Master of Science in Materials Science

Permanent URI for this collectionhttp://192.248.9.226/handle/123/15929

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item: Thesis-Abstract
Comparison of corrosion behavior of steel reinforcement bars in ordinary Portland cement and Portland Pozzolana cement environments
(2022) De Costa KBMVS; Guluwita SP
In the Sri Lankan cement market present time blended hydraulic cement which is composited with fly ash or blast furnace slag are given a noticeable marketing share as supplementary cement. It has obtained more popularity for incorporating higher workability and achieving a higher lateral strength in the construction industry. But due to the pozzolanic reactivity of blended cement, there is a possibility of reduction of pH of concrete or cement mortar which may be detrimental to the passivity of reinforced steel. In this study, the comparison of corrosion effect was researched with 15% fly ash blended cement as the pozzolanic cement (Bag-cement of Blended hydraulic cement) and Ordinary Portland cement. Coarse aggregates were excluded to get a clearer picture of the corrosion effect with the change of cement type. The cement mortar mixtures with 1.0: 3.0: 0.5 of cement: sand: water respectively, from both cement types were prepared. Specimens were cast in moulds with reinforcement bars to prepare the specimens for the pull-out test, Half cell potential test, compression test & loss of mass (due to corrosion). After casting test specimens were salt-conditioned by dipping in 5% NaCl solution for 30 minutes per day for 180 days. Pull-out and compression test results acknowledge that pozzolanic cement contributes higher lateral strength than ordinary Portland cement. After the compression test, reinforced steel bars were removed from the cubes and it was observed that no corrosion has happened in bars that were fully enclosed with (both types of: PPC and OPC) cement covers. Therefore, it reveals that 15% of fly ash blended hydraulic cement does not disturb the passivity layer of steel reinforcements as a result of consumption of Ca(OH)2. This study can be extended for further research with 25% or higher ratios of fly ash blended hydraulic cement.
item: Thesis-Abstract
Modification of mix design to utilize fly ash and gliricidia ash in concrete paving block
(2022) Amunugama HMTM; Adikary, SU
Last few decades demand for renewable energy has increased. Among those resources, biomass is widely used to produce energy as it renewable and low-cost material. Therefore, it has led to the accumulation of industrial byproducts such as wood ash. Wood ash is the byproduct produced from the biomass power plant as used for the generation of electricity. The production of cement leads to emitting a large number of greenhouse gases caused environmental disasters all around the world. Also, cement is the expensive cost factor in manufacturing cement-based products. Concrete paving block (CPB) is a successful alternative for asphalt or concrete pavement. It is different from other paving methods from manufacturing, structural design, installation and replacing techniques, etc. It can be easily placed and removed when it is damaged. The present study was conducted to produce low-cost and performance-effective (complying with the standard requirements) paving blocks by using industrial by-products produced from the Tokyo Cement Ⓡ biomass power plant. Laboratory trials were carried out at the Tokyo cement construction research center laboratory which has been accredited as per ISO 17025. The 15MPa mix designs were used as per SLS 1425 standard. 5%, 10%, 15%, 20% of wood (Gliricidia) ash was replaced from cement content for mix design. workability, dimensions, verification of visual aspects, compressive strength, flexural strength, total water absorption were determined. Workability was reduced when increasing the percentage of wood ash. Dimensions were measured of all of the paving blocks. The length, width, and height of the B05 block have deviated from standard specifications. Visual aspects have shown that when increasing the wood ash percentage texture of those blocks was roughened. Smoothness has gradually decreased when increasing the wood ash percentage. Flexural strength and compressive strength have also been reduced when increasing the wood ash percentage. Total water absorption value has increased when increasing the wood ash percentage. Due to the increase of porosity of the paving block. Therefore, from all the results observed it can be concluded that 20% replacement of wood ash (B05) results were exceeded the standard requirements in SLS 1425. Also, we observed the scanning electron microscope (SEM) images of cross-sections of all 05 block types. It shows a gradual increment in porosity by increasing the wood ash percentage. Materials cost per cubic meter of every block type were calculated. The lowest materials cost is shown by the B05 type. 15% wood ash replacement (B04) results were complying with the standard requirements and show 2nd lowest materials cost from all block types.
item: Thesis-Abstract
Developing a model to predict the propagation of sulfide stress corrosion of steel used for petroleum pipelines
(2021) Deemantha MBA; De Silva GIP
Sulfide stress corrosion (SSC) is a deleterious type of corrosion that is abundant in petroleum refineries. SSC easily attacks oil country tubular goods (OCTG) in petroleum refineries. The main factors that affect SSC can be identified as the pressure/tensile stress applied on the metal, H 2 S concentration and time period. It can be identified that the environmental conditions of petroleum refineries provide optimum conditions for the initiation and propagation of SSC. Therefore petroleum refinery plants conduct timebasis routine inspections to detect the sulfide stress corrosion. When a severe corrosion is detected at an inspection routine, pipelines are required to be replaced. The unusual behavior of the propagation of SSC cracks may lead drastic failures before it is identified through an inspection routine. Therefore the petroleum industry is expecting to use an accurate model that can predict the initiation and propagation of sulfide stress corrosion. However, the mechanism of SSC has not been clearly revealed yet. The principle aim of this study is developing a model that can predict the propagation of depth of sulfide stress corrosion in API 5L Grade B steel as a function of applied load (tensile load), pH value and time duration. API 5L Grade B steel was procured from Sri Lanka petroleum corporation as a seamless pipe. The model has been established based on the experimental values of depth of sulfide stress corrosion under different predetermined test environmental conditions kept within the pH value of 2.7 – 3.5, applied load of 400 – 800 N and time duration of 15 – 45 days. The depth of sulfide stress corrosion was measured using the scanning electron microscope images of cross sections of corroded steel specimens. The temperature and the pressure of the test environments were maintained at 24±3 0 C and 1 atm respectively. Further, the model was validated by another data set obtained within the aforementioned, same ranges of parameters. All the laboratory experiments were conducted in accordance with ANSI/NACE TM0177-2016 standard test method. In addition to the development of the model, the propagation behavior of SSC was investigated under the above mentioned different test environmental conditions. The microstructures that were observed through scanning electron microscope (SEM) and SEM/EDAX elemental profile plots were obtained to investigate the Sulfur distribution within the crack. According to the experimental results, it was able to develop a model that predicts the propagation of depth of sulfide stress corrosion. The model prediction values were in good agreement with the experimental values. However model tends to underestimate the depth of corrosion values when time duration closes to 30 days. Since the model has been constructed and validated within the pH value from 2.7 to 3.5, applied loads from 400 N – 800 N and time durations from 15 days to 45 days, the model is expected to be given the accurate predictions only within the aforementioned test environmental conditions. The SEM images of cross sections of corroded specimens showed that crack initiation occurred after 15 days at all different test environmental conditions. Further, crack propagation occurred transversely, developing branches through the cross section until 30 days of time duration and the behavior of the propagation of crack was completely changed at 45 days of time duration.
item: Thesis-Full-text
Effects of carbon black and graphene oxide additions on properties of ordinary portland cement composite
(2020) Chandima AMB; Guluwita SP
The effect of the carbon black (CB) and graphene oxide (GO) on the mechanical properties and microstructure of cement mortar composite were studied by preparing CB-cement composite (CBCC) and GO-cement composite (GOCC) mortars. These properties were investigated by treating the cement mortar with 0.01% to 0.1% of GO and 0.1% to 1.0% of CB of the cement weight. The results revealed that the highest compressive strength obtained for 0.4% of CBCC and for 0.04% of GOCC. The incorporation of CB and GO to the cement motor simultaneously increased the compressive strength of the samples drastically. The highest increase of the compressive strength was equal to 43.27% for specimens evaluated at the age of 2 days for the cement composite specimens of 0.4% CB and 0.03% of GO. The addition of 0.4% of CB increased the flexural strength of cement motor up to 53.54% and 0.03% of GO increased the flexural strength of cement motor up to 46.54% for 28 days. The addition of the combination of 0.3% CB and 0.04% GO to the cement composite enhanced the flexural strength by 60.61%. GO was found to be able to accelerate the hydration process by forming the flower-like cement hydration crystals which contribute to the enhancement of the early mechanical properties. The analysis of the microstructure relieved that the addition of CB provides the filling effect while GO could affect the growth form of cement hydration products.
item: Thesis-Full-text
Failure investigation of bell 412 main rotor blade trim tabs and study of suitable adhesive material application with a new trim tab design
(2020) Dheerasinghe PMGSD; Sivahar V
The Bell 412 helicopter is a type of aircraft in the Sri Lanka Air Force (SLAF) inventory which is accorded specialty status due to its role in the transportation of VVIPs in Sri Lanka. Over three decades of operation, the failure of trim tabs, a bigger issue of Main Rotor Blades (MRBs) have been identified. MRB is a glass fibre construction and the titanium trim tabs are bonded by manufacturer-recommended adhesives. This failure could hamper the efficient usage of the helicopter operation and may result in the blade being inoperable. This issue currently persists and this research is focused on a study of the failure of the Bell 412 main rotor trim tab and explores the possibility of a suitable adhesive material application with a new trim tab design to resolve the problem. During the initial findings, it has been observed that the prevalent condition is attributed to the failure of the adhesion between the trim tab and the Main Rotor Blade. To identify the root causes, adhesion properties were tested using a modified floating roller peel test (FRPT). Further, the fracture mechanism was observed and Differential Thermal Analysis (DTA) techniques were utilized. In this study, it was also observed that the original design of the trim tab itself propagates the failure and thus, another area of focus in this research was to optimize the design of the same. In addition, the study proceeds to investigate suitable adhesive material properties which would be better suited to resolve this critical issue.
item: Thesis-Full-text
Sustainable development of un-refined fly ash in eco-friendly high-volume fly ash concrete structures
(2020) Niroshan K; Guluwita SP
Sustainable development in concrete industries is reducing the cement consumption in overall the world. Huge amount of carbon dioxide gas is released to the atmosphere during the production time of Portland cement. Carbon Dioxide is the leading contributor for the greenhouse effect and it directs to the global warming of world. In the present situation, most of the developed countries are thinking about these issues and implement severe rules and regulations to limit of the carbon dioxide emissions. So supplementary cementitious materials are required to reduce the consumption of Portland cement for the sustainable development. Fly Ash is one of the most abundant supplementary cementitious materials in worldwide. It is a by-product and waste material in thermal power stations. Disposal of fly ash is one of the major problems in the power stations because it leads to many environmental issues. Utilization of Fly Ash in the concrete industries, assure sustainable development by reducing cement consumption and also reduce the emission of carbon dioxide to the environment. The superior properties of fly ash provide much support to improve the rheological properties of fresh concrete and produce ultimate strength as well as better durability in long term hardened concrete. From the broad view it can be ensured that the usage of High-Volume Fly Ash is an environmentally friendly process and also it will enhance the quality of concrete such as high-performance concrete.
item: Thesis-Full-text
2D - 3D Hybrid perovskites for perovskite solar cells
(2020) Gunasekara HKYPG; Sewvandi GA
Hybrid Organic-Inorganic Perovskites (HOIP) have been studied extensively and grown popular. Especially in Three-dimensional (3D) Perovskites, achieving power conversion efficiency (PCE) exceeds 23%. Nevertheless, some of the morphological imperfections will limit their structural capabilities. Pinholes in discontinuous perovskite films induces the huge leakage current which can cut down the device efficiency and creates a short circuit. Therefore, it is essential to deposit a compact film with passivated defects. Two-dimensional (2D) halide perovskites, conversely attracted significant attention and become a positive alternative with their uncomplicated synthesis, stability, and excellent photoelectric properties. This study, investigates the formation and properties of 2D Tetrabutylammonium lead halide (TBAPbBrxI3-x) HOIP. Tetrabutylammonium ion is a large cation, and more likely forms a 2D perovskite structure which was confirmed by the XRD spectrum. Substantiate by SEM images, TBAPbBrxI3-x establishing and favors crystals with enhance orientation and few grain boundaries and. However, the absorption spectra of the film shows an excitonic peak at 411 nm and a clear band edge at 450 nm. Resulting in poor absorbance in the visible range, with optical band gap of 2.76 eV, narrowing the ability to use TBAPbBrxI3-x alone in solar cells. Conversely, TBAPbBrxI3-x can use as separate capping layer on the top of 3D perovskite layer, enhancing the properties of the 3D perovskite layer. Incorporating TBAPbBrxI3-x into CH3NH3PbI3 shows a better film formation with few holes. The application of mixed perovskite layers incorporated solar cells will result in better structural and optoelectronic properties.
item: Thesis-Full-text
Derivation of nanofibrillated cellulose from locally available rice straw
(2020) Ratnakumar A; Samarasekara AMPB; Amarasinghe DAS
Cellulose has become a wonder material in the present context of research and development since it is fibrous and tough, hence biodegradable, biocompatible, and renewable natural polymer. Nowadays, rice straw as a cellulose source has gained momentum as rice is one of the major crops grown in most of the tropical and subtropical countries of the world where half of the world population consuming it as the major food source. Rice straw is the agricultural production residue from rice cultivation which is considered as an agricultural waste and cause decay related issues in the plantation. This biological waste material if utilized can be a renewable feedstock for the production of value added products for special applications. Sri Lanka being an agricultural country holds twentieth position in the worldwide rice production. However, a large amount of rice straw is generated per annum as a by-product of rice production in the country. Even though rice straw is utilized in various ways, there is a possibility for a value addition by extracting its constituents such as nanofibrillated cellulose from this commercially underutilized waste material and thereby embracing a bioeconomy approach in the country. In this study, nanofibrillated cellulose (NFC) was extracted from Sri Lankan rice straw varieties BG352, Murunkan, Pachchaperumal and Moddaikaruppan in two distinct stages. Initially, rice straw was subjected to a series of chemical traetments to eliminate the non-cellulosic constituents. Then the obtained chemically extracted cellulose fibers were separated into nanofibers via high-intensity ultrasonication (HIUS) treatment. Structural, thermal and morphological characteristics of nanofibers and their intermediate products were determined. FTIR analysis confirmed that the chemical composition of nanofibers was mainly cellulose where amorphous natured hemicellulose and lignin were effectively removed during chemical treatments. Study revealed that around 25 - 38 percent cellulose was extracted from the four rice straw varieties via chemical process. From these chemically extracted cellulose fibers around 17 - 45 percent of nanofibrillated cellulose were extracted via high-intensity ultrasonication process. Morphology of rice straw during the extraction process was distinct when the non-cellulosic components were removed. Results indicated that the efficient multi-step treatment process yielded nanofibers with potential advanced applications. Chemical extraction method is found to be the most efficient method for cellulose extraction from lignocellulosic biomass. Therefore, it is of paramount important to investigate the influence of parent materials on the synthesis process and the properties of the yield. Effect of particle size distribution of locally available traditional rice straw Murunkan on cellulose extraction was studied. Study revealed that after the series of chemical treatments rice straw with particle size distribution below 75 μm (Mu-75) yielded 27.19 ± 0.98 percent and rice straw with particle size distribution between 150 μm to 250 μm (Mu-250) yielded 38.31 ± 0.86 percent. Out of these cellulose fibers, around 63 percent of NFC was extracted from Mu-75 and around 55 percent of NFC from Mu-250. SEM images showed that the diameters of the extracted nanofibres from Mu-250 ranged from 75 to 200 nm whereas nanofibers from Mu-75 ranged between 27 – 104 nm. These findings will have profound influence upon extracting nanofibrillated cellulose from agricultural biomass.
item: Thesis-Full-text
Use of waste polyethylene for property improvement of concrete
(2020) Karunarathna TAK; Samarasekara AMPB; Weragoda VSC
Polyethylene waste products, especially thin polyethylene bag wastes have become a global problem in Environment Pollution Control Management. The primary objective of this project was to manufacture a property improved Polymer-Concrete Composite mix for building construction, using waste polyethylene grocery bags, made out of high-density polyethylene (HDPE). This is proposed as a means of reuse for this polymer product which would give even more benefits. Research observations, including laboratory test reports indicated that the blending of suitable percentages of polyethylene flakes in to the concrete mixes gives higher workability performance in fresh concrete and it improves the durability characteristic of hardened concrete. It was verified by controlled laboratory tests that the adding of appropriate proportions of polyethylene cut fragments to grade C30/20 concrete gives very good fresh concrete properties like cohesiveness and workability (flowability) and improved hardened concrete durability properties like higher compressive strength, lower water absorption, low initial surface absorption (ISAT), low water penetration and lower Rapid Chloride Permeability (RCPT). This research also proposes theoretical explanations for the observations of property changes.
item: Thesis-Full-text
Synthesis and characterization of reduced graphene oxide for supercapacitors
(2020) Perera PSD; Adikary SU
The main focus of this investigation was to add value to high purity Sri Lankan graphite. Reduced graphene oxide(rGO) was synthesized using locally available graphite from Kahatagaha mines and purity was recorded as 99%. Modified Hummers method was used to synthesize rGO. Synthesized rGO was characterized using Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM) and X-ray Diffraction Spectroscopy(XRD). The specific capacitance was recorded as 0.45Fg-1 in rGO. The specific capacitance of the capacitor was calculated using cyclic voltammetry testing at 10mVs-1. SEM analysis shows the rGO surface character, larger surface area and warped morphology of rGO. In this research, we were able to develop rGO material from locally available graphite for capacitor applications without surface activation. Numerous research projects are ongoing in this field with ultra-pure (99.99%) graphite materials but the purity of locally sourced graphite recorded as 90% to 99% without value addition. Therefore, the usability of local graphite to develop rGO seen prospective for its super capacitance performance, however, future improvement is needed.
item: Thesis-Full-text
Extraction and characterization of microfibrillated cellulose from textile cotton waste
(2020) Jayasinghe JMR; Samarasekara AMPB; Amarasinghe DAS
Cotton is a natural staple fiber that almost consist with cellulose compared to wood. The major economic value of the cotton is in Textile Industry. In the past recent years, cotton consumption demand was increased than the production. In textile industry cotton are blending with various other synthetic fibers such as polyester, nylon and lycra to obtained desirable properties. Therefore, the fabric recycling methods are quite complicated although it is highly available as pre-consumer garment waste. In this work a method was developed to identify the amount of cotton present in the cotton/polyester blended fabric by using Fourier transformed infrared (FTIR) second-order derivative spectrum. Then the cotton waste composition was determined and used to extract cellulose. Then purify cellulose was subjected to extract Micro Fibrillated Cellulose (MFC) by using acid hydrolysis method. MFC has very high economic value compared to cotton fabric waste in various applications such as bio-composites, medicine, cosmetic, pharmaceutical, tissue engineering, bio-sensors, paints and coating, flexible electronics, air filters and high tech applications including aviation and automobile. However, the major challenge of extracting MFC is the low amount of yield in acid hydrolysis, although it considered to be as most cost effective method of MFC extraction. Laboratory extracted small quantities are not sufficient in industrial applications such as in reinforcing composites. Three experimental factors including; acid concentration, hydrolysis time and temperature show the highest effect in yield and quality of MFC. Therefor this experiment was designed to optimize the three independent factors effect on two responses of yield (%) and Width (nm) of MFC. Response surface methodology was employed to design the experiment and ANOVA statistical test results were used to determine the significance of the parameter effect on acid hydrolysis. Further extracted MFCs physical and structural properties were discussed. Morphological features and size of the fibers were examined by scanning electron microscopy (SEM), structural features and chemical functionality was determined by Fourier transformed infrared (FTIR) spectroscopy, degree of crystallinity was obtained by X-ray diffraction (XRD) spectroscopy and thermal properties were determined by Thermo gravimetric analysis (TGA).
item: Thesis-Full-text
Cost effective method to analyze lubrication oil
(2020) Rathnayake TNA; Amarasinghe DAS
The lubricating oil analysis is the most common method to identify the condition of any machinery. There are various ways to analyze lubricating oil, and those methods are based on an individual examination of lubricant properties such as Viscosity, Total Base Number (TBN), Total Acidic Number (TAN), Water Content, Impurities (element analysis), etc. However, to carry out these analyses, sophisticated pieces of equipment are required. They are costly and need specific environmental conditions. Furthermore, as the tests are done in a laboratory, away from the machine, carefully collected lubricating oil samples must be transported to them. The whole process, from collecting samples to obtained results, takes a considerable amount of time. Therefore, this process will hamper the maintenance program's efficiency since the machine has to be kept in idle until receiving the results. Hence, it is of utmost importance to have a cost-effective and faster results-giving method to analyze lubricating oil at the place where the machines are installed. Then the operator himself can check the condition of lubricating oil to ensure the safe and smooth operation of the machine. A comprehensive literature survey was carried out to understand the current trends in lubricating oil analysis. Most of the tests described in the literature are based upon Physical, Chemical, Electro-magnetic and Optical methods. The proposed design is based on an optical technique that deals with the Refractive Index (RI) since it is an indicator of the physical as well as the chemical property characteristic of a substance. The critical angle of a material is directly related to RI. Therefore, monitoring the critical angle changes leads to an understanding of the quality of the lube-oil. During the design stage, special attention was paid to the cost of the fabrication and user-friendliness of the device. The performance of a proposed lube-oil analyzer was assessed using Shell Gardenia 40 (lubricating oil used in high-speed marine engines of Fast Attack Craft) lubricant. The lubricant used for different operating hours were analyzed. This analysis unveiled that, though Original Equipment Manufacturer (OEM) emphasize changing the lubricating oil after 500 hours, lube-oil quality has not deteriorated below the specified levels at this stage. This shows that the lifetime of lube-oil can be further extended, and frequent quality testing of lube-oil can save large sums of money without putting the machine life into any danger. The results obtained from the proposed device was compared with the tests carried out according to the American Society for Testing and Materials (ASTM) standards. Moreover, forced diluted lube-oil samples were analyzed using the proposed device. Both tests confirm the effectiveness of the proposed device.
item: Thesis-Full-text
Fabrication of roofing sheets using agricultural waste materials
(2020) Ferdinandus DP; Samarasekara AMPB
Modern roofing products are very popular in various applications due to their specific features to satisfy the local and global demand. Asbestos roofing products are currently used as a roofing solution in very large scale worldwide due to its competitiveness. However, these products indicated some environmental and health problems during and after the usage. The key objective of this research is to develop an environmentally friendly roofing product to cater local and global market based on locally available agricultural waste materials. Since Sri Lanka is an agricultural based country, paddy cultivation is a key area of an agricultural sector. Large amount of waste materials generated after the paddy harvest. They are used in some of the applications but most of applications these waste create social and environmental issues. One of the key aspects of this research is to provide value addition to these locally available paddy wastes. The developed roofing product was a rice and paper waste based polymer product and it indicated low cost and biodegradable properties. The replica and the mould were fabricated in accordance with the available roofing sheet standard. This developed roofing product displayed the minimum water permeability and water absorption features. Product provided the required loading bearing capacity. All produced product showed UV resistivity during the testing period without showing any appearance change on inner surface or outer surface. According to the experimental results, sample containing 65% dry rice husk and 35% paper satisfied the usage requirements successfully. These products can be used as environmentally friendly, low cost, decomposable substitute that can easily be manufactured using locally available agricultural waste and available technologies
item: Thesis-Full-text
Fabrication and characterization of surface modified nanofibrillated cellulose incorporated polypropylene composites
Kahawita, KDHN; Samarasekara, AMPB
Increasing demand for materials with improved properties leads to acquiring advancement of nanomaterial. Therefore, Interest in nanocellulose has been increasing exponentially in recent years. Nanocellulose extracted from plant materials are divided into two main two categories as nanofibrillated cellulose (NFC) and nanocrystalline cellulose (NCC). Compared to NCC, NFC has gained more attention due to attractive properties such as high mechanical properties, reinforcing ability and aspect ratio. Reinforcement of NFC with synthetic polymer materials is an interesting area in the polymer-based researches over the past decades to enhance mechanical and thermal properties as well as to deplete the environmental pollution. Polypropylene is one of the widely used thermoplastic materials as matrix material in engineering composite applications. In nature, NFC is hydrophilic and polypropylene is hydrophobic. Therefore, surface modification of NFC reinforcement is necessary to prepare a nanocomposite with good performance. The prepared nanocomposite material can be used for many engineering applications. In the present research discuss mechanical, thermal and water absorption properties of polypropylene with up to 5 wt. % loading of unmodified and silane surface modified NFC reinforced composites. Scanning electron microscopic images, Fourier-transform infrared spectra, X-ray diffractograms and thermal gravimetric analysis were used to characterize the raw materials and surface modified NFC samples. The best thermal resistance and mechanical properties were given by the 3.5% silane surface modified NFC loaded polypropylene composite such as the hardness, tensile strength, and impact strength values are respectively 7.4%, 12.6%, and 86.1% higher than that of untreated NFC reinforced composite materials and neat polypropylene. In addition, the composite sample has the intermediate level of water absorption (0.1 wt. %) and processability (21.1 g/10 min) with respect to all the other samples including pure polypropylene.
item: Thesis-Full-text
Development of a classification system for Sri Lankan timber species based on physical properties
(2019) Madhuwanthi MAR; Sivahar V
An investigation was carried out on selected twenty five Sri Lankan timber species to study different wood properties which are commonly applied in the timber industry in Sri Lanka. Wood density, modulus of rupture, modulus of elasticity, compression strength at rupture and compression in elastic limit at direction of parallel to grain were tested by five samples of each specimen at moisture content between 12% - 15%. The obtained results were analysed to find correlation among properties and to develop a classification based on the wood properties. BS 373:1957 (1999) standard was followed to test small clear samples in sample sizing, testing and calculation procedures. Three point bending test, compression parallel to grain test were applied to investigate mechanical properties and by measuring weight and volume at 12%-15% moisture content, density was calculated. Obtained results described a fair correlation among density and mechanical properties specially, modulus of rupture and modulus of elasticity. These results can be used to predict the mechanical properties with respect to density and vice versa. Above properties were referred to develop the classification into four basic grades as super grade, high grade, medium grade and low grade. Further any relationship could not be found between the timber classification published by State Timber Corporation and it proved that this classification is not based on the wood properties. It is recommended to extent the research by increasing types of properties, number of species and samples with various age limits and growing conditions and height of the trees. This could be benefitted to improve the effectiveness of the classification based on properties and to develop standards of the timber industry in Sri Lanka.
item: Thesis-Full-text
Characterization of locally available mica minerals for capacitor applications
(2019) Siriwardhane TAEI; Adikary SU
Mica is a group of minerals of the hydrated alumino silicate of iron, magnesium, potassium, lithium and sodium etc. Commercially, the two most widely used micas in the electrical industry are the muscovite and phlogopite types. Phlogopite is the widely available mica type in Sri Lanka. Micas from different mining locations (Mathale, Mailapitiya, Badulla and Kebethigollewa) in Sri Lanka were characterized using XRD and SEM methods. Two different methods, namely ceramic method and flake method were used to study the dielectric properties of locally available mica. Dielectric behaviour of mica characterized above has been investigated by measuring capacitance (C) and loss tangent (D) at selected frequencies, with a precision LCR meter in a controlled environment. Then the relative permittivity, εr for each specimen was calculated and behaviour of εr with frequency was studied. Five flake specimens each obtained from four different locations and five ceramic disc specimens each prepared with powdered mica of two different locations were used for the study. Size, shape and method of preparation of the specimens were kept constant throughout the experiment. Graphs between εr and log10[frequency] of silvered mica flakes, and that of silvered mica discs were plotted separately. Accordingly, samples prepared by both methods have also been compared. Finally, average loss tangent Davg values of silvered mica were plotted as a function of average relative permittivity, (εr) avg at defined frequencies and investigated location wise. Scanning Electron Microscopic (SEM) analysis of Mathale and Mailapitiya samples confirmed that they have typical mica like flaky structures with layers. The XRDs of mica samples from different locations revealed different crystal structures & poly types. Sample from Mathale revealed two crystal structures Phlogopite 1 M and Phlogopite 3T, while Mailapitiya sample revealed two crystal structures Phlogopite 1 M and Biotite. Phlogopite 1 M and Hendricksite (Zinc- rich mica) were found fairly abundantly and Wustite (Fe0.92 O) was found in small concentrations in Badulla sample, while Phlogopite 3T was found abundantly in Kebethigollewa sample. Dielectric properties including dielectric constant (εr) and dielectric loss tangent (D) have been done in the frequency range from 1 kHz to 1MHz. The results showed that the dielectric constant (εr) and loss tangent (D) decrease with the increasing frequency at room temperature. As per the results, Kebethigollewa flake mica and sintered Mathale mica were the best types with higher εr and lesser D, at low radio frequency ranges. However, flake mica showed comparatively higher εr values than that of mica dielectrics obtained from the same source and manufactured by ceramic method. These results are also found compatible with the results of similar studies carried out by the researches in different countries. Hence, it can be concluded that locally available mica can be applied as dielectrics for capacitors within low radio frequency range. Even though both methods can be used, flake method is more suitable for applications which require higher εr values while ceramic method is better, where low capacitance applications are required. Ceramic method may be further developed by using other techniques such as slip casting method. Kebethigollewa and Mathale mica flakes are the best sources in terms of dielectric properties.
item: Thesis-Full-text
Variation in yield strength and elongation of re-bars manufactured using local ingots
Perera, KPAS; Guluwita, SP
Recycling of scrap steel to produce ribbed steel bars is a common practice followed in many countries. Selection of the best composition of ingredients for the melt is a huge challenge faced by the manufacturers in the scrap recycling industry. A major problem faced by them during the recycling process is the difficulty they have in controlling the levels of undesirable residual elements such as Cu, Ni, Sn, As, Cr, Mo, Pb, etc., that come with scraps. In SLS 375:2009 and BS 4449 Standards, the ‘maximum percentage by mass’ of residual elements is represented by the “Carbon Equivalent Value”. Carbon Equivalent (CE) value is used to understand how different alloys and residual elements affect the strength of steel. In ingot casting, a good control of ladle treatment is required for the proper control of de-oxidation and de-sulphurisation chemicals and residuals. An extensive study was carried out by referring to the literature and benchmarking the best practices of several steel makers to improve the ingot casting process. In this dissertation, the results of the experimental investigation on the effects of alloying and residual elements on yield strength and elongation of TMT bars is presented. The experimental study was focused on identifying the most suitable mixed proportion of ferro-silicon to ferro-silico-manganese, and the best controllable range of CE values to be used during melting to ensure that the products manufactured are consistent in quality. The quantities of the main alloying chemicals mixed together are changed to make the diluted percentage of manganese content in the bath solution to be 0.8% by mass. The ingots and TMT bar samples prepared were tested to see how the Carbon Equivalent value and the mixed proportion of alloying chemicals affect the yield strength and elongation of the finished bars. It was revealed that a consistent yield strength and elongation of each TMT bar of a set can be achieved by having the Carbon Equivalent value in the range 0.37
item: Thesis-Full-text
Evaluation of suitability of 1,4- dimethylpiperazine as a substitute catalyst of polyurethane foam production
(2018) Samarappuli, IP; Liyanage, NMVK
The flexible polyurethane foams have been fabricated from polymeric 4,4’-di-phenylmethane diisocyanate (MDI) and polyols. Catalysts play a major role in polyurethane foam preparation controlling the reaction profile throughout the reaction time. As a substitute catalyst 1,4- dimethylpiperazine promotes gelling reaction as well as blowing reaction as predicted. Effect of 1,4-dimethylpiperazine on polyurethane foam formation was investigated by varying the additive concentration while keeping all the other factors constant. Sample of standard dimensions were prepared from the resultant foam. They were used for density test compression set test, tensile strength and elongation tests. The tests were carried out as per the ASTM -D3574 standards. The reaction profile has moved to slower direction in terms of gelling time, rise time, curing time in the presence of 1,4-dimethylpiperazine compared to the control catalyst. This is due to the less reactivity of the test catalyst. The resultant controlled behavior of the 1,4- dimethylpiperazine could be more useful in applications such as complex molding. Other physical properties such as foam density, hardness, tensile strength, compression set test value lie within the comparable range which could again be useful in molding conditions. It is concluded that 1,4-dimethylpiperazine is a good delayed action catalyst which is found to be better for in-mold flowability and slow cure times with comparable foam properties.
item: Thesis-Abstract
Improving quality of cast products and enhancing energy efficiency of cold blast cupola at government factory
Wathuge, KP; Guluvita., SP
The conventional blast cupola in Sri Lanka is faced with new challenges such as how to minimize the energy consumption and economically produce good cast iron product with available resources. The important factor for economical and trouble free operation of the cupola is refractory repair. The selection of refractory and repair work should be carried out adhering to the described procedure and with trained personnel. Energy efficiency of the cupola can be improved by oxygen enrichment and correct cupola selection for refurbishing. Unlike several capital- intensive options, oxygen is a flexible tool requiring a minimal capital investment and the operating cost. Oxygen enrichment through tuyre injection system can reduce the coke consumption, increase melt rate, reduce raw material cost, recycle environmental hazard waste and reduce the emission of flue gases. The proper selection of refractory bricks for each zones of cupola minimized the operational cost, maintenance cost and increased the capacity of cupola.
item: Thesis-Abstract
Effect of external geometry on the fatigue behavior of fillet-welded transvers stiffeners in ship building
Seneviratne, ST; Munasinghe, RGNDS
This dissertation describes a study of the fatigue behavior of stiffeners on flange fillet welded joints stressed perpendicular to the weld line. The study included an experimental phase in which the fatigue life and cracking behavior of stress concentration region was to determined. This experimental study concentrated on the fatigue behavior in the transition region low fatigue cycles. The finite element technique was used to determine the compliance of stress regions. The second phase of the study was the determination of the effect of wrapping in the stiffener-to-flange weld upon the fatigue life and the fracture mechanics (behavior) in stress intensified regions. The third phase of the study was to determine the impact of undercuts at the stiffener scallop and flange edge upon fatigue strength. It was found that wrapping the welds around the stiffener had no impact upon the fatigue life.