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.

The grinding fluid dedicated for ceramics is one of the effective methods to realize efficient grinding of ceramics. The blockage of grinding fluid dedicated for ceramics is researched in this paper. On basis of the fundamental principles of organic chemistry, the influence from changes of organic acid, organic alcohol carbon chain and functional group on the blockage of grinding wheel are investigated respectively in this paper. According to the experiment result: the blockage area of grinding wheel increases along with the increase of low-carbon chain acid and alcohol, but for the long-carbon chain, the blockage area on grinding wheel decreases with the increase of the number of carbons; the influences of adding functional group are highly related to the hydrophile-lipophile (HLB value), which is finally formed by organic matters and has regular changes.

The bone ingrowth in hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) was not clearly explained in the past investigation. We understand this confusion was due to the difference of the porosity and pore size of the implant materials, and impurities and the heterogeneous chemical composition of the materials. In this study, pure HA and pure β-TCP with the same structure were implanted in the distal femurs of 24 mature male rabbits. The amount of ceramics and of regenerated bone were measured after 4, 12 and 24 weeks, respectively. There was a large amount of bone in β-TCP at 4 weeks, but they decreased at 24 weeks. Meanwhile there was the smaller amount of regenerated bone in HA at 4 weeks, but increased at 12 and 24 weeks, and then decreased after 24 weeks. The peak value of the amount of regenerated bone in HA and β-TCP was almost the same.

This study evaluated the possibility of obtaining bioactive coatings on polyethylene/bioactive glass composites exhibiting a very good mechanical performance. High molecular weight polyethylene (HMWPE) was reinforced with 10 to 40% (wt.) of a bioactive glass (BGE1) and a glass-ceramic (BGE1C), in the SiO₂-3CaOP₂O₅-MgO system. The composites were compounded by twin-screw extrusion (TSE) and then injection moulded into dumb-bell tensile samples. The composites presenting adequate mechanical properties were then coated with a bioactive layer by two methodologies: (i) an adapted biomimetic route using a similar glass as a precursor of calcium-phosphate (Ca-P) film deposition, and (ii) the production of a ‘sandwich’ with bioactive glass particles, previously mixed with UHMWPE powders, made to adhere to both faces of tensile samples by compression moulding. The obtained results indicated that it is possible to produce composites presenting a modulus of 11.2 GPa coupled with a tensile strength of around 117 MPa. The developed composites could be coated with a Ca-P layer by an adapted biomimetic route. Furthemore, the ‘sandwich’ route allowed for the production of load-bearing composites, presenting a highly bioactive surface, which strongly adheres to the HMWPE matrix composites.