Master of Science in Materials Science

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

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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
Analysis of corrosion of aircraft fluid pressure lines using eddy current
Edirisinghe, DR; Sivahar, V
The metal tubes are often used in aircraft to convey fluids to one or more destinations as they are capable of withstanding high levels of internal pressure and hoop stresses. The internal surfaces of fluid carrying metal tubes are frequently corroded once the inner walls are contacted with stagnated fluid for a long period of time. Once corroded, the fluid lines are to be replaced as they become unairworthy. The detection is difficult as there is no method developed for the corrosion detection of small diameter Aluminium metal tubes. This study is to carry out eddy current inspections on small diameter metal tubes and to carry out a qualitative analyze on eddy current impedance plane displays, building up a relationship on the resultant signals. It is also to distinguish the different characteristics of impedance plane displays of internal corrosion and crack signals. A qualitative analysis is the objective in this study as detection of corrosion is the prime objective for the aircraft fluid pressure lines. Since, neither the aircraft manufacturer nor pressure lines manufacturer has given any tolerances for corrosion, irrespective of the depth and the spread of corrosion, the fluid lines are to be replaced with new lines, if the corrosion is detected. Therefore, this study is limited only for a qualitative analysis and will be an eye opener for another study for a quantitative analysis.
item: Thesis-Full-text
Analysis of fast attack craft rudder failure
Gunarathna, AHGPN; Guluwita, SP
It is observed that frequent rudder failures of Sri Lanka Navy’s fast attack craft which are equipped with conventional propulsion system. Therefore, it was unable to effectively utilize these craft for operational requirements in the Navy. In this research it was analyzed both recently failed fast attack craft rudder and existing rudder fabrication process in order to minimize this type of rudder failures in future. Analysis of failed rudder and the existing rudder fabrication process was done through macro/micro level inspection, chemical composition analysis and micro hardness testing of relevant materials. Analysis revealed that rudder failed from the welded joint where rudder blade connected to rudderstock and weakening of the weld joint during fabrication. The weld joint was weakened due to formation of intermetallic phases, carbide precipitation, porosities and hot cracks in the heat affected zone of the weld. Therefore, finally rudder was failed as a result of fatigue failure. Use of similar low carbon stainless steel with suitable welding electrodes to ensure final weld lies in austenite region with containing 4% to 12% ferrite in the weld could overcome this issue.
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-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-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
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-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
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-Abstract
Development of a high thermal shock resistant ceramic body suitable for cookware
Pussepitiya, PPSS; Adikary, SU
Development of a ceramic based cookware body with adequate thermal shock resistance was successfully developed using low cost raw materials. The objective of this work was to determine the composition and thermal shock resistance of a ceramic body suitable for a direct flame cookware. To achieve this objective cookware body should have low thermal expansion coefficient, high strength, low water absorption and high thermal shock resistance. In this study ball clay, talc, alumina and zirconium silicate were used as starting raw materials and twenty five samples were investigated with different compositions. All samples were wet-mixed, shaped by slip casting, dried and fired to temperature 12500C in an electric furnace. Modulus of Rupture (MOR) was tested by the three point bending method; the thermal conductivity of each body was measured with Lee’s disk method and the Coefficient of Thermal expansion (CTE) was measured by thermo mechanical analyzer. The thermal shock resistance of each sample was calculated with Kingery’s formula. Optimum thermal shock resistance of 74 KJm-1s-1was achieved for a body composition of 45% of clay, 15% of talc, 15% of alumina and 25% of zirconium silicate which was fired to 12500C. Further modulus of rupture and coefficients of thermal expansion of the ceramic body were 74 MPa and 30.2×10-7 /0C respectively. These results suggest that the ceramic body is suitable to be used in cookware applications.
item: Thesis-Abstract
Development of a mathematical model to relate the ageing parameters to hardness and tensile strength of al 6063 alloy
(2023) Sivanujan S; De Silva GIP
Deformations, failures, and the wearing-off effect are common in Al 6063 structures due to their low strength and hardness, respectively. Industries have age-hardened Al 6063 alloy to improve its properties to a specified level depending on the components being produced. Industries do trials before production and check to see if the product has achieved its required levels of properties. This trial-and-error method is time-consuming, and further, it is not acceptable from an engineering perspective. For this reason, industries are looking for a model that will provide an accurate prediction of the hardness and tensile strength for the parameters associated with aging. In this research, a mathematical model was developed to predict the most efficient combination of aging parameters to achieve the required tensile strength and hardness of Al 6063. The model was developed based on the experimental tensile strength and hardness values for the 25 combinations obtained by varying aging time and temperature at five levels. Tensile strength and hardness were measured using the universal tensile testing machine and the Vickers hardness tester, respectively. Further, the model was developed using the SPSS statistical software and validated with data sets obtained from the literature. For the purpose of finding the most efficient combination of tensile strength and hardness, the model was developed as a computer program based on the Python programming language. In addition to the development of the model, the influence of precipitate size distribution on the tensile strength and hardness variation of Al 6063 alloy with aging temperature and time was investigated. Micro-structures were observed, and precipitate types were identified using a scanning electron microscope and an energy dispersive spectrometer (SEM/EDS). The precipitate size distribution was determined based on SEM images using MIPAR image analysis software. Beyond the peak age stage, a significant increase in the percentage of precipitates larger than 1.5 μm and a decrease in the percentage of precipitates smaller than 0.75 μm were accompanied by a decrease in tensile strength and hardness.
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.
item: Thesis-Abstract
Effect of reflux temperature on synthesis of chitosan / nano-hydroxyapatite composites
Gunathilaka, EHGJ; Adikary, SU
Effect of reflux temperature on synthesis of Chitosan / nano Hydroxyapatite composite In this study, effect of reflux temperature for synthesis of chitosan / Nano-hydroxyapatite composites was investigated. Chitosan / Nano-hydroxyapatite composites were synthesized using co-precipitation technique at different reflux temperatures of 30 0C (Room temperature), 70 0C and 90 0C. Chitosan, acetic acid, calcium hydroxide and phosphoric acid were used as starting materials. 70/30 weight ratio of chitosan / Nano-Hydroxyapatite composites was selected for the study. H3PO4 / acetic acid / chitosan solution was added at a rate of 3 ml/min using a burette into stoichiometric weight of Ca(OH)2 solution under vigorous stirring. The pH value of the solution was continuously monitored using a pH meter. The resulting suspension was refluxed and aged for 24 h while being stirred. The precipitate was filtered and washed with distilled water. This procedure was repeated for the selected reflux temperatures. The characteristics of nano hydroxyapatite, ceramic powder / chitosan composite were investigated by Differential Thermal Analysis (DTA), Fourier Transformation Infrared (FTIR) spectroscopy and X-ray diffraction (XRD). Particle size was determined by XRD patterns using Scherrer’s equation. It was observed that particle size increases with increasing the reflux temperature. Both the size and shape of HA crystals, SEM images shows that nano HA particles were dispersed in the Chitosan matrix and the surface become rough and more porous.
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-Abstract
Establishment of correlation factor for the carbon steel rods tested under tensile load and three point bend test
Muthurathna, SK; Weragoda, VSC
Steel is one of the major construction materials which play an important role in the construction industry in Sri Lanka. The supply of durable construction materials is always identified as one of the major obstacles to improved construction in developing countries whether in the cities or in the rural areas. The reinforcement of concrete with steel rods is more safe, efficient and more economical. It has excellent bonding properties as well as high yield/proof stress and elongation. Most of the sales outlets do not provide information on the grade of steel. Hence laboratory testing to verify the steel grade is more essential before its use in construction purposes. Requirements for ribbed steel bars for the reinforcement of concrete are specified in SLS 375. It specifies two grades of steel bars: RB 460 and RB 500. Corresponding British Standard : BS 4449 issued in 2005 provides for three grades of steel, all of which should have a characteristic yield strength of 500 N/mm2 (MPa) but differing in respect of other properties such as tensile / yield strength ratio and total elongation at maximum force. The requirements specified in SLS 375 cover, material requirements (chemical properties), dimensions and mass per metre, surface geometry, and mechanical properties (Tensile / Yield strength ratio) total elongation at maximum force. One of the main difficulties faced in quality assurance of the concreting steel bars (mainly 25mm and above) in Sri Lanka is the lack of facilities to determine the tensile strength, yield strength and elongation, which are the key parameters determining the quality of the material. Lack of standardized equipment having sufficient capacity to perform tensile tests often leads to incorrect quality assessments of the steel products. To develop a mathematical relationship between results of tensile test and three-point bend test for all available bar sizes of cold twisted bars and thermally treated steel bars are being measured and obtained the relations with 0.2% proof stress in tensile testing with 0.04% offset yield stress in three point bend testing for each bar diameters.
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-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
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
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
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.