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Analysis of fatigue crack properties of the weld metal of gas metal Arc welded 300WA steel
Author(s)
February, Eugene J.
Date Issued
2006
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
Welded joints are major causes for concern in the engineering arena for two
basic reasons. In the first instance the weld is known to be a region of
weakness within a structure and is caused by residual and applied stress
concentrations. Secondly, the behaviour of the stress patterns is somewhat
difficult to predict accurately due to the difficulty of conforming to the geometry
and process parameters.
The experimental procedure in this work commenced with specimens being
welded with a technique very commonly used in industry. The residual stresses
generated by thermal fluctuations from the welding process cannot be
predicted easily and is viewed as a problem as increased stress levels
promotes failure. Residual stresses were then determined with the use of an
ultrasonic stress measuring device. Strain gauges were used to measure
strains in the welded specimens and these strains converted to stresses. The
results of the two methods were compared and analysed.
Compact tensile specimens were used to perform fatigue testing. The results
confirmed findings from earlier research such as the proportion of cyclic life
spent on initiating the crack. Hardness tests were performed to determine if
any relationship existed between fatigue failure, yield strength and hardness.
Finally metallurgical analysis revealed the phases and structures of the weld
and heat-affected zones.
The findings of this research indicate that close relationships exist between the
cycles to crack initiation and ultimate fracture, the hardness, yield stress and
the fatigue life of the weld as well as between the grain diameter and the yield
stress. Furthermore it is shown that there was not enough information
gathered in this research to conclude that the life expectancy of 300WA welded
steel can be predicted. However recommendations are made for future
research in the prediction of failure of the 300WA welded steel.
basic reasons. In the first instance the weld is known to be a region of
weakness within a structure and is caused by residual and applied stress
concentrations. Secondly, the behaviour of the stress patterns is somewhat
difficult to predict accurately due to the difficulty of conforming to the geometry
and process parameters.
The experimental procedure in this work commenced with specimens being
welded with a technique very commonly used in industry. The residual stresses
generated by thermal fluctuations from the welding process cannot be
predicted easily and is viewed as a problem as increased stress levels
promotes failure. Residual stresses were then determined with the use of an
ultrasonic stress measuring device. Strain gauges were used to measure
strains in the welded specimens and these strains converted to stresses. The
results of the two methods were compared and analysed.
Compact tensile specimens were used to perform fatigue testing. The results
confirmed findings from earlier research such as the proportion of cyclic life
spent on initiating the crack. Hardness tests were performed to determine if
any relationship existed between fatigue failure, yield strength and hardness.
Finally metallurgical analysis revealed the phases and structures of the weld
and heat-affected zones.
The findings of this research indicate that close relationships exist between the
cycles to crack initiation and ultimate fracture, the hardness, yield stress and
the fatigue life of the weld as well as between the grain diameter and the yield
stress. Furthermore it is shown that there was not enough information
gathered in this research to conclude that the life expectancy of 300WA welded
steel can be predicted. However recommendations are made for future
research in the prediction of failure of the 300WA welded steel.
Additional information
Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2006.
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Analysis of fatigue crack properties of the weld metal of gas metal arc welded 300wa steel.pdf
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