Abstract
Metal magnetic memory (MMM) testing method has been proved to be a valid approach to monitor early damage and predict fatigue life, but there is no systematic description and comparison about the characteristics of MMM signals for welding and non-welding specimens with different materials under tension-compression fatigue. Thus, the fatigue tests for Q345B and Q345qC welding and non-welding specimens were carried out and the MMM testing was done synchronously. Then, based on the normal components of MMM signals, H p (y), and its variations, ΔH p (y), the slope of ΔH p (y) fitting curves, K C , and the average of ΔH p (y) signals on the whole testing line, ΔH p (y) ave , were extracted as the characteristic parameters for Q345B and Q345qC non-welding specimens, respectively. Additionally, the gradient of “peak–vale” on H p (y) signals curves, k, and the average of H p (y) signals in the scope of welding zone, H p (y) ave , were extracted as the characteristic parameters for Q345B and Q345qC welding specimens, respectively. Some conclusions can be drawn by comparison: the variation laws of H p (y) signals with cyclic loads are related to the material. The characteristic parameters for welding and non-welding specimens with the same material have a certain similarity. Then, the failure of non-welding steel can be warned early by K C or ΔH p (y) ave when the fatigue life has 20% left, but the damage degree of welding specimen should begin to be valued highly once the k or H p (y) ave is decreasing. Finally, the fatigue life of welding and non-welding specimens with different materials can be evaluated effectively by using corresponding magnetic characteristic parameters.
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