Abaqus results file (.fil)

The results file Abaqus/Standard (and Explicit, with *FILE OUTPUT) writes on request with *NODE FILE and *EL FILE: the one route into Abaqus results that needs neither the ODB API nor an Abaqus installation. For .odb see the roadmap (an exporter script is planned). The input deck itself is the abaqus format.

Format name	abaqus_fil
Extensions	.fil (also recognised by content, ASCII and binary)
Read / Write	✓ / —
Extra dependencies	—

Reading

import meshioplusplus

mesh = meshioplusplus.read("job.fil")                        # the first increment
last = meshioplusplus.abaqus_fil.read("job.fil", time_step=-1)
times = meshioplusplus.abaqus_fil.time_values("job.fil")
series = meshioplusplus.read_sequence("job.fil")             # every increment

read(filename, points_only=False, arrays=None, time_step=0). Both engines (the C++ core and the pure-Python reference) read the same meshes.

Records

A .fil file is a sequence of records [length, key, attributes…] of 8-byte words.

• Binary (the default): 512-word blocks, each one Fortran record, in the writing machine's byte order (both orders and 4- or 8-byte markers are recognised, and files without markers are read too). A record may cross block boundaries; the last record of an increment is padded to the end of its block.
• ASCII (*FILE FORMAT, ASCII): each record starts with *; items are I + a two-digit digit count + the digits, D (or E) + a 22-character real, A + 8 characters, run together on 80-column lines. Items are read by width, so a * inside a text item does not start a record.

Key	Read as
1900 / 1990	an element and its continuation: a cell, its label kept as cell_data["abaqus:id"]
1901	a node, its label kept as point_data["abaqus:id"]
1931 / 1932, 1933 / 1934	a node set / element set and its continuation: a point / cell region
1940	a label cross-reference: a set name longer than 8 characters is written as a number, resolved here (assembly sets keep Abaqus's ASSEMBLY_INSTANCE_SET spelling)
2000 / 2001	the start and end of an increment: a step
1911	an output request: nodal or element records follow
1	the element header (element, integration or node point, section point, location) of the element records after it
1921, 1922, 1902	release, heading, active degrees of freedom: skipped
contact (15xx), element matrices (10xx), modal generalised (301–310), substructure	skipped with a warning

Element types map through the .inp table and, for the ones it does not list, by family and node count (C3D…, CPE…/CPS…/CAX…, shells S…, membranes M3D…, trusses and beams); their nodes are in meshio++'s order. Types with no meshio++ cell (user elements, connectors, springs) are skipped with a warning.

Steps and data

Every increment is a step: time_step selects one (0 = first, negative counts from the end), and field_data carries meshio:time (the total time), abaqus:step, abaqus:increment, abaqus:step_time and abaqus:procedure. The increment's records become data named by the Abaqus identifier (U, V, A, RF, CF, COORD, NT, … for nodes; S, E, SINV, PE, LE, PEEQ, MISES, ENER, NFORC, … for elements; key_<n> for a key without one):

Where	Becomes
nodal record	point_data, NaN for nodes without a value
element record at the integration points (location 0)	cell_data of shape (cells, points × components), point-major
at the centroid (1) or for the whole element (5)	cell_data of shape (cells, components)
at the element nodes (2)	cell_data of shape (cells, nodes × components), point-major in the cell's node order
averaged at the nodes (4)	point_data
rebar (3)	skipped

Every array is rectangular and has the same width in every cell block, so every writer can hold it (VTU, XDMF, …): the widest block sets the number of points and components, and the other blocks are padded with NaN. Per-point data is flattened point-major, column point × components + component; its (points, components) is field_data["abaqus:layout:<name>"], so a.reshape(len(a), *layout) restores it. A single column drops its axis. Section points above 1 (shell and beam layers; continuum elements write 0) get @sp<k> appended to the name: S holds the first layer and the solids, S@sp5 the fifth layer. A block with no value for a field holds NaN.

Components keep the file's order, as every reader does (mesh data model): a solid's S is 11, 22, 33, 12, 13, 23, where meshio++'s six-component convention is xx yy zz xy yz zx. Von Mises does not depend on the order of the shear components; for principal values, swap the last two first. Von Mises is also SINV's first component when the run wrote invariants; otherwise compute it from S with the tensor-invariants operation on a (cells, 6) array, such as the mean over the points.

Validation

No free solver writes .fil and no Abaqus licence was available. The fixtures under tests/python/meshes/abaqus_fil/ are real Abaqus 2023 ASCII output from pybaqus's test suite (MIT), whose U and integration-point S match pybaqus's own reading on all 236 values, and synthetic files written record by record from the Abaqus guide in ASCII and both binary byte orders. A 16 MB binary file from AbaqusFilFile-Translator's example (not committed) reads with its nine increments. The roadmap's check against a run's .dat printout still needs a real Abaqus run.