الفهرس 
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Abstract
The fatigue behavior of welded joints prepared using manual metal arc welding in low carbon steel was investigated. The effects of grain size, incomplete penetration and the introduction of backing groove welding, on the fatigue limit and the mechanical properties was also investigated.
A rotating bending fatigue testing machine using the wohler principle with a rotating cantilever specimen was constructed for purpose of fatigue testing.
Experiments were carried out to determine the effect of welding on mechanical properties such as tensile, impact and hardness tests, micrographs were taken to study the effect of welding process on the microstructure of the material.
The low carbon steel used was locally produced in the Egyptian Iron & Steel Company AT Helwan , The welding electrodes were also locally produced in Industrial Gases Company at Mustruad. The welding method used was manual metal arc welding which is commonly used.
The results of the present investigation has indicated that grain refinement in low carbon steel increases both the strength and the fatigue limit of the parent material but has no significant effect on the fatigue behavior or the mechanical properties of the welded joints. As a result of weld defects, welded joints generally exhibited a lower resistance to fatigue as compared to the parent material.
In complete penetration reduced significantly the fatigue strength of low carbon steel, such a defect is equivalent to a pre-existing crack in a relatively hard microstructure which contains some hydrogen as a result of welding with rutile electrodes and to which hydrogen atoms readily diffuse during cyclic stressing.
Introducing a back side groove resulted in a higher resistance to fatigue failure as compared to a joint with a singlV-preparation. Depositing the back-side pass can relax the transverse residual stresses, induce residual compressive stresses and reduce the possibility of the occurrence of incomplete penetration.