OpenUCT :: Browsing by Author "Marcus, Kashif"

Browsing by Author "Marcus, Kashif"

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Open Access
A comparative evaluation of manufacturing technologies and their effect on morphology and mechanical properties of poly-(propylene-ethylene) copolymers
(2002) Sello, Maitse P; Marcus, Kashif; Sole, Brian Michael
This project is a technological benchmark exercise for Sasol Polymers where different poly (propylene-ethylene) copolymer grades from five foremost licensed manufacturing PP technologies are evaluated. These copolymer grades were manufactured using the following processes: Novolen PP technology (Sasol grades), Innovene PP technology (BP grades), Spheripol PP technology (Basell grades), Univation PP technology (DOW grades) and Borstar PP technology (Borealis grades). Form this investigation, thirty different grades where evaluated to determine their structural morphology in relation to their physical and mechanical properties. For the ease of analysis, the grades are grouped into three ethylene content ranges; low ethylene contents (below 8%), medium ethylene contents (between 8 -10%) and high ethylene contents (above 10%). Within each of these ethylene content ranges, there is a melt flow index (MFI) range, which increases from low to high. The differences in the MFI added further complications, especially when trying to determine optimum mechanical properties of the copolymer grades. The impact test results show that the toughness is at a maximum at low MFI, and then drops drastically as the MFI increases. Since an addition of ethylene improves the toughness of the copolymer, it was observed that by considering MFI's below 35 g/10 min, the toughness could be enhanced by increasing ethylene content. Grades with MFI's below 35 g/10 min show a drastic increase in impact strength at ethylene content around 8.5%. SEM results show that particle size and spacing are independent of ethylene contents for the grades examined. However, for the BP and DOW grades, the ratio between interparticle distance and particle size decrease steadily with increasing ethylene content. The Basell and BP grades showed a narrow rubber particle size distribution followed by Sasol grades. The DOW grades showed a broad particle size distribution. TEM results show that the internal morphology of the rubber particles differ from grade to grade, with the Sasol and BP grades showing several numbers PE inclusions within the rubber particles, whilst Basell grades having only few PE inclusions. It was observed that those grades with several PE inclusions have a better impact performance compared with those with fewer inclusions.
Open Access
Development of low cost thermal insulating materials
(2005) Meletse, Thabo Frans; Marcus, Kashif
The disadvantaged people in South Africa are unfortunate by virtue of their financial status. It was estimated in 1992 that 20 % of the South African population live in informal settlements. The houses in these settlements are found to be very energy inefficient. This study was aimed at developing low cost thermal insulating materials that can be used to increase energy efficiency of the houses in these informal settlements. This was done by firstly studying the properties of thermal insulation materials. Furthermore, common thermal insulating materials in South Africa were studied and evaluated. Only recycled polymeric based materials were examined for selecting the raw materials that were used to investigate the feasibility of the thermal insulating materials from waste material. The experimental work was extended to construct a thermal conductivity rig that was to be used in measuring the thermal conductivity of both the developed and existing thermal insulating materials. The expanded polystyrene obtained from Sagex (Pty) Ltd and polyester obtained from Isotherm (Pty) Ltd. were evaluated and compared to the manufactured recycled polymer slabs and expanded polyethylene foams (EPEF). Expanded polyethylene foam and recycled polymer slab samples were subjected to mechanical and physical testing. A temperature comparison test and thermal conductivity determination were conducted on both the expanded polyethylene foam (EPEF) and recycled polymer slab (RPS) samples. The scanning electron microscope (SEM) was used to reveal the micro-structures of all the developed thermal insulating material samples. The expanded polystyrene and polyester thermal insulating materials were also examined using the SEM. Optical microscopy was only used on RPS samples. It was found in this research, that the properties that govern the viability of thermal insulating materials are: thermal conductivity (k-value), thermal resistance (R-value), combustibility, moisture absorption and the presence of hazardous gases during burning. The temperature comparison test showed that the recycled polymer slab (RPS) and expanded polyethylene foam (EPEF) retards the flow of heat to levels comparable to that of the locally obtained thermal insulation. The comparative cut bar method was found to be relatively cheap to design and it was ideal for the measurement of the thermal conductivity of polymeric based materials. The k-value of all the EPEF samples was measured to be around 0.04 W.m-¹K-¹ and the RPS k-value was found to be 0.05 W.m-¹K-¹. This is attributed to air pockets with lower conductivities values, found within the structure of the polymeric thermal insulating materials. The porous structure is evident from the SEM micrographs of both the EPEF and RPS samples. One grade of expanded polyethylene foam, the SPX80, had accumulated less moisture when moisture absorption was compared with other EPEF samples. The RPS material did have a propensity for absorption of water. The flammability retardant tests have showed that gypsum board has to be incorporated during service for the RPS and SPX80. The mechanical testing results also suggest that both the EPEF and RPS need to be supported when installed in a ceiling, for example.
Open Access
Evaluation of metal dusting of nickel-chromium-iron based alloys in a laboratory environment
(2006) Marekwa, Mpho David; Marcus, Kashif
The deposition of carbon from a carbon-rich environment onto structural materials is prevalent in petrochemical and chemical industries such as in the production of syngas, iron reduction plants, petroleum refineries, carbon dioxide cooled nuclear plants, fuel cells using molten salts and hydrocarbons, and the recycle-gas loop equipment of coal-gasification units. The consequence of carbon deposition is a metal related degradation phenomenon known as "Metal dusting". Metal dusting results in rapid material wastage and/or thinning of material, producing hemispherical pits and grooves as the affected material disintegrates into a mixture of carbon and metal particles. The aim of this study was to elucidate material factors that cause or contribute to metal dusting. This was achieved by refurbishing the in-built metal dusting rig to carry out experimental tests on a laboratory scale. The objectives of this research were to simulate a metal dusting environment, characterize the resistance of various alloys to metal dusting, and to evaluate the effects of surface treatment and temperature on metal dusting. Metal dusting was induced on a wide variety of nickelbased and iron-based alloys which were capable of forming chromium oxide scales in a flowing CO-HrH20 atmosphere at 650°C and 500°C. Some of the alloys were heat treated at 850°C for an hour prior to exposure and others were ground to 600 grit SiC. Some degree of metal dusting attack was observed for all alloys tested except for an alloy with high chromium and nickel content. The results indicated that metal dusting is much more aggressive at lower temperatures than at high temperatures. It was also observed that the surface working of the alloys had a very significant effect to metal dusting resistance as well as the amount of scale forming elements additions and the presence of certain carbides forming elements. The preheat treatment seemed not to have a Significant effect on the resistance to metal dusting.
Open Access
Evaluation of the MD shear test method as a criterion for predicting box compressive strength
(2004) Jones, John David; Marcus, Kashif
Corrugated board is a composite sandwich type material used in the packaging industry worldwide. In the design of corrugated boxes, the stacking strength is an important design parameter. Current research shows that box failure is inﬂuenced by the ﬂexural rigidities of the panel and its transverse shear rigidities. McKinlay proposed a new method to measure the MD transverse shear stiffness of corrugated board. This research was aimed at designing a ﬁxture to perform the MD shear test and to evaluate its performance. In addition, the properties that inﬂuence box strength were to be investigated. These properties were then to be used in improved box strength predictions. It was found that the designed MD shear ﬁxture was able to measure the transverse shear stiffness of corrugated board in the MD direction with a high degree of accuracy and reproducibility. This method was much easier to perform than the standard block shear test method and also much quicker. This was a very important factor considering the application of this testing method in a research and development environment. In addition, the stiffness test exhibited good possibilities for use as a quality control tool. Extensive testing showed that the material used in the manufacture of corrugated board had a strong inﬂuence on board and box strength. In addition, it was found that the separation of the faces in a corrugated board structure had an inﬂuence on the strength and stability of the box. Factors such as the manufacturing process and board structure were also found to have an effect on box strength. Box strength predictions were performed using the methods available in the literature. These predictions had good correlation with the experimental box compression values. It was shown that box strength can be accurately predicted from liner and ﬂuting properties and this capability is an important tool in box strength design.
Open Access
An investigation into the impact fracture behaviour of poly (propylene-ethylene) copolymers using an instrumented low temperature drop weight impact tester
(2001) Patil, Ravindra; Marcus, Kashif; Sole, Brian
This dissertation examines the drop weight impact behaviour and fracture of poly (propylene - ethylene) copolymers at cryogenic temperatures. A cryogenic temperature facility was incorporated into the existing instrumented drop weight impact tester to allow for variation of the impact test temperatures.
Open Access
Investigation of strain rate sensitivity of polymer matrix composites
(2004) Ochola, Robert O; Marcus, Kashif; Nurick, Gerald N
An investigation into high strain rate behaviour of polymer composites was performed by developing a finite element model for a fibre reinforced polymer (FRP) plates impacted at varying strain rates. The work was divided into three facets, firstly to characterize the FRP material at varying strain rates, to develop a constitutive model to elucidate the relationship between strain rate and ultimate stress and lastly to use the experimental data to develop a finite element model. Experimental work performed in support of this model includes material characterization of unidirectional carbon and glass fibre reinforced epoxy at varying impact strain rates. The data is then used to develop a suite of constitutive equations that relate the strain rate, ultimate stress and material loading type. The model is of a linear and non-linear viscoelastic type, depending on the type of loading and is applicable to a FRP plate undergoing out-of-plane stresses. This model incorporates techniques for approximating the quasi-static and dynamic response to general time-varying loads. The model also accounts for the effects of damage, the linear and non-linear viscoelastic constitutive laws reporting failure by instantaneously reducing the relevant elastic modulus to zero. An explicit solver is therefore utilised in order to ensure stability of the numerical procedure. Glass fibre reinforced plastics (GFRP) was found to be more strain rate sensitive in all directions when compared to carbon fibre reinforced plastics (CFRP). The validation process therefore involves plate impact experimental testing on GFRP plates. The data from these experiments compare to within 8% of the finite element model that incorporates both damage and the developed strain rate sensitivity constitutive equations. For the first time a model that includes progressive damage with built-in strain rate sensitivity is developed for these particular FRP systems. Furthermore, the ultimate stress has been related to strain rate using an empirical technique. This technique allows for the prediction of dynamic ultimate stresses given the quasi-static ultimate stresses, again for this particular material systems.
Open Access
Investigation of the characteristics of kenaf fibre reinforced polypropylene composites
(2008) Kim, Soeyeh; Marcus, Kashif
This research work focus on the characterisation of the mechanical and thermal properties of kenaf fibre reinforced polypropylene composites. The composites were fabricated by extrusion followed by injection and compression moulding. The effects of fibre content, coupling agent content (MAPP), different types of moulding processes and addition of filler materials (kenaf core) were observed through mechanical, thermal and microscopic testing.
Open Access
An investigation of the failure mechanisms of thermoplastic composites at various rates of strain and temperatures
(2003) Netangaheni, Phumudzo T; Marcus, Kashif; Nurick, Gerald N
The focus of this project is on the deformation behaviour of thermoplastic composites. The materials used were polypropylene and polyamide resins with glass fibres and talc as fillers. These materials were provided by PLASTAMID (pty) ltd. The injection moulded specimens of polypropylene, polyamide 6-6, 30% talc filled polypropylene, 30% short glass fibre reinforced polypropylene and 30% short glass fibre reinforced polyamide 6-6 were tested in tension, flexure and impact (lzod, Charpy and drop-weight). Two different injection-moulding machines were used for specimen manufacture. These were an automated injection moulding machine simulating good control of processing conditions and a simple hand operated injection moulding machine simulating different processing and cooling (crystallisation) conditions. The mechanical tests were performed at different rates of strain and temperatures. The mechanical results show higher ductility of the unfilled polypropylene material. The strength and the elastic modulus of the materials are different for different materials. Addition of short glass fibres enhances the mechanical properties of polypropylene and polyamide 6-6. Talc fillers reduce the tensile, Izod and Charpy impact properties of polypropylene while the flexural and dropweight impact strength is increased. Optical and scanning electron microscopy were used to observe the microstructural features and deformation behaviour such as matrix plastic deformation, matrix crazing and tearing, fibre-matrix debonding, fibre fracture, fibre orientation and crack propagation. These deformation behaviours are influenced by the test conditions such as strain rate, temperature and the type of the test conducted. The deformation behaviour is also dependent on the constituents of the material. The mechanical test response together with the macro- and microscopic features observed on the fracture surfaces of tested specimens are evidence of the various mechanisms of failure that take place in different thermoplastic composites. The understanding of the mechanical response and the failure mechanisms of thermoplastic matrix composites is important in the design and processing stages.
Open Access
An investigation of the feasibility of composite turbine compressor blades
(2000) Branehög, Johan; Marcus, Kashif
A study has been conducted as to the feasibility of using a carbon fibre reinforced polymer (CFRP) composite to replace the titanium alloy (Ti-6Al-4V) for the manufacture of turbine compressor blades. These blades are used in the first compression stage of a gas turbine and suffer from high stresses at the roots and rotor discs induced by the high centrifugal forces during operation and are sensitive to vibrations. The blades are of a transonic type with typical rotational speeds of up to 10 000 rpm. The lighter composite blade will reduce stresses on the rotor disc and on the blade root itself as well as having more controllable vibration frequencies. This project considers the potential problems of replacing a titanium alloy with a carbon epoxy composite.
Open Access
Micromechanisms of polymer sliding wear
(1993) Marcus, Kashif; Allen, Colin
A study has been made concerning the tribological behaviour of ultrahigh molecular weight polyethylene (UHMWPE) during water-lubricated reciprocating sliding wear. The experimental work has been extended to study also the effect of molecular weight, fillers, lubrication, counterface roughness and sliding configuration on the polymer's transfer characteristics. The wear behaviour of polytetrafluoroethylene (PTFE) has been included for comparative studies. The worn material was studied using stylus profilometry, optical microscopy, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), Transmission electron microscopy (TEM), X-ray fluorescence (XRF), X-ray diffraction (XRD), differential scanning calorimetry (DSC), infrared spectroscopy (IR) and mass spectrometry. The effect of two fillers, namely glass beads and a titanium-based inorganic filler on the friction and wear behaviour of UHMWPE has been investigated as a function of counterface roughness (Rₐ). It was found that the filled material exhibited lower wear rates than the unfilled material on the rougher counterface. The filled material was also found to be more sensitive to a change in Rₐ and showed higher wear rates than the unfilled polymer on the smooth counterface. A uniform and coherent transfer film is found on the rougher counterface but the transfer film for the titanium-based filler was patchy on the smooth counterface. No coherent transfer film was found when sliding was conducted parallel to the grinding direction on the steel counterface, resulting in relatively high wear rates. Polymer transfer was patchy, the amount increasing as the sliding distance increased. The observed phenomena are explained in terms of mechanical interlocking and chemical bonding of the polymeric material with the metal counterface. An increase in molecular weight did not significantly improve the wear resistance of the UHMWPE. Small variations in counterface roughness values (Rₐ) were found to have a much greater effect on the wear rates than changes in molecular weight. The steady-state wear rate of the polymer was furthermore found to be more dependent on an adherent transfer film rather than a change in bulk morphology. Although PTFE exhibited low friction coefficients, the high wear rates obtained by this polymer is explained by the polymer's inability to form a transfer film under water lubrication, while any film that forms under dry sliding wear is easily peeled off the surface. Significant improvements in wear are found when fillers are added to the polymer. The wear rates for PTFE under dry sliding are similar to those obtained for UHMWPE under water lubrication. Transfet of UHMWPE material to the metal counterface during sliding wear involves interlamellar shear of the polymer and results in the development of a highly oriented transfer film. Significant differences have been found in the degree of crystallinity, crystallite size and orientation in the deformed surface layers of the polymer and debris compared with those of the bulk polymer. The worn surface of the polymer shows slightly increased crystallinity but the crystallinity of the debris is much higher than that of the bulk whilst the crystallite size is much reduced.
Open Access
Structure-property relationships in poly-(propylene-ethylene) copolymers
(1999) Mange, Siyabonga; Marcus, Kashif
This thesis examines the relationship between the microstructural and the mechanical properties of poly-(propylene-ethylene) bi-phasic copolymers. The copolymers investigated covered a comonomer content ranging between 4 and 23 percent ethylene. Nine grades were considered, with variables such as the melt flow index, the degree of crystallinity, the molecular weight distribution and the effect of a nucleating agent being examined. These copolymers have been characterised in order to gain a better understanding of the interrelationship between the morphological structure and their physical, mechanical, thermal and thermo-mechanical properties. The toughness of the copolymers can be enhanced at low temperatures by increasing the ethylene content, at the expense of a loss in stiffness. A study of the microstructure using the scanning electron microscope indicates that a good balance between these two properties can be achieved through a uniform size and spatial distribution of the ethylene-propylene rubber particles within the polypropylene homopolymer matrix. The transmission electron microscope shows the ethylene-propylene rubber (EPR) to be agglomerates of smaller particles, with some crystallinity within the EPR being evident.
Open Access
A study of the feasibility of advanced hybrid thermoplastic composites for aerospace and automotive applications
(2008) Ofosu, Osei; Marcus, Kashif
The development of new technologies and the demand for improved performance has resulted in the need for materials with high specific strength and stiffness. Fibre reinforced polymer materials have found increased application in the automotive and aerospace industries by virtue of their excellent specific properties, good corrosion resistance, toughness and fatigue properties. This study aimed at the feasibility of developing an advanced hybrid thermoplastic composite for aerospace and automotive applications. This was done by first researching the types and functions of current thermoplastic composites used in the aerospace and the automotive industries. Thereafter, an advanced thermoplastic resin was selected as matrix to develop the hybrid composites which were then characterised by mechanical and physical testing.
Open Access
The tribological behaviour of glass filled polytetrafluoroethylene(PTFE) under dry and water lubrication
(2003) Klaas, Nkosana V; Marcus, Kashif
This study was aimed at establishing the tribological behaViour of 25 % wt glass fibre filled polytetrafluoroethylene (PTFE) under dry sliding conditions. The experimental work was extended to compare and include its wear behaviour with other fillers such as bronze, carbon and graphite and to conduct tests under under water lubrication. Polyester-based materials, Vesconite and Vesconite Hilube, were used in this study for comparison purposes as well. The worn polymer pin surfaces and the counterfaces were studied by means of optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EOS), x-ray photoelectron spectroscopy (XPS) and surface profilometry. X-ray diffraction (XRO) and differential scanning calorimetry (OSC) were employed to study the changes in crystallinity and morphology of PTFE composite wear surfaces during the sliding process. The effect of the different forms of glass, viz. glass fibres, glass beads (hollow and solid beads) and glass flakes on the friction and wear behaviour of PTFE was investigated. The effect of additions of small amounts of additive such as molybdenum disulphide, MoS₂ and pigments on the wear rate of glass fibre filled PTFE was also investigated. The results show that the addition of glass fillers to PTFE reduce the wear of PTFE by three orders magnitude while keeping the coefficient of friction more or less unchanged. The reduction in wear upon addition of the glass to PTFE was attributed to the formation of a coherent and adherent transfer film to the counterface during the sliding process. The transfer film formed by unfilled PTFE was quite patchy and non-adherent to the metal counterfaces.
Open Access
Tribology in coal-fired power plants
(2005) Moumakwa, Donald Omphemetse; Marcus, Kashif
A series of alumina ceramics and silicon carbide (SiC) particulate composites were evaluated in terms of their erosive and abrasive wear behaviour under different conditions, with the aim of reducing wear damage in power plants. The alumina ceramics tested ranged in composition from 90% alumina to 97% alumina content. A nitride fired and an oxide fired SiC particulate composites were also tested for comparison. The impact angle, impact velocity, as well as particle size and type were varied for solid-partide erosion, whereas effects of the applied load, abrasive speed and type of abrasive were studied for abrasive wear. The target materials were also evaluated in terms of morphology and mechanical properties including hardness, flexural modulus and flexural strengths. The erosion rates of the tested alumina ceramics increase with an increase in the impact angle, reaching a maximum at 90°. The high purity 96% alumina dry-pressed body has the best erosion resistance at most impact angles, while the 92% alumina dry pressed body has the worst erosion resistance. The erosion rates also increased with an increase in particle impact velocity, resulting in a velocity exponent (n) value of 1.5. A decrease in the erosion rate was observed for both an increase in particle size range and a decrease in erodent partide hardness. At all angles of impact, solid partide erosion of the target materials is dominated by intergranular fracture and surfaces are typically characterized by erosion pits. The five alumina target materials also show a marked increase in erosion rates when the test temperature is increased from ambient to 150°C. The abrasive wear rates for the materials increased with both applied load and abrasive speed, owing to increased tribological stresses at the contacting asperities. There is also a general trend of increasing abrasion resistance with increasing alumina content. Severe wear, characterized by fracture and grain pullout, is the dominant mechanism of material removal during abrasive wear. This was accompanied by the formation of grooves on the wear surfaces. Although this study was successful in terms of material selection for wear damage reduction in power plants, it also highlighted significant factors and modifications that might need to be considered in future studies.

Browsing by Author "Marcus, Kashif"

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