Skip to content

3.1 Input data format

Jump to bottom
Eric Breitbarth edited this page Sep 3, 2024 · 14 revisions

We use a standardised and human-readable ASCII format as input for CrackPy. This has the advantage that output from almost any data source can be easily converted. Therefore, it is advantageous for academic or research use. Each input set consists of two files:

  • nodemap.txt
  • connections.txt (optional)

Nodemap

The nodemap file stores the nodal or facet data. This file is crucial as all processes are based on it. Metadata or comments can be stored in the header, identified by the symbol #. The data section includes individual columns containing nodal coordinates, displacement vector, and strain tensor defined for plane strain conditions.

# Process data:
# specimen                      : Dummy2
####################################################################################################
# SIGNALS:
# force                         : value_element       : 14985.6119156
# displacement                  : value_element       : -9.17953395844
#
# Kraft                         : analog_input        : 15102.5390625
# Verschiebung                  : analog_input        : -7.6751708984375

####################################################################################################
#        ID;         x_undef [mm];         y_undef [mm];         z_undef [mm];               u [mm];               v [mm];               w [mm];             epsx [%];             epsy [%];            epsxy [1];           epseqv [%]
         1;       -80.0564567626;        84.9779203814;         0.1509636527;    0.003655774286017;    0.059203740209341;   -0.158300071954727;   -0.185958549380302;   -0.112336091697216;   -0.000613267708104;    0.310294896364212
         2;       -79.2904753387;        85.0053386055;         0.1975326408;    0.001983210910112;    0.060109287500381;   -0.155325025320053;   -0.209498479962349;   -0.005866464227438;   -0.000913561263587;    0.267783910036087

Where:

  • ID is the node number.
  • x_undef, y_undef, z_undef are the nodal cooridnates in the undeformed reference coordinate system, given in milimeters.
  • u, v, w are the displacements in x, y and z direction, given in milimeters.
  • epsx, epsy, epsxy are the componentens of the Cauchy's strain tensor. Note that $\varepsilon_{\mathrm{x}}$ and $\varepsilon_{\mathrm{y}}$ are given in %, while $\varepsilon_{\mathrm{xy}}$ is given without a ratio!
  • epseqv is the equivalent von Mises strain and is optional as it can be computed in CrackPy.
  • The separator is a semicolon ;

Connections

The connection file is optional and is mainly used for plotting. It stores how the nodes within the elements of the mesh are connected to each other. This file is based in the vtk format. Within CrackPy we use pyvista.UnstructuredGrid for precessing the data.

      Type;  Element #;     Node 1;     Node 2;     Node 3
          3;          1;        108;          1;          0
          3;          2;        109;          2;          1
          3;          3;        110;          3;          2

Zeiss GOM ARAMIS export

For export of data from Zeiss GOM ARAMIS see: ARAMIS Exporter

Ansys export

We developed the following export script for Ansys Mechanical using PyMAPDL. See fe_model.py for the full code.

Caution! The shear strains ($\varepsilon_{\mathrm{xy}}$, $\varepsilon_{\mathrm{yz}}$ and $\varepsilon_{\mathrm{xz}}$) used in Ansys are the technical shear strains, which are twice as large as the tensor shear strains [see Ansys Mechanical APDL Theory Reference - 2.1.1. Stress-Strain Relationships]]. The relationship is $\varepsilon_{xy} = 0.5 \cdot \gamma_{xy}$. Therefore we need to multiply epto_xy by 0.5.

    def export_nodemap(self, filename) -> None:
        """Saves the current Ansys node data into a txt-file called 'Nodemap'.

        Args:
            "filename" (str): Name of the nodemap file.
        """

        # Change to post-processing
        self.mapdl.post1()
        self.mapdl.set('last')
        self.mapdl.allsel()

        # Get coordinates, displacements, strains, and stresses
        node_list = self.mapdl.get_array(entity='NODE', item1='NLIST')
        node_loc_x = self.mapdl.get_array(entity='NODE', item1='LOC', it1num='X')
        node_loc_y = self.mapdl.get_array(entity='NODE', item1='LOC', it1num='Y')
        node_loc_z = self.mapdl.get_array(entity='NODE', item1='LOC', it1num='Z')

        u_x = self.mapdl.get_array(entity='NODE', item1='U', it1num='X')
        u_y = self.mapdl.get_array(entity='NODE', item1='U', it1num='Y')
        u_z = self.mapdl.get_array(entity='NODE', item1='U', it1num='Z')

        epto_xx = self.mapdl.get_array(entity='NODE', item1='EPTO', it1num='X') * 100.0
        epto_yy = self.mapdl.get_array(entity='NODE', item1='EPTO', it1num='Y') * 100.0
        epto_xy = self.mapdl.get_array(entity='NODE', item1='EPTO', it1num='XY') * 0.5
        epto_eqv = self.mapdl.get_array(entity='NODE', item1='EPTO', it1num='EQV') * 100.0

        s_xx = self.mapdl.get_array(entity='NODE', item1='S', it1num='X')
        s_yy = self.mapdl.get_array(entity='NODE', item1='S', it1num='Y')
        s_xy = self.mapdl.get_array(entity='NODE', item1='S', it1num='XY')
        s_eqv = self.mapdl.get_array(entity='NODE', item1='S', it1num='EQV')

        export_data = np.asarray([node_list, node_loc_x, node_loc_y, node_loc_z, u_x, u_y, u_z,
                                  epto_xx, epto_yy, epto_xy, epto_eqv, s_xx, s_yy, s_xy, s_eqv]).T

        with open(os.path.join(self.OUTPUT_PATH, f'{filename}_nodemap.txt'), 'w') as file:
            file.write('# Header for nodemap file\n')
            current_time = datetime.now().strftime("%d/%m/%Y %H:%M:%S")
            file.write(f'# {"date":>16}: {current_time}\n')
            file.write(f'# \n')
            file.write(f'# {"index":>10}; '
                       f'{"x_undef":>12s}; {"y_undef":>12s}; {"z_undef":>12s}; '
                       f'{"ux":>12s}; {"uy":>12s}; {"uz":>12s}; '
                       f'{"eps_x":>12s}; {"eps_y":>12s}; {"eps_xy":>12s}; {"eps_eqv":>12s}; '
                       f'{"s_x":>12s}; {"s_y":>12s}; {"s_xy":>12s}; {"s_eqv":>12s}\n')

            for i, line in enumerate(export_data):
                file.write(f'{line[0]:12.1f}; {line[1]:12.6f}; {line[2]:12.6f}; {line[3]:12.6f}; '
                           f'{line[4]:12.6f}; {line[5]:12.6f}; {line[6]:12.6f}; '
                           f'{line[7]:12.6f}; {line[8]:12.6f}; {line[9]:12.6f}; {line[10]:12.6f}; '
                           f'{line[11]:12.6f}; {line[12]:12.6f}; {line[13]:12.6f}; {line[14]:12.6f}\n')

    def export_vtk(self, filename):
        """Saves the current Ansys results as vtk file.

        Args:
            "filename" (str): Name of the vtk file.
        """

        self.mapdl.post1()
        self.mapdl.set("LAST")
        self.mapdl.allsel()

        # Define PyVista unstructured grid object and fill it with data
        grid = self.mapdl.mesh.grid
        grid.point_data['node_list'] = self.mapdl.get_array(entity='NODE', item1='NLIST')
        grid.point_data['u_x'] = self.mapdl.get_array(entity='NODE', item1='U', it1num='X')
        grid.point_data['u_y'] = self.mapdl.get_array(entity='NODE', item1='U', it1num='Y')
        grid.point_data['u_z'] = self.mapdl.get_array(entity='NODE', item1='U', it1num='Z')
        grid.point_data['epto_xx'] = self.mapdl.get_array(entity='NODE', item1='EPTO', it1num='X') * 100.0
        grid.point_data['epto_yy'] = self.mapdl.get_array(entity='NODE', item1='EPTO', it1num='Y') * 100.0
        grid.point_data['epto_xy'] = self.mapdl.get_array(entity='NODE', item1='EPTO', it1num='XY') * 0.5
        grid.point_data['epto_eqv'] = self.mapdl.get_array(entity='NODE', item1='EPTO', it1num='EQV') * 100.0
        grid.point_data['s_xx'] = self.mapdl.get_array(entity='NODE', item1='S', it1num='X')
        grid.point_data['s_yy'] = self.mapdl.get_array(entity='NODE', item1='S', it1num='Y')
        grid.point_data['s_xy'] = self.mapdl.get_array(entity='NODE', item1='S', it1num='XY')
        grid.point_data['s_eqv'] = self.mapdl.get_array(entity='NODE', item1='S', it1num='EQV')
        grid.save(os.path.join(self.OUTPUT_PATH, f'{filename}_mesh.vtk'), binary=False)
        return grid

For a full example see:

Clone this wiki locally