In the present study, Si3N4 ceramics with pore gradient structure were prepared by spark plasma sintering (SPS) technique. Silicon nitride ceramics with different controlled porosities were prepared by using ZrP2O7 as...
In the present study, Si3N4 ceramics with pore gradient structure were prepared by spark plasma sintering (SPS) technique. Silicon nitride ceramics with different controlled porosities were prepared by using ZrP2O7 as a binder material and heat treated at 1100 °C in a pressureless nitrogen atmosphere. Si3N4 ceramics with controlled porosity of 34–47% were obtained. The distribution of porous structure was homogenous. Fully dense Si3N4 ceramics could be sintered at 1400∼1600 °C by using MgO and alumina Al2O3 as the sintering aids. Pore gradient structure was formed by laminating the Si3N4 porous ceramics and powder mixture was used to obtain fully dense ceramics, and then sintering at 1400–1600 °C. Microstructure of sintered samples was observed by scanning electronic microscope (SEM) and the change of phase compositions was analyzed by X‐ray diffraction (XRD). The results showed that these samples exhibited a good porous graded structure with a highly porous layer and a dense surface layer. The major phase of the Si3N4 ceramics was still α phase.
An analytical model of normal ballistic impact on the ceramic/metal gradient armor, which is based on modified Alekseevskii‐Tate equations, has been developed. The process of gradient armour impacted by the long rod ...
An analytical model of normal ballistic impact on the ceramic/metal gradient armor, which is based on modified Alekseevskii‐Tate equations, has been developed. The process of gradient armour impacted by the long rod can be divided into four stages in this model. First stage is projectile's mass erosion or flowing phase, mushrooming phase and rigid phase; second one is the formation of comminuted ceramic conoid; third one is the penetration of gradient layer and last one is the penetration of metal back‐up plate. The equations of third stage have been advanced by assuming the behavior of gradient layer as rigid‐plastic and considering the effect of strain rate on the dynamic yield strength.
The effect of ceramic/metal gradient armor's components characteristic on its impact‐resistant characteristic has been investigated by a new modified Alekseevskii‐Tate equation. The following researching work is...
The effect of ceramic/metal gradient armor's components characteristic on its impact‐resistant characteristic has been investigated by a new modified Alekseevskii‐Tate equation. The following researching work is done by the former model [1]: the effect of ceramic layer on the impact‐resistant characteristic, the effect of gradient layer on the impact‐resistant characteristic and the effect of metal layer on the impact‐resistant characteristic.
Extrusion gelation freeform fabrication process is an extrusion-based freeforming technique capable of fabricating complex shaped monolithic ceramic prototypes by the sequential deposition and solidification of cerami...
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Extrusion gelation freeform fabrication process is an extrusion-based freeforming technique capable of fabricating complex shaped monolithic ceramic prototypes by the sequential deposition and solidification of ceramic suspensions from a computer aided design model. In this process, ceramic parts are produced using an extrusion nozzle suitable for extruding ceramic suspensions. In this study, the processing parameters influencing on manufacturing Al2O3 parts were discussed. Air pressure on top of suspensions, rotating speed of screw, nozzle diameter and scan speed are the main factors to influence the dimensional precision of ceramic bodies. By optimizing these processing parameters, the green bodies were fabricated with high precision. The sintered samples with homogenous microstructure and ∼97.6% relative density could be prepared by sintering of these green bodies at 1600°C for 2 hours.
The structural change in phase transition of hybrid （Cl2H25NH3）2MnCl4 was investigated. The temperature and the structures of the phase transition is investigated by thermal gravimetry （TG） and differential scanni...
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The structural change in phase transition of hybrid （Cl2H25NH3）2MnCl4 was investigated. The temperature and the structures of the phase transition is investigated by thermal gravimetry （TG） and differential scanning calorimetry （DSC）, infrared spectrum （IR） and X-ray diffraction （XRD）. The results suggest that the phase transition is reversible and the structural change arises from the conformation change of the organic chain. The interlayer distance increases when the hybrid transforms from low temperature phase to high temperature phase. This is explained by the diffusion of gauche-bond along the organic chains and they move away from each other when the phase transition occurs. Combining the experimental data with theoretical calculation, we propose that organic chain of the hybrid in high temperature phase is the conformation of gauche-bond alternating with trans bond （noted as GTG＇TGTG＇TGTG＇T）.
A multi‐particle 2D plane strain model was used to investigate the dynamic compressive properties of ceramic particle reinforced metal matrix composites (MMCs) in this paper. Ceramic particles were simulated as circl...
A multi‐particle 2D plane strain model was used to investigate the dynamic compressive properties of ceramic particle reinforced metal matrix composites (MMCs) in this paper. Ceramic particles were simulated as circles with different diameters, which were randomly and discretely embedded in the matrix. The constitutive relationship of ceramic material was characterized by Johnson‐Holmquist (JH‐2) damage model. The matrix was assumed to be power‐law strain hardening material, coupled with power‐law strain rate hardening. The ceramic/metal interface was assumed to be perfect. The predicted stress‐strain curves by the numerical models agreed well with those of experiments and unit cell analysis formulae developed by Bao and Lin [3]. The effects of overall strain rates and ceramic volume fraction on the dynamic behavior of the composites had been investigated by this numerical model. The effect of particles' distribution on the particles' damage was also discussed. The results show that the distribution and volume fraction of the particles have obvious effect on the particles' damage.
A new micromechanical method, called the Weighted Residual Self‐Consistent Scheme (WRSCS), is developed to study the effective thermal conductivity of particulate composites. WRSCS provides us with a new approach to ...
A new micromechanical method, called the Weighted Residual Self‐Consistent Scheme (WRSCS), is developed to study the effective thermal conductivity of particulate composites. WRSCS provides us with a new approach to the approximation of effective thermal conductivity of particulate composites with arbitrary phase geometry based on the thermal conduction theory of two‐phase materials within the framework of SCS. FE analyses of a generalized multi‐inclusion model and GSCS model are also carried out in the prediction of the effective thermal conductivity at different inclusion volume fractions. Results show that the effective thermal conductivity depends not only on the properties and volume fractions of its constituents, but also on the geometric shape of the particulate.
Two phosphonic acids: dodecylamine-N, N-dimethylenephosphonic acid (DDPA) and dodecylphosphonic acid (DPA), were used to modify zirconia stationary phase in this paper. The result of FTIR and element analysis indicate...
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Two phosphonic acids: dodecylamine-N, N-dimethylenephosphonic acid (DDPA) and dodecylphosphonic acid (DPA), were used to modify zirconia stationary phase in this paper. The result of FTIR and element analysis indicated that DPA adsorbed on zirconia with Lewis acid-base interaction;however, DDPA adsorbed mainly with chelating effect. Apart from the hydrophobicity, DDPA-ZrO2 had cation-exchange and anion-repellent interaction which was useful for the separation of polar compounds.
This paper used amino-terminated polyether, and amino-terminated polyurethane mixture as curing agent to cure the epoxy resin. A series of epoxy elastmors was gotten. The curing products of epoxy elastomers were chara...
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This paper used amino-terminated polyether, and amino-terminated polyurethane mixture as curing agent to cure the epoxy resin. A series of epoxy elastmors was gotten. The curing products of epoxy elastomers were characterized by DSC and FT-IR respectively. The fracture surface morphologies of the cured products were observed by scanning and transmission electron microscopy analysis. The results showed that the impact toughness of the cured products reaches 52.1 kJ/m2 and the elongation of fraction reaches 160% as well as good mechanical properties.
A coupled and uncoupled non-linear thermomechanical finite element analysis using ANSYS have been carried out to analyze the heat transfer and associated thermal stresses during different simulated thermal shock proce...
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A coupled and uncoupled non-linear thermomechanical finite element analysis using ANSYS have been carried out to analyze the heat transfer and associated thermal stresses during different simulated thermal shock processes, and the results of two analyses are discussed. It indicates that piezocaloric effect can be neglect when thermal shock intensity is mild and piezocaloric effect should be taken into account when thermal shock intensity is severe.
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