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F R Jones - One of the best experts on this subject based on the ideXlab platform.
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the role of matrix cracks and Fibre matrix debonding on the stress transfer between Fibre and matrix in a Single Fibre fragmentation test
Composites Part A-applied Science and Manufacturing, 2012Co-Authors: Anbu Clemensis Johnson, S A Hayes, F R JonesAbstract:The Single Fibre fragmentation test is commonly used to characterise the Fibre/matrix interface. During fragmentation, the stored energy is released resulting in matrix cracking and/or Fibre/matrix debonding. Axisymmetric finite element models were formulated to study the impact of matrix cracks and Fibre/matrix debonding on the effective stress transfer efficiency (EST) and stress transfer length (STL). At high strains, plastic deformation in the matrix dominated the stress transfer mechanism. The combination of matrix cracking and plasticity reduced the EST and increased STL. For experimental validation, three resins were formulated and the fragmentation of an unsized and uncoupled E-glass Fibre examined as a function of matrix properties. Fibre failure was always accompanied by matrix cracking and debonding. With the stiff resin, debonding, transverse matrix cracking and conical crack initiation were observed. With a lower modulus and lower yield strength resin the transverse matrix crack length decreased while that of the conical crack increased.
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phase stepping photoelasticity for the measurement of interfacial shear stress in Single Fibre composites
Composites Part A-applied Science and Manufacturing, 2006Co-Authors: F M Zhao, S A Hayes, E A Patterson, F R JonesAbstract:Abstract Phase-stepping photoelasticity has been used to study the fragmentation of an E-glass Fibre in epoxy resin and evaluate quantitatively its interfacial adhesion. To investigate the interfacial response of an E-glass Fibre with differing degrees of adhesion, it was coated by plasma-polymerisation with a crosslinked conformal film of 90% acrylic acid and 10% 1,7-octadiene. The stress distribution within the resin at the Fibre–matrix interface and the adjacent matrix has been described in detail using contour maps of fringe order. From these, the interfacial shear stress profiles at Fibre-ends have been calculated. With a cold-cured epoxy resin a good interface was formed between uncoupled unsized E-glass, while a poor interface was achieved with the plasma polymer coated Fibre. Further, it was clearly demonstrated that chemical bond formation between the functional plasma polymer coating and the matrix was incomplete leading to the formation of an interphase epoxy resin of low yield strength. We now have a technique capable of probing the micromechanical response of interphases as a function of chemical bond formation.
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Fibre matrix stress transfer through a discrete interphase part 1 Single Fibre model composites
Composites Part A-applied Science and Manufacturing, 2001Co-Authors: S A Hayes, R Lane, F R JonesAbstract:Abstract This paper reports a study of the effect of an interphase on strain development in Fibre-fragments. In order to form an interphase, an epoxy resin with known properties was applied to the surface of unsized reinforcing Fibres and cured. These were then embedded in a matrix resin coupon, prior to fragmentation testing. The study included an examination of the effect of interphase thickness, by applying multiple coats of one of the resins, and the effect of the interphase properties, by varying the coating resins. It was found that the average fragment lengths at saturation were difficult to distinguish, as a result of the scatter introduced by the statistical distribution of Fibre strengths. However, the strain interval between onset of fragmentation and saturation was found to be more sensitive to variations in the interphase properties. A finite element model was used to examine the strain development in the fragments in more detail. The mechanical properties of the Fibre, interphase and matrix were accurately incorporated into the model, providing a realistic representation of the state of strain in the experimental samples. The predicted deformations around the Fibre-break provided an explanation for the experimental observations.
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Single Fibre fragmentation test for assessing adhesion in Fibre reinforced composites
Journal of Materials Science, 1998Co-Authors: D. Tripathi, F R JonesAbstract:The Single Fibre fragmentation test for measuring the properties of the Fibre–matrix interface in Fibre-reinforced composites is reviewed. Special emphasis has been paid to the recent stress transfer models in Single Fibre composites and its application to the development of a suitable data reduction technique for the fragmentation test. The complexities of the correlation of the micromechanical results to the properties of the macrocomposites have been highlighted.
W P Boshoff - One of the best experts on this subject based on the ideXlab platform.
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the response of cracked steel Fibre reinforced concrete under various sustained stress levels on both the macro and Single Fibre level
Construction and Building Materials, 2017Co-Authors: P D Nieuwoudt, Adewumi John Babafemi, W P BoshoffAbstract:Abstract If Fibre reinforced concrete structures are to be accurately designed, an understanding of the time-dependent response under sustained loadings and in the cracked state must be well understood. It is known that the Fibres pull-out with time under sustained loadings. However, the quantification of the pull-out creep is still understudied, particularly under uniaxial tensile loading. In this study, the tensile creep response of cracked steel Fibre reinforced concrete under varying sustained stress levels has been performed. Furthermore, Single Fibre pull-out and pull-out creep tests were also undertaken to describe the mechanisms responsible for the crack widening of steel Fibre reinforced concrete. The influence of Fibre orientation angle, Fibre mechanical anchorage, stress level, and Fibre pre-slipping on the pull-out response at the Single Fibre level was also investigated. X-ray computed tomography (CT) scans of specimens subjected to pull-out creep tests are also shown to demonstrate the prominent mechanisms causing the time-dependent pull-out of steel Fibres. All tests were performed under a controlled environment. The results of the investigations have revealed that the tensile creep of cracked steel Fibre reinforced concrete increases as the stress level increases. X-ray CT scan images have shown that instantaneous pull-out is caused by the collapse of the interface between the Fibre and the matrix. This damage to the interface also increases with time under sustained loading and increased load levels. At higher stress levels, pull-out creep increases due to micro-cracking at the region of the hooked end of the Fibre.
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tensile creep of cracked steel Fibre reinforced concrete mechanisms on the Single Fibre and at the macro level
2017Co-Authors: W P Boshoff, P D NieuwoudtAbstract:This paper reports on tests done to investigate the mechanisms causing the increased tensile creep of cracked Fibre reinforced concrete (FRC) members when a sustained load is applied. It is important to understand the mechanisms as this will pave the way for improvements that can be made to reduce this creep and will also assist in creating prediction models as it will be based on the fundamental mechanisms involved. This paper presents results of uni-axial tensile creep tests of cracked steel Fibre reinforced concrete (SFRC) and also tests at the Single Fibre level. Single Fibres were embedded in the matrix and pull-out at different rates and sustained loading was also applied to the Single, embedded Fibres. It was found that the Single Fibre pull-out creep test results can be directly linked to the uni-axial tensile tests. It was also shown that the pull-out creep is proportional to the load up to at least 50 % of the ultimate load after which the pull-out creep increases non-linearly. This can be ascribed to micro-cracking around the hooked-end of the Fibre. Lastly, it is postulated that the interfacial transition zone between the Fibre hooked-end and the concrete matrix plays a significant role in the pull-out creep behaviour.
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characterising the time dependant behaviour on the Single Fibre level of shcc part 2 the rate effects on Fibre pull out tests
Cement and Concrete Research, 2009Co-Authors: W P Boshoff, Viktor Mechtcherine, Gideon P A G Van ZijlAbstract:This paper is the second part of a two paper series about the time-dependant behaviour of Strain Hardening Cement-based Composite (SHCC) on the Single Fibre level. Having dealt with mechanisms of creep in SHCC in the first part, this paper reports Single Fibre pull-out tests that were done to investigate the effect of the pull-out rate on the mechanical response of the interface between the Fibre and the matrix. It was found that not only the pull-out resistance increased with an increase of the pull-out rate but the probability of Fibre rupture during pull-out as well. Another important finding was that the interfacial shear resistance and slip-hardening coefficient are not only dependant on the pull-out rate, but also the embedment length.
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characterising the time dependant behaviour on the Single Fibre level of shcc part 1 mechanism of Fibre pull out creep
Cement and Concrete Research, 2009Co-Authors: W P Boshoff, Viktor Mechtcherine, Gideon P A G Van ZijlAbstract:SHCC (Strain Hardening Cement-based Composite) has been designed and optimised to overcome the main weaknesses of ordinary concrete, which is its brittleness. SHCC shows a high tensile ductility and can resist the full load at a tensile strain of more than 4%. An in depth investigation into the time-dependant behaviour is still lacking for SHCC. This paper is the first part of a two paper series about the time-dependant behaviour on the Single Fibre level. In this paper, the tensile creep behaviour of SHCC is studied to distinguish mechanisms of creep. Tensile creep and shrinkage test results are reported for dumbbell type SHCC specimens. The specimens are pre-cracked to simulate in-service conditions, with subsequent sustained load at various levels, here chosen as 30%, 50%, 70% and 80% of the ultimate resistance. To distinguish the sources of significant creep deformation under these sustained loads, Single Fibre pull-out tests are performed under sustained load. It is shown that the time-dependent Fibre pull-out is a significant source of time-dependent deformation, along with the formation of new cracks in SHCC under sustained load.
Gideon P A G Van Zijl - One of the best experts on this subject based on the ideXlab platform.
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characterising the time dependant behaviour on the Single Fibre level of shcc part 2 the rate effects on Fibre pull out tests
Cement and Concrete Research, 2009Co-Authors: W P Boshoff, Viktor Mechtcherine, Gideon P A G Van ZijlAbstract:This paper is the second part of a two paper series about the time-dependant behaviour of Strain Hardening Cement-based Composite (SHCC) on the Single Fibre level. Having dealt with mechanisms of creep in SHCC in the first part, this paper reports Single Fibre pull-out tests that were done to investigate the effect of the pull-out rate on the mechanical response of the interface between the Fibre and the matrix. It was found that not only the pull-out resistance increased with an increase of the pull-out rate but the probability of Fibre rupture during pull-out as well. Another important finding was that the interfacial shear resistance and slip-hardening coefficient are not only dependant on the pull-out rate, but also the embedment length.
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characterising the time dependant behaviour on the Single Fibre level of shcc part 1 mechanism of Fibre pull out creep
Cement and Concrete Research, 2009Co-Authors: W P Boshoff, Viktor Mechtcherine, Gideon P A G Van ZijlAbstract:SHCC (Strain Hardening Cement-based Composite) has been designed and optimised to overcome the main weaknesses of ordinary concrete, which is its brittleness. SHCC shows a high tensile ductility and can resist the full load at a tensile strain of more than 4%. An in depth investigation into the time-dependant behaviour is still lacking for SHCC. This paper is the first part of a two paper series about the time-dependant behaviour on the Single Fibre level. In this paper, the tensile creep behaviour of SHCC is studied to distinguish mechanisms of creep. Tensile creep and shrinkage test results are reported for dumbbell type SHCC specimens. The specimens are pre-cracked to simulate in-service conditions, with subsequent sustained load at various levels, here chosen as 30%, 50%, 70% and 80% of the ultimate resistance. To distinguish the sources of significant creep deformation under these sustained loads, Single Fibre pull-out tests are performed under sustained load. It is shown that the time-dependent Fibre pull-out is a significant source of time-dependent deformation, along with the formation of new cracks in SHCC under sustained load.
Jörg Müssig - One of the best experts on this subject based on the ideXlab platform.
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improvement and analysis of Fibre matrix adhesion of regenerated cellulose Fibre reinforced pp mapp and pla composites by the use of eucalyptus globulus lignin
Composites Part B-engineering, 2014Co-Authors: Nina Graupner, Holger Fischer, Gerhard Ziegmann, Jörg MüssigAbstract:The presented study investigates the influence of Eucalyptus globulus lignin as a natural additive on the Fibre/matrix interaction of lyocell (regenerated cellulose Fibre) in different matrices (polylactide – PLA, polypropylene – PP, maleic-anhydride-grafted-PP – MAPP). For this purpose, lyocell Fibres were treated with a lignin–ethanol solution. It was shown that the Fibre tensile strength was not affected by the lignin-treatment. The viscosity of the PLA matrix was reduced by adding lignin. This effect might lead to a better wettability of the Fibres but the mechanical characteristics of PLA were not affected by the treatment. Apparent Fibre/matrix adhesion was assessed using a Single Fibre pull-out test and a Single Fibre fragmentation test. Both testing procedures revealed a trend of improved interfacial shear strength for the lignin-treated Fibres compared with untreated Fibres for all investigated matrices. Additionally the apparent interfacial shear strength was investigated with short bending tests and double-notched tensile tests on lyocell/PLA composites. A significant increase was observed for lignin-treated composites compared to untreated composites. Microscopic investigations revealed a rougher Fibre surface with lignin particles. The higher specific Fibre surface can also lead to improved apparent Fibre/matrix interaction. Furthermore, it is hypothesised that van-der-Waals forces between the hydrophilic Fibres and the more hydrophobic matrix are favoured by the less hydrophobic character of lignin.
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interfacial studies of natural Fibre polypropylene composites using Single Fibre fragmentation test sfft
Composites Part A-applied Science and Manufacturing, 2011Co-Authors: A. Awal, G. Cescutti, Subrata Bandhu Ghosh, Jörg MüssigAbstract:Abstract For the potential use and new applications of natural Fibre reinforced plastics, it is crucial that the mechanical behaviour of these composites is fully understood. Single Fibre fragmentation tests (SFFT) were carried out to compare the fragmentation phenomenon in two natural Fibres/polypropylene (PP) composites. Polypropylene was used with maleic anhydride (MAPP) as a coupling agent for this study. The SFFT test results are significantly affected by both sample preparation method and testing conditions. Therefore, the influence of sample preparation, gauge length as well as strain rate were studied. By considering test reproducibility and practical findings, a gauge length of 15.5 mm and a test speed of 0.2 mm/min were selected for interfacial shear strength (IFSS) characterisation. Owing to the stiff nature of flax and ramie Fibre, Weibull distribution was used to analyse Fibre strength statistics.
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Fibre matrix adhesion of natural Fibres cotton flax and hemp in polymeric matrices analyzed with the Single Fibre fragmentation test
Composite Interfaces, 2008Co-Authors: Tim Huber, Jörg MüssigAbstract:In this research the adhesion and the resulting interfacial shear strength (IFFS) between the natural Fibres flax, hemp and cotton and the polymer matrices polypropylene with coupling agent (MAPP) and polylactide acid (PLA) was surveyed with the Single Fibre fragmentation test (SFFT). The adhesion between MAPP and the Fibres was good enough to produce fragments, whereas the adhesion between PLA and flax was too weak to transmit enough tension for Fibre cracks which is clearly visible on SEM-photographs. Comparing the IFFS values of the Fibres in MAPP with an equal Fibre diameter shows that the IFFS value of flax is highest with 7.09 N/mm2 followed by hemp 6.13 N/mm2. The IFFS of cotton is a lot smaller (0.664 N/mm2). The critical fragmentation or fragmentation length of the bast Fibres flax (3.16 mm) and hemp (3.20 mm) in MAPP is smaller than the critical fragmentation length of cotton (5.03 mm). The adhesion between the lignocellulosic Fibres and MAPP is much better than between the lignin and pectin fre...
P D Nieuwoudt - One of the best experts on this subject based on the ideXlab platform.
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the response of cracked steel Fibre reinforced concrete under various sustained stress levels on both the macro and Single Fibre level
Construction and Building Materials, 2017Co-Authors: P D Nieuwoudt, Adewumi John Babafemi, W P BoshoffAbstract:Abstract If Fibre reinforced concrete structures are to be accurately designed, an understanding of the time-dependent response under sustained loadings and in the cracked state must be well understood. It is known that the Fibres pull-out with time under sustained loadings. However, the quantification of the pull-out creep is still understudied, particularly under uniaxial tensile loading. In this study, the tensile creep response of cracked steel Fibre reinforced concrete under varying sustained stress levels has been performed. Furthermore, Single Fibre pull-out and pull-out creep tests were also undertaken to describe the mechanisms responsible for the crack widening of steel Fibre reinforced concrete. The influence of Fibre orientation angle, Fibre mechanical anchorage, stress level, and Fibre pre-slipping on the pull-out response at the Single Fibre level was also investigated. X-ray computed tomography (CT) scans of specimens subjected to pull-out creep tests are also shown to demonstrate the prominent mechanisms causing the time-dependent pull-out of steel Fibres. All tests were performed under a controlled environment. The results of the investigations have revealed that the tensile creep of cracked steel Fibre reinforced concrete increases as the stress level increases. X-ray CT scan images have shown that instantaneous pull-out is caused by the collapse of the interface between the Fibre and the matrix. This damage to the interface also increases with time under sustained loading and increased load levels. At higher stress levels, pull-out creep increases due to micro-cracking at the region of the hooked end of the Fibre.
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tensile creep of cracked steel Fibre reinforced concrete mechanisms on the Single Fibre and at the macro level
2017Co-Authors: W P Boshoff, P D NieuwoudtAbstract:This paper reports on tests done to investigate the mechanisms causing the increased tensile creep of cracked Fibre reinforced concrete (FRC) members when a sustained load is applied. It is important to understand the mechanisms as this will pave the way for improvements that can be made to reduce this creep and will also assist in creating prediction models as it will be based on the fundamental mechanisms involved. This paper presents results of uni-axial tensile creep tests of cracked steel Fibre reinforced concrete (SFRC) and also tests at the Single Fibre level. Single Fibres were embedded in the matrix and pull-out at different rates and sustained loading was also applied to the Single, embedded Fibres. It was found that the Single Fibre pull-out creep test results can be directly linked to the uni-axial tensile tests. It was also shown that the pull-out creep is proportional to the load up to at least 50 % of the ultimate load after which the pull-out creep increases non-linearly. This can be ascribed to micro-cracking around the hooked-end of the Fibre. Lastly, it is postulated that the interfacial transition zone between the Fibre hooked-end and the concrete matrix plays a significant role in the pull-out creep behaviour.
