American Welding Society Forum
i have received a report on weld cracking that states that the cause of the crack is the movement of the bridge during the laying of the weld and this opinion is supported by some evidence of fracture surfaces being displaced in the cracks. what is meant by 'fracture surfaces being displaced'? and does anyone out there have any info on movement effecting the welding on in service bridge structures?
imagine that you've made a horizontal weld. Imagine that the weld developed a vertical crack. The crack has split the weld into two parts, one at your right and the other one at your left hand side, right? Now imagine that you move the two parts vertically by a sixteenth of an inch with your hands. When doing this, you don't pull the two halves apart, rather, you slide them one over the other, taking care to keep them in contact. At this point, the two parts are still in contact but they've been displaced one sixteenth of an inch from their original position, right?
This is the "fracture surfaces being displaced". It's obvious that in your case it happened because you welded the bridge while the trains were running on it. The heavy vibration caused by the passage of the trains cracked the welds when they were still hot. If I was the boss at that job, I'd make the welds in a period that the trains are not passing on the bridge.
Giovanni S. Crisi
Sao Paulo - Brazil
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