6,907 research outputs found

    Structure-property relationships in glass reinforced polyamide, part 2: The effects of average fiber diameter and diameter distribution

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    We present the results of an extensive study of the influence of average fibre diameter and the width of the diameter distribution on the performance of injection moulded glass-fibre reinforced polyamide 66. In the average fibre diameter range from 9-18m dry-as-moulded (DaM) composite unnotched impact and tensile strength decreased significantly. The composite notched impact performance and tensile modulus showed little dependence on fibre diameter. The influence of broadening the fibre diameter distribution by blending glass fibre samples of different average diameter was found to be particularly negative on the level of composite unnotched impact when compared at equal number average diameter. After hydrolysis treatment the composite tensile strength and modulus exhibited a large drop compared to the DaM results. In contrast, the unnotched impact results became insensitive to fibre diameter after hydrolysis. The average level of unnotched impact after hydrolysis was sufficiently high to show an increase over DaM when the fibre diameter was above 14m. Residual fibre length correlated significantly with fibre diameter with a lower average length for thinner fibres. The interfacial shear strength was found to be in the range of 26-34 MPa for DaM composites. There was a highly significant inverse correlation between the DaM interfacial strength and the average fibre diameter. It is shown that results from both tensile and unnotched impact measurements can be brought back to single trend lines by using a Z average value for the average fibre diameter which is more heavily weighted to the thicker fibres in the distribution

    The influence of fibre length, diameter and concentration on the impact performance of long glass-fibre reinforced polyamide 6,6

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    Results of an investigation of the mechanical performance of injection moulded long glass-fibre reinforced polyamide 6,6 composites are presented. The glass-fibre content in these composites was varied over the range of 10-50% by weight using fibres with average diameters of 10, 14 and 17 μm. Impact testing was carried out at −40, 23 and 80 °C on dry-as-moulded and boiling water conditioned samples. The results from these long fibre composites are compared with standard extrusion compounded short glass-fibre materials. Data on the influence of fibre diameter, fibre concentration, residual fibre length, hydrothermal conditioning and testing temperature on the composite performance in notched and unnotched pendulum impact tests and multiaxial instrumented impact tests are presented and discussed. All of the above parameters are shown to have significant influence on impact performance. However, the level of these effects is shown to depend on which type of impact test is being considered

    The influence of fibre length and concentration on the properties of glass fibre reinforced polypropylene: 5. Injection moulded long and short fibre PP

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    We present results of a step by step comparison of the mechanical performance of injection moulded 'long' (LF-PP) and 'short' (SF-PP) previous termglass fibre-polypropylenenext term compounds. The study allows direct comparison of the mechanical performance of long and short previous termfibrenext term systems in the same resin at the same previous termfibrenext term diameter, and the effect of previous termfibrenext term diameter in short previous termfibrenext term compounds. Furthermore, the comparison of these three systems has been made over the 0-40 wt% previous termfibrenext term content range. At the same previous termfibrenext term diameter and previous termfibrenext term content LF-PP gives significant improvements in room temperature tensile and flexural strength, notched and unnotched impact resistance. The improvement in impact resistance is higher still at lower test temperature. LF-PP also gives increasingly higher modulus over SF-PP as the strain is increased. The effect of lowering the previous termfibrenext term diameter in SF-PP has been shown to increase both strength and unnotched impact, but not to the levels obtained with LF-PP at higher previous termfibrenext term diameter. Notched impact and modulus of SF-PP were relatively unaffected by reduction of the previous termfibrenext term diameter. The relative mechanical data are shown to conform well to available models. The results are discussed in terms of the relevant micro-mechanical parameters of these materials

    A Kantian Argument for Sovereignty Rights of Indigenous Peoples

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    Kant’s non-voluntarist conception of political obligation has led some philosophers to argue that he would reject self-government rights for indigenous peoples. Some recent scholarship suggests, however, that Kant’s critique of colonialism provides an argument in favor of granting self-government rights. Here I argue for a stronger conclusion: Kantian political theory not only can but must include sovereignty for indigenous peoples. Normally these rights are considered redress for historic injustice. On a Kantian view, however, I argue that they are not remedial. Sovereignty rights are a necessary part of establishing perpetual peace. By failing to acknowledge the sovereignty of native groups, states once guilty of imperialism leave open the in principle possibility for future violence, even though no current conflict exists. Only in recognizing self-government rights can states truly commit to the cosmopolitan ideal

    Why are natural fibres failing to deliver on composite performance?

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    The poor performance of natural fibres as composite reinforcements where the focus on chemical aspects has not yet delivered the "holy grail" of glass fibre replacement in volume applications is discussed. An explanation is proposed based on the anisotropic structure of these fibres and its influence the composite interphase

    Understanding the impact performance of injection moulded long fibre reinforced polyamide

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    Short fibre reinforced thermoplastics have been used in the automotive industry for many years and there has recently been a strong growth in the use of polyamide based materials in under-the-hood applications. More recently there has been an increasing growth in the use of long fibre thermoplastic composite systems in semi-structural and engineering applications. Glass fibre reinforced polyamides are excellent composite materials in terms of their high levels of mechanical performance and temperature resistance. However the mechanical properties of polyamide based composites decrease markedly upon the absorption of water and other polar fluids. There also exist a number of well documented differences in the structure performance relationships of short fibre reinforced polyamide and polypropylene composites and it can be expected that there will also be differences when we compare these resins reinforced with long fibres. In this paper we present data on the mechanical performance of long fibre reinforced polyamide 6,6 which may be relevant to the above discussion. We have prepared injection moulded long fibre reinforced polyamide 6,6 samples with a range of glass contents (0-50 % wt) using glass fibres having average fibre diameters of 10, 14, and 17 μm. Mechanical performance has been determined for both "dry as moulded" state and after hydrolytic conditioning and compared with reference short fibre composites based on 10 μm diameter fibre in the same resin system. We will focus our discussion on the effects of fibre length, fibre diameter and fibre concentration on the impact performance of these composites. We will show how it is important to discriminate between notched (Figure 1) and unnotched (Figure 2) testing when discussing impact performance as these two properties show very different structure-performance relationships

    Structure-property relationships in glass-reinforced polyamide, Part 3: Effects of hydrolysis ageing on the dimensional stability and performance of short glass-fiber-reinforced polyamide 66

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    We present results on an in-depth study of the effects of hydrolysis testing on the mechanical performance, weight change, and dimensional stability of injection moulded glass-fibre reinforced polyamide 66 based on two chopped fibre products with different sizing formulations. Composite and resin samples have been characterised both dry as moulded and after conditioning at either 120°C or 150°C for a range of times up to 1000 hours. The results reveal that hydrothermal ageing in water-glycol mixtures results in significant changes in the mechanical performance, weight, and dimensions of these materials. The negative effects of conditioning could be mitigated to some degree by the appropriate choice of the glass fibre sizing; however the sizing effect diminished with increasing conditioning time. All materials showed a weight increase due to conditioning at 120°C which was typical of a single Fickian diffusion process and there was clear evidence of multiple processes involved when conditioning at 150°C. It was not apparent that the glass fibre sizing affected the dimensional stability of the composites. We show that there is a strong correlation between the swelling of these samples and the level of fluid adsorption. Although the PA66 resin showed reasonably homogeneous swelling, the composites exhibited different levels of swelling depending on direction. These effects were well in line with the known effects of fibres on restriction of the matrix deformation (mechanical, thermal or moisture swelling) in the fibre direction. These differences correlate well with the average fibre orientation with respect to the various direction axes. Composite tensile strength and unnotched impact resistance appeared to scale inversely with the level of swelling of the material
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