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Hi sgdon, "The point we trying to understand now is why G12 has no relationship with E1 and E2 and v12, all in principle material direction with no regards to XY coordinates." The shear modulus for a plane X of any material is a function of the poisson ratio and the two direct stiffnesses at...

Hi sgdon, I think what is confusing you is the fact the E1 and E2 are the same for a woven composites is leading you to believe that the 1-2 plane should be isotropic. Dont let this fool you, the 1-2 plane is definitely not istropic, youve got fiber in the 1 direction and youve got fiber in the...

Hi sgdon, I believe the relationship G12=E1/(1+2v+E1/E2) should be Gxy=E1/(1+2v12+E1/E2) where 1,2 are principal material coordinates and x,y are of an off-axis rotated coord system. You get this equation by substituting an off-axis angle of 45 deg into the full relationship between...

"If you are doing a static stress analysis, use of strain energy (density) would be directly related to stress. Consequently, there would be no obvious advantage to using strain energy (density) over stress in a static analysis." I disagree. Look at the example I posted in the other thread on...

I forgot to mention one other reference which I think will help: "Loading, Degradation and Repair of F-111 Bonded Honeycomb Sandwich Panels – Preliminary Study" http://www.dsto.defence.gov.au/corporate/reports/DSTO-TR-1041.pdf

"My objective is to be able to asses what acceptable damage limits would be." As far as I know there is still a great deal of work going on to determine what "acceptable" damage from impacts should be for sandwich aerostructures. NASA Langley did a lot of work to try to establish industry...

Hi, The FAA also has a good paper available on the web which might be of help to you: "Review of Damage Tolerance for Composite Sandwich Airframe Structures" research.faa.gov/aar/tech/docs/techreport/99-49.pdf Erik

Hi, For potted inserts a great reference is ESA PSS-03-1202, "Insert Design Handbook". We ran a series of tests a while back and the failure loads all fell within 5% of what was predicted with the ESA methodology. For sandwich panels in general (including damage assesment) try "The Handbook of...

There is a section in the Basic Dynamics book of the NASTRAN manual which describes the large mass method and it recommends that the "dummy" mass be 10^6 times the mass of the entire structure. Erik

Hi, As far as NASTRAN goes, the large mass method is no longer necessary as of version 2004 because direct enforced acceleration in dynamic solution sequences was implemented...actually officially it was included in v2001 (there is a good explanation in the v2001 release guide) but there were a...

jsboy, Be careful because if what you are really after is the total force acting at a node you are much better off in NASTRAN getting it from the grid point forces (GPFORCE). The freebody tool in PATRAN is great for visualizing the grid point force output. Remember that the forces calculated...

jsboy, Remember that, just like in classical plate theory, the force/moment values are given per unit length, i.e. its not the total force/moment acting on a node. The values are calculated by integrating the stresses over the element thickness. Erik