Densification of 8Y‐Tetragonal‐Stabilized Zirconia Optoceramics with Improved Optical Properties by Y Segregation

8% Yttria‐stabilized zironcia (8YSZ) transparent ceramics have a wide technological applications. Segregation of the Y around the grain boundaries is favored by slow heating rate. The optimized sintering parameters helped in obtaining transparent ceramics of 8YSZ with a high percentage of cubic phase in addition to the presence of tetragonal phase. HRTEM was used to verify the grain growth suppression and to observe the presence of the cubic phase. The presence of cubic phase has suppressed the grain growth, which increased the transparency in the visible and infrared region without the addition of dopants or by utilizing high pressure.     

The heat treatment and the gelation are strong determinants of the kinetics of milk proteins digestion and of the peripheral availability of amino acids

This study aimed to determine the kinetics of milk protein digestion and amino acid absorption after ingestion of four dairy matrices by six minipigs: unheated or heated skim milk and corresponding rennet gels. Digestive contents and plasma samples were collected over a 7 h-period after meal ingestion. Gelation of milk slowed down the outflow of the meal from the stomach and the subsequent absorption of amino acids, and decreased their bioavailability in peripheral blood. The gelled rennet matrices also led to low levels of milk proteins at the duodenum. Caseins and β-lactoglobulin, respectively, were sensitive and resistant to hydrolysis in the stomach with the unheated matrices, but showed similar digestion with the heated matrices, with a heat-induced susceptibility to hydrolysis for β-lactoglobulin. These results suggest a significant influence of the meal microstructure (resulting from heat treatment) and macrostructure (resulting from gelation process) on the different steps of milk proteins digestion.     

Fatigue crack growth and load redistribution in Ti/SiC composites observed in situ

Sequential synchrotron X-ray microtomography and diffraction have been applied to follow the growth of fatigue cracks and the associated load redistribution in a Ti/SiC fibre composite. A sequence of micron resolution tomographs reveal for the first time how the cracks progress from ply to ply around the fibres. Complementary high spatial resolution (40 μm) diffraction scans interleaved between the tomographic image acquisitions during the fatigue experiment have enabled the fibre strains and thereby the interfacial shear stress to be mapped as a function of crack growth. The matrix crack front was found to bow out between fibres, eventually reconnecting further downstream. This leads to the prolonged retention of bridging matrix ligaments and increased crack path tortuosity. The rate of crack growth was found to slow somewhat as a fibre is approached. As the crack grew past the fibres under observation the extent of the sliding region and the level of the fibre bridging stress increased. The interfacial shear strength after fatigue was around 60 MPa in the crack-tip region, in common with previous experiments.     

Influence of moisture content on the specific methanogenic activity of dry mesophilic municipal solid waste digestate

The objective of this study was to evaluate the influence of moisture content on the specific methanogenic activity (SMA) of a fresh dry mesophilic digestate from a municipal solid waste digester plant. For this purpose, SMA tests were performed under mesophilic conditions in 500 mL glass bottles of volume used as batch reactors, during a period of 20–25 days. Cellulose, propionate and acetate were used as substrates (5 g_COD kg^?1 digestate) at four different moisture contents, ranging from 65 to 82%. The moisture content strongly influenced the specific methanogenic activity. The highest SMA values were observed at a moisture content of 82% (11.1, 7.8 and 6.0 mg_COD g_VS^?1 d^?1 for cellulose, propionate and acetate spikes, respectively). SMA and moisture content were found to be linearly linked. Dry digestion at low water content is thus detrimental to the biological activity, probably due to physical limitations. Copyright © 2011 Society of Chemical Industry     

Influence of closure on the 3D propagation of fatigue cracks in a nodular cast iron investigated by X-ray tomography and 3D volume correlation

Synchrotron X-ray tomography was performed during in situ fatigue crack propagation in two small-size specimens made of nodular graphite cast iron. While direct image analysis allows us to retrieve the successive positions of the crack front, and to detect local crack retardation, volume correlation allows for the measurement of displacement fields in the bulk of the specimen. The stress intensity factors (SIFs), which are extracted from the measured displacement fields and the corresponding local crack growth rate all along the front, are in good agreement with published results. In particular, it is possible to link the non-propagation of a crack with crack closure in the crack opening displacement maps or with a local value of the measured SIF range. It is shown that a non-uniform closure process along the crack front induces an asymmetric arrest/growth of the crack.     

Crack closure and stress intensity factor measurements in nodular graphite cast iron using three-dimensional correlation of laboratory X-ray microtomography images

Three-dimensional (3-D) tomographic images of a nodular graphite cast iron obtained using a laboratory X-ray source were used to analyze the opening of a fatigue crack during in situ mechanical loading. Direct image analysis and digital image correlation are utilized to obtain the 3-D morphology and front location of the crack, as well as the displacement fields in the bulk of the specimen. From digital image correlation results it is possible to extract the crack opening displacement (COD) map in the whole sample cross-section and to compute stress intensity factors (SIFs) all along the crack front, even for COD values that are less than the image resolution. The comparison of COD maps with local values of the SIF enabled for an estimation of the opening SIF (K_op) equal to 6 MPa m^1/2.