A strain-based fracture model for stress corrosion cracking of low-alloy steels

The stress corrosion cracking (SCC) behavior of 4135 steel under different heat treatments is analyzed in an attempt to relate microstructural characteristics with macroscopic measurements of SCC resis-tance, especially the very impressive improvements associated with changes from intergranular (IG) to transgranular (TG) fracture paths. Considering that local hydrogen embrittlement at the crack tip causes SCC processes, a local cracking criterion, based on a critical strain depending on hydrogen concentration, is assumed to control the process. Stress corrosion cracking is viewed as a discontin-uous series of unstable crack extensions through the locally embrittled regions. The model developed on this basis explains the macroscopic behavior observed at the threshold situation and partially at stage II propagation and clarifies the role of the metallurgical variables in each of the types of fracture detected.     

Metabolism of quercetin by Cunninghamella elegans ATCC 9245

Incubation of quercetin with Cunninghamella elegans ATCC 9245 yielded three metabolites, including quercetin 3-O-β-D-glucopyranoside, kaempferol 3-O-β-D-glucopyranoside and isorhamnetin 3-O-β-D-glucopyranoside. Glucosylation, O-methylation and dehydroxylation were involved in the process, among which dehydroxylation has never been found in Cunninghamella. Quercetin was completely metabolized in 72 h.     

Chemical composition of olive by-product and modifications through enzymatic treatments

The purpose of the present work was to study the dietary fibre (DF) fraction of olive cake and modify the fibre structure through enzymatic treatments in order to improve the sensory quality of this by-product for its incorporation into a baked product. Two different commercial enzyme preparations were used for enzymatic modifications: Viscozyme L, a hemecellulase/cellulase multi-enzyme complex, and Olivex which contains different pectolitic main activities as well as various side activities, hemicellulases and cellulases. DF consists of 800 g total dietary fibre per kg dry matter. More than 91% of the DF are insoluble and the monosaccharide composition of this fraction indicates the presence of mainly cellulose and xyloglucans or xylans. Approximately 75% of the uronic acids found in olive cake are associated to the insoluble DF (IDF). Arabinans and uronic acids polysaccharides are the major fibre components in the soluble DF (SDF) fraction. Enzymatic treatments with commercial preparations caused changes in the DF content and in the IDF:SDF ratio depending on enzyme concentrations and incubation time. Baking experiments showed that a substitution of 10% of wheat flour by enzymatically modified olive cake led to an improved texture compared to products containing untreated cake.     

Fracture toughness of irradiated and recovered vessel steels

This paper presents the fracture toughness measurements carried out on three vessel steels in an irradiated condition and after a post-irradiation recovery treatment. A statistical approach and the fracture parameters corresponding to two theoretical models of the fracture tests are used for evaluating toughness. Test results show that the neutron fluence gradually transforms the fracture behaviour of the vessel steels from ductile to brittle and seriously reduces their fracture toughness. The effectiveness of the recovery treatment, as evaluated from the toughness measurements, is confirmed, although the efficiency is not the same for the steels and depends on the evaluation parameter except in the case of almost complete recovery. The recovery effect increases with the received neutron fluence if the toughness values after treatment are compared with those in the irradiated condition rather than those in the as received condition.     

Cyclic maximization of non-Gaussianity for blind signal extraction of complex-valued sources

This article presents a new algorithm for the blind extraction of communications sources (complex-valued sources) through the maximization of negentropy approximations based on nonlinearities. A criterion based on the square modulus of a nonlinearity of the output is used. We decouple the arguments of the criterion so that the algorithm maximizes it cyclically with respect to each argument by means of the Cauchy-Schwarz inequality. A proof of the ascent of the objective function after each iteration is also provided. Numerical simulations corroborate the good performance of the proposed algorithm in comparison with the existing methods.     

SOLVENT EXTRACTION OF LEAD BY TRILAURYLAMMONIUM CHLORIDE DISSOLVED IN TOLUENE FROM DIFFERENT CHLORIDE MEDIA

The extraction of Pb(II) from chloride solutions by trilaurylammonium chloride (TLAHC1) dissolved in toluene has been studied by metal distribution measurements. The work has been performed at three different aqueous chloride concentrations (1.0, 2.0 and 3.0 mol.dm^?3NaCl). The treatment of the experimental data at each chloride concentration agrees with the stoichiometry of the extracted metal species in the organic phase while the values of their equilibrium constants are different for the various chloride concentrations. The extraction process is explained by the following extraction reactions

The corresponding logarithmic values of K₂and K₅at the different chloride concentrations, I, are: K₂K₅, I; 4.62, 8,51, 1.0; 4.54, 8.38, 2.0; 4.48, 8.32, 3.0. The values obtained have been correlated by using the Specific Interaction Theory (S.I.T.) and the interaction coefficient for the Pb²⁺,Cl^?ions as well as the thermodynamic constants, Kn⁰, have been determined.     

Influence of operating variables on the aqueous-phase reforming of glycerol over a Ni/Al coprecipitated catalyst

A systematic study focused on the aqueous-phase reforming of glycerol has been carried out in order to analyze the influence of several operating variables (system pressure, reaction temperature, glycerol content in feed, liquid feeding rate and catalyst weight/glycerol flow rate ratio) on the gas and liquid products. A continuous flow bench scale installation and a Ni/Al coprecipitated catalyst were employed. The system pressure was varied from 28 to 40 absolute bar, the reaction temperature was analyzed from 495 to 510 K, the glycerol content in the feed was studied from 2 to 10 wt%, the liquid feeding rate was changed from 0.5 to 3.0 mL/min and the catalyst weight/glycerol flow rate ratio varied from 10 to 40 g catalyst min/g glycerol. The main gas products obtained were H₂, CO₂ and CH₄, while the main liquid products were 1,2-propanediol, ethylene glycol, acetol and ethanol. A W/m_glycerol ratio of 40 g catalyst min/g glycerol, 34 bar, 500 K, 5 wt% glycerol and 1 mL/min, resulted in a high yield to H₂ (6.8%), the highest yield to alkanes (10.7%), the highest 1,2-propanediol yield (0.20 g/g glycerol) and the highest ethylene glycol yield (0.11 g/g glycerol). The highest acetol yield (0.06 g/g glycerol) was obtained at 34 bar, 500 K, 5 wt% glycerol, 20 g catalyst min/g glycerol and 3 mL/min.     

Fracture and fatigue failure in the Spanish codes for design of steel structures

This work describes from a Fracture Mechanics view the failure prevention approaches recently embodied in the European and Spanish codes for the design of steel structures. The codes formulate the design rules to prevent fatigue and fracture failures in terms of engineering practice, with the Fracture Mechanics foundations underlying them not being apparent. The design simplifications assumed are presented in the framework of Fracture Mechanics.     

Can the maximum volume fraction ensure optimum reinforcement in short-fiber composites?

Short sisal fiber composites (SSFCs) based on a pectin matrix were prepared and characterized mechanical and optically. Different concentrations (1–30 wt %) of fibers were used to evaluate the packing effect on the reinforcement of a polymer matrix. Theoretical models were used to obtain the maximum packing or volume fraction (ϕ_max) of randomly oriented short fibers and its relationship with the mechanical parameters. A higher elastic modulus and tensile strength were observed when the fiber content was increased in the composite at a fixed aspect ratio (length/diameter = 2.8). Material selection charts showed that SSFCs with a fiber concentration of 20 wt % had a higher reinforcement effect at ϕ_max, as was predicted through theoretical models. Nevertheless, SSFCs with a fiber concentration of 7 wt % presented optimum reinforcement because it resulted in the strongest and lightest composite material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47821.