Attachments:mat57_default.k Modeling recoverable foams poses several challenges in crash worthiness as well as in low-to-medium impact velocity conditions. This is due to its relatively low stiffness when compared with structural materials which has an indirect effect on its contact-impact interactions with other materials. To review the best practices when modeling such components, we can consider…
Beginning version 971 and later, LS-DYNA allows easy way to store models in a central location for use at run time. This feature can be turned on using *INCLUDE_PATH which takes unlimited number of absolute directory names. When INCLUDE_PATH is used, LS-DYNA first checks the file, specified using *INCLUDE keyword, in the local directory and…
Over the past decade, the ability of simulations driving the design has grown rapidly and today’s confidence in simulations results is a good testament to it. Two significant areas that have contributed to this is the “Numerical Modeling Awareness” and “Design Domain Knowledge” gained over the years by design and analysis community. Numerical modeling awareness…
When solving static or quasi-static type problems, the default Implicit Static solver (IMAS=0 in CONTROL_IMPLICIT_DYNAMICS) requires a well-conditioned model, with no rigidbody modes, to get good convergence behavior. It is often difficult to prevent rigidbody modes especially when its dependent on contact-impact conditions. In such cases, use of Implicit Dynamics solver (IMAS=1) can help us…
Mass-scaling is a term that is used for the process of scaling the element’s mass in explicit simulations to adjust its timestep. The primary motivation is to change (usually increase) the global compute timestep which is limited by the Courant’s stability criteria. LS-DYNA allows two different types of mass-scaling using the DT2MS parameter from *CONTROL_TIMESTEP…
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…
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…
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%…
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.…
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…
