Clarifying the effect of sintering conditions on the microstructure and mechanical properties of β-tricalcium phosphate

The effect of the sintering conditions (temperature and time) on the microstructure (density and grain size) and mechanical properties (hardness, elastic modulus, and strength) of β-tricalcium phosphate (β-TCP) bioceramics fabricated from Ca-deficient commercial powders is analyzed. Contrary to current general opinion, it is demonstrated that the optimal sintering temperature to maximize the mechanical performance of this β-TCP material is not necessarily below the β ? α transformation temperature (1125 °C). In particular, optimal performance was achieved in samples sintered at 1200 °C for 3 h, since it was not until higher temperatures or longer sintering times that microcracking develops and mechanical properties are degraded. It is argued that the residual stresses developed during this reversible transformation do not lead to microcrack propagation until sufficiently large starting flaws develop in the microstructure as a consequence of grain growth. Implications of these findings for the processing routes to improve sintering of this important bioceramic are discussed.     

Development of a site-specific ecological risk assessment for contaminated sites: part I. A multi-criteria based system for the selection of ecotoxicological tests and ecological observations

A two modules Decision Support System (DSS-ERAMANIA) was developed in order to support the site-specific Ecological Risk Assessment (ERA) for contaminated sites. Within the first module, the TRIAD and the Weight of Evidence approaches were used to develop a site-specific Ecological Risk Assessment framework including three tires of investigation. Selected ecological observations and ecotoxicological tests were compared according to Multi Criteria Decision Analysis (MCDA) methods and expert judgment, and the obtained ranking was used to identify a suitable set of tests, at each investigation tier, to be applied to the examined case study. A simplified application of the proposed methodology, implemented in the Module 1 of the DSS-ERA-MANIA, is described and discussed.     

Highly Regio- and Stereoselective Diels-Alder Cycloadditions via Two-Step and Multicomponent Reactions Promoted by Infrared Irradiation under Solvent-Free Conditions

Infrared irradiation promoted the Diels-Alder cycloadditions of exo-2-oxazolidinone dienes 1-3 with the Knoevenagel adducts 4-6, as dienophiles, leading to the synthesis of new 3,5-diphenyltetrahydrobenzo[d]oxazol-2-one derivatives (7, 9, 11 and 13-17), under solvent-free conditions. These cycloadditions were performed with good regio- and stereoselectivity, favoring the para-endo cycloadducts. We also evaluated the one-pot three-component reaction of active methylene compounds 20, benzaldehydes 21 and exo-2-oxazolidinone diene 2 under the same reaction conditions. A cascade Knoevenagel condensation/Diels-Alder cycloaddition reaction was observed, resulting in the final adducts 13-16 in similar yields. These procedures are environmentally benign, because no solvent and no catalyst were employed in these processes. The regioselectivity of these reactions was rationalized by Frontier Molecular Orbital (FMO) calculations.     

Enhancing Osteoconduction of PLLA-Based Nanocomposite Scaffolds for Bone Regeneration Using Different Biomimetic Signals to MSCs

In bone engineering, the adhesion, proliferation and differentiation of mesenchymal stromal cells rely on signaling from chemico-physical structure of the substrate, therefore prompting the design of mimetic "extracellular matrix"-like scaffolds. In this study, three-dimensional porous poly-L-lactic acid (PLLA)-based scaffolds have been mixed with different components, including single walled carbon nanotubes (CNT), micro-hydroxyapatite particles (HA), and BMP2, and treated with plasma (PT), to obtain four different nanocomposites: PLLA + CNT, PLLA + CNTHA, PLLA + CNT + HA + BMP2 and PLLA + CNT + HA + PT. Adult bone marrow mesenchymal stromal cells (MSCs) were derived from the femur of orthopaedic patients, seeded on the scaffolds and cultured under osteogenic induction up to differentiation and mineralization. The release of specific metabolites and temporal gene expression profiles of marrow-derived osteoprogenitors were analyzed at definite time points, relevant to in vitro culture as well as in vivo differentiation. As a result, the role of the different biomimetic components added to the PLLA matrix was deciphered, with BMP2-added scaffolds showing the highest biomimetic activity on cells differentiating to mature osteoblasts. The modification of a polymeric scaffold with reinforcing components which also work as biomimetic cues for cells can effectively direct osteoprogenitor cells differentiation, so as to shorten the time required for mineralization.     

Several questions about electrochemical rehabilitation methods for reinforced concrete structures

Electrochemical realkalisation (ERA) and electrochemical chloride removal (ECR) have shown their capacity to eliminate, in just a few weeks, the causes of corrosion in reinforced concrete structures (RCS), and for this reason are currently receiving very special attention. Nevertheless, the present state of the art has not progressed enough to dissipate doubts about the efficiency of ERA and ECR as electrochemical rehabilitation methods (ERM) for corroding RCS. A series of highly important questions persist, and continue to be cause of controversy among specialists in the construction sector, which can be summed up in one all-encompassing question, namely:

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Is removing the sources of corrosion in RCS sufficient to stop rusting?To obtain a response to this capital question, electrochemical corrosion analysis techniques are used to study the responses of clean and precorroded steel electrodes embedded in small mortar specimens without chloride additions and large mortar slabs with and without chloride contamination. According to the results obtained, ERM are efficient in delaying the start of corrosion if used preventively. However, if applied too late they do not assure the repassivation of rebars with high precorrosion levels and consequently are not useful.

     

Fatigue behaviour of bolted joints

This paper analyzes the tensile fatigue behaviour of bolted joints constituted by commercial steel bolts. They were tested under both monotonic and fatigue tensile loading, with different R-ratio. Results show that under increasing monotonic tensile loading the bolted joint is not the failure zone of the bolt, whereas such a bolted joint is the failure region under cyclic loading. The fatigue life decreases with the increase of the stress range and with the maximum stress, and pre-loading enlarges the fatigue life. Fatigue fracture surface shows a geometry of crescent moon in the case of short cracks and such a shape evolves towards a quasi-straight crack front in the case of long cracks. Fatigue fracture usually happens at the root of the first notch inside the bolted joint, although fracture initiation may happen in several consecutive notch roots, increasing the initiation angle of the fatigue crack as the applied stress diminishes.     

Analysis of a delayed fracture criterion for lifetime prediction of viscoelastic polymer materials

In this work a multi-axial yield/failure model for viscoelastic/plastic materials is applied, which was developed by Naghdi and Murch (in J.?Appl. Mech. 30:321?C328, 1963) and later extended and refined by Crochet (in J.?Appl. Mech. 33:327?C334, 1966), to predict long-term creep rupture of polymers. The criterion defines a function, which depends on time, the viscoelastic properties and applied stress, to establish an empirical law with creep yield (fracture). In this work a linear relationship is proposed, defined as a time-dependent failure criterion, which can be applied for extrapolation purposes. A comparative analysis using energy-based failure criteria is performed. It is proved, for the polymers considered in this study, that the proposed time-dependent failure criterion holds for long times. Experimental data are used to illustrate the applicability of this time-dependent failure criterion.     

Physical Virology: Direct Measurement of Phage phi29 Stiffness Provides Evidence of Internal Pressure (Small 15/2012)

A 3D AFM topography rendition of a phage phi29 (red) adsorbed on mica (blue) is shown by P. J. de Pablo and coworkers, where part of the viral DNA (yellow) has been ejected through the tail. The phi29 bacteriophage translocates part of its DNA into the host by releasing the elastic energy arising from the internal pressure created during the DNA-packing process. Pushing with the AFM tip on the phage enables the direct measurement of the stiffness to estimate its internal pressure, just as a tyre may be pressed with fingers.     

Comparative study of laser welding in tailor blanks for the automotive industry

The increasing demand put on automotive industry to reduce car costs and fuel consumption has led to the design of innovative technological solutions. These new concepts aim at higher productivities, better quality, and improved performances of the final product. The use of tailor blanks in automotive industry is an example of a successful innovation which is nowadays used in many companies worldwide. The main objective of the present study is to assess laser welding of tailor blanks in steel, comparing the performance of the three types of high-power lasers, CO₂, Nd/YAG, and fiber laser, in terms of productivity, costs, and weld quality. Mechanical properties have also been targeted as these are essential for the formability of the welded blanks.     

Capillary Pressure Determination from Sorption Isotherms for Mixtures of Porous Solids

Capillary pressure and relative permeability are important parameters for characterization of the draining of fluid phases in porous media. In this work, capillary pressure and relative permeability were evaluated in porous solids with distinct morphological properties, namely NaY zeolite, kaolin, and alumina as well as their binary mixtures in the compositions of 20, 40, 60, and 80% in mass fraction. The objective of the present work was to verify the influence of the composition of the solid mixture and the structural characteristics of the components on capillary pressure and relative permeability. Capillary pressure as a function of saturation of the material was determined from moisture desorption isotherms. The results showed that structural characteristics greatly influence capillary pressure and permeability. The obtained capillary pressure in microporous materials was higher than that in macroporous and mesoporosous materials at the same saturation. It was verified that when microporous materials were present in the mixture, the capillary pressure of the binary mixtures tended to approach the capillary pressure of the microporous materials, since micropores control the adsorption and desorption processes.