Gross plastic deformation of axisymmetric pressure vessel heads

The gross plastic deformation and associated plastic loads of four axisymmetric torispherical pressure vessels are determined by two criteria of plastic collapse: the ASME twice elastic slope (TES) criterion and the recently proposed plastic work curvature (PWC) criterion. Finite element analysis was performed assuming small and large deformation theory and elastic–perfectly plastic and bilinear kinematic hardening material models. Two plastic collapse modes are identified: bending-dominated plastic collapse of the knuckle region in small deformation models and membrane-dominated plastic collapse of the cylinder or domed end in large deformation models. In both circumstances, the PWC criterion indicates that a plastic hinge bending mechanism leads to gross plastic deformation and is used as a parameter to identify the respective plastic loads. The results of the analyses also show that the PWC criterion leads to higher design loads for strain hardening structures than the TES criterion, as it takes account of the effect of strain hardening on the evolution of the gross plastic deformation mechanism

Design by analysis of ductile failure and buckling in torispherical pressure vessel heads

Thin shell torispherical pressure vessel heads are known to exhibit complex elastic-plastic deformation and buckling behaviour under static pressure. In pressure vessel Design by Analysis, the designer is required to assess both of these behaviour modes when specifying the allowable static load. The EN and ASME boiler and pressure vessel codes permit the use of inelastic analysis in design by analysis, known as the direct route in the EN Code. In this paper, plastic collapse or gross plastic deformation loads are evaluated for two sample torispherical heads by 2D and 3D FEA based on an elastic-perfectly plastic material model. Small and large deformation effects are considered in the 2D analyses and the effect of geometry and load perturbation are considered in the 3D analysis. The plastic load is determined by applying the ASME twice elastic slope criterion of plastic collapse and an alternative plastic criterion, the Plastic Work Curvature criterion. The formation of the gross plastic deformation mechanism in the models is considered in relation to the elastic-plastic buckling response of the vessels. It is concluded that in both cases, design is limited by formation of an axisymmetric gross plastic deformation in the knuckle of the vessels prior to formation of non-axisymmetric buckling modes

Recent developments in steel friction stir welding : Project HILDA

Friction stir welding of steel presents an array of advantages across many industrial sectors compared to conventional fusion welding techniques. Preliminary studies have identified many positive effects on the properties of welded steel components. However, the fundamental knowledge of the process in relation to structural steel remains relatively limited, hence industrial uptake has been essentially non-existent to this date. The European-funded project HILDA, the first of its kind in terms of breadth and depth, is concerned with enhancing the understanding of the process on low alloy steel, establishing its limits in terms of the two more significant parameters which can be directly controlled, tool traverse and rotational speed, thus improving its techno-economic competitiveness to fusion welding. A detailed study investigated the effect of process parameters on the evolved microstructure. In parallel, a full programme of mechanical testing was undertaken to generate data on hardness, impact toughness and fatigue. From this, it has been established that friction stir welding of steel produces high integrity joints that exhibit excellent fatigue properties. From a simulation perspective, a local microstructural numerical model has been developed to predict the microstructural evolution within the weld zone during friction stir welding of low alloy steel. This model concentrates on predicting grain size evolution due to dynamic recrystallization with respect to tool traverse and rotational speed. Furthermore, a computational efficient local-global numerical model capable of predicting the thermal transients, stir and heat affected zone, residual stresses and distortion produced by friction stir welding of DH36 plates is presented

Evaluating plastic loads in torispherical heads using a new criterion of collapse

In ASME Design by Analysis, the plastic load of pressure vessels is established using the Twice Elastic Slope criterion of plastic collapse. This is based on a characteristic load-deformation plot obtained by inelastic analysis. This study investigates an alternative plastic criteria based on plastic work dissipation where the ratio of plastic to total work is monitored. Two sample analyses of medium thickness torispherical pressure vessels are presented. Elastic-perfectly plastic and strain hardening material models are considered in both small and large deformation analyses. The calculated plastic loads are assessed in comparison with experimental results from the literature

Recent developments in steel friction stir welding : project HILDA

Friction stir welding of steel presents an array of advantages across many industrial sectors compared to conventional fusion welding techniques. Preliminary studies have identified many positive effects on the properties of welded steel components. However, the fundamental knowledge of the process in relation to structural steel remains relatively limited, hence industrial uptake has been essentially non-existent to this date. The European-funded project HILDA, the first of its kind in terms of breadth and depth, is concerned with enhancing the understanding of the process on low alloy steel, establishing its limits in terms of the two more significant parameters which can be directly controlled, tool traverse and rotational speed, thus improving its techno- economic competitiveness to fusion welding. A detailed study investigated the effect of process parameters on the evolved microstructure. In parallel, a full programme of mechanical testing was undertaken to generate data on hardness, impact toughness and fatigue. From this, it has been established that friction stir welding of steel produces high integrity joints that exhibit excellent fatigue properties. From a simulation perspective, a local microstructural numerical model has been developed to predict the microstructural evolution within the weld zone during friction stir welding of low alloy steel. This model concentrates on predicting grain size evolution due to dynamic recrystallization with respect to tool traverse and rotational speed. Furthermore, a computational efficient local-global numerical model capable of predicting the thermal transients, stir and heat affected zone, residual stresses and distortion produced by friction stir welding of DH36 plates is presented.peer-reviewe

Development of an anthropomorphic robot hand and wrist for teleoperation applications

In this work, we are developing an anthropomorphic robot hand and wrist to be teleoperated by a human using a glove input device. The present model of the hand is intended for use in grasping operations, and consists of a palm, two fingers, an opposed thumb, and two wrist joints that provide pitch and roll movements. Each of the three digits of the robot hand has two pitch joints to enable flexion and extension, and incorporates a new passive switching mechanism that allows a single actuator to drive the two joints successively. The hand/wrist system has a total of five independent degrees-of-freedom. It is driven by five remotely located DC motors through servo control, and the drive from the motors is transmitted to the hand and wrist joints through flexible sheathed cables acting as tendons. The work focuses on replicating as closely as possible the shape, size, natural motions and applied forces of the human appendage, while keeping the complexity of the robot hand and wrist to a minimum. The first prototype of the hand has been demonstrated, and is capable of holding a wide variety of objects of different shapes and sizes using both precision-type and power-type grasp configurations.peer-reviewe

Patient decision-making about emergency and planned stoma surgery for IBD: a qualitative exploration of patient and clinician perspectives

Background: Many IBD patients worry about stoma forming surgery (SFS), sometimes enduring poor bowel-related quality of life to avoid it. Anticipation of SFS and whether expectations match experience is under-reported. This qualitative study explored influences on patients’ SFS decision-making, and compared pre-operative concerns with post-operative outcomes. Methods: We purposively recruited participants with IBD from UK hospital outpatient and community sources, and IBD clinicians from public hospitals. Four focus groups and 29 semi-structured patient participant interviews, and 18 clinician interviews were audio recorded, transcribed, and analysed thematically. Participants had a current temporary, recently-reversed, or permanent stoma, or were stoma naïve. Results: Four themes emerged: Pre-operative concerns and expectations, Patient decision-making, Surgery and recovery, and Long-term outcomes. Participants and clinicians agreed about most pre-operative concerns, that outcomes were often better than expected, and support from others with a stoma is beneficial. Patient decision-making involves multiple factors, including disease status. Some clinicians avoid discussing SFS, and the phrase ‘last resort’ can bias patient perceptions; others recommend early discussion, increasing dialogue when medical management becomes ineffective. The post-operative period is particularly challenging for patients. Stoma acceptance is influenced by personal perceptions and pre- and post-operative clinical and social support. Conclusion: Patients need balanced information on all treatment options, including surgery, from an early stage. Early multi-disciplinary team dialogue about SFS, and contact with others living well with a stoma, could enable informed decision-making. Life with a stoma is often better than anticipated, improving quality of life and control. Ongoing specialist nursing support aids recovery and adjustment

The TNF-α antagonist etanerceptreverses age-related decreases in colonic SERT expression and faecal output in mice

Treatment for chronic constipation in older people is challenging and the condition has a major impact on quality of life. A lack of understanding about the causes of this condition has hampered the development of effective treatments. 5-HT is an important pro-kinetic agent in the colon. We examined whether alterations in colonic 5-HT signalling underlie age–related changes in faecal output in mice and whether these changes were due to an increase in TNF-α. Components of the 5-HT signalling system (5-HT, 5-HIAA, SERT) and TNF-α expression were examined in the distal colon of 3, 12, 18 and 24- month old mice and faecal output and water content monitored under control conditions and following the administration of etanercept (TNF-α inhibitor; 1 mg Kg-1). Faecal output and water content were reduced in aged animals. Age increased mucosal 5-HT availability and TNF-α expression and decreased mucosal SERT expression and 5-HIAA. Etanercept treatment of old mice reversed these changes, suggesting that age-related changes in TNFα expression are an important regulator of mucosal 5-HT signalling and pellet output and water content in old mice. These data point to “anti-TNFα” drugs as potential treatments for age-related chronic constipation

Priority knowledge needs for implementing nature-based solutions in the Mediterranean islands

Mediterranean islands face significant environmental challenges due to their high population density, reliance on imports, and water scarcity, exacerbated by increasing risks from climate change. Nature-based solutions (NbS) could address these challenges sustainably and with multiple benefits, but their uptake in policy and planning is limited, and stakeholder perspectives are conspicuously lacking from current research. Here, we report the results of a collaborative, multi-stakeholder exercise to identify priority knowledge needs (KNs) that could enhance the uptake of NbS in Mediterranean islands. We used a well-established iterative prioritisation method based on a modified Delphi process. This was conducted by the authors, environmental policy and practice stakeholders from across the Mediterranean islands, representing business, government, NGOs and research. We developed a long list of potential KNs through individual submissions, and prioritised them through voting, discussion and scoring. Excepting workshop discussion, all individual contributions were anonymous. We present the 47 resulting KNs in rank order, classified by whether they can be addressed by knowledge synthesis and further research, or demand action in policy and practice. The top priority KNs are i) a more precise definition of NbS, ii) which NbS are adapted to dry Mediterranean conditions? iii) how to increase the adoption and use of NbS in urban plans?, iv) how can buildings and built-up areas be modified to accommodate green infrastructure and v) cost-benefit analysis of urban green spaces. In collaboration with these stakeholders, our findings will determine future research strategies on NbS implementation in the Mediterranean islands

Aging of the mammalian gastrointestinal tract: a complex organ system

Gastrointestinal disorders are a major cause of morbidity in the elderly population. The gastrointestinal tract is the most complex organ system; its diverse cells perform a range of functions essential to life, not only secretion, digestion, absorption and excretion, but also, very importantly, defence. The gastrointestinal tract acts not only as a barrier to harmful materials and pathogens but also contains the vast number of beneficial bacterial populations that make up the microbiota. Communication between the cells of the gastrointestinal tract and the central nervous and endocrine systems modifies behaviour; the organisms of the microbiota also contribute to this brain–gut–enteric microbiota axis. Age-related physiological changes in the gut are not only common, but also variable, and likely to be influenced by external factors as well as intrinsic aging of the cells involved. The cellular and molecular changes exhibited by the aging gut cells also vary. Aging intestinal smooth muscle cells exhibit a number of changes in the signalling pathways that regulate contraction. There is some evidence for age-associated degeneration of neurons and glia of the enteric nervous system, although enteric neuronal losses are likely not to be nearly as extensive as previously believed. Aging enteric neurons have been shown to exhibit a senescence-associated phenotype. Epithelial stem cells exhibit increased mitochondrial mutation in aging that affects their progeny in the mucosal epithelium. Changes to the microbiota and intestinal immune system during aging are likely to contribute to wider aging of the organism and are increasingly important areas of analysis. How changes of the different cell types of the gut during aging affect the numerous cellular interactions that are essential for normal gut functions will be important areas for future aging research