Designing of a Fleet-Leader Program for Carbon Composite Overwrapped Pressure Vessels

Composite Overwrapped Pressure Vessels (COPVs) are often used for storing pressurant gases on board spacecraft when mass saving is a prime requirement. Substantial weight savings can be achieved compared to all metallic pressure vessels. For example, on the space shuttle, replacement of all metallic pressure vessels with Kevlar COPVs resulted in a weight savings of about 30 percent. Mass critical space applications such as the Ares and Orion vehicles are currently being planned to use as many COPVs as possible in place of all-metallic pressure vessels to minimize the overall mass of the vehicle. Due to the fact that overwraps are subjected to sustained loads during long periods of a mission, stress rupture failure is a major concern. It is, therefore, important to ascertain the reliability of these vessels by analysis, since it is practically impossible to show by experimental testing the reliability of flight quality vessels. Also, it is a common practice to set aside flight quality vessels as "fleet leaders" in a test program where these vessels are subjected to slightly accelerated operating conditions so that they lead the actual flight vessels both in time and load. The intention of fleet leaders is to provide advanced warning if there is a serious design flaw in the vessels so that a major disaster in the flight vessels can be averted with advance warning. On the other hand, the accelerating conditions must be not so severe as to be prone to false alarms. The primary focus of the present paper is to provide an analytical basis for designing a viable fleet leader program for carbon COPVs. The analysis is based on a stress rupture behavior model incorporating Weibull statistics and power-law sensitivity of life to fiber stress level

Fracture model with variable range of interaction

We introduce a fiber bundle model where the interaction among fibers is modeled by an adjustable stress-transfer function which can interpolate between the two limiting cases of load redistribution, the global and the local load sharing schemes. By varying the range of interaction several features of the model are numerically studied and a crossover from mean field to short range behavior is obtained. The properties of the two regimes and the emergence of the crossover in between are explored by numerically studying the dependence of the ultimate strength of the material on the system size, the distribution of avalanches of breakings, and of the cluster sizes of broken fibers. Finally, we analyze the moments of the cluster size distributions to accurately determine the value at which the crossover is observed.Comment: 8 pages, 8 figures. Two columns revtex format. Final version to be published in Phys. Rev.

An assessment of the strength of knots and splices used as eye terminations in a sailing environment

Research into knots, splices and other methods of forming an eye termination has been limited, despite the fact that they are essential and strongly affect the performance of a rope. The aim of this study was to carry out a comprehensive initial assessment of the breaking strength of eye terminations commonly used in a sailing environment, thereby providing direction for further work in the field. Supports for use in a regular tensile testing machine were specially developed to allow individual testing of each sample and a realistic spread of statistical data to be obtained. Over 180 break tests were carried out on four knots (the bowline, double bowline, figure-of-eight loop and perfection loop) and two splices (three-strand eye splice and braid-on-braid splice). The factors affecting their strength were investigated. A statistical approach to the analysis of the results was adopted. The type of knot was found to have a significant effect on the strength. This same effect was seen in both types of rope construction (three-strand and braid-on-braid). Conclusions were also drawn as to the effect of splice length, eye size, manufacturer and rope diameter on the breaking strength of splices. Areas of development and further investigation were identified

Failure due to fatigue in fiber bundles and solids

We consider first a homogeneous fiber bundle model where all the fibers have got the same stress threshold beyond which all fail simultaneously in absence of noise. At finite noise, the bundle acquires a fatigue behavior due to the noise-induced failure probability at any stress. We solve this dynamics of failure analytically and show that the average failure time of the bundle decreases exponentially as the stress increases. We also determine the avalanche size distribution during such failure and find a power law decay. We compare this fatigue behavior with that obtained phenomenologically for the nucleation of Griffith cracks. Next we study numerically the fatigue behavior of random fiber bundles having simple distributions of individual fiber strengths, at stress less than the bundle's strength (beyond which it fails instantly). The average failure time is again seen to decrease exponentially as the stress increases and the avalanche size distribution shows similar power law decay. These results are also in broad agreement with experimental observations on fatigue in solids. We believe, these observations regarding the failure time are useful for quantum breakdown phenomena in disordered systems.Comment: 13 pages, 4 figures, figures added and the text is revise

Global maps of soil temperature.

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km <sup>2</sup> resolution for 0-5 and 5-15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km <sup>2</sup> pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

Probabilistic models of the stress-rupture of composite materials: Phase III. Progress report, June 15, 1978-June 14, 1980

The development of static and time dependent models for the failure of composite materials has been pursued. These models are based on the chain-of-bundles probability model for composite failure wherein local load sharing among non-failed fiber elements in a bundle plays a key role. At the outset, it was believed that the static model was well developed in the literature by others, and that work on the time dependent versions could proceed. In these versions, the viscoelasticity of the matrix was to be the cause of the time effects. Unfortunately, initial studies showed the published analysis on the static case to be superficial, and a rigorous extension to the time dependent case was not possible. A thorough investigation of the static model was carried out. Sophisticated analytical and numerical techniques were developed to treat the static model, and these show promise of being extendable to the time dependent case. Exact analysis has been performed on composites with few fibers to gain insight, and a powerful recursive technique has been developed to treat composites of larger sizes

Strength distribution and size effects for the fracture of fibrous composite materials

Random network models have recently been developed in the physics literature to explain the strength and size effect in heterogeneous materials. Applications have included the breakdown and brittle fracture. Unfortunately, conventional scaling approaches of statistical mechanics have yielded incorrect predictions, and new approaches have been proposed which build on field enhancement occurring near the tips of critical, random clusters together with the statistical theory of extremes. New distributions and size scalings for strength have been proposed and supported through Monte Carlo simulation. Here we consider an idealized, one-dimensional model for the failure of such networks where elements of constant strength may be initially present or absent at random. Our idealized rule for local stress redistribution near breaks reflects features we find in a discrete mechanics model that has limiting forms consistent with continuum theories for cracks. We obtain rigorous asymptotic results for the strength distribution and size effect with constants and exponents that are known. The validity of various analytical approximations in the literature is then discussed

A day in the life of a Ménière's patient: understanding the lived experiences and mental health impacts of Ménière's disease

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.Concepts of social practice are increasingly being used to understand experiences of everyday life, particularly in relation to consumption and healthy lifestyles. This paper builds on this in the context of lives disrupted and reshaped by chronic illness. It uses social practice theory to examine the lived experiences of individuals with Ménière’s disease; a long-term progressive vestibular disorder, defined by episodes of severe and debilitating vertigo, aural fullness, tinnitus and sensorineural hearing loss. Drawing on the findings of 20 in-depth narrative interviews with Ménière’s patients, and eight spousal/partner interviews, we explore the impacts of the condition on sensory, temporal, spatial and social dimensions of the body. In doing so, we highlight the intensely embodied sensory and emotional work required to maintain connections between the ‘competences’, ‘materials’ and ‘meanings’ that constitute and sustain the performance of both mundane and meaningful social practices over time. As connections between these elements of social practice are disrupted during more active phases of the condition, affected individuals may be defected from old practices and recruited to new ones, often requiring both time and social support to find meaning or pleasure in these alternative ways of being in the world.Many thanks go to all the study participants for sharing their experiences; Mr. David Whinney (Ear Nose and Throat Consultant at Royal Cornwall Hospital Treliske), Clinical Project Advisor; the Ménière’s Society for funding the study; and PenCLAHRC (the National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care South West Peninsula) for providing follow-on funding. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR, the Department of Health or the Ménière’s Society. We would also like to thank the two anonymous reviewers for their valuable feedback on an earlier draft of this paper

Negotiating nature's weather worlds in the context of life with sight impairment

This is the final version. Available on open access from Wiley via the DOI in this recordWe have seen longstanding research interest in diverse nature-society relations, including contentious debates regarding what nature is, the role of humans within or apart from it, and how varied types of non-human nature shape different societies and individuals within society. Within this work, relatively little attention has been paid to an important aspect of nature experienced everyday; people’s “weather-worlds”. These encompass the qualities of sensory experience that are shaped by fluxes in the 2 medium – the air – in which we routinely live and breathe. Such currents, forces and pressure gradients underwrite our capacities to act and interact with both the animate and inanimate materials and beings we encounter as we negotiate our everyday lives. We focus on these weather worlds here, drawing on the findings of an in-depth qualitative study exploring how people with varying forms and severities of sight impairment describe their nature experiences; with the weather emerging as an immediate and often highly visceral form of everyday nature encounter amongst all participants. We reflect on the ephemeral qualities of people’s weather-worlds, highlighting their potential to comfort, invigorate and connect, but also to disorientate, threaten and isolate, at times supporting moments of wellbeing, at others exacerbating experiences of impairment and disability. In doing so, we highlight how attending to the weather is essential if we are to fully understand people’s emplaced experiences of wellbeing, impairment and disability with(in) diverse forms of multi-elemental, assembled ‘nature’.Economic and Social Research Council (ESRC