Hello!

I discovered a bug in Abaqus 2017.HF9. Abaqus solver ignores auto time incrementalization constriants in the case of using UMAT user subroutine where PNEWDT = 2 is specified. Increment size can grow unlimitedly despite specified constraints. A script for creation of model and user subroutine file can be found in the attachment.

Steps to reproduce the bug:

1. Rename Model_for_bug_demonstration.txt to Model_for_bug_demonstration.py (sorry, it's not possible to attach *.py file here).
2. Rename umat_isotropic.txt to umat_isotropic.for (sorry, it's not possible to attach *.for file here).
3. Run the python script Model_for_bug_demonstration.py to create the model.
4. Run Job-1 with the user subroutine umat_isotropic.for.
5. Watch increment sizes in job monitor.

Input file contains the following parameters:

*Step, name=Step-1, nlgeom=NO, inc=10000
*Static
10., 200., 0.001, 10.

UMAT contains the record:

PNEWDT = 2

Job monitor gives the following sequence of increment sizes:

INC INC SIZE
1 10.00
2 20.00
3 40.00
4 80.00
5 50.00

The bug has been found in Abaqus 2017.HF9 (FIX PACK 1803). There is no such bug in Abaqus 2016.HF7 (FIX PACK 1646). OS version: Windows 10 Pro 1703.

Best regards,
Mikhail Kozlov