Effects of Preform Shear on Tensile Properties of a Woven C/SiC Composite

This article addresses effects of weave defects in an angle‐interlock C‐fiber preform on the tensile properties of the resulting fully processed C‐fiber/SiC‐matrix composite. For this purpose, a preform was intentionally sheared in a controlled manner after weaving. The resulting distortions were quantified by analyzing high‐resolution images of the preform surface after the first step of matrix processing, while the tows were still clearly visible. Comparisons are made of tensile test results on specimens cut from this composite panel and from a pristine panel in select loading orientations. Strain maps obtained by digital image correlation are used to identify local strain variations that are attributable to weave defects. The results are discussed in terms of: (i) the shear‐normal coupling that arises in loading orientations of present interest, and (ii) the geometric effects of tow misalignment on tow continuity along the specimen gauge length. The composite is found to perform in a robust manner, in the sense that the tensile properties are not sensitive to the presence of the defects.     

Secondary electron amplification using single-crystal CVD diamond film

The current amplification characteristics of an unbiased 8.3-μm-thick single-crystal CVD diamond film are examined using secondary-electron-emission measurements. In particular, the intensity and energy distribution of transmitted and reflected secondary electrons are measured and used to examine the transport and emission properties that govern the current amplification process. Overall, the measurements confirm the excellent transport and emission properties of single-crystal CVD diamond, as compared to polycrystalline CVD diamond films studied previously. Specifically, the transmitted and reflected energy distributions measured from the single-crystal diamond are nearly identical, with a sharp, narrow (FWHM = 0.35 eV) emission peak dominating the spectra. However, the transmitted distributions are more fully thermalized as a result of the longer transport distances. In fact, transmitted electrons are detected even after traveling more than 8 μm through the film, which demonstrates the potential for excellent transport efficiency. Maximum transmission gains of 3–4 are obtained, which is encouraging under such field-free conditions. However, the results of the study indicate that the transmission process is being limited by diffusive transport in the unbiased diamond film.     

Dependence of Silicon Carbide Product Morphology on the Degree of Mechanical Activation

Mechanical activation before carbothermic reduction can substantially enhance the formation of SiC from SiO₂and carbon mixtures. However, the morphology (e.g., particles or whiskers) of SiC formed from mechanically activated SiO₂and carbon mixtures is dependent of the degree of mechanical activation and the condition of the subsequent carbothermic reduction. These phenomena are investigated and rationalized based on the increased reactivity of the reactants and SiC formation mechanisms.     

An in-Depth Analysis of the Swelling,Mechanical, Electrical,and Drug Release Properties of Agar–Gelatin Co-Hydrogels

Agar–gelatin-based co-hydrogels were prepared with different compositions of the agar and the gelatin fractions. The intermolecular hydrogen bonding was higher in the co-hydrogels as compared to the gelatin hydrogel. Swelling studies indicated diffusion-mediated swelling. The electrical stability of the co-hydrogels was higher as compared to the gelatin hydrogel. Though the firmness of the co-hydrogels was higher, Weichert model of viscoelasticity indicated that the inherent mechanical stability of the gelatin hydrogel was superior. The release of ciprofloxacin hydrochloride was predominately Fickian diffusion-mediated. In gist, the co-hydrogels can be tried as polymeric constructs for controlled drug delivery applications.     

C-terminal His-tagging results in substrate specificity changes of the thioesterase I from Escherichia coli

The biochemical properties of Escherichia coli thioesterase I, His-tagged (HT) on the C-terminal, were systematically analyzed and compared with that without the His-tag (WT). These two types of enzymes exhibit similar optimal temperature and pH dependence, but subtle differences were detected. Kinetic studies revealed that the k _car/JK _m values of the HT enzyme for the substrates palmitoyl-CoA and p-nitrophenyl dodecanoate were 36- and 10-fold lower than those of the WT, respectively. In contrast, HT had a fivefold increased catalytic efficiency for p-nitrophenyl acetate, and up to fourfold increases toward phenylalanine- and tyrosine-derived ester substrates, l-NBPNPE (N-carbobenzoxy-l-phenylalanine p-nitrophenyl ester) and l-NBTNPE (N-carbobenzoxyl-l-tyrosine p-nitrophenyl ester), respectively. For l-NBPNPE and l-NBTNPE, the increases were attributed to the higher k _cat values with little changes in K _m, whereas the increase for p-nitrophenyl acetate was mainly attributed to the lower K _m value. It is concluded that addition of six hydrophilic histidine residues on the C-terminus resulted in a change in substrate specificity of E. coli thioesterase I toward more hydrophilic substrates.     

Characteristics of the Transformation of Retained Austenite in Tempered Austempered Ductile Iron

Controlling the amount of retained austenite is a concern in austempered ductile iron formation. Retained austenite has a strong influence on austempered ductile iron properties, such as hardness and wear resistance. In this research, the characteristics of the transformation of retained austenite were investigated as a function of the number of tempering cycles. The hardness of the austempered ductile iron samples was measured, and the specific amount of retained austenite was analyzed by x-ray diffraction (XRD). Wear tests were conducted on a ball-on-flat sliding fixture. The tempering process was found to have no effect on the hardness of the austempered ductile iron samples. This may be due to retained austenite being partially converted into brittle quenched martensite during the tempering process. However, tougher tempered martensite was also formed from existing martensite. The two effects seemed to offset each other, and no significant differences occurred in overall hardness. XRD analysis showed that under the same austempering temperature and holding time, the amount of retained austenite decreased with additional tempering cycles. Also, with the same holding time and tempering cycles, less retained austenite was contained in the matrix at higher austempering temperatures. This was due to more high carbon content austenite and needle-like ferrite being present in the austempered ductile iron matrix. In addition, tempered austempered ductile iron exhibited significantly higher wear resistance as compared to traditionally treated ductile iron.     

Location of steel reinforcement in concrete using ground penetrating radar and neural networks

Ground-penetrating radar is becoming increasingly popular for use as a non-destructive assessment method for investigating reinforced concrete structures. The amount of data collected however can be very large and take a significant level of subjective experience to interpret. This study focuses upon the use of a neural network approach to automate and facilitate the post-processing of ground penetrating radar results. The radar data is reduced to a simplified data set by using an edge detection routine. Signal reflections from reinforcing bars displaying a hyperbolic image format are detected using a multi-layer perceptron (MLP) network with a single hidden layer containing 8 nodes to recognise a simplified hyperbolic shape. Training and testing of the network was carried out making use of an emulsion analogue tank, simulating the properties of concrete, and using real concrete specimens. The results showed that the use of a MLP neural network approach could be quite effective in automating the identification and location of embedded steel reinforcing bars from a radar investigation. Accurate estimation of depth, or cover, requires a reliable knowledge of the dielectric properties of the concrete, and recent work using a specially-developed wideband horn antenna for direct determination of in situ properties is also outlined.