S.Y. Du

Oxidation and ablation of 3D carbon-carbon composite at up to 3000 °C

Abstract The reactivity of fine-weave pierced 3D carbon-carbon composites in air at temperatures up to 3000 °C was studied. The corrosion morphology and microstructure of oxidized samples were investigated by XPS, SEM, and XRD techniques, and the non-equilibrium nature of the oxidation process was pointed out. A thermochemical ablation model of Cue5f8C composites controlled by gas phase diffusion and reaction kinetics was developed.

A simple engineering approach in the prediction of the effect of stress ratio on fatigue threshold

In situ SEM observations [1] have revealed that fatigue crack propagation 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 a load cycle. Based on the crack tip plasticity a theoretical analysis has been performed and a model has been set up to consider the effect of the applied stress ratio on fatigue threshold. The obtained results have been compared with a wide range of published test data and good agreement has been achieved. This method is very easy to use and no fatigue crack closure measurement is needed, therefore this model is significant in engineering application.

Ceramic green tape extrusion for laminated object manufacturing

Abstract Al 2 O 3 and SiC green tapes with 0.2 mm thickness used for LOM (laminated object manufacturing) were prepared from a 75 wt.% ceramic suspension in a LDPE based organic vehicle followed by extrusion. Rheological characterization of the alumina and SiC suspensions were studied. TG-DTA analysis was carried out in air and microstructures were examined by SEM.

Fractal model of the dipole moments of conducting particle chains

Abstract A self-similar fractal model is developed for calculating the dipole moments of linear chains of equally spaced conducting spheres immersed in uniform electric field. We assume that chains may be treated as larger equivalent spheres with same dipole moment and that two such imaginary spheres behave like two real ones. The effective radii of the equivalent spheres are determined from a fractal generating process. In this process, only the knowledge of particle pair is required. The fractal dimension is determined, which is only a function of the spacing of the spheres. The longitudinal and transverse dipole moments are expressed as simple functions of the fractal dimension and the number of the spheres in a chain. The results for touching spheres are in excellent agreement with the known numerical calculations of the image method. Comparison is made with the nearest-neighbor approximation, which is extended to the transverse case here. The fractal model is acceptable.

Fractal characterization of the dipole moments of dielectric particle chains

Abstract A simple self-similar fractal model is presented for obtaining the dipole moments of dielectric particle chains subjected to uniform electric field. The chains are replaced by equivalent spheres, and the effective radii of these spheres are determined from a fractal generating process. The dipole moments are determined in terms of the effective radii and are expressed as simple functions of the fractal dimension and the number of the particles in chain. The computed results for the longitudinal dipole moments are consistent with the previous calculations of the linear multipole expansion. The many-sphere nature of the moments of chains is well understood.