Browsing by Author "Munasinghe, RGNDS"

Now showing 1 - 8 of 8

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
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: Conference-Abstract
Correlation between ultrasonic attenuation and hardness of tool steels
(2008) Dayananda, HGSM; Munasinghe, RGNDS; Sivahar, V
Theory of propagation and reflection of ultrasonic waves in metals in used to locate the internal defects of engineering components. It is observed that the energy absorption of ultrasonic waves (attenuation) in a metal depends on the physical and mechanical properties of metals. In this work efforts are made to find the correlation between attenuation and hardness of metals using ultrasonic waves. Commercially available Ultrasonic Flaw Detector bas been used to measure the attenuation of the ultrasonic waves of tool steel (DF2) which has been beat treated to change its hardness. The experimental curve is compared with theoretical equation and it was observed that the experimental values confirm the theoretically proven co-relationship.
item: Conference-Full-text
Corrosion behavior of steel in different atmospheric conditions
(2013) Adikari, AAMT; Munasinghe, RGNDS; Jayatileke, S
Corrosion of metals makes a large impact on the economy of a ountry. Therefore, it is important to take remedial actions to prevent structures, machinery and vehicles from corrosion. Among the various types of corrosion the corrosion that occurs in the atmosphere is known as atmospheric corrosion and it accounts for more failures than other types of corrosion. To take preventive actions against atmospheric corrosion of metals, it is essential to study the corrosivity of the atmosphere by analyzing factors that influence it. The corrosivity of the atmosphere mostly depends on several atmospheric variables, such as relative humidity, temperature, rainfall, chloride deposition rate, pollutant gases like nitrogen and sulfur oxides. In order to study the severity of the atmosphere which promotes the metal corrosion three types of commonly used structural materials mild steel, stainless steel 304 and 316 were exposed in two different atmospheric conditions. Two corrosion test panels were placed in two geographical locations and loss of weight due to corrosion was continuously measured in all three types of metals. The atmospheric variables in the two locations were also continuously recorded. Finally, these data were fitted with the power model in order to predict the rate of corrosion under particular atmospheric conditions. With the predicted corrosion rate under a particular atmospheric condition it is possible to take ecessary preventive measures during the design or in the service of metallic structures, machinery and vehicles etc. The broad aim of this research work is to collect adequate data to develop a corrosion model to redict the corrosion rate in any atmospheric environment in Sri Lanka using measured atmospheric variables and thereby establish a 'corrosion map 'for Sri Lanka.
item: Conference-Abstract
Effect of corrosion surface topography on fatigue life of low carbon steel
(Department of Materials Science and Engineering, 2019-01) Munasinghe, RGNDS; Piyathilake, SAKVM; Bandara, HMLS; Rangana, DMP; Sivahar, V
One of the main research areas of Metallurgical Engineering is associated with the estimation of fatigue life of atmospherically corroded metallic structural components. It has been studied extensively worldwide and most of the researchers in this area have focused on statistical analysis of fatigue strength of alloy steels and other metals deteriorated due to pitting corrosion. The scope of this work is focused on the fatigue behavior of low carbon steel, exposed to coastal-atmospheric corrosion which omits pitting. Studying the change in surface topography with exposure time, due to atmospheric corrosion is one of the two main objectives of this research. Evaluating the change in fatigue life of corroded samples with changing surface topography due to corrosion is the second objective. Fatigue life is taken as the number of cycles to failure, and it is evaluated by experimental and numerical methods (FEA). The surface topography is evaluated quantitatively using Scanning Electron Microscopy and 3D MountainMaps^"^ software. The quantitative data obtained on surface features are then represented in a finite element model to evaluate their fatigue performance using fatigue analyzing FEA software. The significance of this work is that it helps to explain the difference between simulated and experimentally determined fatigue life of atmospherically corroded low carbon steel, which can be ultimately used in estimating the life expectancy of corroded structural steel components.
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: Conference-Abstract
Effect of penetration of corrosion on the load-bearing capacity of mild steel
(Department of Materials Science and Engineering, 2019-01) Jayasooriya, ED; Munasinghe, RGNDS; Sivahar, V; Sitinamaluwa, HS
The field of Metallurgical Engineering associated with the estimation of the service life of corroded structural members which has been studied in extensive detail, the world over. Most of the research work in this area have focused on the general attack (uniform corrosion) faced by steels across a range of atmospheres. 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. Mild steel samples were corroded in an aggressive atmosphere over a 5-month period, subjected to periodic tensile testing and corrosion mass-loss analyses and examined under optical and electron microscopy. Through the identification and measurement of the penetration of corrosion using scanning electron microscopy, this research managed to correlate corrosion mass-loss and tensile load-loss data with said microscopic measurements. The results showed that the actual fracture 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. As a result of this correlation, the research concluded that allowances ought to be made for the penetration of corrosion when the remaining service life of corroded load-bearing members has to be calculated more accurately.
item: Thesis-Abstract
Modelling of the vulcanization process of thick-walled natural rubber articles
(7/2/2011) Weragoda, VSC; Gunapala, PY; Munasinghe, RGNDS
A computer-based technique was developed to render the state of cure in thick-walled natural rubber compounds as measured by the oscillating disk rheometer torque. The method was based on a mathematical function derived to replicate the rate of change in the rheometer torque with respect to the curing time and the curing temperature. The mathematical function was able to trace the temperature related changes in the rheometer curves of different rubber compounds exceptionally well, at a 99.9% level of certainty. This was used to model the vulcanisation process for thick-walled articles through a deterministic simulation approach, which was made it possible to predict the scorch time, curing time, and the time for onset of reversion to a precision within ±5%, as verified against programmed a temperature profile curing in a rheometer. This study also investigated the variation of the thermal conductivity and the thermal diffusivity of rubber compounds during the curing process, to determine the effectiveness of such variations in estimating the curing time of thick-walled rubber articles. The experiments were carried out using a modified hot wire technique. The coefficient of variation in the thermal diffusivity was estimated at 20%, and the same for the thermal conductivity was found to be 15%, for the compounds tested. The simulation model showed that this variation was not significant in affecting the curing time.