Frictional Instabilities and Carbonation of Basalts Triggered by Injection of Pressurized H2O- and CO2- Rich Fluids

The safe application of geological carbon storage depends also on the seismic hazard associated with fluid injection. In this regard, we performed friction experiments using a rotary shear apparatus on precut basalts with variable degree of hydrothermal alteration by injecting distilled H2O, pure CO2, and H2O + CO2fluid mixtures under temperature, fluid pressure, and stress conditions relevant for large-scale subsurface CO2storage reservoirs. In all experiments, seismic slip was preceded by short-lived slip bursts. Seismic slip occurred at equivalent fluid pressures and normal stresses regardless of the fluid injected and degree of alteration of basalts. Injection of fluids caused also carbonation reactions and crystallization of new dolomite grains in the basalt-hosted faults sheared in H2O + CO2fluid mixtures. Fast mineral carbonation in the experiments might be explained by shear heating during seismic slip, evidencing the high chemical reactivity of basalts to H2O + CO2mixtures

Investigations into pulsed ultra-high magnetic field single-turn coil systems and [theta]-pinch electromagnetically-driven flux compression devices

Magnetic flux densities exceeding 100 T are termed 'ultrahigh' magnetic flux densities and are necessarily developed using pulsed energies. Two particular laboratory techniques are commonly used to produce magnetic fields of this size; the single turn coil (STC) technique and the electromagnetically driven flux compression (EMFC) technique. Over recent years there has been a strong drive to improve both of these systems and to develop them further. This has primarily been achieved by analytical simulation as well as by innovative design solutions. This thesis investigates both techniques, and in particular details the development of an accurate finite element model used in predicting the behaviour of STC systems as well as detailing experimental advances made using a-pinch EMFC systems, including in particular the use of an insulator–metallic phase transition cascade

An optical investigation into the lubrication of cylindrical roller bearings

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Small Engine Flash Vapor JP-8 Fuel Injector Testing, Simulation and Development

Following U.S. Army’s single fuel initiative, Wankel rotary engines used in U.S. Army’s shadow unmanned aerial vehicles (UAVs) need to be retrofitted from running on aviation gasoline (AVGAS) to JP-8. The feasibility of retrofitting the engine with a flash vapor direct fuel injector was investigated. A commercial off-the-shelf direct fuel injector was used in the study. A photo detector measurement tool was developed to measure high frequency (>100 Hz) injection event. A coupled electrical-electomagnetics-fluid-mechanical system was simulated to understand the pintle dynamics during an injection event. Optimal injector power drive was revealed to be a multi-stage current profile. A flash heater was designed and tested to be capable of heating up JP-8 from room temperature to its vaporization temperature (>310F) under one tenth of a second at the required flow rate. An ignition test rig was built to compare ignition behavior between AVGAS and heated JP-8. Test result showed that the 550F pre-heated JP-8 had equal or superior ignition pressure rise / ignition delay time than AVGAS

Characterization of Detonation Phenomena Observed in High-Speed Visible Imagery

Measurements for radius, angular velocity, initial time of observation, and final time of observation were made for turbulent vortices around detonation fireballs. A proxy for vortex power, determined through unit analysis, was found to correlate well to initial (and final) time of observation with R2 equal to 0.8572. The linear trend on a log10-log10 plot was indicative of a rapid decrease (over 10-1 s) in power associated with the decay of the fireball. Predictions, based on turbulent spectral theory were made for root-mean-square velocity fluctuations and Reynolds numbers, both as functions of time. In addition, reflected shock speeds inside the fireball were found to be, on average, 69% higher than those of the un-reflected shock outside. This difference in speed was used to estimate the adiabatic exponent inside the fireball. Values of the adiabatic exponent were found to range between 1.08 and 1.3, while exhibiting a decreasing trend in time, and a weak quadratic dependence on time. Lastly, comparisons of the primary and secondary shock velocities showed that the secondary shock was faster in six out of ten events. For two events, the speeds were equal to within the uncertainty of the measurements. The speed of the secondary shock varied from 1.8% to 30% faster than the primary shock

Performance of multi-component polymers at high strain rates

More and more, advanced polymer and composite materials are being applied in engineering situations where a high resistance to loading at high rates of strain, such as by impact or blast deformation, are a vital requirement. Specific examples exist in the fields of defence and sport research and development for personal, and in the case of the former, vehicular, protection. There are obvious advantages to the use of polymer materials for these applications in augmenting the more widely used metals and ceramics, most notably the evident reduction in weight, and it is believed that with suitable nano-reinforcement these materials may exhibit improved combat survivability. The current study concerns the effect that nano-reinforcements in the form of Carbon Black, Titanium Dioxide, Exfoliated Hectorite Nanoclay and Carbon Nanotubes; have upon the high strain rate mechanical properties of structural variants of Polyethylene (Linear Low Density Polyethylene, LLDPE; High Density Polyethylene, HDPE; Ultra-High Molecular Weight Polyethylene, UHMWPE) and blends of UHMWPE and HDPE. The testing samples were manufactured using a novel process developed in the Loughborough University Materials Department, which has produced well-dispersed specimens. The formed nanocomposite samples were studied using an in-house four-bar Split Hopkinson Pressure Bar (SHPB) system for high strain rate performance, instrumented dropweight for intermediate strain rates and a conventional commercial Hounsfield H50KM universal testing machine for quasi-static strain rate compressive tests. The experimental results recorded for un-reinforced materials are used as a reference to allow comparative analysis of any effect the nano-reinforcements or the blending process have upon the structure, performance and properties of the composite material. From the mechanical testing, it was seen that the stress-strain behaviour of Polyethylene is highly strain-rate-dependent, as plots of the average representative yield stress as a function of strain rate show a bilinear relationship when plotted on a logarithmic strain rate scale, with the gradient of the curve rising sharply at around 103s-1. Concerning the addition of the nanofiller materials, it was seen that there was an increase in the flow and yield stresses and the energy absorption characteristics of the resulting composite with the magnitude dependent upon whether it was a pure or blended polymer that was reinforced. Of the aforementioned fillers it was seen that the addition of Carbon Nanotubes in the small concentrations studied resulted in the greatest increase in properties compared to the pure polymers, closely followed by the Carbon Black fillers. Also of note, the un-reinforced blended samples showed significant increases in flow stress, yield stress and energy absorption when compared to the constituent UHMWPE and HDPE polymers. Additionally, a complete set of Differential Scanning Calorimetry and density measurements were made before testing to assess any changes in the properties after reinforcement or blending, and to help in the interpretation of the results from the different mechanical tests

A study of the dynamics of the plasma filled rod pinch

The Plasma Filled Rod Pinch (PFRP) is a radiographic source used in high power flash x-ray machines. The purpose of this study is to provide detailed measurements of the plasma pre-fill required in the PFRP; then use these as a basis for 3D MHD simulations of the dynamics of the plasma in the PFRP. Several interferometry systems were developed to analyse the density of the plasma pre-fill - a fibre optic based interferometer gave information at a single point over time and a CW laser-based system giving 12 temporally and spatially resolved interferograms. Thomson scattering and spectroscopic analysis were also undertaken, enabling estimates of the electron density of the plasma in the order of 1018 /cm2 at the source with a divergence of 25 - 30°. The velocity of the plasma expansion was found to vary with the charging voltage for the system, with velocities of 8,500 – 14,500 m/s. The 12 frame interferometry system was then used to study the plasma from 6 guns placed around a central rod, a similar orientation to that used in PFRP experiments. The plasma guns were subsequently modelled as simple plasma sources, and the parameters of the plasma were set so that its behaviour matches the experimental data. The model has been used to simulate possible scenarios that could affect the performance of the PFRP. This study has provided suggestions that the snowplough phase is very resilient to variations away from the standard configuration. Future work will hopefully include simulations featuring the Hall term.Open Acces

An Experimental Technique for Developing Intermediate Strain Rates in Ductile Metals

Quantifying the strain-rate sensitive dynamic properties of structural materials is an important area of research in the solid mechanics field. Property evaluation is typically accomplished using dynamic tests which involve rapid loading or impact of specimens. In these tests, inertial forces and wave propagation make it difficult to accurately record the material response to a loading condition at an equivalent location. Furthermore, these tests typically generate high strain rates (in excess of 103 s−1) and an experimental method for generating rates of strain in the intermediate strain rate regime which is relatively simple, low cost, and reliable is still lacking. This research effort develops an experimental technique for generating tensile plastic strain rates up to 102 s−1 in ductile metals. The technique relies on an impact from a load cell instrumented drop weight machine capable of delivering a suitable impact velocity and energy to globally deform a slotted beam specimen. At impact, a state of plastic uniaxial tensile stress is created in the ligament underneath a slot. The ligament is instrumented with an electrical-resistance strain gauge, and the strain history from the gauge is measured and stored in a digital oscilloscope. The Johnson-Cook constitutive equation is assumed to reflect the material behavior and its parameters are determined through a matching of the experimental strain history with a finite element simulation