Narrow Results

The widespread use of modeling and simulation for design of armor systems is critically dependent on the accuracy of the underlying structure of such simulations. Acceptance of these tools hinges upon end user trust in the predicted results. As the overall implementation of a design code can be composed of a number of material models, it is essential that those models accurately reflect true physical behavior. Computations are performed using the Johnson-Holmquist (JH) constitutive model for brittle materials for penetration problems into ceramics, as implemented in both the Eulerian CTH and the Lagrangian EPIC shock physics codes. The results of the computations are compared and the influence of the numerics and material model coupling are evaluated. A description of some important computational features involving finite elements and meshless particles are also outlined, with observations on the direction of future code and model development.

Design of reproducible, simple and efficient nanofabrication routes has become a frontier topic in the emerging field of nanotechnologies. In this chapter we discuss the "state of the art" of ceramics micro- and nanofabrication techniques. We pay special attention to progress in this field made during the last five years.

In this chapter we will discuss about the progress on the use of lithographic tools to create nanoscale ceramic patterns or the potential of soft lithography to create ceramic structures by means of liquid ceramic precursors. The chapter also describes advances on the use of self-assembly and self organization to achieve nanostructured ceramic surfaces. In the final part, we discuss about the possibility of combining physical vapour deposition with micromolding techniques to obtain nanostructured ceramic subtrates.

Ceramic components for engineering applications are generally produced by the powder route. Residual stress and inhomogeneities in the process can result in defects and hence affect the component properties. As a result, a full understanding of the material constitutive modeling governing the sintering process is necessary.

In the present work, we examined the constitutive laws of the sintering mechanisms and identified the most appropriate constitutive relationship and mechanism for stage 1 of sintering of Al₂O₃ ceramics. With this identified constitutive relationship, sintering potential involved during sintering can be found and the process can be improved.

To identify the dominant constitutive law and corresponding sintering mechanism, pure alumina powder was used as raw material and two sintering methods (free sintering and hot pressing) were employed. Experiments were designed in such a way that the results can be used to determine the sintering potential and verify the appropriate sintering mechanism. It was concluded that interface reaction controlled sintering dominates the stage 1 of sintering in our selected experiment parameters.

In high speed machining, the cutting force changes constantly as the tool becomes worn out. Taking ceramic flank milling as an example, three axial cutting forces were recorded using measuring instruments during the cutting process, with the data forming a time series. Fractal theory was then employed in analyzing these signals. The results show that the cutting force signals of the three axial directions are all kept invariant separately when the cutting process is smooth. However, the situation changes as the cutting tool becomes worn out. Further study indicates that the signal in Y-axial direction changed first as the cutting tool wore out and the fractal dimension of Y-axial cutting signal increases correspondingly. This conclusion could provide a meaningful method for evaluating the cutting quality of ceramics, and can also be useful for assessing the tool wearing in high speed machining.