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Solid output

Q: In LS-DYNA, solid element stresses are reported at the centre of the element.
Does this mean the stresses are calculated, for fully integrated element, at all
integration points and then report the average at the centre of the element?

A: In general, yes, but you have some options.   It is possible to output
data from all 8 integration points
of a type 2 solid to the d3plot file.  This is done by setting NINTSLD
to 8 in field 1 of card 3 of *database_extent_binary.
Then using LS-PrePost to postprocess,
History > Int.pt  plots the selected component at all 8 integration points.
When NINTSLD=8, all 8 integration points are output to dynain (assuming
*interface_springback_lsdyna is in the input deck, of course).

In 971 R4.2, you can set INTOUT=STRESS or ALL (*database_extent_binary)
and have stresses output for all the integration points to a file called
eloutdet (*database_elout governs the output interval and
*database_history_solid governs which elements are output).  Setting
NODOUT=STRESS or ALL  in *database_extent_binary will write the
extrapolated nodal stresses to eloutdet.

Updated documentation describing the aforementioned input parameters is in
the 971 R5 draft of the Users Manual (contact your LS-DYNA distributor for link).

Q: Is there any way to plot LS-DYNA nodal stresses and strains instead of having them at the centre of the element??

A: To get stresses on the outside surface of a part modeled with type 1
solids, you would need to add a 'coating' of very thin shell elements
(same material as solid) on the outside surface with the shells sharing
nodes with the solids.  The shell stress would then represent the
outside surface stress.  For type 2 solids, no shell coating is
necessary if extrapolation from the 8 element integration points to the
nodes is considered sufficiently accurate.  See answer to Question 1.


Q: Can I get stresses/strains in the local element system?  How is that system defined?

A:  Yes.  Toggle from "Glob" to "Local" in LS-PrePost.
This can be done either from the Fcomp menu or from the History menu of LSPP 2.4.
In invoking the "Local" output feature, LSPP assumes stress and strain are written to d3plot
in the global coordinate system (default, CMPFLG=0).
Per D. Wynn, local in solid is the same as for shells except we take the mid plane between 1,2,3,4 and 5,6,7,8

jpd
_____________ Information below may restate some of what appears in the Q/A above. _________________

 

It is possible to output data from all 8 integration points of a type 2 solid to the D3PLOT file. This is done by setting NINTSLD to 8 in field 1 of card 3 of *DATABASE_EXTENT_BINARY

LS-PrePost accesses this additional data when producing fringe/contour plots. 

  • History > Element plots still uses an average value of the 8 integration points.
  • History > Int.pt plots the selected component at all 8 integration points.


When NINTSLD=8, all 8 integration points are output to dynain (assuming *INTERFACE_SPRINGBACK_LSDYNA is in the input deck, of course).

NEIPH in *DATABASE_EXTENT_BINARY controls the number of extra history variables written to ELOUT and D3PLOT. The number of extra history variables written to dynain is 1+NSHV (NSHV defined in *INTERFACE_SPRINGBACK_LSDYNA) where the last history variable appears to be initial volume.

STRFLG set to 1 will invoke output of the strain tensor. If NINTSLD is set to 8, it appears that only the average of the 8 IP is output for each strain measure (excluding effective plastic strain which is not associated with STRFLG=1).

The ELOUT file contains only the values at the element centroid (average of 8 IP).