To define a cross section and output the cross-sectional resultant forces in the updated cross-sectional coordinate system, two alternative approaches can be followed. 1) Define the cross section in the input file using the keyword *DATABASE_CROSS_SECTION_PLANE. Select ITYPE=2 and use ID to reference the section’s coordinate system. The coordinate system should be defined using *DEFINE_COORDINATE_NODES with FLAG=1 so that the local coordinate system is updated at every time step based on the position of three nodes. The resultant cross-sectional forces are calculated by LS-DYNA in the updated local coordinate system and are written in the output file secforc which can be loaded in LS-PrePost. 2) Define a cross section in LS-PrePost after loading d3plot. This can be done by selecting FEM > Model and Part > Section Plane. In the Section Plane window, select “3Nds” for defining the cross-sectional plane using three nodes. Also, select “FixM” for the cross section to be fixed to the model and be updated based on the position of the three nodes. Then press “Cut” and then “Force”. Next, check the option “Plane coordinate system”, select the section force component to be plotted, and press “Plot”. This will plot the section forces with respect to the updated local coordinate system. With this approach the calculation of the element forces is done by LS-PrePost, independently of LS-DYNA, using the element stress data written in d3plot.