THF (d3thdt) File
THF (d3thdt) File
| Stress | Stress tensors are in the global cartesian system unless the option to use material axes has been invoked for orthotropic materials (CMPFLG on *DATABASE_EXTENT_BINARY). By default results are available at top and bottom integration points and mid-surface but values can be output for all through thickness integration points by using MAXINT on *DATABASE_EXTENT_BINARY |
| Strain | The Strain tensors output is optional. Values are in the global cartesian system unless the option to use material axes has been invoked for orthotropic materials (CMPFLG on *DATABASE_EXTENT_BINARY). Only values at the top and bottom integration points are output. T/HIS will average these values for the mid surface. |
| Forces & Moments | Force and moment resultants are <data> per unit width, and are written in the element local axis system. Refer to "Theory of Plates and Shells", Timoshenko, for a precise definition of these values. |
| Extra | The "Extra History" data components will only appear in the menu if they have been selected for output (NEIPS on *DATABASE_EXTENT_BINARY). These are output for the same surfaces / integration points as the stress tensor values. |
Through Thickness Integration Points
| NOTE: | The top and bottom "surfaces" are not the outer fibres if the default Gaussian integration rules are used, but rather the outer and inner integration points. The relationship between integration point location and shell thickness depends on the number of integration points used. |
The following diagram shows locations of integration points with respect to shell half-thickness (t/2) assuming the default Gaussian integration rules have been used:
| No of Points | Distance of outer fibres from neutral axis as a proportion of t/2 |
|
|
0.0 (membrane) |
|
|
0.577 t/2 |
|
|
0.775 |
|
|
0.861 t/2 |
|
|
0.906 |
The "top" (or outer) point is on the positive local Z side of the element neutral axis. The output of shell data from Ansys LS-DYNA will fall into one of two categories, and the "surface" options available in T/HIS depend on this.
| NOTE: | It is possible to use non-default integration schemes in Ansys LS-DYNA which may locate the integration points at different places. This is an advanced topic: contact Oasys Ltd Support for advice. |
Default output case: 3 "surfaces"
In this case, regardless of how many integration points the shell elements may actually have through their thickness, Ansys LS-DYNA writes out:
| Top surface : | Top integration point |
| Centre surface : | Computed neutral axis value |
| Bottom surface : | Bottom integration point |
Note that the "centre" surface here is the neutral axis value.
For membrane elements all three sets of values will be the same.
Optional output case: user-defined number of integration points
The number of through thickness integration points written to the THF file can be modified using the value of MAXINT on the *DATABASE_EXTENT_BINARY card. If this parameter is changed then all thin and thick shell output written to the THF file will have MAXINT data slots for integration points in the file, regardless of how many integration points a given element may have through its thickness.
If MAXINT is not 3 then the order in which data is written to the THF file is controlled by the actual number of integration points of integration points in a shells formulation. The following table illustrates output for the case of MAXINT not equal to 3
| Data slot in file | Shell with 3 Integration points | Shell with 5 Integration points | Shell with any other nunber of integration points |
| #1 | Middle |
Middle | Bottom | | Top |
| #2 | Bottom | Bottom | |
| #3 | Top | Bottom + 1 | |
| #4 | zero | Top - 1 | |
| #5 | zero | Top | |
| #6 | zero | zero |
| NOTE: | The THF file does NOT contain any information on the number of integration points each shell was defined with. |
| No explicit neutral axis value is calculated or output. | |
| The outcome of writing more integration points than have been used in a shell formulation is undefined. | |
| There is no guarantee that the "centre" surface in this context is the neutral axis value: this will depend upon the element integration scheme. In addition where the "centre" value has been averaged from a pair of points, when the number of layers is an even number, it will definitely not be the neutral axis value: consider plastic strain in a section in pure bending! |
The ZTF file generated by PRIMER can help to resolve some of these problems.
THF File + ZTF File
If a ZTF file had been generated using PRIMER then T/HIS can use additional information from the ZTF to correctly work out the number of integration points each shell element was defined with. If an attempt is made to output data for a surface that does not exist in the THF file then T/HIS will generate a warning message and a NULL curve will be generated.
In addition to working out the correct number of through thickness integration points for each element T/HIS can also use the information in the ZTF to identify models where MAXINT has been set to a -ve number in order to generate data for multiple in-plane integration points.
Effect of plotting "Top" surface on models with MAXINT = 6 and MAXINT = 9 whit and without a ZTF file.
| MAXINT = 6, no ZTF file | MAXINT = 6, ZTF file present | MAXINT = 9, no ZTF file | MAXINT = 9, ZTF file present | |
| Shell 1 has 4 integration points | Undefined (#int points < 6) | Correct (int point #4) | Undefined (#int points < 9) | Correct (int point #4) |
| Shell 2 has 6 integration points | Correct (int point #6) | Correct (int point #6) | Undefined (#int points < 9) | Correct (int point #6) |
| Shell 3 has 9 integration points | Incorrect (6th integration point) | Warning message as #int points < 6 | Correct (int point #9) | Correct (int point #9) |
In-plane Integration Points
In some versions of Ansys LS-DYNA it is now possible to write out data for all 4 in-plane integration points for fully integrated shells by setting MAXINT on the *DATABASE_EXTENT_BINARY card to a -ve number. For example specifying a value of -8 will generate data for 8 layers each with 4 in-plane integration points. If this option is used then all the elements will be written out using this option regardless of whether they are fully integrated or not.
As there is no information in the THF to indicate that data for 4 in-plane integration points has been written to the file then the file format will be exactly the same as for an analysis with a +ve value of MAXINT 4 times larger. For example MAXINT = -8 and MAXINT = 32 will both produce THF files with 32 integration points worth of data and there is no way for T/HIS to know which value of MAXINT was used to generate the data. The ZTF file generated by PRIMER can help to resolve this problem.
If multiple in-plane integration points are written to the THF file then they are written in the following order.
| Layer 1 - in-plane int point #1 |
| Layer 2 - in-plane int point #1 |
| .... |
| Layer n - in-plane int point #1 |
| Layer 1 - in-plane int point #2 |
| Layer 2 - in-plane int point #2 |
| .... |
| Layer n - in-plane int point #2 |
| Layer 1 - in-plane int point #3 |
| .... |
| NOTE: | If non fully integrated shells are included in the list of elements written to the THF file then in some versions of Ansys LS-DYNA the 2nd, 3rrd and 4th in-plane values will all be zero. Care should therefore be taken if the 4 in-plane values are averaged. |
| In some versions of Ansys LS-DYNA the 1st in-plane integration point is correctly written out using the global axis system while the 2nd, 3rd and 4th in-plane values are written using the elements local coordinate system. Care should therefore be taken if the 4 in-plane values are averaged. |