Advanced constitutive modelling for creep-fatigue assessment of high temperature components

Creep-fatigue assessment procedures for the design of high-temperature components should ensure lifetime predictions which are safe but not excessively conservative. Adoption of more accurate assessment procedures than are presently available enable the availability of power plant with greater operating flexibility. Operating flexibility is becoming a key market driver due to the increased interest in the use of intermittent renewable energy sources (e.g. wind, solar) which place focus on a requirement for turbo-machinery to be capable of reduced start-up and shut-down times. This study introduces a creep-fatigue assessment procedure for the design of high-temperature components required for flexible operation. In particular, it considers alloys with high creep-fatigue deformation/damage interaction characteristics such as the advanced martensitic 9–11%Cr steels which are widely used for power plant applications. The procedure takes advantages of advanced constitutive models and implements them in a state-of-the-art mechanical assessment procedure for calculating high-temperature component life times.     

Anisotropic meta-models for computationally expensive simulations in nonlinear mechanics

Nonintrusive methods are now established in the engineering community as a pragmatic approach for the uncertainty quantification (UQ) and global sensitivity analysis (GSA) of complex models. However, especially for computationally expensive models, both types of analyses can only be completed by employing surrogates that replace the original models and are considerably less expensive. This work studies the construction of accurate and predictive meta-models for their use in both UQ and GSA, and their application to complex problems in nonlinear mechanics. In particular, meta-models based on radial functions are examined and enhanced with anisotropic metrics for improved predictiveness and cost effectiveness. Three numerical examples illustrate the performance of the proposed methodology.     

A Highly Emissive Surface Layer in Mixed‐Halide Multication Perovskites

Mixed‐halide lead perovskites have attracted significant attention in the field of photovoltaics and other optoelectronic applications due to their promising bandgap tunability and device performance. Here, the changes in photoluminescence and photoconductance of solution‐processed triple‐cation mixed‐halide (Cs_0.06MA_0.15FA_0.79)Pb(Br_0.4I_0.6)₃ perovskite films (MA: methylammonium, FA: formamidinium) are studied under solar‐equivalent illumination. It is found that the illumination leads to localized surface sites of iodide‐rich perovskite intermixed with passivating PbI₂ material. Time‐ and spectrally resolved photoluminescence measurements reveal that photoexcited charges efficiently transfer to the passivated iodide‐rich perovskite surface layer, leading to high local carrier densities on these sites. The carriers on this surface layer therefore recombine with a high radiative efficiency, with the photoluminescence quantum efficiency of the film under solar excitation densities increasing from 3% to over 45%. At higher excitation densities, nonradiative Auger recombination starts to dominate due to the extremely high concentration of charges on the surface layer. This work reveals new insight into phase segregation of mixed‐halide mixed‐cation perovskites, as well as routes to highly luminescent films by controlling charge density and transfer in novel device structures.     

Hardware Sequencing of Inflatable Nonlinear Actuators for Autonomous Soft Robots

Soft robots are an interesting alternative for classic rigid robots in applications requiring interaction with organisms or delicate objects. Elastic in?atable actuators are one of the preferred actuation mechanisms for soft robots since they are intrinsically safe and soft. However, these pneumatic actuators each require a dedicated pressure supply and valve to drive and control their actuation sequence. Because of the relatively large size of pressure supplies and valves compared to electrical leads and electronic controllers, tethering pneumatic soft robots with multiple degrees of freedom is bulky and unpractical. Here, a new approach is described to embed hardware intelligence in soft robots where multiple actuators are attached to the same pressure supply, and their actuation sequence is programmed by the interaction between nonlinear actuators and passive ?ow restrictions. How to model this hardware sequencing is discussed, and it is demonstrated on an 8‐degree‐of‐freedom walking robot where each limb comprises two actuators with a sequence embedded in their hardware. The robot is able to carry pay loads of 800 g in addition to its own weight and is able to walk at travel speeds of 3 body lengths per minute, without the need for complex on‐board valves or bulky tethers.     

Design of high fastness acid dyes for silk: a chemometric approach

A chemometric strategy tor the design of acid dyes for silk is reported. A small set of representative dyes was selected by the technique of fractional factorial design, using the principal properties of the substituents as design variables. The selected dyes were synthesised and fastness properties on silk were measured. Wash fastness and light fastness values were related to the chemical structure by the partial least squares (PLS) method. The models were used to predict the fastness of new dyes of the same class and to optimise the structure.     

Structural models of critical regions in old-type r.c. frames with smooth rebars

Structural assessment of existing reinforced concrete constructions under gravity loads and seismic actions has a high social and economical impact; actually in many European countries, most of the buildings dates back to 1960s and 1970s and cannot ensure satisfactory seismic response, since many areas have been later classified as seismic or since design has been carried out according to obsolete codes. These structures are generally reinforced with smooth bars that exhibit poor bond and need specific anchoring end details. In the present paper, some key aspects of structural models of smooth reinforcement for old-type r.c. frame analysis are reported. Results of experimental tests on smooth reinforcement and circular hook anchoring devices are also used to discuss some aspects of behavioural models of beam to column critical regions.     

Analytical authentication of organic products: an overview of markers

Consumers' interest in organic foods is increasing and so is the need for robust analytical tools for their authentication. This review focuses on the most promising biomarkers/analytical approaches that are available for the authentication of organic produce. Food products have been subdivided into two groups: foods of plant origin (crops) and foods of animal origin (meat, milk and dairy products, eggs and fish). For each food category the most suitable biomarkers are presented and their potential for authentication is discussed. In the light of current knowledge, it is unlikely that the authentication of organic food products can be attained by the measurement of a single marker. Analytical approaches based on the measurement of multiple markers and/or complex chemical or physical profiles/fingerprints supported by multivariate statistical analysis seem considerably more promising in this respect. For the development of robust classification models, well‐designed experimental studies must be performed that rely on data sets that are both well balanced and of sufficient size to ensure that all relevant sources of variation for the target biomarkers are included in the reference database. Copyright © 2012 Society of Chemical Industry     

The behavior of dietary fiber in the gastrointestinal tract determines its physiological effect

A diet rich in dietary fiber (DF) is considered healthy and recommended dietary intake of DF is established all over the world. The physiological effect of DF is mostly related to its behavior during digestion. In this review, the behavior of DF in the human digestive tract is discussed and linked to its physiological effect with special attention to four aspects of such behavior: (i) the modulation of bioavailability by the plant cell walls, (ii) the effect of DF on the rheological and colloidal state of digesta, (iii) the binding of DF with phenolic compounds, bile salts, mineral ions, and digestive enzymes, and (iv) DF fermentation in the large intestine and the corresponding effect on microbiota composition. It is stressed that the detailed chemical characterization of DF is crucial to explain its effect on health and that DF behavior in the digestive tract can be modulated by interactions with other food and meal components so that information of the bare content in DF of food is not sufficient to predict its physiological effect.