Home Forums General Discussion Specifications N Strip Sensitivity

Per SAE J443 the “A” strip lower boundary of use is 4A. “N” strips are to be used below 4A which equates to roughly 12N. (3 times)
AMS2430 3.11.1 sets the upper limit boundary for drawing specifications that list only one intensity. It states -0 to +30% of the stated requirement or .003 inch whichever is more.

My problem with the AMS 2430 3.11.1 “rule” is that there seems to be an omission with regard to the scaling of the strips. If we were to have a requirement of “peen to intensity 4A” the limits of intensity are 4A to 7A. If one was to move these intensity limits to the N strip scale we would have limits of 12N to 21N. (3 times)

AMS2430 3.11.1 does not account for strip “scaling” therefore if we had a drawing requirement of “peen to intensity 12N” (approximate equivalent to a 4A intensity) our intensity limits get moved from 12N to 21N mentioned earlier to 12N to 16N by applying the 30% rule of AMS2430 3.11.1. This is a reduction of three times in the intensity tolerance zone just by changing from the A strip “scale” to the N strip “scale”. Effectively the allowable compressive stress tolerance band of the peened component is getting penalized three times by changing strip scales from A to N.

This could explain why the industry perceives N strips as extremely sensitive. Should the N strip not be given three times the room to move on N scale? Can you see how dramatically the control would be affected if one was to use an N strip at or in close proximity to a 4A intensity requirement?

SlYdEr