Papers by Author: Shan Yi Du

Abstract: Silicon carbide prepared by chemical vapor deposition (CVD) is one of the important candidate materials for space mirror and high-power mirror such as laser mirror, because of its superior performances such as low density, high melting point and homogeneity. In this paper, the SiC coatings were deposited on the substrates of reaction bonded silicon carbide (RB-SiC) by CVD process. Then, the morphologies of the deposits were examined with scanning electron microscopy. The crystalline phase of the as-deposited films was confirmed with X-ray diffractometry. And the adhesion between the CVD film and the substrate was rated with scraping method. As a result, the morphologies of the deposits, i.e. whiskers at 1050°C or films at 1100°C, are different from that of the substrate. And the mean diameter of the deposits at 1100°C is larger than that at 1050°C. Furthermore, the crystalline phase of the as-deposited film is determined as β-SiC and the adhesion is firm enough not to be peeled off with the scraping test.

Abstract: Silicon carbide is one of the best materials for satellite mirror and chemical vapor deposition (CVD) is an effective method of preparing SiC whiskers and films. In this paper, SiC whiskers or films were deposited on substrates of RB-SiC in an upright chemical vapor deposition furnace of Φ150mm × 450 mm with methyltrichloride silicane (MTS) as precursor gas and H2 as carrier gas under dilute gases of different H2/Ar ratio and different deposition temperature between 1050°C and 1150°C. The morphology and composition of the CVD-SiC grown on RB-SiC substrate were determined by scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. As a result, whisker-like, worm-like or ball-like SiC can be respectively obtained dependent on different deposition conditions such as H2/Ar ratio and deposition temperature, and the composition of the productions are determined as β-SiC by XRD. Furthermore, the deposition mechanisms of different morphologies of SiC are introduced.

Abstract: Framed curing mold is subjected to an uneven thermal load, gravity force and the pressures from composite parts and auxiliary tools during autoclave processing of thermosetting composite structures. And those loads induce the warpage of framed-mold. The warpage of framed-mold during autoclave processing influences dimensional precision of composite parts. In the present work, a three-dimensional finite element model for prediction of the warpage of framed-mold during autoclave processing has been developed. This model solved the coupling problem between the deformation and the temperature distribution of framed-mold and allows analysis of all major identified deformation influencing factors. And numerical predictions compare quite well with experimental measurements. A parametric study was performed using FEM program to examine the effect of varying the thickness of framed-mold, the shape and the dimension of mold vents.

Abstract: A new system of thermoset styrene-based shape-memory polymer (SMP) filled with carbon black (CB) is investigated. To realize the electroactive stimuli of SMP, the electrical conductivity of SMP filled with various amounts of CB is characterized. The percolation threshold of electrically conductive SMP filled with CB is about 3% (volume fraction of CB), which is much lower than many other electrically conductive polymers. When applying a voltage of 30V, the shape recovery process of SMP/CB(10 vol%) can be realized in about 100s. In addition, the thermomechanical properties are also characterized by differential scanning calorimetery (DSC).

Abstract: Recently, there is interest in triggering shape recovery of shape-memory polymers(SMPs) by novel non-external heating. In this paper, many hard works have been carried out to make SMP induced by solution. The main challenge in the development of such polymer systems is the conversion of solution-induced effects at the molecular level to macroscopic movement of working pieces. This paper presents a systematic study on the effects of solution on the glass transition temperature (Tg). The results reveal that the hydrogen bonding of shape memory polymer (SMP) was aroused by the absorbed solution that significantly reduces Tg of polymer. The mechanism behind it is solution firstly intenerates polymeric materials till the Tg of polymer lowered down to the temperature of ambient, then hydrogen bonding interaction improves the flexibility of polymeric macro-molecular chains. Thus, the shape memory effect (SME) can undergo solution-driven shape recovery. In addition, it provides a new approach that the SMP can be induced by applying non-energy stimulus. The Dynamic Mechanical Analyzer (DMA) results reveal that the modulus of polymer was softened gradually with immersion time increasing. The experimental result is approximate to the theory.

Abstract: The heat convection was considered the main heat exchange type in the autoclave where CFRP pressure vessel was cured in this analysis. To determine the heat convection coefficient, it needed the combination of theoretical calculation and temperature test. In the theoretical calculation, the determination of the heat convection coefficient was considered as an inversion problem of thermal conduction. By adjusting convection coefficient value in the finite element calculation, optimization method was employed to obtain a good agreement between calculated temperature and measured temperature. In the temperature test, the metallic liner of CFRP pressure vessel was used as test component to record temperature data which was compared with the calculated temperature. The calculated results reveal that the maximum value in convection coefficient sequence is 19.87 W/m2/K; the minimum value is 0.16 W/m2/K; the maximum temperature deviation between calculation and test is 1.67 °C. The results present the equivalent thermal boundary condition for the simulation of curing process of CFRP pressure vessel.

Abstract: The oxidation behavior of ZrB2-20 vol.% SiC (ZS) and ZrB2-20 vol.% SiC containing 20 vol.% short carbon fiber (ZSC) was studied using thermal gravimetric analysis and oxyacetylene torch test. It was shown that weight gains changed from 3.71 wt.% for ZS to 4.57 wt.% for ZSC after heating 10°C /min to 1450°C in air. A thin layer of Si-rich glass and then a depletion layer of SiC was found on the cross section of both materials and carbon fiber of ZSC exposed in air was oxidized. Under oxyacetylene, an average mass loss of 0.8 wt.% for ZS and 0.9 wt.% for ZSC was measured after 180 seconds. After exposure, an oxidized layer with the formation of ZrO2 and SiO2 was found on the surface of both materials. Meanwhile, fiber in the surface of ZSC appeared oxidized and removed.

Abstract: In-situ SEM observations have revealed that fatigue crack propagation in aluminium alloys is caused by the shear band decohesion around the crack tip and the formation and cracking of the shear band is mainly caused by the plasticity generated in the loading part of the load cycle. This shear band decohesion process has been observed to occur in a continuous way over the time period during the load cycle. Based on this observation, in this study, the transient fatigue crack growth rate, da/dt, has been used to obtain the relationship between the conventional used parameter da/dN and the applied driving force. It is proven that two parameters are necessary in order to accurately describe fatigue crack propagation rate per stress cycle, da/dN. The well known stress ratio effects on fatigue crack propagation rate can be correlated by this model.

Abstract: AlN-SiC-TiB2 ceramics were synthesized by self-propagating high temperature synthesis (SHS) and hot isostatic pressing (HIP) methods. The powder mixtures of Al, 6H-SiC and TiB2 were shaped by isostatic cool pressing method, and then combustion reaction was carried at the pressure of 100-200 MPa N2 by an ignitor. The solid solution of AlN and 2H-SiC in AlN-SiC-TiB2 ceramics was formed. The phase composition and microstructure were investigated by XRD and SEM. The mechanical properties of composite were measured as functions of composition. The maximum value of flexural strength and fracture toughness of composites were 430 MPa and 3.9 MPa⋅m1/2 respectively.

Abstract: This paper is concerned about a design of a new deployable antenna actuated by 6 shape memory alloy (SMA) hinges. The antenna consists of 6 radial, tensioned, parabolic, deployable ribs connecting to a central hub. The hinge, located at each rib, is used of the Nitinol SMA material due to the ability to generate large strains and electrical resistive actuation. The elongated SMA wire is heated by an electrical current, caused to contract in response to a converse thermally-induced phase transformation. The resulting tension creates a moment, imparting rotary motion between two adjacent beams. The concept and operation of deployable antenna system are discussed in detail, and a dynamic simulation is presented. A series of experiments are performed on the SMA actuator to investigate the system behavior in the process of deployment. Results indicated that the hinge with low speed rotation and easy fabrication achieves reliable actuation for the deployment of the antenna, and the antenna demonstrates a high deployment-to-stowage volume ratio.