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What changes during a VSR Treatment ?
Metal workers have long observed changes in the behavior of long metal components during straightening: If the part contained residual stress, perhaps from welding or hot-straightening, it was harder to bend. In other words, to achieve a certain deflection ( X in the illustration ) a larger force F was required. This can be represented graphically. On the chart on the right, the green line represents a high-stress condition; the red line, a low-stress condition. The slope of the line represents the inverse of the spring constant, k, however k is inflated by the presence of stress. Long term, it will be a constant.
During the VSR Process, which requires plotting of the workpiece amplitude and motor power vs. vibrator RPM, with sufficient speed to intercept workpiece resonance, one or more resonance peaks will be plotted. In this simplified illustration, the vertical axis is amplitude, which could be deflection, but also can be velocity or acceleration. The latter is the most commonly used, since acceleration is proportional to the force the workpiece experiences, based upon Newton's 2nd Law:
F = ma
The horizontal axis is the excitation frequency or speed, which can be either Hz or RPM. Although not linear, this is related to the force output of the vibrator.
The original / baseline scan is green (like a "green"casting, i.e., likely to have stress) and the scan after stress relief, revealing peak growth, is red. This is the most common change seen during vibratory stress relief. To monitor peak growth, it is necessary to peak on top of the peak. Being off peak will make it very unlikely to see peak growth.
What was not clear during the early days of the VSR Process, or if using primitive equipment, is the connection between these two changes. In actuality, they are looking at the same phenomenon, from two different perspectives, static (on the left) and dynamic (on the right).
Here is an actual example: A VSR Chart of a 125 ton capacity lifting yoke, click the dark button to see or download the report showing how this chart was made.