How to zero the EPS field in dyanin, before transferring to Static Structural?

Mike Magnier

This is for transferring LS-DYNA results (dynain ASCII file format) into Static Structural, via an External Model system. The effective plastic strain (EPS) data in dynain may be incompatible with the material model used in Static Structural. Zeroing EPS can fix errors associated with this, and means that only the stress tensor is transferred.

Mike Magnier

Below is a Python script to achieve this. The script reads the dyanin file line by line, it recognizes the start of the *INITIAL_STRESS_SOLID/SHELL blocks, it locates the EPS field, replaces it with zero, then writes out dynain.k, ready to be imported.

The script should support both standard and LARGE format, and it should skip over any number of extra history variables. N.B: the script has had limited testing.

# -*- coding: utf-8 -*-


"""

Created on Tue Feb 17 11:06:17 2026


Description:

Zeroes plastic strain (eps) values in a dynain file and writes a renamed

dynain.k file for import into Ansys Workbench material models without

hardening.


Assumes LS-DYNA-style fixed-width formatted keyword blocks.


© 2026 ANSYS, Inc. Unauthorized use, distribution, or duplication is prohibited

"""


import re

import math



# Regex to detect a line containing 8 integers separated by whitespace.

# This identifies the "element header" line inside INITIAL_STRESS blocks.

first_line_pattern = re.compile(r"""

^\s*[+-]?\d+\s+

[+-]?\d+\s+

[+-]?\d+\s+

[+-]?\d+\s+

[+-]?\d+\s+

[+-]?\d+\s+

[+-]?\d+\s+

[+-]?\d+\s*$

""", re.VERBOSE)



def is_8_integers(line):

    """Return True if line appears to contain 8 integer fields."""

    return bool(first_line_pattern.match(line))



input_file = "dynain"

output_file = "dynain.k"



# Flags tracking where we are in the keyword deck

shell_block = False

solid_block = False

element_block = False


row_count = 0

out_lines = []



with open(input_file, "r") as f:

    for line in f:


        stripped = line.lstrip()


        # --- Detect start of shell stress block ---

        if stripped.upper().startswith("*INITIAL_STRESS_SHELL"):

            shell_block = True

            out_lines.append(line)

            continue


        # --- Detect start of solid stress block ---

        if stripped.upper().startswith("*INITIAL_STRESS_SOLID"):

            solid_block = True

            out_lines.append(line)

            continue


        # --- First data line inside shell block ---

        if shell_block and is_8_integers(line):

            element_block = True


            # Parse control values from fixed columns

            nhsv = int(line[20:30].strip())   # number of history vars

            large = int(line[60:70].strip())  # large-format flag


            # Define formatting parameters based on LS-DYNA format

            if large == 0:

                eps_line = 1        # which row contains strain

                eps_position = 7    # which field in that row (starting from 0)

                nhsv_per_line = 8

                field_width = 10

            else:                   # if LARGE format

                eps_line = 2

                eps_position = 2

                nhsv_per_line = 5

                field_width = 16


            nhsv_lines = math.ceil(nhsv / nhsv_per_line)


            # Pre-build replacement string to exact width

            zero_field = "0.000E+00".rjust(field_width)


            row_count = 0

            out_lines.append(line)

            continue


        # --- First data line inside solid block ---

        if solid_block and is_8_integers(line):

            element_block = True


            nhsv = int(line[20:30].strip())

            large = int(line[30:40].strip())


            if large == 0:

                eps_line = 1        # which row contains strain

                eps_position = 6    # which field in that row (starting from 0)

                nhsv_per_line = 8

                field_width = 10

            else:                   # if LARGE format

                eps_line = 2

                eps_position = 1

                nhsv_per_line = 5

                field_width = 16


            nhsv_lines = math.ceil(nhsv / nhsv_per_line)

            zero_field = "0.000E+00".rjust(field_width)


            row_count = 0

            out_lines.append(line)

            continue


        # --- Modify element data lines ---

        if element_block:

            row_count += 1


            # Replace the target field with zero strain

            if row_count == eps_line:

                upto = eps_position * field_width

                continue_from = upto + field_width

                line = line[:upto] + zero_field + line[continue_from:]


            # Reset counter after full element record processed

            elif row_count == eps_line + nhsv_lines:

                row_count = 0


        # --- Detect end of keyword block ---

        if (shell_block or solid_block) and stripped.startswith("*"):

            shell_block = False

            solid_block = False

            element_block = False


        out_lines.append(line)



# Write modified deck

with open(output_file, "w") as f:

    f.writelines(out_lines)


print("Done.")