2) by use X-ray diffraction was discussed. The error of the analysis can be verified by chemical analysis of Al2O3 content. The method can effectively improve the accuracy of quantitative analysis of the Mullite phase, the error analysis is less than 3%. The error range can meet the accuracy requirement of Mullite content in the production.Studies show that this method is preliminarily solved how to quantitative the content of mullite phase by X-ray diffraction method .

Abstract: Evaluation of the mechanical properties at ultra-high temperatures for ceramic composites is necessary and important for the safety of designing the ceramic components. In this work, a new and novel test method named as local ultra-high temperature together with applied load method (LUHTAL), was developed to determine the tensile, compressive, bending strength and fracture toughness of ceramic composites. The four point bending load was conducted to measure the bending strength and fracture toughness of ceramic composites after the center of the sample was heated up to about 1500-2000°C by oxygen-assisted spray combustion. To check the availability and reliability for this method, typical ceramic materials including ZrB₂/SiC and C/SiC fiber reinforced composite coated with Si, were used as the testing samples. It is indicated that this method is good and feasible for evaluating the mechanical properties of the ceramic composite at ultra-high temperatures in air.

Abstract: The main mechanics behavior character of building silicone sealant is its time dependence£¬which lies in the existence of the interior timepiece or the characteristic time. The creep behaviors were fundamental to evaluating the long-term performance of the building silicone sealant under long-term external loading. A series of creep tests of building silicone sealant were conducted in the laboratory under different combinations of external loads, the characteristics of the creep curve were obtained. In this work, the creep behaviors of building silicone sealant were also investigated under various temperatures at invariable stress. The test measurements show that the creep behavior of building silicone sealant are nonlinear, Nonlinear creep behavior is analyzed by means of the equivalence principle of time-stress, the main creep curve under reference stress was obtained by fitting with the viscoelastic rheological model. So the long-term creep behavior of the building silicone sealant under lower stress can be predicted by short-term creep behavior under higher stress.

Abstract: The mechanical properties of materials and structural components, notably fatigue life, brittle fracture, dimensional stability, deformation and crack propagation can be considerably influenced by residual stresses inside bodies. Accordingly, residual stresses analysis is a compulsory stage in the design of parts and structural elements and in the estimation of their reliability under real service conditions. In this paper, x-ray diffraction and hole-drilling method were used to measure residual stresses in diesel iron castings. The purpose is to determine the residual stresses distribution and analyze the annealing process on the influence of residual stress.