a b s t r a c tPolyurethane foam has been in use for some time in wheelchair seating systems as it offers good pressure relieving capabilities in most cases. However, little characterisation work has gone into seating foam materials by comparison with conventional elastomeric materials. Accurate material models could allow better prediction of foam in-service behaviour, which could potentially improve seating design practises. The objective of this work was to develop an approach for the validation of hyperelastic and viscoelastic material model parameters used to simulate polyurethane foam behaviour. Material parameters were identified from relevant test procedures and implemented in a Finite Element simulation of an ISO foam indentation procedure. Physical test results were compared to results predicted using the identified material parameters. Simulations suggest a good overall agreement between test and model results.
A high speed camera investigation is presented into the behavior of CO 2 dry-ice particles in an application of dry-ice blasting to the defouling of commercial aircraft engine compressors. An image acquisition system is deployed in the compressor section of an aircraft engine and is used to determine the evolution of dry-ice particle size and velocity from the nozzle exit to the entrance to the engine's high pressure compressor as the engine is cranked. A comparison study between CO 2 dry-ice particle laden flows and airflows with single Polyoxymethylene (POM) particles of various diameters is also presented. Measurements are made using a range of blasting system pressures and using sonic and supersonic blasting nozzles. The behavior of large CO 2 dry-ice particles (d P ≥ 1 mm) in this discontinuously and inhomogenously laden flow is compared to that of single POM particles under similar flow conditions and is found to behave similarly. The experiments presented turn out to be useful for supporting development of special purpose dry-ice blasting systems.
In this paper we present an electronic speckle pattern shearing interferometer using a photopolymer diffractive optical element in the form of a holographic grating, in combination with a ground glass to shear the images. The sheared images on the ground glass are further imaged onto a CCD camera. The distance between the grating and the ground glass can be used to control the shear and to vary the sensitivity of the system. The direction of sensitivity is easily controlled by rotation of the diffraction grating around its normal.Introducing photopolymer holographic gratings in ESPSI gives the advantage of using high aperture optical elements at relatively low cost. The fact that the diffractive optical element is a photopolymer layer on glass substrate with thickness of 2mm makes for a compact optical system. The system was successfully used for detection of the resonant frequencies of a vibrating object.Most of the published work on vibration analysis is analytical. Very few experimental results are available in the literature. The well known laser Doppler vibrometers (LDV) and accelerometers used for modal analysis are pointwise measurement techniques, although multipoint LDV is available at significant cost. advantage of shearography over electronic speckle pattern interferometry is that ESPSI is relatively insensitive to external disturbances. Another advantage of the proposed system is that it could be easily converted to a phase-shifting electronic speckle shearing interferometer.
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