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#69 - 12/03/03 12:27 PM T2... how important is it?
Jay T Offline

Registered: 12/03/03
Posts: 2
Loc: Toronto, Ontario, Canada
Good day:
sorry, I think this is the third time I have tryed to send this message...
for some reason it is not showing up
this is the last time i promise

The question I want to ask is how important is to reach T2 before the end of the shot peening cycle?

I know that when we create a saturation curve we determine the saturation point (T1) and using calculations we determine T2.
I know that to determine T2, we must double the exposure time but only have an increase of 10% intensity, which makes me believe T2 is 200% coverage.

This is my dilemma...

In creating a shot peen program to peen complex parts we will have multiple test blocks, which means multiple saturation curves. Getting them to all reach exactly T2 without exceeding T2 on some of the locations is very difficult. I am able to achieve the intensity range on the drawing but the T2 range is rarely in the location I need it to be, occurring either before or after the final intensity.

My Questions
1. Is it necessary to have all the intensities on the part reach T2 on the saturation curves at the end of the program?
2. When the drawings ask for 200% coverage is it ok to exceed T2?
3. If we go over T2 are we creating undue stresses to the part by over peening?

Any advice would be appreciated, thanks.

#70 - 12/03/03 01:16 PM Re: T2... how important is it?
Jack Champaigne Online   content

Registered: 04/20/99
Posts: 319
Loc: Mishawaka, IN, USA
T2 has nothing to do with the actual peening cycle time. It is only used to determine intensity.
1. No, it is not necessary since your peening intensity is already established. Leaving the parts in longer (or even shorter) periods affects coverage but not intensity. Intensity is determined by shot size, hardness, velocity etc. but not exposure time.
2. Again, there is no relationship. To achieve 100% coverage you determine how long it take to make enough dents for 98%. Then for 200% coverage you go twice that time. Did you notice I never said anything about T1 and T2? They have nothing to do with setting your blasting time.
3. See above. If you had instead asked if we peen for more than 200% the answer would be yes you could possibly cause damage or reduction of fatigue life, depending on the particular material and how much over 200% exposure you endured.

#71 - 12/03/03 03:15 PM Re: T2... how important is it?
scottbonar Offline

Registered: 05/06/03
Posts: 9
Loc: Thomasville, GA, US
I agree with Jack's response but wanted to add some thoughts. Do not overlook Jack's first statement "T2 has nothing to do with the actual peening cycle time". It sounds like you are still in the qualification process and if so T2 is important. As you stated all of your test strips will have a saturation curve associated with them. Each saturation curve will include T1 and T2 to prove out the intensity and when it occurs (T1). I do not understand your statement regarding using a caculation to determine T2. Plot the test strip readings and create your curve then let your curve tell you were T1, T2 and your intensity are occuring. Yes with multiple test strips it is sometimes difficult to get the intensity at each strip to occur at the same exposure time but with proper gun location you can get them close.


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