A Stretch/Bend Method for In Situ Measurement of the Delamination Toughness of Coatings and Films Attached to Substrates

A stretch/bend method for the in situ measurement of the delamination toughness of coatings attached to substrates is described. A beam theory analysis is presented that illustrates the main features of the test. The analysis is general and allows for the presence of residual stress. It reveals that the test produces stable extension of delaminations, rendering it suitable for multiple measurements in a single test. It also provides scaling relations and enables estimates of the loads needed to extend delaminations. Finite element calculations reveal that the beam theory solutions are accurate for slender beams, but overestimate the energy release rate for stubbier configurations and short delaminations. The substantial influence of residual stress on the energy release rate and phase angle is highly dependent on parameters such as the thickness and modulus ratio for the two layers. Its effect must be included to obtain viable measurements of toughness. In a companion paper, the method has been applied to a columnar thermal barrier coating deposited onto a Ni-based super-alloy.Engineering and Applied Science

CORRELATION OF SHORT-TERM TO LONG-TERM OXIDATION TESTING FOR ALUMINA FORMING ALLOYS AND COATINGS

Engineering long cyclic oxidation life of high temperature materials requires success on two fronts. First a slow growing protective oxide scale must form during the elevated temperature exposure. To satisfy this aspect, alumina-forming alloys and coatings are widely accepted as leading materials for use in this environment and are the focus of this discussion. The second aspect is the formation of an adherent oxide that resists spallation during thermal cycling. The driving force for spallation is the stored elastic strain energy that develops from stresses in the oxide scale. Once this stored elastic strain energy exceeds the oxide-substrate interfacial toughness, cracking and subsequent spallation occurs followed by rapid oxidation of the substrate. With advances in alloy and coating development resulting in higher operating temperatures and increased service lives, researchers are faced with excessive laboratory time and cost required to perform a long-term cyclic oxidation test.The challenge is to predict long-term oxidation behavior from short-term experiments. Since the rate limiting step to high temperature oxidation is a thermally activated process, previous investigations were performed at increased exposure temperatures for rapid degradation of the alloys and coatings to rank material performance. Others have mechanically induced oxide spallation to give insight on the adherence of oxide scales prior to spontaneous failure. In this investigation, short-term testing is employed to gain insight on long-term performance and to determine inputs into a cyclic oxidation model for life-time prediction. This model operates in an iterative process where one iteration is a thermal cycle. The amount of oxide formed during the high temperature segment is calculated followed by the amount that is lost due to scale spallation during cooling. Retained oxide at the end of this cycle is used as the starting point for the following iteration. The two inputs into this model are the oxide scale growth and spallation behavior. Scale growth behavior corresponds to the isothermal growth kinetics that are experimentally determined by thermogravimetric analysis. Oxide scale spallation behavior is quantified by two short-term experiments of a novel acoustic emission experiment during a 24 hour exposure and the stress measurement of the scale after an exposure to the temperature of interest. Results from these short-term tests and modeled cyclic oxidation are compared to life-times from long-term cyclic oxidation tests

Characteristic length of random knotting for cylindrical self-avoiding polygons

We discuss the probability of random knotting for a model of self-avoiding polygons whose segments are given by cylinders of unit length with radius $r$. We show numerically that the characteristic length of random knotting is roughly approximated by an exponential function of the chain thickness $r$.Comment: 5 pages, 4 figure

Topological entropy of a stiff ring polymer and its connection to DNA knots

We discuss the entropy of a circular polymer under a topological constraint. We call it the {\it topological entropy} of the polymer, in short. A ring polymer does not change its topology (knot type) under any thermal fluctuations. Through numerical simulations using some knot invariants, we show that the topological entropy of a stiff ring polymer with a fixed knot is described by a scaling formula as a function of the thickness and length of the circular chain. The result is consistent with the viewpoint that for stiff polymers such as DNAs, the length and diameter of the chains should play a central role in their statistical and dynamical properties. Furthermore, we show that the new formula extends a known theoretical formula for DNA knots.Comment: 14pages,11figure

Priorities for prehabilitation for patients with upper gastrointestinal cancer: a nominal group consensus study

Purpose: Prehabilitation is a broad and evolving concept that is recommended to improve patient outcomes but is not offered routinely to patients undergoing surgery in centres across the UK. The purpose of this study was to combine existing evidence with expert opinion to establish consensus on the key priorities for prehabilitation interventions in patients undergoing surgery for upper gastrointestinal cancer. Methods: A modified nominal group technique was utilised. Prior to an online meeting, individual ideas were generated in response to questions across three themes: prehabilitation interventions, clinical implementation and behaviour change support, and outcomes and cost-effectiveness. The online meeting included facilitated discussions to clarify and regroup ideas, followed by anonymous ranking of individual ideas. GroupMap™ software was used to collect and analyse the data. Results: Eight individuals attended the meeting in November 2023, including physiotherapists and dietitians experienced in prehabilitation and an experienced patient advocate. A high level of consensus was achieved across many aspects of prehabilitation, with eight out of 89 ideas achieving 100% consensus agreement (9%) and 31 out of 89 ideas achieving consensus of 70% or higher (35%). The main findings demonstrated complete consensus that prehabilitation should be delivered as a multimodal, multidisciplinary intervention that combines all three core aspects (exercise, nutrition and psychological support). Conclusion: The study findings are consistent with developing evidence trends and confirmed which core aspects should be incorporated into prehabilitation interventions for patients undergoing upper gastrointestinal surgery. These insights will help to develop prehabilitation services that are integrated across professions and systems for best patient care

Multi-layered Ruthenium-modified Bond Coats for Thermal Barrier Coatings

Diffusional approaches for fabrication of multi-layered Ru-modified bond coats for thermal barrier coatings have been developed via low activity chemical vapor deposition and high activity pack aluminization. Both processes yield bond coats comprising two distinct B2 layers, based on NiAl and RuAl, however, the position of these layers relative to the bond coat surface is reversed when switching processes. The structural evolution of each coating at various stages of the fabrication process has been and subsequent cyclic oxidation is presented, and the relevant interdiffusion and phase equilibria issues in are discussed. Evaluation of the oxidation behavior of these Ru-modified bond coat structures reveals that each B2 interlayer arrangement leads to the formation of α-Al 2 O 3 TGO at 1100°C, but the durability of the TGO is somewhat different and in need of further improvement in both cases

Analysis of sexual phenotype and prezygotic fertility in natural populations of Fucus spiralis, F. vesiculosus (Fucaceae, Phaeophyceae) and their putative hybrids

In the genus Fucus, the character dioecy/hermaphroditism has undergone multiple state changes and hybridization is possible between taxa with contrasting mating systems, e.g. between the dioecious Fucus vesiculosus and the hermaphrodite F. spiralis. In the context of mating system evolution, we evaluated the potential consequences of hybridization by studying the variation in sexual phenotype and prezygotic fertility. Firstly, as a result of hybridization between the two sexual systems, gender variation may arise depending on the relative importance of genes with large versus small phenotypic effects. We thus qualitatively examined the extent of gender variation within and among individual hybrids in comparison with both parental species. Secondly, if hybridization breaks up co-adapted gene complexes, hybrid fertility may be reduced in comparison with both parental species. Therefore, we also quantified male and female prezygotic fertility in parental species and their hybrids in order to test for reduction in hybrid fitness. A total of 89 sexually mature individuals (20 F. spiralis, 40 F. vesiculosus, 10 hermaphrodite hybrids and 19 dioecious hybrids) were sampled in two geographically distant regions (France and Portugal) and six conceptacles per individual were observed. Within-individual variation was very restricted qualitatively – only one hybrid carried a conceptacle with a different sexual phenotype from the five others – as well as quantitatively. This suggests a simple genetic system for sex determination involving a few genes with major effects. In addition, analyses showed no significant decrease in hybrid fertility compared with parental species. Moreover, hybrids exhibited all sexual phenotypes, suggesting several generations of hybridization and backcrossing and, therefore, that hybrids are reproductively successful. Finally, the occurrence of sterile paraphyses in female and hermaphrodite individuals was interpreted as a relic of male function and suggests that, as in higher plants, evolution from hermaphroditism to dioecy may be the most parsimonious pathway