The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Kent Gylltoft - One of the best experts on this subject based on the ideXlab platform.
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comparative numerical studies of projectile impacts on plain and steel fibre reinforced concrete
International Journal of Impact Engineering, 2011Co-Authors: Ulrika Nystrom, Kent GylltoftAbstract:The enhanced energy absorption characteristics of fibre-reinforced concrete, compared to plain concrete, has in experimentally studies been shown to improve the projectile resistance and motivate its increased usage in protective structures. However, the high cost of undertaking experiments and the high parameter variation and dependency of the experimental setups and results, respectively, make it difficult to draw generic conclusions of how the addition and increased amount of fibres affects the local damage caused by projectile impact, which motivates the use of numerical simulations to study this. The numerical hydrocode AUTODYN was used in a qualitative study of how the addition of different amounts of fibres, modelled as different post-crack relations, influence the depth of penetration and crater formation on the front and Rear Face of a concrete target. Fibres added to the concrete mix had a minor influence on the depth of penetration while the crater size on both front and Rear Faces of the target decreases. The crack propagation beyond the crater on the front Face was also reduced when fibres were added to the concrete. An increased amount of fibres in the concrete showed no effect on the size of the front-Face crater, but led to further decreased size of the crater on the Rear Face of the concrete cylinder. It is concluded that the scabbing crater can be reduced in size and prevented by usage of fibre-reinforced concrete even if the depth of penetration is only slightly less than to penetration depth in plain concrete.
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Comparative numerical studies of projectile impacts on plain and steel-fibre reinforced concrete
International Journal of Impact Engineering, 2011Co-Authors: Ulrika Nystrom, Kent GylltoftAbstract:International audienceThe enhanced energy absorption characteristics of fibre-reinforced concrete, compared to plain concrete, has in experimentally studies been shown to improve the projectile resistance and motivate its increased usage in protective structures. However, the high cost of undertaking experiments and the high parameter variation and dependency of the experimental setups and results, respectively, make it difficult to draw generic conclusions of how the addition and increased amount of fibres affects the local damage caused by projectile impact, which motivates the use of numerical simulations to study this. The numerical hydrocode AUTODYN was used in a qualitative study of how the addition of different amounts of fibres, modelled as different post-crack relations, influence the depth of penetration and crater formation on the front and Rear Face of a concrete target. Fibres added to the concrete mix had a minor influence on the depth of penetration while the crater size on both front and Rear Faces of the target decreases. The crack propagation beyond the crater on the front Face was also reduced when fibres were added to the concrete. An increased amount of fibres in the concrete showed no effect on the size of the front-Face crater, but led to further decreased size of the crater on the Rear Face of the concrete cylinder. It is concluded that the scabbing crater can be reduced in size and prevented by usage of fibre-reinforced concrete even if the depth of penetration is only slightly less than to penetration depth in plain concrete
Ulrika Nystrom - One of the best experts on this subject based on the ideXlab platform.
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comparative numerical studies of projectile impacts on plain and steel fibre reinforced concrete
International Journal of Impact Engineering, 2011Co-Authors: Ulrika Nystrom, Kent GylltoftAbstract:The enhanced energy absorption characteristics of fibre-reinforced concrete, compared to plain concrete, has in experimentally studies been shown to improve the projectile resistance and motivate its increased usage in protective structures. However, the high cost of undertaking experiments and the high parameter variation and dependency of the experimental setups and results, respectively, make it difficult to draw generic conclusions of how the addition and increased amount of fibres affects the local damage caused by projectile impact, which motivates the use of numerical simulations to study this. The numerical hydrocode AUTODYN was used in a qualitative study of how the addition of different amounts of fibres, modelled as different post-crack relations, influence the depth of penetration and crater formation on the front and Rear Face of a concrete target. Fibres added to the concrete mix had a minor influence on the depth of penetration while the crater size on both front and Rear Faces of the target decreases. The crack propagation beyond the crater on the front Face was also reduced when fibres were added to the concrete. An increased amount of fibres in the concrete showed no effect on the size of the front-Face crater, but led to further decreased size of the crater on the Rear Face of the concrete cylinder. It is concluded that the scabbing crater can be reduced in size and prevented by usage of fibre-reinforced concrete even if the depth of penetration is only slightly less than to penetration depth in plain concrete.
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Comparative numerical studies of projectile impacts on plain and steel-fibre reinforced concrete
International Journal of Impact Engineering, 2011Co-Authors: Ulrika Nystrom, Kent GylltoftAbstract:International audienceThe enhanced energy absorption characteristics of fibre-reinforced concrete, compared to plain concrete, has in experimentally studies been shown to improve the projectile resistance and motivate its increased usage in protective structures. However, the high cost of undertaking experiments and the high parameter variation and dependency of the experimental setups and results, respectively, make it difficult to draw generic conclusions of how the addition and increased amount of fibres affects the local damage caused by projectile impact, which motivates the use of numerical simulations to study this. The numerical hydrocode AUTODYN was used in a qualitative study of how the addition of different amounts of fibres, modelled as different post-crack relations, influence the depth of penetration and crater formation on the front and Rear Face of a concrete target. Fibres added to the concrete mix had a minor influence on the depth of penetration while the crater size on both front and Rear Faces of the target decreases. The crack propagation beyond the crater on the front Face was also reduced when fibres were added to the concrete. An increased amount of fibres in the concrete showed no effect on the size of the front-Face crater, but led to further decreased size of the crater on the Rear Face of the concrete cylinder. It is concluded that the scabbing crater can be reduced in size and prevented by usage of fibre-reinforced concrete even if the depth of penetration is only slightly less than to penetration depth in plain concrete
Oren Sadot - One of the best experts on this subject based on the ideXlab platform.
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Analysis of the pressure buildup behind rigid porous media impinged by shock waves in time and frequency domains
Journal of Fluid Mechanics, 2015Co-Authors: O. Ram, Oren SadotAbstract:The transformation of a time-dependent pressure pulse imposed on the front Face of a rigid porous medium sample, mounted in a tunnel, through the sample and a fixed-volume air gap between the Rear Face of the sample and the end wall of a tunnel is studied both experimentally and analytically. In the experiments, rigid porous samples that are placed at various distances from a shock tube end wall are subjected to the impingement of shock waves. The pressure buildup behind the porous sample is monitored and compared with the pressure imposed at the front Face of the porous sample. The shock tube is fitted with a short driver section in order to generate blast-like decaying pressure profiles, which continue to decay after the initial shock impingement. In this scenario, the measured pressure profile at the end wall, which is affected by the properties of the porous medium and the size of the air gap separating its Rear Face and the shock tube end wall, is significantly different from the pressure profile imposed on the front Face of the porous sample. The mechanism governing the pressure transformation provided by the porous medium is attributed to a selective filtration process that attenuates the pressure changes associated with high frequencies. The results of the present study are also analysed in conjunction with previously published analytical and numerical models to achieve a broader understanding of the physical mechanisms affecting the pressure buildup.
Jean Batsale - One of the best experts on this subject based on the ideXlab platform.
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Short time non-destructive evaluation of thermal performances of building walls by studying transient heat transfer
Energy and Buildings, 2019Co-Authors: Yingying Yang, Alain Sempey, Jean Dumoulin, Jean BatsaleAbstract:Thermal performances of building walls are significant for energy conservation. However, very few non-destructive evaluation methods exist to quantitatively diagnose the building walls in situ due to the walls’ large thickness. Moreover, most of the existing methods are inconvenient to implement in situ and take a long characterization time. This paper studies transient heat transfer to estimate the wall's thermal properties based on the thermal quadrupoles modelling. Semi-infinite boundary condition is assumed at the Rear Face of the wall. With this assumption, only the front Face response of the wall is considered. The evaluation time is then effectively reduced within a few hours, and the diagnosis in situ is simplified without the measurement on the Rear Face of the wall. Experiments are carried out on two traditional multi-layered building wall cases using heating lamps. With the measured surFace temperatures and heat fluxes, the unit-pulse response and unit-step response at the front surFace of the investigated wall are reconstructed through a deconvolution approach and a TSVD (Truncated Singular Value Decomposition) inversion. The unit-step response curve is directly characterized by the thermal resistance, thermal effusivity and heat capacity of the wall, thus allowing us to estimate the wall properties. The characterization time for the two cases is less than 10 hours.
Hussein Youlal - One of the best experts on this subject based on the ideXlab platform.
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Analysis of a thermal system by contact for defect detection in homogeneous materials – Validation by infrared thermography
Energy Procedia, 2017Co-Authors: Ahmed Kabouri, Abdelhamid Khabbazi, Hussein YoulalAbstract:Abstract This is mainly a validation by infrared thermography of an experimental contribution for defect detection by contact based on the flash method, generally used to characterize the thermal diffusivity of the material. Indeed, we have conceived and realized a contact thermal sensor consisting of forty-nine type K thermocouples distributed over the Rear Face of the sample to be tested. The thermocouples responses resulted by several thermograms, are given in several measuring points distributed over the entire Rear Face of the sample. We performed a series of experiments using our realized sensor and an infrared camera. Analysis of the experimental results shows that the temperature rise generated by the flash on the Rear Face, represent important information to explore for establish a thermal system by contact for defect detection in homogeneous materials.
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Applied multiresolution analysis to infrared images for defects detection in materials
NDT & E International, 2017Co-Authors: Ahmed Kabouri, Abdelhamid Khabbazi, Hussein YoulalAbstract:Abstract In this paper, an advanced approach to characterize defects in homogeneous materials based on multiresolution analysis of infrared images is presented. This is mainly a non-destructive evaluation technique based on the flash method in transmission mode. An experimental device using infrared thermography was designed and realized. The equipment includes an infrared imager for following the temporal evolution of the temperature in the Rear Face of the tested sample. The other front Face receives a flash from a halogen lamps excitation source. The thermal images generated at the Rear Face are segmented using a wavelet transform multiresolution analysis in order to extract all defects zones and subsequently processed to estimate their corresponding surFace sizes. The experimental results on the test materials with hidden defects show the advantage of the segmentation technique applied to the response images of the system. High precision of the localization and accurate estimation of the surFace sizes of the detected defects are achieved with the advanced method, involving a denoising of the images using a thresholding of wavelet coefficients. The outcome is a significantly improved detection quality, due mainly to the advanced processing, which does not depend on the type, shape and size of the defects.
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Local detection of defects in materials by thermal analysis - flash method
The European Physical Journal Applied Physics, 2016Co-Authors: Ahmed Kabouri, Abdelhamid Khabbazi, Hussein Youlal, Malika Janati-idressiAbstract:This is mainly an experimental contribution about defect detection based on the flash method generally used to characterize the thermal diffusivity of the material. The temperature rise on the Rear Face of the sample generated by the flash provides important information. We have conceived and realized a contact thermal sensor consisting of forty-nine type K thermocouples distributed over the Rear Face of the sample to be tested. The thermocouples responses, as measured by several thermograms, are given in several measuring points distributed over the entire bottom surFace of the sample. Analysis of the experimental results shows that the temperature rise provide important information to establish a thermal system for defect detection in homogeneous materials containing heterogeneities.
