1,133 research outputs found
Singing for Lung Health: service evaluation of the British Lung Foundation programme.
No full textAIMS: Singing for Lung Health (SLH) is a novel intervention for individuals with respiratory disease. Qualitative results suggest benefits to physical, mental and emotional health. Limited data also suggest objective improvements in measures of quality of life with SLH are achievable. It is not known how effective the SLH groups supported by the British Lung Foundation (BLF) in the UK are. The objective was to understand the clinical impact SLH has on individuals with respiratory disease. METHODS: The BLF conducted a questionnaire survey of singers with respiratory disease from new SLH groups set up in 2016-2017. Questionnaires were administered prior to participants' first session and after 12 weeks of singing. Health-related quality of life, patient activation, anxiety and breathlessness outcomes were included. Healthcare resource utilisation including general practitioner (GP) visits, hospitalisations and frequency of inhaler use were recorded. RESULTS: A total of 228 singers participated from 26 SLH groups in the UK. Participants were 70.7 (10.1) years old, 156 (68.4%) were female and 114 (47.5%) had chronic obstructive pulmonary disease (COPD). In all, 113 (49.5%) participants provided 12-week data. There were significant improvements in COPD Assessment Test (CAT) score (Mean = -1.4, CI: (-0.25 to -2.48) ( p = .017)). Furthermore, 45% of singers reported reduced GP visits ( p ≤ .001) and 18% reported reduced hospital admissions ( p = .01). However, there were no significant improvements in general quality of life, anxiety, patient activation, breathlessness or inhaler use. Baseline characteristics were not significantly different between people who completed the 12-week evaluation and those who did not. CONCLUSIONS: This service evaluation found that participants in SLH groups report improvement in respiratory health-related quality of life and a reduction in healthcare utilisation. SLH has potential economic and health benefits. Therefore, to confirm these findings, these endpoints should be evaluated further in large-scale randomised controlled trials (RCTs)
Full-field strain measurement and identification of composites moduli at high strain rate with the virtual fields method
No full textThe present paper deals with full-field strain measurement on glass/epoxy composite tensile specimens submitted to high strain rate loading through a split Hopkinson pressure bar (SHPB) device and with the identification of their mechanical properties. First, the adopted methodology is presented: the device, including an Ultra-High Speed camera, and the experimental procedure to obtain relevant displacement maps are described. The different full-field results including displacement, strain and acceleration maps for two mechanical tests are then addressed. The last part of the paper deals with an original procedure to identify stiffnesses on this dynamic case only using the actual strain and acceleration maps (without the applied force) by using the Virtual Fields Method. The results provide very promising values of Young’s modulus and Poisson’s ratio on a quasi-isotropic glass-epoxy laminate. The load reconstructed from the moduli and strains compares favourably with that from the reading
Investigating the use of rubber to attenuate the effect of blast load applied to a surrogate lower leg
No full textIncludes abstract.Includes bibliographical references (leaves 191-197).Landmines are the epitome of the perfect soldier: always ready, never tiring. Landmines also do not choose their victims - it may very well be an armed and protected soldier or an innocent civilian who activates the detonator. As such, land mines have reached epidemic proportions in the Third World, affecting both combatants and civilians, whether they are on foot or in a vehicle. When stepping on an anti-personnel land mine, traumatic amputation of the foot, lower leg or upper leg is generally expected. However, an anti-vehicle landmine detonating underneath a vehicle can have equally as detrimental results, as the occupants of the vehicle are bound to sustain serious injuries to the lower extremities. These injuries can vary from being less life threatening to being fatal in some extreme cases. Anthropomorphic test devices have been developed and refined over the years to represent the occupant exposed to simulated land mine detonation and then to retrieve valuable technical information from the test data. In the present investigation a simplified aluminium surrogate lower leg was designed, manufactured and subjected to axial blast testing. In addition, a rubber layer representing the sole of a standard army combat boot was placed below the foot model in a separate series of blast tests. The main factors investigated in this study were the effect of varying the amount and positioning of the explosives and the attenuation produced by including the rubber sole layer. The blast tests were conducted using a horizontal ballistic pendulum, with the foot model placed axially in the pendulum. The disc shaped explosives of different mass was placed in the centre of the detonation plate and axially in line with the heel respectively to draw a comparison between the respective stresses induced in the lower leg. As expected, the stress recorded by the strain gauges placed on the lower leg was significantly higher when the explosives were positioned in line with the heel than when placed in the centre of the detonation plate. The same series of blast tests were performed with the rubber sole being included in the test setup. Alternating the positioning of the explosives did not yield a significant difference in induced stress. Investigation of the blast attenuation provided by the rubber layer showed that the peak stress is mitigated by approximately 70%, which was much greater than expected. An elementary analytical solution was performed as a preliminary validation of the experimental test results. Furthermore, a finite element model of the aluminium surrogate foot and the rubber layer was created and a numerical simulation of each blast test was executed. Material data for the aluminium and rubber obtained via Split-Hopkinson Pressure Bar testing were employed to construct the material models used in the finite element model. The results from the numerical simulations compare well to the experimental test results for the blast loading conditions where the rubber layer was excluded from the test setup. In the case where the rubber layer was included in the testing, the trend and shape of the stress graphs obtained from the numerical simulation results agrees with the stress curves recorded during the actual blast tests. However, the peak stresses recorded during the experimental blast tests are found to be significantly higher than the peak stresses yielded by the numerical simulations
OBTENCIÓN DE CURVAS Ɛ-T DE ALUMINIO PLEGADO MEDIANTE UN SISTEMA BARRA DE HOPKINSON (OBTAINING CURVES Ɛ-T OF FOLDED ALUMINUM BY MEANS OF A HOPKINSON BAR SYSTEM)
No full textUn Sistema Barra de Hopkinson fue utilizado para medir altas tazas de deformación a compresión de aluminio plegado. Para ello se seleccionó un material adecuado para las barras del Sistema de Hopkinson que fuera cercano a la impedancia del material a estudiar. Se realizó la instrumentación de la barra mediante galgas extensométricas con un arreglo de puente completo de Wheatstone y un adquisidor de datos. Las gráficas obtenidas de deformación (Ɛ) en función del tiempo (t) muestran un comportamiento típico de materiales de baja impedancia, tal como es reportado en la literatura. La configuración lograda para el Sistema Barra de Hopkinson permitirá obtener la respuesta dinámica de deformación de materiales suaves o de baja impedancia, así como caracterizar las propiedades mecánicas de los mismos.Palabra(s) Clave: Aluminio plegado, Barra de Hopkinson, Materiales suaves. AbstractA Hopkinson Bar System was used to measure high rates of compression deformation of folded aluminum. For this, a suitable material was selected for the bars of the Hopkinson System that was close to the impedance of the material to be studied. The instrumentation of the bar was performed by strain gauges with a complete Wheatstone bridge arrangement and a data acquisition. The graphs obtained from deformation (Ɛ) as a function of time (t) show a typical behavior of low impedance materials, as reported in the literature. The configuration achieved for the Hopkinson Bar System will allow to obtain the dynamic deformation response of soft or low impedance materials, as well as to characterize the mechanical properties of them.Keywords: Folded aluminum, Hopkinson Bar, Soft materials
Numerical investigation of dispersion in Hopkinson Pressure Bar
No full textIncludes bibliographical references (leaves 76-78).The Hopkinson Pressure Bar (HPB) is used as a load-time or displacement-time transducer in impact or blast experiments. The Split Hopkinson Pressure Bar (SHPB) is the accepted form of material testing for strain rates between 102 S-I and 104 S-I. Explicit Finite Element Analysis (FEA) codes are increasingly used to model HPB experiments numerically, due to the complicated boundary conditions imposed by tensile and shear SHPB experiments. However, most publications on numerical modelling of HPB experiments have focussed on the response of the specimen and have paid very little attention to the modelling of the stress wave propagation in the cylindrical bars. This dissertation focuses on the numerical modelling of stress wave propagation in HPBs
Design of a Split Hopkinson Pressure Bar facility for dynamic material characterization
No full textIt is important to know the mechanical response of materials over a full range of strain rates. In machining and stamping, or in ballistic type events such as bullet penetration, shell impacts, and explosive blasts, strain rates of 100 s-1 to 10,000 s-1 or even higher for hyper-velocity impacts, are achieved. A Split Hopkinson Pressure Bar facility is generally used to study the mechanical response of materials at these strain rates. The Split Hopkinson Pressure Bar produces precise data which can be used to study the dynamic response of materials. Over the last 70 years the Split Hopkinson Pressure Bar has been subject to many scrutinous studies which push the boundaries of materials it can test. In this thesis, the design of a compressive Split Hopkinson Pressure Bar facility is presented. The Split Hopkinson Pressure Bar is designed to obey the fundamental assumptions: one-dimensional and undispersed wave propagation as well as uniaxial loading of the specimen. Each subsystem of the compressive Split Hopkinson Pressure Bar is closely examined to outline its role in obeying these assumptions as well as its role in obtaining accurate data acquisition, then a design of each subsystem is presented. The presented facility improves accuracy, functionality, and ease of operation compared to previous work. Improvements in strain gage design increased the maximum attainable impact velocity from 40 m/s to at least 50 m/s. The Split Hopkinson Pressure Bar facility is thoroughly tested to verify the design. The dynamic response of aluminum 6061-T6511 is tested between strain rates of 1,000 s-1 and 6,300 s-1 to verify the accuracy of the facility. Testing showed that the response of 6061-T6511 is strain rate dependent which is consistent with literature. The flow stress of 6061-T6511 increases as strain rate increases from 350 MPa to 400 MPa at a rate of about 0.009 MPa-s. The dynamic response of polycarbonate is reported at strain rates between 1,000 s-1 and 7,000 s-1. The flow stress increases by about 8.2% over the range of strain rates. Super activated carbon and a super activated carbon composite is also studied using aluminum pressure bars, specifically designed for soft materials.M.S.Includes bibliographical reference
Modification of a compressive Split Hopkinson Pressure Bar for dynamic friction characterization
No full textFriction is defined as the resistive force that occurs between two bodies when in motion. The frictional coefficient is used to define a relationship between this resistive force and normal force and is determined experimentally. Derivation of these friction coefficients is traditionally done quasi-statically; at higher operational velocities and normal forces, there is a lack of available testing solutions. A Split Hopkinson Pressure Bar has been used extensively to study the dynamic response of materials between 100 s-1 to 10,000 s-1 in compression, tension and, more recently, torsion. Modifying a compressive Split Hopkinson Pressure Bar provides an opportunity to convert the pressure loading mechanism into a tangential shear load. The presented thesis looks at converting the existing Rutgers Split Hopkinson Pressure Bar apparatus to an experimental method to gather frictional data. The apparatus is designed to be retrofitted onto the already existing Split Hopkinson Pressure Bar and operates on two sources of data: normal force and strain. To gather these streams of data, additional instrumentation is added. The frictional Split Hopkinson Pressure Bar is designed to ensure that accurate and functional data can be produced. This facility serves as a preliminary design iteration for determining dynamic frictional coefficients at Rutgers University. The design theoretically enables testing at normal forces up to 7 kN and velocities up to 27 m/s. Testing on the setup has shown a kinetic frictional coefficient of 0.175 between smooth steel on aluminum at an impact velocity of 8 m/s. A high-speed camera is used to validate sliding motion between speciemens. To monitor stress wave propagation in the bar, a finite element simulation is conducted; the simulation confirms uniaxial wave propagation. Initial testing showed the coefficient to be relatively independent of velocity and normal force.M.S.Includes bibliographical reference
Split Hopkinson pressure bar testing of aluminium alloy 6060 T5
No full textA 13 mm split Hopkinson pressure bar (SHPB)apparatus was used to extract the high strain rate behaviour of aluminium alloy 6060 T5. Striker velocities applied were up to 27.56 m/s. The signals from the two sets of strain gauges were used to analyse the dynamic behaviour of specimens. In this study, the experiment was simulated using an axisymmetric model in LS-DYNA. The simplified Johnson-Cook constitutive model was employed to represent the stress-strain relation of the specimen. A 2D automatic surface-to-surface contact with a friction coefficient of 0.06 was applied at all the contact surfaces. The numerical simulation fits well with the experimental results.M.A. Kariem, J.H. Beynon and D. Rua
Electrokinetic iron pan generation in unconsolidated sediments: implications for contaminated land remediation and soil engineering
No full textElectrokinetic remediation is an emerging technology that has generated considerable interest as a technique for the in situ remediation of clay-rich soils and sediments. Despite promising experimental results, however, at present there is no standardised universal electrokinetic soil/sediment remediation approach. Many of the current technologies are technically complex and energy intensive, and geared towards the removal of 90% or more of specific contaminants, under very specific field or laboratory-based conditions. However, in the real environment a low-tech, low-energy contaminant reduction/containment technique may be more appropriate and realistic. Such a technique, FIRS (Ferric Iron Remediation and Stabilisation), is discussed here. The FIRS technique involves the application of a low magnitude (typically less than 0.2 V/cm) direct electric potential between two or more sacrificial, Fe-rich, electrodes emplaced in, or either side of, a contaminated soil or sediment. The electric potential is used to generate a strong pH (and Eh) gradient within the soil column (pH 2–13), and force the precipitation of an Fe-rich barrier or “pan” in the soil between the electrodes. Geochemical and geotechnical data for FIRS-treated sediments from the Ravenglass estuary, Cumbria, UK indicate that the technique can significantly reduce contaminant concentration in treated soil, by remobilisation of contaminants and concentration on, or around, the Fe-rich barrier. Arsenic, in particular, seems highly amenable to the FIRS treatment, due to its solubility under the high pH conditions generated near to the cathode, and its marked geochemical affinity with the freshly precipitated Fe oxides and oxyhydroxides in the Fe barrier. Geotechnical tests indicate that the Fe barrier produced by the technique is practically impervious (permeability = 10?9 m/s or less), and has moderate mechanical strength (UCS ?11 N/mm2). Notably, a large increase in shear strength in the treated soil near to the anode electrode (due to Fe cementation and/or dewatering) is also observed, without significant loss of porosity. The data indicate that the FIRS technique shows considerable promise as an in situ method for contaminated land remediation and soil water containment, and for improving the mechanical properties of soils (contaminated or otherwise) for civil engineering purposes
Evaluation of the strain rate dependent behavior of a CFRP using two different Hopkinson bars
No full textIn many studies the strain rate sensitivity of a CFRP material is investigated thoroughly in only one layup and loading direction, which brings about challenges in the comparison of the results due to the large layup- and loading mode-dependence of the material behavior. To address this challenge, in this study we characterize one CFRP material comprehensively in different rate dependent configurations. We demonstrate the feasibility of the Hopkinson Bar technique in the high strain rate testing of CFRP materials. We also highlight the importance of carefully designing and analyzing the experiments for each layup separately. That is, we show how notably different material behavior and therefore notably different test requirements are obtained for the nominally same composite material by simply changing the layup. Two different Hopkinson Bar Set-ups were used; a Direct Impact Hopkinson Pressure Bar (DIHPB) for the characterization of the compressive response of the UD material perpendicular to the fiber direction and a Split Hopkinson Tension Bar (SHTB) for the characterization of the tensile response of three different layups: UD material perpendicular to the fiber direction, a ±45-laminate, and a quasi-isotropic layup. For each studied layup, the specimen geometry, mounting concept and testing approach were individually adapted. As a result, it was possible to comprehensively evaluate the high rate response of the CFRP composite at a strain rate of 200 s-1 with a high quality of results
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