The dynamic response of a β titanium alloy to high strain rates and elevated temperatures

The stress-strain behaviour and microstructural evolution of the Ti-6Cr-5Mo-5V-4Al (Ti6554) alloy was systematically investigated using Split Hopkinson Pressure Bar (SHPB) tests over a wide range of strain rates from 1000s-1 to 10,000s-1 and initial temperatures from 293K to 1173K. Dislocation slip is the main deformation mechanism for plastic flow of the Ti6554 alloy at high strain rates. The flow stress increases with increasing strain rate and decreasing temperature. Also the flow stress is more sensitive to temperature than to strain rate. For high strain rate deformations, the strain hardening rate is found to be negative at 293K and increases with increasing temperatures. Flow softening observed at 293K is potentially caused by adiabatic heating. The increment in the strain hardening rate with increasing temperatures may be the result of interactions between thermally activated solute Cr atoms and mobile dislocations. When the temperature is raised to 873K, a novel α precipitate morphology consisting of globular α aligned in strings was observed in specimens deformed at strain rates of 4000 and 10,000s-1. It has hardening effects on the β matrix and is purported to nucleate on dislocations introduced by the high strain rate deformation. Adiabatic shear bands were observed in specimens deformed at higher temperatures (873K). The microstructure inside the shear bands is harder than that outside of the shear bands in the Ti6554 alloy

The cold-rolling behaviour of AZ31 tubes for fabrication of biodegradable stents

Mg alloys are receiving considerable attention for biomedical stents due to their combination of good mechanical properties and high biodegradability. Cold rolling is necessary to process Mg alloy tubes before final drawing and fabrication of the magnesium stents. In this paper, cold-rolled tubes were subjected to a cross-sectional reduction rate (ε) of up to 19.7%, and were further processed at various ratios of wall-thickness to diameter reduction (Q) from 0 to 2.24 with a constant ε of 19.7%. The results show that the cold-rolled tubes exhibited a rise in ultimate tensile strength (UTS), yield strength (YS), and a reduction in elongation as ε increased from 5.5% to 19.7%. UTS, YS and elongation decreased when Q was increased from 0 to 2.24. Mechanical twinning was observed and analysed. Extension twins increased with increasing ε and were almost saturated at a ε of 16.5%. Extension twins play an important role in determining the evolution of mechanical behaviour in the case of increasing ε, whilst contraction/double twins and secondary extension twins have a large effect on mechanical behaviour in the case of varying Q. The results indicate that the proportions and types of twins play a major role in determining the mechanical behaviour of the AZ31 tubes

Constitutive modelling of the flow behaviour of a β titanium alloy at high strain rates and elevated temperatures using the Johnson-Cook and modified Zerilli-Armstrong models

The objectives of this work are to characterize the flow behaviour of the Ti-6Cr-5Mo-5V-4Al (Ti6554) alloy at high strain rates and elevated temperatures using the Johnson-Cook (JC) model and a modified Zerilli-Armstrong (ZA) model, and to make a comparative study on the predictability of these two models. The stress-strain data from Split Hopkinson Pressure Bar (SHPB) tests over a wide range of temperatures (293-1173K) and strain rates (103-104s-1) were employed to fit parameters for the JC and the modified ZA models. It is observed that both the JC and the modified ZA models have good capacities of describing the flow behaviour of the Ti6554 alloy at high strain rates and elevated temperatures in terms of the average absolute error. The modified ZA model is able to capture the strain-hardening behaviour of the Ti6554 alloy better as it incorporates the coupling effects of strain and temperature. However, dynamic recovery or dynamic recrystallization that may happen at elevated temperatures should be taken into consideration when selecting data set for parameters fitting for the modified ZA model. Also the modified ZA model requires more stress-strain data for the parameters fitting than the JC model

The Efficacy of Equine Oral Joint Supplements

Few studies have examined the efficacy of glucosamine, hyaluronic acid, and chondroitin sulfate supplements in horses. The purpose of this study is to determine if the commercially available supplements are meeting the label guarantees, and to analyze any correlation between price point and efficacy of use. The supplemental ingredients of interest to this study are combinations of glucosamine, hyaluronic acid, and chondroitin sulfate. Horses in the study were fed each supplement for a 14-day period with synovial fluid extracted through aseptic arthrocentesis at days 0 and 14. The 12 horses followed a 14-day feeding period accompanied by a 28-day dry out period. This protocol was repeated 3 times, each with a different supplement. During these trials and the dry-out periods, the horses were divided into groups of 4 and exercised at different levels depending on the group. Physical data was collected on days 0 and 14 of each of the 3 trials to determine any physical differences associated with the use of the supplements. The veterinarian scored the horses at a walk and trot before carrying out flexion tests on all 4 limbs. The pulse, temperature, respiratory rate, and body condition scores were also collected. Enzyme-linked immunosorbent assays were used to quantify the amounts of chondroitin sulfate in each sample. The results for the glucosamine and hyaluronic acid are still pending

Manufacturing of biocompatible porous titanium scaffolds using a novel spherical sugar pellet space holder

A new and highly biocompatible space holder material is proposed for manufacturing of porous titanium with open and interconnected pore morphologies through powder metallurgy techniques. Sugar pellets are compacted with titanium powder and then removed by dissolution in water before sintering. The morphology, pore structure and porosity were observed by optical microscopy, SEM and micro-CT. The porous titanium has highly spherical pore shapes, well-controlled pore sizes and high interconnectivity. The results suggest that porous titanium scaffolds generated using this manufacturing route have the potential for hard tissue engineering applications

An investigation of the mechanical behaviour of fine tubes fabricated from a Ti-25Nb-3Mo-3Zr-2Sn alloy

This study investigates the mechanical properties and the deformation mechanisms active in Ti–25Nb–3Mo–3Zr–2Sn fine tubes. Ti–25Nb–3Mo–3Zr–2Sn alloy is a recently developed metastable β titanium alloy intended for biomedical applications. Tensile tests were carried out on the fine tubes. The modulus of the Ti–25Nb–3Mo–3Zr–2Sn fine tubes increased with reductions in the diameter for tubes in the cold rolled and annealed conditions. In comparison with cold rolled tubes, the annealed tubes exhibit increased strain hardening behaviour and superior ductility. Mechanical twins, stress-induced martensitic transformation and the textures of the β and α″ phases were investigated. The results show that the fine tubes exhibit different moduli which are related to the evolution of β and α″ phase textures during processing. Cold rolling facilitates the transformation from β to the α″ phase and mechanical {332}〈113〉 twinning. For the annealed tubes, mechanical twinning as well as primary and secondary martensitic transformations was activated at specific levels of tensile strain. Twins developed with increasing levels of strain, and secondary martensitic transformations occurred within the twinned β regions. Annealed fine tubes exhibit multistage strain hardening behaviour and superior ductility due to the synergetic effects of twinning induced plasticity and transformation induced plasticity during tensile deformation

Optimising degradation and mechanical performance of additively manufactured biodegradable Fe–Mn scaffolds using design strategies based on triply periodic minimal surfaces

Additively manufactured lattices based on triply periodic minimal surfaces (TPMS) have attracted significant research interest from the medical industry due to their good mechanical and biomorphic properties. However, most studies have focussed on permanent metallic implants, while very little work has been undertaken on manufacturing biodegradable metal lattices. In this study, the mechanical properties and in vitro corrosion of selective laser melted Fe–35%Mn lattices based on gyroid, diamond and Schwarz primitive unit-cells were comprehensively evaluated to investigate the relationships between lattice type and implant performance. The gyroid-based lattices were the most readily processable scaffold design for controllable porosity and matching the CAD design. Mechanical properties were influenced by lattice geometry and pore volume. The Schwarz lattices were stronger and stiffer than other designs with the 42% porosity scaffold exhibiting the highest combination of strength and ductility, while diamond and gyroid based scaffolds had lower strength and stiffness and were more plastically compliant. The corrosion behaviour was strongly influenced by porosity, and moderately influenced by geometry and geometry-porosity interaction. At 60% porosity, the diamond lattice displayed the highest degradation rate due to an inherently high surface area-to-volume ratio. The biodegradable Fe–35Mn porous scaffolds showed a good cytocompatibility to primary human osteoblasts cells. Additive manufacturing of biodegradable Fe–Mn alloys employing TPMS lattice designs is a viable approach to optimise and customise the mechanical properties and degradation response of resorbable implants toward specific clinical applications for hard tissue orthopaedic repair

Author Correction: Convalescent plasma for hospitalized patients with COVID-19: an open-label, randomized controlled trial (Nature Medicine, (2021), 27, 11, (2012-2024), 10.1038/s41591-021-01488-2)

In the version of this Article initially published, there was an omission in the member list for the CONCOR-1 Study Group. Valérie Arsenault (Héma-Québec, Montreal, Quebec, Canada) has now been included in the CONCOR-1 Study Group in the online version of the article

Comics, graphic narratives, and lesbian lives

Lesbian comics and graphic narratives have gained unprecedented cultural presence in the twenty-first century. Yet despite the surge in interest in the work of artists such as Alison Bechdel, and despite the existence of a substantial online archive about lesbian comics created by artists, readers, and collectors, relatively little critical attention has been directed to this work. The chapter begins to fill this gap. Taking the Bechdel’s work as its start-and-end point, it provides an overview of major developments in lesbian comics and contextualises them including in relation to the gendered conditions of possibility that define comics culture