Output global matrix

With an extra step in input file job.inp, one can output global matrix with:

*MATRIX GENERATE, STIFFNESS
*MATRIX OUTPUT, STIFFNESS, FORMAT=COORDINATE

The first line generates a binary file job_X1.sim, which can be reused by Abaqus. The second line generates a text file job_STIF1.mtx, which can be read by MATLAB with:

m = load('job_STIF1.mtx');
m = spconvert(m);

Input global matrix

First, set all element with a null material property such as:

*SOLID SECTION, ELSET=ELEMENTS-ALL, MATERIAL=MAT-NULL
*MATERIAL, NAME=MAT-NULL
*ELASTIC
1.E-36, 0.3

Then, read the job_X1.sim file:

*MATRIX INPUT, NAME=K_ext, INPUT=job_X1.sim, MATRIX=STIFFNESS, SCALE FACTOR=1.0
*MATRIX ASSEMBLE, STIFFNESS=K_ext

The second line assembles the matrix $\mathbf{K}_\mathrm{ext}$ (read from job_X1.sim) to the model with a null stiffness matrix $\mathbf{K}_0$.