Mixed mode fatigue and fracture in planar geometries: Observations on Keq and crack path modelling

The mixed mode I‐II fatigue and fracture is briefly reviewed, addressing experimental and numerical modelling aspects, and focusing on planar specimens. One major challenge concerns the determination of equivalent stress intensity factor (K_eq) in mixed mode situations. Several approaches were compared through the determination of K_eq/K_I over a wide range of values of K_I/K_II or K_II/K_I. Whereas all different approaches converge to the same value as K_I/K_II increases, the same does not happen for large K_II/K_I, where differences between values of K_eq persist. In the regions of 0 < K_I/K_II < 2 and 0 < K_II/K_I < 2, no stable trend of results can be defined. Experimental fatigue crack growth results are presented for Al alloy AA6082‐T6. Compact tension specimens, modified with holes, and four‐point bending specimens under asymmetrical loading promoting mixed mode situations, were subjected to fatigue crack growth tests, where crack path and crack growth rate were measured. The presentation of the fatigue crack growth data was made using a Paris law based upon K_eq. Differences in the Paris law constants were found for the different K_eq criteria. Recent developments in numerical techniques, as the implementation of the extended finite element method (XFEM) in finite element software packages allows to determine accurately crack paths in mixed mode fracture. This article highlights concepts for mixed‐mode fatigue and fracture and supporting data, identifying challenges still to be overcome.     

A new risk prioritization model for failure mode and effects analysis

Failure modes and effects analysis is a framework that has been widely used to improve reliability by prioritizing failures modes using the so‐called risk priority number. However, the risk priority number has some problems frequently pointed out in literature, namely its non‐injectivity, non‐surjectivity, and the impossibility to give weights to risk variables. Despite these disadvantages, the risk priority number continues to be widely used due to its higher simplicity when compared with other alternatives found in literature. In this paper, we propose a novel risk prioritization model to overcome the major drawbacks of the risk priority number. The model contains 2 functions, the risk isosurface function that prioritizes 3 risk variables considering their order of importance in a given risk scenario, and the risk prioritization index function which prioritizes 3 risk variables considering their weights. The novelty of the proposed model is its injectivity, surjectivity, and ease of use in failure modes prioritization. The performance of the proposed model was analyzed using some examples typically used to discuss the conventional risk priority number shortcomings. The model was applied to a case study and its performance correlated with other risk prioritization models. Results show that the failure modes prioritization reached with the proposed model agrees with the expectations made for the risk scenario.     

OntoILPER: an ontology- and inductive logic programming-based system to extract entities and relations from text

Named entity recognition (NER) and relation extraction (RE) are two important subtasks in information extraction (IE). Most of the current learning methods for NER and RE rely on supervised machine learning techniques with more accurate results for NER than RE. This paper presents OntoILPER a system for extracting entity and relation instances from unstructured texts using ontology and inductive logic programming, a symbolic machine learning technique. OntoILPER uses the domain ontology and takes advantage of a higher expressive relational hypothesis space for representing examples whose structure is relevant to IE. It induces extraction rules that subsume examples of entities and relation instances from a specific graph-based model of sentence representation. Furthermore, OntoILPER enables the exploitation of the domain ontology and further background knowledge in the form of relational features. To evaluate OntoILPER, several experiments over the TREC corpus for both NER and RE tasks were conducted and the yielded results demonstrate its effectiveness in both tasks. This paper also provides a comparative assessment among OntoILPER and other NER and RE systems, showing that OntoILPER is very competitive on NER and outperforms the selected systems on RE.     

The combined application of extrusion and enzymatic technology for extraction of soybean oil

This paper describes a new technological process for soybean oil extraction. The process deals with the combined effect of thermoplastic extrusion of beans and the subsequent action of hydrolytic and proteolytic enzymes in aqueous medium to recover the oil, thus, avoiding solvent application. The thermoplastic extrusion is fundamental for the process, because it facilitates the action of enzymes in oil containing cells, reduces the non-hydratable phosphatides and promotes protein denaturation by reducing the emulsion stability and thus enhancing the oil extraction. The main parameters affecting the oil yield are: the temperature and diameter of the die in the extrusion process, the dilution, the concentration of enzymes and the incubation time of the enzymatic treatment. The highest yield was obtained under the following conditions: extrusion of beans at 90°C and exit die of 6 mm, enzymatic incubation time of 6 h, extruded soy/water dilution ratio 1:10 and concentration of enzyme 6%. With these conditions 88% of the oil were obtained after centrifugation. Moreover, the aqueous enzymatic extraction is easier than solvent extraction, and leads to high value products: a solvent-free meal more suitable for human consumption, a protein hydrolysate that can be used as ingredient for liquid foods and an oil of better quality. The non-hydrolyzed meal contains ca 25% of original soybean protein and the residual oil. The protein hydrolysate in the liquid phase contains ca 75% of the total protein in the original grain with a molecular weight below 20 kDa.     

Composite coatings based on linear and branched block copolymers for hydroxyapatite deposition in simulated body-fluid

ABSTRACT

In this work, the fabrication of composite coatings based on block copolymers and silicates deposited on stainless-steel plates through electrophoretic deposition technique was studied. Linear poly(?-caprolactone), and poly(dimethylsiloxane-block-ε-caprolactone) copolymers were obtained through ROP polymerization, whereas branched poly(hydroxyethyl methacrylate-co-(hydroxyethylmethacrylate-graft-ε-caprolactone)-block-ε-caprolactone) copolymers were synthesized by a one-pot technique by combining ROP and RAFT synthesis. SEM micrographs revealed homogenous and dense structures over the metallic substrate and the absence of micro-cracks. Thermal characterization revealed residual percentages of solids between 63% and 72% wt/wt. Finally, an in-vitro assessment confirmed the presence of a hydroxyapatite layer over coatings after immersion in a simulated body-fluid solution by XRD analyses.     

The study of morphology,thermal and thermo‐mechanical properties of compatibilized TPU/SAN blends

The compatibilizing efficiency of three different compatibilizers in thermoplastic polyurethane/styrene‐co‐acrylonitrile (TPU/SAN) blends was investigated after their incorporation via melt‐mixing. The compatibilizers studied were poly‐ε‐caprolactone (PCL), a mixture of polystyrene‐block‐polycaprolactone (PS‐b‐PCL) and polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA), and a mixture of polyisoprene‐block‐polycaprolactone (PI‐b‐PCL) and polybutadiene‐block‐poly(methyl methacrylate) (PB‐b‐PMMA). All compatibilizers were synthesized by living anionic polymerization. Investigations of thermal and thermo‐mechanical properties performed by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DTMA), respectively, were systematically classified into two groups, i.e. blends of TPU or SAN with 20 wt% of different compatibilizers (so‐called limit conditions) and TPU/SAN 25/75 blends with 5 wt% of different compatibilizers. In order to determine the compatibilizer's location, morphology of TPU/SAN 25/75 blends was studied with transmission electron microscopy (TEM). Different compatibilization activity was found for different systems. Blends compatibilized with PCL showed superior properties over the other blends. Polym. Eng. Sci. 44:838–852, 2004. © 2004 Society of Plastics Engineers.     

Combustion‐thermal‐sprayed recycled poly(ethylene terephthalate)

Thermal‐sprayed polymer coatings have been used as protection against corrosion and wear. In this study, poly(ethylene terephthalate) (PET) powder, which was obtained from postconsumer beverage bottles, was deposited on 1020 steel by low‐velocity flame‐spray technology. The chemical and structural changes in PET due to the thermal‐spray processing were investigated with Fourier transform infrared spectroscopy and X‐ray diffraction. Changes in tribological behavior were examined by pin‐on‐disk testing and three‐dimensional profilometry. The results show that coatings had the same functional groups as the PET beverage bottles. However, the degree of crystallinity was modified. These changes were rationalized in terms of possible structural modifications of the PET polymer. The study showed evidence that the pin‐on‐disk wear developed by an abrasion process through a ploughing mechanism, although a fatigue mechanism could not be disregarded. A low friction coefficient between PET and steel was confirmed. In the as‐sprayed condition, the PET coatings showed higher friction, likely because of a higher coarse debris production rate during the pin‐on‐disk testing. Heat treating the as‐sprayed coating to increase the amorphous PET content improved the sliding behavior by increasing wear resistance. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3159–3166, 2004     

The role of gel electrolyte composition in the kinetics and performance of dye-sensitized solar cells

Gel-type polymer electrolytes based on the copolymer poly(ethylene oxide-co-epichlorohydrin) and the plasticizer γ-butyrolactone (GBL) were optimized and applied in dye-sensitized solar cells. The plasticizer added to the electrolyte allowed the dissolution of a higher concentration of salt, reaching conductivity values close to 1 mS cm⁻¹ for the sample prepared with 30 wt% of LiI. Raman spectroscopy confirmed polyiodide formation in the electrolyte when the salt concentration exceeds 7.5 wt%, introducing a significant contribution of electronic conductivity in the electrolyte. The devices were characterized under AM 1.5 conditions and the I-V curves were fitted using a two diode equation. Increasing the concentration of LiI-I₂ accelerates dye cation regeneration as measured by transient absorption spectroscopy; however, it also contributes to an increase in the dark current of the cell by one order of magnitude. The best performance was achieved for the solar cell prepared with the electrolyte containing 20 wt% of LiI, with efficiencies of 3.26% and 3.49% at 100 and 10 mW cm⁻² of irradiation, respectively.     

Viability of L. acidophilus microcapsules and their application to buffalo milk yoghurt

Lactobacillus acidophilus was microencapsulated by complex coacervation followed by lyophilisation to be applied in buffalo milk yoghurt. The viability of the probiotics was evaluated for the microencapsulation process, during storage and under simulated gastrointestinal conditions. Four buffalo milk yoghurt-test trials were prepared varying the form of the microorganisms (free and microencapsulated) and the final fermentation pH (4.5 and 5). The acidity, pH and microorganisms’ viability in the yoghurts were evaluated. Results showed that the microencapsulation technique used in this work preserved the counts of L. acidophilus higher than 10⁷ UFC/g at refrigerated conditions, but it did not provide protection to the microorganisms at a pH similar to the human stomach. For the yoghurts, the final fermentation pH did not show significant effects on the variables evaluated. Yoghurts prepared with microencapsulated cultures presented lower values for post-acidification and greater stability compared to the product prepared with the addition of the free culture. The obtained product could represent an alternative for buffalo milk intake provided by the benefits of consumption of L. acidophilus.     

Electrochemical impedance spectroscopy investigation of chlorinated rubber‐based coatings containing polyaniline as anticorrosion agent

Corrosion protection of mild steel by a newly developed chlorinated rubber (CR)‐based coating system containing the inherently conductive polymer polyaniline (PAni) as an anticorrosion agent was studied. The synthesis of PAni and preparation of CR‐based paint containing this polymer are described herein. The corrosion behavior of mild steel samples coated with a CR resin, CR/PAni‐EB (emeraldine base), CR/PAni‐ES (emeraldine salt), and CR/DBSA‐doped PAni were investigated in 3.5% NaCl solution. For this purpose, electrochemical impedance spectroscopy and corrosion potential versus time measurements were utilized. It was found that the addition of the two forms of PAni, doped and undoped, to the CR resin increased its corrosion protection efficiency.