Papers by Keyword: Ceramic Matrix Composite (CMC)

Abstract: Intragranular porous aluminum titanate ceramics were prepared by using graphite powder as pore-forming agent and magnesium-doped aluminum titanate powder as starting material. FESEM was employed to observe the microstructure. In order to investigate the expansion behavior and mechanical property, the dilatometric curve and three-point flexural strength of the prepared aluminum titanate ceramics were measured respectively. The results demonstrate that because of the formation of the intragranular pores, the aluminum titanate ceramics are of low thermal expansion and high strength simultaneously.

Abstract: Thermal shock stability for ZrB2-SiCp-Graphite(ZSC) and ZrB2-SiCp-AlN (ZSA) was investigated by water quenching test. It indicated that ZSC may provide more stable thermal shock properties. As shown by SEM of ZSA, surface cracks appeared after it was cooled from 1200 , due to thermal shock instability of the material. Residual flexural strength of ZSA was improved by crack healing after it was cooled from 1450 . However, no surface crack appeared for ZSC after water quenching test. It provided a potential method for improving thermal shock stability of zirconium diboride ceramic matrix composites by introducing proper quantities of graphite.

Abstract: The production of high-quality Ceramic-Matrix Composites often includes matrix deposition by Chemical Vapour Infiltration (CVI), a process which involves many phenomena such as gas transport, chemical reactions, and structural evolution of the preform. Control and optimization of this high-tech process are demanding for modelling tools. In this context, a numerical simulation of CVI in complex 3D images, acquired e.g. by X-ray Computerized Microtomography, has been developed. The approach addresses the two length scales which are inherent to a composite with woven textile reinforcement (i.e. inter- and intra-bundle), with two numerical tools. The small-scale program allows direct simulation of CVI in small intra-bundle pores. Effective laws for porosity, internal surface area and transport properties as infiltration proceeds are produced by averaging. They are an input for the next modelling step. The second code is a large-scale solver which accounts for the locally heterogeneous and anisotropic character of the pore space. Simulation of the infiltration of a whole composite material part is possible with this program. Validation of these tools on test cases, as well as some examples on actual materials, are shown and discussed.

Abstract: This review paper presents a fail-safe approach in designing biomaterials against wear for application in an artificial total hip replacement in view of the recent advances in orthopedic bioengineering materials. It has been established that substantially different alloys should be used for minimizing wear in bearing surfaces. Frictional forces at these rubbing counter-faces must be minimized to prevent loosening of the femoral stem and acetabular socket assembly from their positions secured by the fixation agent. A comparative analysis of various wear-resistant biomaterials resulted in the lowest production of wear particles in a total hip where a ceramic socket articulates against the ceramic ball: it produces only 0.004 cubic millimeters of ceramic wear particles. Surface modification, through the application of coatings, offers the potential to reduce the wear rate without compromising the bulk mechanical behavior of the implant material. These hard coatings were found to include diamond-like carbon, amorphous diamond, and titanium nitride.

Abstract: Acoustic emission (AE) technique was utilized for real-time monitoring the damage evolutions of 2-D and 3-D C/SiC ceramic matrix composites (CMC) under mechanical loading. AE signals for damage initiation and propagation were captured by AE equipment during the entire loading process. Different damage mechanisms of the two kinds of C/SiC composites were revealed on the basis of multi-parameter analysis. The experimental results validate the availability of AE technique on damage monitoring of C/SiC composites. And the AE technique can be used to distinguish the slight differences in damage mechanisms during damage evolution owing to different woven structures.

Abstract: Based on progressive damage theory, a 3D laminated model with an orthotropic property in plane was established to simulate the response of plain weave carbon fiber reinforced silicon carbide(C/SiC) ceramic matrix composites(CMC) under low velocity impact(LVI). Intra-layer damage and inter-layer damage were taken into account, respectively. Three scalar damage variables, associated with the degradation of warp modulus, weft modulus and shear modulus, respectively, were proposed to characterize intra-layer damage evolutions. The intra-layer constitutive model was implemented into MSC.Dytran, via its user subroutine EXFAIL1. The potential delamination region was considered as a discrete cohesive zone. Three vector spring elements were placed into every two adjacent nodes to simulate the inter-layer joints. A scalar damage variables, associated with the degradation of the three vector spring elements, were brought forward to characterize the inter-layer damage evolutions. The inter-layer constitutive model was implemented into MSC.Dytran, via its user subroutine EXELAS. Damage area, indentation depth of C/SiC composite plates and time history of impact force were obtained to compare with experimental results. The numerical results show overall good agreement with experimental results.

Abstract: An experimental study of low-velocity impact characteristics and strength after impact was carried out on both woven fiber-reinforced resin matrix composites and woven fiber-reinforced ceramic matrix composites. The test specimens were impacted using a dropped-weight impact test apparatus with an instrumented spherical tip. Ultrasonic C-scan was used in nondestructive testing to characterize and quantify the impact damage. Much more damage of ceramic matrix composites than that of resin matrix composites occur and process in loading stage. The peak load of resin matrix composites is higher than that of ceramic matrix composites. According to the results of observing optical photographs and C-scan images, the damage area of ceramic matrix composites is greater than that of resin matrix composites and the difference increases as the energy increases. Damage resistance of ceramic matrix composites is lower than that of resin matrix composites, but damage tolerance of ceramic matrix composites is higher than that of resin matrix composites.

Abstract: A blend superabsorbent resin from CMC and PVA grafted acrylic acid was prepared by solution polymerization without crosslinker. It was characterized by TG to understand thermal stability. SEM and ESEM was used to observe the surface morphology and the network structure. And the absorbency in double distilled water and in 0.9% NaCl solution was measured. The results showed the superabsorbent resin synthesized in this study is stable at temperature lower than 385°C. The thermal stability is good. SEM results indicated that dry resin has rough surface on cross section and good property of membrane. It is found in ESEM photographs that it has uniform network structure made from numerous connecting polygonal membranes and there are holes on the membranes. The absorbency in distilled water and 0.9% NaCl solution are1392.9g/g and 128.5g/g. It has high swelling rate and good salt-resistance.

Abstract: Dense ZrB2-20vol.%SiC-10vol.%BN (ZSB) ceramic composites by introducing BN as the third phase are fabricated through hot pressing sintering under inert gas protected. The static oxidation behavior of the ZrB2-SiC-BN ceramic composite at 1200°C in air is analyzed using differential thermal analysis technique, and the surface morphology of the composites after oxidation at 1200°C is examined using scanning electron microscopy along with energy dispersive spectroscopy. The microstructure change and oxidation behaviors of the ZrB2-SiC-BN ceramic composite are investigated. The effect of BN grain size is analyzed and the oxidation mechanism in ceramic composites is discussed correspondingly.

Abstract: A computer simulation of the sintering process of two-phase ceramic tool materials has been developed using a two-dimensional hexagon lattice model mapped from the realistic microstructure. The relationship between simulation time and real duration time has been proposed. The mean grain size of simulated microstructure increases with an increase in simulation time, which is consistent with the experimental results.