Starting in LS-DYNA version 970 and later, we can now use expressions instead of digitized values to define an XY curve. Optionally, the expressions can refer to other curves which could be defined using either digitized points or using expressions themselves. Here is an example of its usage: Polynomial Expressions You can define a generic…
In contact-impact interactions, friction plays an important role in accurately capturing the sliding behavior. In LS-DYNA, the coulomb treatment of friction is used where a static and a dynamic friction can be defined which are used to determine the shear force while resisting penetration. By default, all contact definitions model a friction-less sliding which is…
Single surface contacts have dramatically eased the way we currently model the contact-impact treatment for complicated simulation models in LS-DYNA. One of the important considerations is the final thickness used by contact algorithms especially for shell elements. By default, LS-DYNA considers the minimum of thickness specified in the *SECTION_SHELL or from *ELEMENT_SHELL_THICKNESS and the 40%…
For non or poorly converging implicit solutions, the parameter D3ITCTL parameter in *CONTROL_IMPLICIT_SOLUTION may come handy to isolate regions of interest. When D3ITCTL is non-zero, LS-DYNA outputs the model information at each Iterative step into a binary file named D3ITER which is in the same format as D3PLOT. The number of steps for which the…
Several analyses sometimes requires the mapping of nodal positions (coordinates) from a previous run for use in current run. For single component this is a rather easy task since it just involves writing a DYNAIN file for part(s) of interest using *INTEFACE_SPRINGBACK_LSDYNA keyword which would consist of final deformed nodal coordinates and element history variables.…
*INTERFACE_SPRINGBACK provides an easy way to store a part’s state at the end of a simulation for later use. The part’s state consists of element history variables such as stress and strain tensor (in the form of *INITIAL_STRESS/*INITIAL_STRAIN) and also nodal values such as its final coordinates (*NODE). Optionally, when using the THICKNESS option, it…
Starting in LS-DYNA v971, nodal accelerations can be filtered before being output to the ASCII file “NODOUT”. The type of filter can either be a built-in filter based on low-pass Butterworth frequency filter or can be user-defined. The filtering process is turned on by setting the IACCOP=2 in *CONTROL_OUTPUT keyword. The filtering process works by…
The ASCII file “RCFORC” contains the incremental forces contributed by contact algorithms. Due to the nature of the contact-impact interactions, the raw output tends to be very noisy and is of little value. To eliminate the inherent noise in the contact force output, LS-DYNA averages the force magnitude over the preceing output interval which results…
In the area of distributed computing using Massively Parrallel Processing (MPP) LS-DYNA, finite element model decomposition is performed after initial processing of the input deck to “distribute” the model content to compute nodes. There are two primary goals for model decomposition. First goal is of of course to “break-down” the given problem into smaller pieces…
This 4 part article, orignally published in the FEAINFORMATION newsletter between August and December 2001, can be downloaded here: Contact Modeling.pdf
