Research Outputs (Mechanical, Industrial and Aeronautical Engineering)

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For information on accessing School of mechanical, industrial and aeronautical engineering Research Articles content please contact Salome Potgieter by email : salome.potgieter@wits.ac.za or Tel : 011 717 1961

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A novel method to measure residual stresses in unidirectional GFRP.
(Elsevier, 2009-05) Reid, R.G.; Paskaramoorthy, R.
A few methods are available for measuring the residual stresses that occur in the simplest of all possible composites structures - the unconstrained unidirectional laminate. None of them, however, are suitable for use on GFRP. A new method is presented whereby the stresses in a unidirectional GFRP laminate can be determined. The method relies on releasing the constraints between fibre and resin through an annealing process. The strain in the glass fibres is thus obtained, which allows the elastic stresses within the fibres and the resin to be determined. In this way, it is not necessary to take account of plasticity and viscous effects in the polymer in order to determine the stresses within the laminate. Results for unidirectional laminates initially manufactured to contain differing residual stresses are presented and discussed.
Effects of processing conditions on the mechanical and water absorption properties of resin transfer moulded kenaf fibre reinforced polyester composite laminates.
(Elsevier, 2010-11) Rassmann, S.; Reid, R.G.; Paskaramoorthy, S.
This paper focuses on the mechanical and water absorption properties of kenaf fibre reinforced polyester laminates manufactured by resin transfer moulding. Varying processing conditions were considered as alternatives to fibre treatments, thereby potentially avoiding additional cost and complexity in the manufacturing process. Laminates were produced by altering fibre moisture content, mould temperature and mould pressure following injection. Tensile, flexural, impact and water absorption tests were conducted. Processing conditions were found to have little effect on properties except for pressurisation which increased tensile and flexural strength and decreased water absorption at low fibre volume fractions. Examinations using a scanning electron microscope showed that all the laminates failed by fibre pull-out.
An extension to classical lamination theory for use with functionally graded plates.
(Elsevier, 2011-01) Reid, R.G.; Paskaramoorthy, R.
An extension to classical lamination theory is presented for the improved analysis of thin to moderately thick functionally graded plates. The method results in an explicit formulation that accommodates any through-thickness variation in the elastic, hygrothermal and piezoelectric properties of each layer. Additionally, variations in the material rotation angle, temperature, moisture content and electric field strength through each layer are taken into account. The method relies on representing with polynomial series the variation in both the properties of each ply and the hygrothermal and piezoelectric loading. Validation problems are presented that demonstrate the application and accuracy of the method.
Effect of resin system on the mechanical properties and water absorption of kenaf fibre reinforced laminates.
(Elsevier, 2011-03) Rassmann, S.; Paskaramoorthy, R.; Reid, R.G.
The objective of this study is to compare the mechanical and water absorption properties of kenaf (Hibiscus cannabinus L.) fibre reinforced laminates made of three different resin systems. The use of different resin systems is considered so that potentially complex and expensive fibre treatments are avoided. The resin systems used include a polyester, a vinyl ester and an epoxy. Laminates of 15%, 22.5% and 30% fibre volume fraction were manufactured by resin transfer moulding. The laminates were tested for strength and modulus under tensile and flexural loading. Additionally, tests were carried out on laminates to determine the impact energy, impact strength and water absorption. The results revealed that properties were affected in markedly different ways by the resin system and the fibre volume fraction. Polyester laminates showed good modulus and impact properties, epoxy laminates displayed good strength values and vinyl ester laminates exhibited good water absorption characteristics. Scanning electron microscope studies show that epoxy laminates fail by fibre fracture, polyester laminates by fibre pull-out and vinyl ester laminates by a combination of the two. A comparison between kenaf and glass laminates revealed that the specific tensile and flexural moduli of both laminates are comparable at the volume fraction of 15%. However, glass laminates have much better specific properties than the kenaf laminates at high fibre volume fractions for all three resins used.
The effects of alkali-silane treatment on the tensile and flexural properties of short fibre non-woven kenaf reinforced polypropylene composites.
(Elsevier, 2012-09) Asumani, O.M.L.; Reid, R.G.; Paskaramoorthy, R.
Kenaf fibre reinforced polypropylene composites were manufactured by compression moulding. The kenaf fibre was considered in three forms; untreated, treated with sodium hydroxide solution and treated with sodium hydroxide solution followed by three-aminopropyltriethoxysilane. The effects of these chemical treatments on the tensile and flexural properties of the composites were investigated. Mechanical test results show that alkali treatment followed by three-aminopropyltriethoxysilane treatment (alkali-silane treatment) significantly improves the tensile and flexural properties of short fibre non-woven kenaf polypropylene composites. In particular, the specific tensile and flexural strengths of alkali-silane treated kenaf composites with 30% fibre mass fraction are, respectively, only 4% and 11% lower than those of composites made using glass fibre. Scanning electron microscopy examination shows that the improvements in the tensile and flexural properties resulting from alkali-silane treatment can be attributed to better bonding between the fibres and matrix.
Extension of the layer removal technique for the measurement of residual stresses in layered anisotropic cylinders.
(Springer, 2014-09) Carpenter, H.W.; Reid, R.G.; Paskaramoorthy, R.
An extension of the layer removal technique is presented that allows the residual stresses within multilayered anisotropic pipes of any wall thickness to be determined. The method inherently satisfies the self-equilibrium requirement and limits the effects of measurement errors to the region local to the error. The thickness of each layer that is removed need not be uniform and is entirely independent of the thickness of each ply of material. Four example problems are considered. The first three allow results to be compared between the present method and previous work. The fourth problem demonstrates the method on a thick walled anisotropic pipe built up of +45°/-45° plies for which no solution was previously available.
Measurement of the Distribution of Residual Stresses in Layered Thick-Walled GFRP Pipes.
(Springer, 2014-11) Carpenter, H.W.; Reid, R.G.; Paskaramoorthy, R.
The objective of this study is to measure the axial, circumferential, shear and radial residual stress distributions in three thick-walled glass fibre reinforced plastic (GFRP) filament-wound pipes, two of which are layered. The measurement of residual stresses was carried out using a recently published layer removal method which overcomes the limitations of previous techniques and can be applied to layered anisotropic pipes of any wall thickness. Layers of approximately 0.3 mm thickness were incrementally ground from the outer surface of the pipes. The resulting strains were measured on the inner surfaces. A least-squares polynomial was fitted to each measured data set, and used to calculate the corresponding stress distributions. All of the resulting axial, hoop and shear stress distributions adhere to the requirement of self-equilibrium and the radial stress distributions all vanish to zero at the inner and outer surfaces. The radial stresses of the layered pipes showed a tendency to have two peaks, one for each layer, a consequence of the two-stage manufacturing process of these pipes. The measured axial and hoop stresses of all three pipes were similar at the inner surfaces despite significant differences in the stiffnesses in the principal directions arising from different wind angles.
The effect of residual stresses and wind configuration on the allowable pressure of thick-walled GFRP pipes with closed ends.
(Springer, 2015) Carpenter, H.W.; Reid, R.G.; Paskaramoorthy, R.
An investigation into the benefits of winding thick-walled glass fibre reinforced plastic (GFRP) pipes with two layers of different winding angles is presented. It is shown that layered pipes allow significantly greater internal pressures to be carried than can be achieved by pipes wound only at +/- 55 degrees if process induced residual stresses are ignored. It was found, also, that residual stresses severely reduce the allowable operating pressure of GFRP pipes. The reduction was most significant for the layered pipes, however, and this severely impacts on their utility. The most efficient pipe was nevertheless found to be a layered pipe, wound with a +/- 65 degrees/+/- 47 degrees combination. This pipe gives a 12 % improvement on the allowable pressure of the +/- 55 degrees pipe. This small performance benefit is achieved at the cost of significantly greater manufacturing complexity, and so the +/- 55 degrees pipe is probably still the most practical wind configuration.
The response of layered anisotropic tubes to centrifugal loading.
(Elsevier, 2016-04) Carpenter, H.W.; Reid, R.G.
The displacement-based elastic solution for layered anisotropic tubes is extended to allow for the presence of centrifugal loading. The additional terms in the stress-strain equations derived in this work are validated by comparing the results obtained using the current solution against those determined using finite element simulation of rotating thin and thick-walled glass fibre reinforced plastic tubes of arbitrary anisotropic lay-up. The solution is presented in such a form that it can be utilised to determine the linear thermo-mechanical behaviour of rotating tubes with anisotropic lay-up, subjected to any combination of internal and external axisymmetric pressure, axial loading, torsional loading, and constant temperature change.
Project Management Assessments (PMAs): an empirical study
(Southern African Institute for Industrial Engineering, 2018) Siriram, Rajenlall
The objectives of this research are to: a) compare project management assessments (PMAs) from four firms across four industry sectors (75 PMAs are evaluated using known statistical techniques); b) validate the results through an expert panel; c) apply Pearson’s correlation analysis to find links in the PMA constructs and see how these links relate to the overall project result; and d) identify areas for further research. Three hypotheses are tested, and reveal differences and similarities in project management practices. The results provide interesting opportunities for researchers and for project management practitioners. Finally, a discussion, the limitations of the study, and suggestions for further research are presented.

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