MSC Marc input deck (.dat) and post file (.t19)

MSC Marc's input deck (the .dat file Marc Mentat writes and the solver reads) and its formatted post file (.t19, the ASCII twin of the binary .t16 results file). meshio++ reads both: the deck's mesh and sets, and the post file's mesh, sets and results, one increment at a time.

Format names	marc (input deck), marc_t19 (formatted post file)
Extensions	.dat (shared with Tecplot: a .dat file that opens as a Marc deck is Marc's), .t19; both also recognised by content
Read / Write	✓ / — (read-only)
Extra dependencies	—

Reading

import meshioplusplus

mesh = meshioplusplus.read("job.dat")                 # a Marc deck (a Tecplot .dat still reads as Tecplot)
post = meshioplusplus.read("job.t19", time_step=-1)   # the last increment
meshioplusplus.marc.time_values("job.t19")            # every increment's time
for time, mesh in meshioplusplus.read_sequence("job.t19"):
    ...

meshioplusplus convert job.dat job.vtu
meshioplusplus convert job.t19 'inc_{step}.vtu'      # one .vtu per increment

read_t19 (and read on a .t19) also takes points_only and arrays (read only the named arrays). The binary .t16 is not read: Marc writes the .t19 beside it when the POST option asks for a formatted file (its fourth field set to 1), and .t16 files need Marc's own PyPost library.

Which .dat is Marc's

.dat is Tecplot's extension too. A .dat file is read as a Marc deck when its first line that is not a $ comment starts with a Marc parameter (title, sizing, extended, elements, version, table, processor, alloc, setname, end ...) with no = in it, and an END, CONNECTIVITY or COORDINATES line follows in the first 64 KB. Anything else stays Tecplot's: a Tecplot header's TITLE = "..." has its =. Both engines apply the same check: the C++ registry in its format resolution (as it does for MFEM's .mesh), the Python reader by refusing a file that fails it so that the Tecplot reader is tried next. meshioplusplus.sniff_format recognises both a deck and a post file whatever their names.

The input deck

A deck has three sections: parameters, up to END; the model definition, up to END OPTION; and the history definition (load cases), which is not read. From the parameters only EXTENDED matters: it doubles every field's width. The model definition options read are:

• COORDINATES: a header (coordinates per node, node count), then a node number and its coordinates per line. Nodes need not be numbered in order; a node defined twice keeps its last definition. Decks with two coordinates per node (plane and axisymmetric models) get z = 0.
• CONNECTIVITY: a header, then per element its number, its Marc element type and its nodes; an element with more than 14 nodes continues on the next lines.
• DEFINE ELEMENT SET and DEFINE NODE SET (and their ordered ELSQ/NDSQ forms): see Sets.

Every other option is skipped, its data lines with it. Fields are read in any of Marc's three layouts, which a deck may mix line by line:

• fixed: 5-column integers and 10-column reals;
• extended (after EXTENDED): 10-column integers and 20-column reals. Marc Mentat writes reals with 16 digits and an exponent without a letter, 6.666666666666666-1, and a negative value fills its field, so it touches the one before it (7-1.666666666666666-1): fields are cut by column, never split on blanks;
• free: comma-separated items; a lone item is followed by a comma (1,).

Reals may use E or D exponents or none. $ starts a comment line.

Element types

Every Marc element type meshio++ maps lists its nodes in meshio++'s order (corners first, the face 1-2-3(-4) numbered so that its normal points into the element, then the mid-edge nodes of the bottom face, the top face and the vertical edges), so no node permutation applies. Checked against the Volume B descriptions and on real Marc Mentat decks, where every cell is positively oriented and every mid-edge node sits at its edge's midpoint.

meshio++ cell	Marc element types
line	9, 31, 52, 98
line3	64
triangle	2, 6, 138, 158, 201
triangle6	124, 125, 126, 128, 200
quad	3, 10, 11, 18, 75, 139, 140
quad8	22, 26, 27, 28, 30, 53, 54, 55
tetra	134, 135, 157 (its fifth node, a bubble, is dropped)
tetra10	127, 130, 133
wedge	136, 137
hexahedron	7, 43, 117, 123; with repeated nodes a wedge, pyramid or tetrahedron, as LS-DYNA's and Radioss's bricks
hexahedron20	21, 44, 57 (with repeated corners, kept as is with a warning)

Elements of other types are skipped with one warning listing them; their node count must be known to read a deck whose elements continue on further lines, so an element of an unknown type with more than 14 nodes is refused. cell_data["marc:element"] holds each cell's element number and cell_data["marc:type"] its Marc type.

Sets

DEFINE ELEMENT SET name and DEFINE NODE SET name become cell and point regions named as the deck names them. A set's list is read left to right:

• element or node numbers, and ranges a TO b (or THROUGH) with an optional BY step, counting up or down;
• the names of sets defined before it, of the same kind;
• AND (the default), EXCEPT and INTERSECT combining what follows with what came before;
• a line ending in C (or CONTINUE) continues on the next.

A member element with no cell (a skipped type) drops out of the region; a member number the deck never defines is an error. Edge, face, integration-point and other set kinds are skipped with a warning.

The post file

The formatted post file (post file revision 9 or later, Volume D's PLDUMP2000) is a sequence of blocks, =beg=5xxnn (name) ... =end=, in 13-column fields (i13, e13.6; a negative real touches the field before it). The model blocks come first, then one group of blocks per increment between **** and ----.

.t19	meshio++
element connectivities (507), nodal coordinates (508)	points and cells, with the element types above
sets (513): element and node sets	cell and point regions
an increment's time; its frequency (modal, harmonic) or buckling factor	field_data["meshio:time"]
the increment and sub-increment numbers (517)	field_data["marc:increment"], "marc:subincrement"
each nodal vector (524): Displacement, Reaction Force, Temperature ...	point data under the file's name, (points, components) or (points,)
the imaginary part of a complex harmonic vector	point data <name>@imag
element post codes at the integration points (523)	cell data per code, flattened point-major as the Abaqus .fil reader does so that every writer holds it: (cells, points × components) with field_data["marc:layout:<name>"] = [points, components]; (cells, components) or (cells,) when elements have one integration point, with no layout

Element post codes. Each code is named by its label in the file, or else by its meaning in Volume C's Table 3-3 (Equivalent Von Mises Stress for 17, Temperature for 9 ...), or post code <n>. A tensor (codes 301 total strain, 311 stress, 321 plastic strain, 341 Cauchy stress, 401 elastic strain, 411 global stress ... written as six consecutive codes) becomes one six-component array, components 11 22 33 12 23 31, that is xx yy zz xy yz zx; the order is checked on a real Marc post file, whose von Mises stress (code 17) matches its stress tensor's. A code of layer n (code + 1000 n) gets the suffix @layer<n>. A cell whose element has no cell (a skipped type) drops its values.

An increment that remeshes the model (block 519) is refused. Contact bodies, springs, distributed loads, tyings and global variables are skipped.

Validation

No Marc licence was available. The readers are checked against:

• Real Marc Mentat 2020 decks: the twelve decks of DAMASK's Marc element library tests (element types 6, 7, 11, 21, 27, 54, 57, 117, 125, 127, 134 and 136, extended format), not committed (they are AGPL). Every cell is positively oriented, every mid-edge node sits at its edge's midpoint, and the element and node sets resolve (the grain sets partition the elements).
• A real .t19 written by Marc (two 8-node bricks, from the FEDES project's examples), not committed: its mesh, sets, loads and stress tensor read as the file describes them.
• Fixtures written from the manuals, in tests/python/meshes/marc/ by tools/gen_marc_fixtures.py: the same model in fixed and extended format, a free-format deck with a collapsed brick and an unknown type, a plane-strain deck, and a two-increment post file.

The C++ and Python readers agree bit for bit on all of them.

Not read

• The history definition (load cases, boundary conditions, loads), and model definition options other than the three above (materials, geometry properties, boundary conditions, tables).
• Edge and face sets (DEFINE EDGE SET, FACE SET, elem:face members), and the post file's edge and face sets.
• The binary post file .t16, and post files of revision 8 or earlier.
• Marc element types not in the table above (Herrmann, interface, gasket, rebar, the 15-node wedge, whose element number was not confirmed).
• INCLUDE files of a deck.