@John_Holtz, I considered Mark's posted words in greater detail and attempt here to support his effort directly with these comments:
@Anonymous: "Tensile testing of very thin copper plate to understand strength and eventual location of breaking point for various geometry configurations. Not trying to even get out anywhere near the ultimate stress. Due to stability issues, I have throttled it back to only displace the thickness of the plate.
When I run this in 2D, it is quite unstable with the time step level fluctuating wildly and it is very sensitive to mesh (the sharp corners certainly don't help here). Varying mesh (both discrete and non-discrete), using mid-side nodes, Rayleigh damping, Updated Lagrangian and 4th order integration don't seem to help much here.
Force displacement curve seems pretty choppy."
kjo's REPLY:
- Note that I am new to this forum's posting app, so, my content and threading may not be orthodox... apologies!
- Do not have enough data to reproduce all critical input... so this effort is all qualitative and speculative
- Revised model to 0.100" thick plate, approximating copper (could not readily find plastic mechanical properties)
- To understand "... strength... and breaking point" the local geometry would need the radii shown for appropriate accuracy
- Great width assumed, relative to thickness, so this 3D brick model (imported from SW) uses plane-strain BC's
- Molded S-shape assumed otherwise residual stresses are significant due to forging process
- Shell elements could be used but cannot reflect the nonlinear through-thickness stress-strain profiles accurately
- The source of the "choppy" force-displ. curve is due to the sequential tangent modulus stiffness reductions per element integration point
- An MES dynamic solution adds vibratory responses to be navigated by the solver adding to the total error norm per step
- Use of a Nonlinear static solution removes dynamic accelerations but the solver parameter defaults are not as well refined as for MES
- I suspect the use of an Abaqus explicit solution? Hence the selection of 1 sec event?... or is this the true event time?
- If the event occurs over 1 second, then the straining could require higher strain rate material properties too
- SimMech's explicit solver for an MES solution which should be attempted
Other model, material and solution parameters:
- Straight lengths are less than Mark's
- Mesh is only slightly finer but more uniform
- Material is probably still too stiff... picking up more load (if load units are lbs-force?)
- VM bilinear isotropic hardening model used
- Very small time steps used
- Updated lagrangian formulation used
- MES & other modeling defaults accepted (if I recall them all)

