1,721,006 research outputs found
Long term condition monitoring of tapestries using image correlation
Full text linkDigital Image Correlation (DIC) is used to extract non-contact full-field three-dimensional displacement and in-plane strains from an historic tapestries. A DIC-based approach is devised that allows the effect of RH variations on a tapestry to be quantified. A historical tapestry has been monitored in a closely controlled environment and in the natural environment. The results revealed that very small variations in RH can have significant effects on strain. An automated long term monitoring approach has been devised to allow strain data to be extracted in real time from tapestries in remote locations. The results show that DIC provides better understanding of the effect of RH fluctuations on strain which will ultimately lead to more insight into the degradation process of historical tapestries. The paper demonstrates the potential for using DIC as a condition monitoring tool
Moisture uptake in monolithic and composite materials: edge correction for rectanguloid samples
No full textExperiments on moisture uptake of monolithic and composite materials are generally performed by immersing rectanguloid (square plate) samples in water. An edge correction factor is derived which, in a mathematically simple way, takes water uptake through all 6 faces (2 broad and 4 smaller faces) into account. Analysis shows this edge correction factor to be very accurate (deviations typically less than 2%). New expressions for moisture uptake in composites with unidirectionally aligned fibres are derived, by incorporating this edge correction factor as well as proper boundary conditions which depend on volume fraction of fibres. Experimental data on moisture uptake in these types of composite samples is successfully analysed using these expressions
The cohesive mechanical properties of a toughened epoxy adhesive as a function of cure level
No full textThe cohesive performance of an epoxy adhesive as a function of cure applied is evaluated through the use of mechanical testing, thermal analysis and electron microscope techniques. These materials characterisation techniques allow a complete analysis of the reference material in terms of mechanical behaviour, surface topography and thermally induced events during cure. The effect of cure level within the adhesive was explored by examining all the material properties as a function of post cure duration and temperature. Post cure temperature and duration were found to be directly proportional to the amount of curing reactions taking place within the system, with increases in post cure duration found to lower the temperatures required to cure to a specific level. The mechanical properties of the adhesive varied as a function of post cure harshness with a number of mechanisms conteributing to the strength during post cure. The elastic modulus of the material was found to decrease with increases in post cure temperature, more so than with increases in post cure duration. Large increases in ductility were witnessed at certain cure levels for each mode of loading. As curing levels are increased the glass transition temperature increases until a point where the energy required to cause the transition falls and the Tg is lowered. The morphology of the toughener has been characterised with spherical elements ranging from 0.06 -0.75micron, and inter- phase spacing also noted along with the distribution of elements. basic mechanical testsing of the adhesives were carried out in the form of lap shear and t-peel testing on mild steel substrates, the correlation with glass transition temperature being stronger in these modes
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
Carbon-based atomic oxygen sensors
No full textCarbon-based sensors have been developed to measure the atmospheric neutral atomic oxygen (AO) flux experienced by spacecraft in low Earth orbit (LEO). Thick- and thin film carbon sensor elements were deposited on an alumina substrate between thick film gold tracks and silver palladium solder pads. AO flux is deduced by measuring resistance changes as the carbon film erodes, and applying a simple theory. Measured resistance increases during exposure in a ground-based AO facility compare favourably with theoretical predictions. These sensors appear to offer a number of advantages compared with similar silver-based sensors that have been flown previously, particularly for small satellite missions with significant mass/power constraints
Hygrothermal ageing of plant oil based marine composites
No full textIn this paper, the effect of hygrothermal ageing on the flexural properties of glass/epoxy, glass/linseed oil and glass/castor oil composites is reported. Plant oil based resins offer renewable and potentially less toxic alternatives to conventional largely petroleum based marine composites. The long-term performance of these novel composites needs to be investigated and understood before using them in structural applications. In this research it was found that in the unaged condition, the flexural properties of glass/epoxy were significantly higher than both glass/castor oil and glass/linseed oil composites. After ageing in water at 40 °C for 46 weeks, the properties of glass/castor oil were comparable to glass/epoxy while the properties of glass/linseed oil were remarkably lower. The decrease in glass/linseed oil performance was explained in terms of the changes in the failure modes caused by moisture uptake
The implications of hygrothermal ageing on flexural properties of glass reinforced linseed and castor oil based polymer composites
No full textMeasurement of 5-eV atomic oxygen using carbon-based films: preliminary results
Full text linkCarbon-based sensors have been developed to measure the atmospheric neutral atomic oxygen (AO) flux experienced by spacecraft in low Earth orbit. Thin- and thick-film carbon sensor elements were deposited onto an alumina substrate between thick-film gold tracks and silver palladium solder pads. AO flux is deduced by measuring resistance changes as the carbon film erodes and applying a simple theory. A wide range of responses were observed that are dependent on the deposition process and post deposition annealing. The deposition methods used were dc magnetron sputtering, e-beam evaporation, and screen-printing. The sensors tested compare favorably with similar silver-based sensors that have been flown previously on small satellite missions with significant mass/power constraints
Application of time frequency analysis on data from a low velocity impact using fibre optic sensors
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