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MRTABS1 MRTABS2

MRTABS1 MRTABS2

(OP)
Dear All,

I know this topic has been covered many times but wanted to just get some more clarification on some details. I had testing done on A356 test coupons and received back the stress vs. strain curve. I assume this is the engineering stress-strain curve and converted it to true stress-strain using the standard text book formula (Microsoft excel). I am running MD Nastran 2010 with Marc in the back ground (Sol 600). I realize my analysis is a small strain problem (<5% STRAIN) and it should not matter. However I am getting varying results.

Questions:

• Should I be using Sol 600 for small strain? My material card is MATEP and not MATS1? Is this okay because the documentation states MATEP Is more for large strain?
• I have about 300 data points but am using only about 10 points to define the curve. What should the distribution selection be more on the stress side or the strain side. Should I bias more early and larger gaps later in the strain?
• Should I be using the engineering stress-strain or the true stress-strain curve in Table 1. I have seen people say both is the right way?
• The default MRTABS1 is (0). If I use the converted true stress-strain curve should I not use option (4) because I have already done the conversion in excel?
• Is it better to put in the engineering curve and let Nastran convert to true stress-strain using maybe option (1) for MRTABS1?
• I am starting my table with my first point at Yield? The default for MRTABS2 is (0) which wants the first point to be (0,). I have been using option (1) and skipping the (0,0). Does it really matter? I ran some tests and it gives the same answer.


Sorry for the long questions but I would like an experience person to maybe clarify this so I can put it to rest.

Thanks in advanced.

TheCADGUY

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