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The Range
Rifle & Shotgun Discussion
Empirical Evidence for AR Supremacy ???
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<blockquote data-quote="Shadowrider" data-source="post: 892057" data-attributes="member: 3099"><p>Okay I'll chime in here since I too have a good bit of experience with shot peening in the aerospace and oil field industries and also a good bit of experience with government procurement for the military. KurtM you are pretty close on the shot peening. I will point out that you can get compressive stress imparted far deeper than the depth you state. Shot size and material, part material and heat treat condition all play a role. But suffice it to say it makes a hell of a difference in multiple areas. Fatigue cracks propagate from a surface in tension. Never from a surface in compression. The point of shot peening is to impart this compressed layer to "fend off" a fatigue crack propagating in the first place. It doesn't last forever but it greatly extends the parts life. Secondly all parts to be shot peened should have no sharp corners at all. Everything should be radiused, particularly groove corners and all concave features. Otherwise you can impart a stress riser by the shot peening itself and it will roll edges like crazy.</p><p></p><p>As to the mil-spec issue others have stated it exactly right. If there is a requirement for a part to have a AISI 4140 steel heat treated to 145KSI strength and you make it out of AISI 4345 and heat treat it to 185 KSI to improve it? The source inspector will reject the entire lot. Even though it really is better in every respect. Simply because it does not meet the specification. If they wanted it better they would have required it in the 1st place. So mil spec is not always the best.</p></blockquote><p></p>
[QUOTE="Shadowrider, post: 892057, member: 3099"] Okay I'll chime in here since I too have a good bit of experience with shot peening in the aerospace and oil field industries and also a good bit of experience with government procurement for the military. KurtM you are pretty close on the shot peening. I will point out that you can get compressive stress imparted far deeper than the depth you state. Shot size and material, part material and heat treat condition all play a role. But suffice it to say it makes a hell of a difference in multiple areas. Fatigue cracks propagate from a surface in tension. Never from a surface in compression. The point of shot peening is to impart this compressed layer to "fend off" a fatigue crack propagating in the first place. It doesn't last forever but it greatly extends the parts life. Secondly all parts to be shot peened should have no sharp corners at all. Everything should be radiused, particularly groove corners and all concave features. Otherwise you can impart a stress riser by the shot peening itself and it will roll edges like crazy. As to the mil-spec issue others have stated it exactly right. If there is a requirement for a part to have a AISI 4140 steel heat treated to 145KSI strength and you make it out of AISI 4345 and heat treat it to 185 KSI to improve it? The source inspector will reject the entire lot. Even though it really is better in every respect. Simply because it does not meet the specification. If they wanted it better they would have required it in the 1st place. So mil spec is not always the best. [/QUOTE]
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