Fracture of glass in tensile and bending tests

To fully characterize the mechanical behavior of ceramics, it is useful to study their response to both tensile and bending tests. In this investigation, a quantitative comparison is made between tensile and bending results from (circularly) cylindrical glass rods of borosilicate glass and of fused silica. These experimental results show that in each material, the Weibull exponentm is approximately the same for both types of test. The fractured samples clearly showed that all failures initiated at surface-located flaws. The stress level at which the probability of fracture in tension equals 50 Pct was determined; the maximum tensile stress for 50 Pct probability of fracture in bending was also determined. The ratio of these two stresses was predicted previously from simple, theoretical considerations based upon the applicability of the Weibull function and on the distribution of defects in the specimens. This theoretical result is inconsistent with the experimental observations in view of the fractography. Therefore, it is concluded that failure in the materials tested is not satisfactorily described by Weibull statistics.     

Analytical Determination of the Distribution of Polishing Time over the Surface of Polished Tiles

Several kinds of glossiness pattern can be seen on the surface of porcelain stoneware tiles right after the polishing process, as a function of the kinematics performed by the polishing heads. For the newest generation of industrial polishing trains, where a transverse oscillation is included, there is still a great need for literature about the resulting patterns. This paper intends to find the spatial distribution of time under polishing analytically using the kinematics equations involved in the polishing process. The measured values of glossiness collected from three polished tiles are also presented. The importance of adopting a good kinematics for the polishing process has been highlighted, and the equations developed herein are useful tools for further attempts at optimizing the polishing process.     

Huygens's principle and rays in uniaxial anisotropic media. II. Crystal axis orientation arbitrary

We continue and extend Paper I [M. Avenda?o-Alejo et al., J. Opt. Soc. Am. A 19, 1669-1674 (2002)] to the more general case where the crystal axis is not parallel to the surface normal. The procedures and the derivations follow those of Paper I. The result enables one to trace extraordinary rays in and out of a prism as well as through a crystal whose refracting surfaces are not planar.     

Outcome of rehabilitation of adult cochlear implant patients

Cochlear implantation is nowadays a well-accepted method of auditory rehabilitation in selected adults and children. We present rehabilitation data on 21 adult patients provided with the Nucleus CI22M.     

The <Emphasis Type="Italic">k</Emphasis>-Track Assignment Problem on Partial Orders

The k-track assignment problem is a scheduling problem in which a collection of jobs, represented by intervals, are to be processed by k machines. Two different jobs can be processed by the same machine only if the corresponding intervals do not overlap. We give a compact formulation of the problem and state some polyhedral results for the associated polytope, working in the more general context where job compatibility stems not necessarily from intervals but rather from an arbitrary strict partial order.This authors research was financially supported by the Portuguese Foundation for Science and Technology (FCT).     

Optimization of the Kinematics Available in the Polishing Process of Ceramic Tiles by Computational Simulations

This work investigated the influence of the kinematics involved in the polishing process of stoneware tiles over the spatial distribution of abrasive contacts. The basic intention was to delimit the best combinations of both forward and transverse oscillation motions that would result in a uniform polishing effect over the tile surface. Such uniformity was quantitatively represented by the variance of the distribution of polishing time. By means of computational algorithms, a wide range of both forward speed and oscillation frequency were simulated in order to obtain the corresponding distributions of polishing time. The results highlight the importance of adopting good kinematics to avoid excessive polishing gradients. Thus, a large number of kinematic conditions could be potentially recommended, whereas many others were found to be primarily inadequate. In view of this, the simulations carried out herein can be suggested as a useful guide for future phenomenological investigations, and also as a useful tool for polishing industries.     

The use of recycled low-density polyethylene films from protective prepreg for the development of nanocomposites with bentonite clay

Prepreg is a pre-impregnated composite fiber where a thermoset polymer matrix material is present. Before being used, these materials are kept at low temperatures and have a low-density polyethylene (LDPE) film for your protection. The increase in the use of structural composites based on prepregs causes an increase in the amount of protective LDPE film. This material is usually discarded or incinerated and can cause great damage to the environment. Thus, the present work aimed to study the feasibility of recycling up to 100% of protective LDPE (rLDPE) to develop blends-based nanocomposites with rLDPE/virgin LDPE (60/40, 70/30, 80/20, 90/10 and 100/0) with the addition of 5 wt% of compatibilizer agent (maleic anhydride grafted LDPE, LDPE-g-MA), and 1 wt% of bentonite (BNT) using a co-rotational twin-screw extruder, followed by hot pressing in a hydropneumatic press and die-cutting. Water absorption test, thermal aging resistance, morphological characterization by scanning electron microscopy, mechanical properties by Izod impact strength and tensile tests, and differential scanning calorimetry were performed. By the results, it was possible to verify the viability of 100% of the recycling of rLDPE. The results showed a good distribution of 1 wt% of BNT in the matrix, better mechanical properties when compared with virgin LDPE. Furthermore, the thermal properties, water absorption test, and thermal aging resistance showed no statistical differences between the samples. These results confirm the effectiveness and the environmental gain in the use of the recycled material.