Shock Response Analysis

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blizzard Member Join Date: Jul 2006 Posts: 6	Shock Response Analysis 02/06/2008 3:24 PM
	I have a small unit that will be subjected to MIL-S-901D shock (light hammer blow). This blow will impart a 125-200 G shock on the unit. I am attempting to calculate the potential deflection and bending/shear stress on the unit before hand. I have calculated the deflection using Steinberg, and the bending stress based on that deflection. How much more stress can material take if the stress is transient as apposed to steady state? I would assume that a material that would yield at 30 ksi steady state might not yield when subjected to stresses twice that for say, 40 ms. Any help would be appreciated.
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taejonkwando Power-User Join Date: Dec 2006 Posts: 441 Good Answers: 20	#1 Re: Shock Response Analysis 02/07/2008 11:02 AM
	I think your assumption of momentarily exceeding the material yield strength is due to the extra energy required to overcome the material's inertia. While it is true inertial loads do contribute to the apparent yield strength they are only momentary and the ultimate yield strength is always within the manufacturers published specification. Inertia is what allows a lead bullet to penetrate, for example, an oak board. The greater the velocity the more inertial resistance to maleability so your calculations regarding the RATE of deformation are where you will find you transient stress values. __________________ intellectuals solve problems, geniuses prevent them ~ Einstein
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blizzard Member Join Date: Jul 2006 Posts: 6	#2 In reply to #1 Re: Shock Response Analysis 02/07/2008 11:45 AM
	That makes sense. Is there a way to calculate the maximum allowable transient stress? I need to come up with a definitive value for a "transient yield strength" in order to determine the max allowable stress.
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taejonkwando Power-User Join Date: Dec 2006 Posts: 441 Good Answers: 20	#3 In reply to #2 Re: Shock Response Analysis 02/08/2008 6:30 PM
	Oh my gosh, you've forced me to plow through my old forging handbooks to look for some nonproportional loading equations and something about Polizzotto's and Melan's Theorems as I vaguely remember. On the flip side I googled Polizotto, Melan and found the information but it's in one of those sites which charge you $. However try this; http://www3.interscience.wiley.com/cgi-bin/abstract/110547265/ABSTRACT?CRETRY=1&SRETRY=0 it's free and may start you on your way. I apologise for being of so little help right now but I must plead schedule and personal distractions (death of a dear friend). I will try to give you a better answer in the near future. TK __________________ intellectuals solve problems, geniuses prevent them ~ Einstein
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