Faculty of Engineering, Materials Engineering

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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-Abstract
Characterization and modeling of thermo-mechanical behavior of solid tires with graphite as a heat transfer enhancer
(2023) Somaweera, D; Abeygunawardane AAGA; Weragoda VSC; Ranathunga S
The solid resilient tire construction consists of three layers namely tread, cushion and base. The cushion or the middle layer provides a comfortable ride but also needs to reduce the heat buildup when the tire is subjected to heavy loads. Repeated loading on the cushion compound causes heat generation due to hysteresis and combined with the heat due to friction from tread needs to be relived promptly to reduce the risk of tire damage. The aim of the study is to enhance the thermal properties of the cushion compound of the solid tire using Sri Lankan vein graphite powder as a filler. This study reports mechanical, chemical and thermal properties of vein graphite powder sourced from Bogala mines, Sri Lanka. Five varieties of graphite powder samples were chosen to investigate their potential for application and each were characterized through Thermal Constant Analyzer, Differential Scanning Calorimetry, and Ultrasonic pulse-echo method. The ultrasonic method was adopted to obtain measurements of the Poisson's ratio (ϑ), Young's modulus (E), and Shear modulus (G) of the graphite powder samples. Highest value of thermal conductivity, volumetric heat capacity, and thermal diffusivity was reported from the grade of graphite powder possessing larger particle size. The study also focused on the improvement of the mechanical, curing, and thermal properties of vein graphite filled cushion compounds. The results showed a decrease in tensile strength with the graphite powder content. Maximum torque and the cure time were not significantly changed with the graphite particle content. Furthermore, results revealed a 66% of increase in thermal conductivity at the 10% of graphite particle addition to the compound relative to the unfilled cushion compound. It was observed that tensile strength decreased (with increased hardness) due to low interfacial adhesion and air gaps present between graphite particles and the compound. Furthermore, Dynamic mechanical analysis was performed on the vein graphite filled solid tire compounds to investigate the interaction between graphite and the polymer matrix. Next, an empirical equation, derived from the relationship between theoretical and experimental thermal conductivity values, was established to model the for graphite-iii filled solid tire compound. This equation is a valuable tool for estimating thermal conductivity within the 0-10% graphite filler loading range. Then, a comprehensive tensile test and thermal conductivity test simulations were carried out using Abaqus software and compared the obtained results with experimental data, which was observed to have reasonable correlation.
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
Characterization of locally available montmorillonite clay minerals to be used as nano particles
(2016-01-16) Wanasinghe, DD; Adikary, SU
The research work describes the extraction of nano particles of Montmorillonite clay from local clay deposits located in the dry zone of the country, and its characterization techniques using X-Ray diffraction, Fourier Transform Infrared Spectroscopy, Differential Thermal Analysis and Thermogravimetry analysis, Scanning Electron Microscope, and particle size analysis. Montmorillonite gained an increased attention during the past decade due to the superior properties imparted in polymer-clay nano composite synthesized with nano particles of Montmorillonite. These composites synthesized in this way have superior mechanical and thermal properties compared to their bulk counterparts. At present the local demand for Montmorillonite is fulfilled by imported Montmorillonite which is a purified form of bentonite. It has been found by previous research activities, that in Sri Lankan clay deposits located in the dry region, Montmorillonite is available mixed with other minerals. The main ingredients of these deposits are Montmorillonite and kaolinite. Physically Montmorillonite and Kaolinite are so similar that they are very difficult to be separated from a mixture. However these two minerals have a difference in their specific gravities which can be used to separate the two minerals. This research describes how this separation could be carried out in detail finally leading to the extraction of Montmorillonite from local clay deposits. The clay used in the experiment underwent several purifying processes followed by characterization processes. The characterization of the final extracted clay reveals that it consists of Montmorillonite and the particle size of these falls below 100 nm. This indicates that these extracted Montmorillonite nano particles can be used to synthesize polymer-clay nano composite.
item: Thesis-Abstract
Characterization of weld defects in single V-butt welded mild steel plates using ultrasonic A-scan technique
(3/15/2012) Tennakoon, TMR; Munasinghe, RGNDS
In Ultrasonic A-Scan technique the depth and the size of the defects in a material can be determined by the position and amplitude of the reflected echo on the CRT screen. However the main difficulty in ultrasonic testing is that the precise recognition of the defect type. In conventional ultrasonic A-scan methods recognition of the defect type (porosity, slag, crack etc.) is ascertained by a series of movement of the probe as rotational, orbital, lateral and transverse to observe the echo pattern. Here the human eye perceives many facts simultaneously by moving a transducer in infinite increments in 3D to seek out additional information-the mind sorts and processes the accumulated real-time facts and combines them with empirical data from experience and case history before making final decision on the defect.These uultrasonic echo patterns are quite complex since those may contain many signals other than defect echoes, same defect may display different echo patterns, different defects may display similar echo patterns and the amplitude and shape of the signal may change due to slight movement of the testing probe. Therefore the interpretation of defects using this technique is very complicated and totally depends on the experience of the operator who carries out the testing. Hence only well-experienced NDT personnel can identify defect type using this method. This is one of the main drawbacks related to Ultrasonic A-scan technique. The objective of this research is to study the relationship between type of defect and echo amplitude in single-V butt welded steel plates and to propose a new concept to identify defect type with the help of a self developed software which will be cheep, portable and simple to understand by the operator. To achieve this objective initially a mathematical relationship between echo amplitude and defect type was developed for common weld defects in single-V butt welded steel plates (slag, porosity, crack etc.) using newly derived mathematical equations for above defects. Since the amplitude of the echo signal affects by the defect size this parameter alone can not be used to identify the type of defect. As such the possibilities of using few other features such as width of defect echo, position of defect and change of probe angle also were considered. Experimental results show that any individual defect in single-V butt welded mild steel plates produces echo signals with unique pulse width and range of amplitude levels. In addition the results show that lack of penetration can be identified using a second probe angle in addition to single probe angle as use in conventional methods. Lack of side-wall fusion can be identified by using position of probe with respect to weld center line. These individual characters of defects, which are inherent to those defects, were used to predict the type of unknown defects using a self developed software programme named “ULTRASL1”. The significance of this work is that the introduction of a specialized procedure with a software programme to identify type of defect, so that Non-Destructive Testing personnel with any level of experience can share the expertise of the best operators in the industry. Hence it will support to reduce one of the main problems concerning ultrasonic testing i.e. the difficulties in recognition of defect type. The work was limited for defects like slag(volumetric), isolated pore, porosity, lack of inter-run fusion, lack of side-wall fusion, crack and lack of penetration in single-V butt welded mild steel plates.
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
Computational study on lead alternative perovskites for perovskite solar cells
(2020) Kumarasinghe KAMM; Galhenage AS
Hybrid organic-inorganic metal halide based perovskite solar cells (PSCs) lie at the heart of the emerging technologies of the solar cells due to their ability to increase the cell efficiencies dramatically over the last decade. CH3NH3PbI3 based PSCs show the highest performances; still, the toxicity of Pb has been the limiting factor for the commercialization of organic lead iodide based solar cells. Thesis discusses about the variations of properties in terms of electronic and dielectric properties due to the substitution of Sn and Bi in place of Pb. A systematic study of ab-initio calculation on the electronic properties of CH3NH3PbI3, CH3NH3SnI3, and CH3NH3BiI3 was performed. The results of the calculated band structures and the density of states of investigated materials reveal that CH3NH3PbI3 exhibits an energy band gap, effective masses of charge carries, and available density of states in favorable values for high performance solar cells than those of CH3NH3SnI3 and CH3NH3BiI3. CH3NH3PbI3 also consist of high dielectric capacity and better energy storage ability than CH3NH3SnI3 and CH3NH3BiI3. Above mentioned facts are the main reasons behind low-performance of Pb-free PSCs and it is paramount important to engineer the band gaps of those perovskites to obtain high performances.
item: Thesis-Abstract
Conversion of Sri Lankan iron ore into high quality pellets to be used in iron making
(2015-06-24) Guluwita, SP; Fernando, WLW; Munasinghe, RGNS
Iron ores and lime are two of the available raw materials in Sri Lanka for iron making. However, proven reserves of iron ore deposits in Sri Lanka have not been scientifically estimated as yet. There is no indication of the occurrence of coal deposits in Sri Lanka for the utilization to produce iron using the blast furnace. Therefore, it is important to investigate the possibility of producing high quality iron ore pellets using locally available resources as a substitute for sponge iron which is imported to use in the cupola furnace. In this study it was aimed at obtaining high quality iron ore pellets with required strength, porosity and degree of reduction by varying pellet compositions, firing temperature and soaking time. The pellets prepared with 100 parts of Dela Iron ore, 7 parts of Aruwakkalu lime and 7 parts of coke which was sintered at 1250°C for 10 min gave the optimum crushing strength, apparent porosity and degree of reduction. The subsequent melting of these pellets in the lab scale cupola recovered iron as “metallic pigs‟, which conformed to alpha iron having high purity.
item: Thesis-Abstract
Correlation between corrosion rate and ultrasonic attenuation on steel
Dayananda, HGSM; Sivahar, V; Munasinghe, RGNDS
Corrosion is the gradual destruction of material, usually metal, by chemical reaction with its environment. Usually the corrosion rate cannot be measured directly which needs sample preparation, fixing of samples in a particular environment, measuring the weight loss during a given period of time and measuring other parameters (time of wetness, SO2 & NO2 concentration, etc.). This research work was based on measuring the corrosion rate using ultrasound technique, which can be named as a nondestructive testing method. Ultrasound defined as the sound waves, which has a frequency more than 20 kHz. To investigate the behavior of corrosion in accelerated atmospheric conditions mild steel samples was exposed to the concentrated NaCl solution. The assessment mainly conducted by evaluating the loss of mass of specimens against the ultrasonic attenuation. Weight loss is the parameter of corrosion rate and it has a relationship with the surface roughness of the samples. The surface roughness of the samples have an influence on the ultrasonic attenuation. Therefore, corrosion rate has a relationship between ultrasonic attenuation. In this project, efforts were made to find a correlation between surface roughness and ultrasonic attenuation. An equation was derived to calculate the corrosion rate if the ultrasonic attenuation is measured. This method has the advantage of assessing the corrosion rate without sample preparation on a given component.
item: Thesis-Full-text
Correlation between the degree of corrosion and the ultrasonic parameters in steel
(2020) Piyathilake SAKVM; Sivahar V
In metallurgical engineering, corrosion is considered as one of the main reasons for the failure of metallic components. The main reason for this is that, the corrosion is a phenomenon which is mainly influenced by the nature itself. It is very important to eliminate or reduce corrosion since it can lead to major disasters which can negatively affect the human lives and properties. Inaccurate estimations, inaccessibility of the areas of corrosion, limitations for the destructive tests can be identified as some of the main reasons for the wrong and misleading preliminary corrosion investigations, which lead to catastrophic failures. Conventionally, the degree of corrosion is determined using destructive testing methods. Also, most of the research work in this area has focused on the uniform corrosion/general attack faced by steels across a range of atmospheres. With those methods, the real degree of corrosion cannot be revealed since it is difficult to address regarding the corrosion penetrations or pits. Therefore, those are inaccurate up to some extent. In contrast to that, Ultrasonic testing methods would be more effective and convenient to overcome above limitations and would be able to open a new area of estimating the degree of corrosion accurately. Also this study sought to contribute to this field by examining whether the penetration of corrosion beyond the general attack has a significant effect on the load-bearing capacity of mild steel. Also,in some cases such as in bridges and pipelines ultrasonic non-destructive method would be really advantageous since it is not only non-destructive but also it will allow reaching inaccessible locations easily. Further,an Ultrasonic wave can easily propagate through steel and its attenuation would provide a measurable reading to express the degree of corrosion including every minor detail. The research work is basically focused on measuring the degree of corrosion accurately using ultrasound attenuation. The selected steel materials were subjected to corrosion in a standard accelerated environment for a defined period of time. Then after a set of experiments, the degree of corrosion has been represented by the weight loss per unit iii area, corrosion rate and the corrosion penetration depth in to the material. Furthermore, the research work was able to cover the area of the mechanical property deterioration. The tensile samples were also corroded in the same standard accelerated environment as mentioned above, and subjected to periodic tensile testing and corrosion weight loss analyses. Further, the corroded samples were examined under optical and scanning electron microscopy to observe the penetration behavior of corrosion in to the material. The results showed that the actual breaking loads deviated negatively from the expected load-bearing capacity, which was determined through conventional methods. This deviation showed a close correlation to the increase of penetration of corrosion with time. Meanwhile, the ultrasound attenuation related to each of those corroded samples was measured simultaneously. Finally, all the data were analyzed through mathematical software such as MATLAB and SPSS to generate final correlations. Thereby, a nondestructive method through ultrasound attenuation was developed to determine the accurate degree of corrosion and to predict the remaining load bearing capacity of corroded structures.
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 glazed clay body suitable for cookware
(7/22/2011) Jayawardane, JTST; Adikary, SU
This research work describes development of a glazed red clay cookware body with adequate thermal shock resistance. Two red clay deposits were investigated (Malwana and Hambanthota region) which are currently used for pottery industry. X-ray diffraction analysis (XRD), chemical analysis, differential thermal analysis (DTA) and scanning electron microscopic investigation (SEM) were used to determine the clay properties. Thermal compatibility of red clay and different fritted glazes were investigated using thermal expansion and thermal shock resistance of individual body/glaze components. This investigation revealed that the coefficient of thermal expansion of red clay was lower than all tested glazes. Therefore it was difficult to formulate a suitable glaze to match the red clay body. Quartz was incorporated into red clay to increase the thermal expansion of the body. According to the results, thermal shock resistance decreased with increasing quartz content of the body. The thermal shock resistance and coefficient of thermal expansion of red clay body were investigated with different proportions of quartz asl0%, 20%, 30%, 35% and 40% at a firing temperature of 10500C and isothermal holding time 30 minutes. The behaviours of the thermal conductivity, thermal shock resistance and important mechanical properties such as modulus of rupture and modulus of elasticity of each formulated body were studied. The results revealed that thermal conductivity increased with increasing quartz content of the body. Modulus of rupture and modulus of elasticity were decreased with increasing quartz content of the body. Initially to preserve the red colour appearance of the product, it was decided to use a transparent glaze and three transparent glazes were investigated. Coefficients of thermal expansion of these transparent glazes were theoretically compatible with body composition having a quartz content of 30%. Actual size cookware samples were fabricated and required properties were tested under actual domestic conditions. But they were not successful on direct heating test. Body compositions with 35% and 40% quartz were investigated and they also gave the same results. Hence it was necessary to develop a body with better thermal shock resistance having low quartz content. For this purpose glaze with low coefficient of thermal expansion was required and a semi matt glaze was selected by partially sacrificing the red colour appearance of the body. Malwana red clay body with 25% quartz hewing a coefficient of thermal expansion 60.31xl0·7 x' and thermal shock resistance 0.97 kJ m-1s-1 and the glazes having coefficient of thermal expansion in the range of (49-51) xl0-7 K-1 and thermal shock resistance in the range of (1.10-1.20) kJ m-1s-1 could be effectively used to manufacture a glazed red clay cookware product. It can be concluded that a suitable body composition for glazed cookware production could be formulated by incorporating quartz in correct proportion to kaolinitic type red clay.
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-Full-text
Development of a method to predict the plasticizer evaporation of PVC insulated electrical cables
(2019) Egodage DP; Amarasinghe DAS; Attygalle D; Weragoda VSC
Though insulation is critical to the performance of an electrical cable the assessment of the status of an insulation is still a major challenge. Since the root cause of most electrical cable failures is due to insulation deterioration, if the rate of aging can be predicted, properly scheduled, appropriate maintenance programs can nearly eliminate cable failures. The kinetics of plasticizer evaporation of polyvinyl chloride based locally manufactured electrical cable insulations were investigated. Plasticizer evaporation is a slow process under low temperatures and would take years to study under such conditions. Therefore, accelerated conditions were used to get readings within the limited timeframe. Nevertheless, data obtained under accelerated conditions was mapped to normal conditions through Arrhenius approach. Deconvoluted derivative thermograms were used to identify the initial plasticizer percentages and Arrhenius approach was used to map accelerated condition measurements to ambient temperature evaporation rates. As cables are subjected to time varying temperature profiles a method for finding the equivalent temperature could be developed using kinetics of plasticizer evaporation whereby the operating life of the cable can be determined. The developed method could be applied for an electrical cable under a roof which is subjected to fluctuating thermal stress throughout the day and required time to evaporate critical level of plasticizer was determined.