1,720,977 research outputs found
Evaluating impact damage in CFRP using fibre optic sensors
No full textDamage in unidirectional carbon/fibre composite resulting from both low and high velocity/energy impacts was evaluated using embedded fibre Bragg grating (FBG) sensors, C-scan and microscopic analysis. It was found that the FBG sensors located 10mm from the impact site could detect residual strains from a 0.33J (1.3ms-1) impact which was not detectable by C-scan or visual inspection. The measured residual strain increased with impact energy and damage changed from matrix cracking to severe delaminations.. High velocity impacts (225ms-1, 11J) resulted in test panel perforation and delaminations. FBG sensors located within a distance of 2 - 3 the damage radius detected residual strain from the impact. With an array of embedded sensors it is believed that it will be possible to identify the site of both low and high velocity energy impacts and predict the damage from the response of the adjacent sensors providing the sensors are located sufficiently close to the impact sit
Application of time frequency analysis on data from a low velocity impact using fibre optic sensors
No full textSensors and technologies for in situ dissolved methane measurements and their evaluation using Technology Readiness Levels
No full textDissolved methane measurements rely on the time-consuming collection of discrete water samples followed by gas-chromatography analysis. To date, this approach has proved useful for broad interpretation of environmental processes. However, it limits comprehension of environmental processes that are highly variable in space and or time. This has led to increased interest in in situ dissolved methane sensors to augment data from point sampling.So far, three sensing strategies have been explored using:1) gas-phase measurements after gas extraction through semi-permeable silicon membranes;2) measurements using biosensors; and,3) optical measurements (e.g., surface-plasmon resonance and surface-enhanced Raman spectroscopy).Optical measurements may represent the future for in situ dissolved methane sensing.We review and evaluate different in situ methane sensors and technologies using Technology Readiness Levels
Adaptation of an osmotically pumped continuous in situ water sampler for application in riverine environments
No full textWe present the design of an osmotic water sampler that is adapted to and validated in freshwater. The sample is drawn into and stored in a continuous narrow bore tube. This geometry and slow pump rate (which is temperature dependent: 0.8 mL/d at 4 °C to 2.0 mL/d at 28 °C) minimizes sample dispersion. We have implemented in situ time-stamping which enables accurate study of pump rates and sample time defining procedures in field deployments and comparison with laboratory measurements. Temperature variations are common in rivers, and without an accurate time-stamping, or other defining procedure, time of sampling is ambiguous. The sampler was deployed for one month in a river, and its performance was evaluated by comparison with manually collected samples. Samples were analyzed for major ions using Ion Chromatography and collision reaction Inductively Couple Mass Spectrometry. Despite the differences of the two sampling methods (osmotic sampler averages, while manual samples provide snapshots), the two data sets show good agreement (average R2 ≈ 0.7), indicating the reliability of the sampler and at the same time highlighting the advantages of high frequency sampling in dynamic environments
Discrimination and analysis of phytoplankton using a microfluidic cytometer
No full textIdentification and analysis of phytoplankton is important for understanding the environmental parameters that are influenced by the oceans, including pollution and climate change. Phytoplanktons are studied at the single cell level using conventional light-field and fluorescence microscopy, but the technique is labour intensive. Flow cytometry enables rapid and quantitative measurements of single cells and is now used as an analytical tool in phytoplankton analysis. However, it has a number of drawbacks, including high cost and portability. We describe the fabrication of a microfluidic (lab-on-a-chip) device for high-speed analysis of single phytoplankton. The device measures fluorescence (at three wavelength ranges) and the electrical impedance of single particles. The system was tested using a mixture of three algae (Isochrysis Galbana, Rhodosorus m., Synechococcus sp.) and the results compared with predictions from theory and measurements using a commercial flow cytometer (BD FACSAria). It is shown that the microfluidic flow cytometer is able to distinguish and characterise these different taxa and that impedance spectroscopy enables measurement of phytoplankton biophysical properties
Combined use of spot samples and continuous integrated sampling in a study of storm runoff from a lowland catchment in the south of England
No full textWe have used two different sampling techniques to study the geochemical response of a small lowland rural catchment to episodic storm runoff. The first method involves traditional daily spot sampling and has been used to develop a standard end-member mixing analysis (EMMA) of the relative contributions of ground water flow and surface runoff to the total stream flow. The second method utilizes a continuous sampling device, powered by an osmotic pump, to produce an integrated 24-h sample of the stream flow. When combined with the EMMA results from the spot samples, analyses of the integrated samples reveal the presence of a third component that makes a significant contribution to the dissolved NO3, Ca and K export from the catchment during the rising limb of the hydrographic profile of a storm event following a prolonged dry period. The storm occurred in the middle of the night, so that the response of the stream chemistry was not captured by the daily samples. We hypothesize that this third component is derived from the flushing of stored soil water that contains the geochemical signature of decaying vegetation
Temporal Optimization of Microfluidic Colorimetric Sensors by Use of Multiplexed Stop-Flow Architecture
No full textWe present two microfluidic architectures (continuous flow and multiplexed stop flow) for miniaturized colorimetric nutrient sensors. These systems are compared with respect to the temporal response (for optimization of sampling rate) and reduction of reagent consumption. The continuous-flow system is capable of a sampling rate of 60 samples·h–1, limited by Taylor dispersion. The novel multiplexed stop-flow (MSF) microsystem architecture is not limited by dispersion. A demonstration MSF system consisting of two stop-flow channels is presented. This requires 12.6 s to load each sample into a measurement channel and when scaled would be capable of a throughput of 285 h–1 (with full color development). The MSF architecture is manufactured in PMMA/Viton/PMMA [where PMMA = poly(methyl methacrylate)], utilizes on-chip valving, and is scalable, thereby permitting sampling at much faster rates (subsecond). Either system is capable of remote deployment and continuous measurement of nutrient concentrations. The MSF system is particularly suited for applications requiring high temporal or spatial resolution; such as from moving vehicles
Development of sensor technology to facilitate in-situ measurement of damage in composite materials for spacecraft applications
No full textCFRP is used in a variety of applications where its high strength to weight ratio and high specific modulus is advantageous. Impact damage can however significantly reduce the strength and the modulus of the material through the creation of areas of delamination, matrix cracking and fibre failure. Such impact damage is often hard to locate and its severity hard to assess. For applications in remote or inaccessible locations traditional methods of damage assessment are not feasible and therefore a method of assessment in-situ and in service is often required to predict the optimal reparation or replacement period. Such a technology is particularly relevant to spacecraft applications where reparation and replacement costs are prohibitive and where impacts are often sustained from micrometeoroid and space debris impingement. Optic fibre Bragg gratings reflect light at a characteristic wavelength which is a function of sensor characteristics, strain and temperature. Changes in strain (or temperature), result in a wavelength shift of the order of 1.2 nm/µε and 10nm/°C. Due to their small size (typically 9µm in diameter) optical fibres containing Bragg grating sensors can be included within the matrix of fibre reinforced plastics with little detriment to their physical properties. Each optical fibre line can contain a number of discrete grating based sensors with as little as 1mm separating each grating. The limit to sensor length is sub-millimetre. These sensors are well suited to CFRP condition monitoring. At present the most significant barrier to the widespread application of this technology is the difficulty in accurately interrogating each grating based sensor to discern its characteristic wavelength at any time. Modifications made to an existing interrogation system to enable impact damage identification are detailed in this paper. A Bragg grating based sensor array was placed in the CFRP structure to enable accurate strain profiling of the material pre-impact and post-impact. This strain information is related to the observed damage. Dynamic strain information (during impact events) has also been recorded. The importance of this data for the development of the sensor technology is discussed
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