How contact works in LS-DYNA?

How contact works in LS-DYNA?

How Contact Works. In LS-DYNA, a contact is defined by identifying (via parts, part sets, segment sets, and/or node sets) what locations are to be checked for potential penetration of a slave node through a master segment. A search for penetrations, using any of a number of different algorithms, is made every time step …

What is contact thickness in LS-DYNA?

For each contact node, the contact thickness is set to the thickness of the shell element that contains it. If SFST/SFMT or SFT are set, scale the thickness (with SFT overriding SFST/SFMT). If SSTHK is 0 and the contact is single surface, limit thickness to 40% of the minimum edge length of the element.

What is Timestep in LS-DYNA?

For SOFT=0 contacts, the surface timstep is proportional to min[sqrt(m/k)] where m is essentially the mass attached to the contact “spring” and k is the contact spring stiffness which is a function of the material bulk modulus and element size (see section 23 in the LS-DYNA Theory Manual).

What is sliding interface energy in LS-DYNA?

The ‘Sliding Energy’ included in GLSTAT equals the sum of “sum of slave/master (SoSM)” from SLEOUT . Note: The frictional energy is included in the sum of slave/master energy. If friction is defind, e. g. in *CONTACT_… via FS and FD , the resulting energy can be found in the database variable frictional energy (FE).

How do you avoid negative volume in LS Dyna?

Some approaches that can help to overcome negative volumes include the following:

1. Simply stiffen up the material stress-strain curve at large strains.
2. Sometimes tailoring the initial mesh to accomodate a particular deformation field will prevent formation of negative volumes.
3. Reduce the timestep scale factor.

How can I reduce my hourglass energy?

A good way to reduce hourglassing is to refine your mesh. The method of loading can affect the degree of hourglassing. A pressure loading is preferred over loading individual nodes as the latter approach is more likely to excite hourglassing modes.

What are the type of contacts commonly used in Dyna?

Single surface. These contact types are the most widely used contact options in LS-DYNA, especially for crashworthiness applications. With these types, the slave surface is typically defined as a list of part ID’s.

Why is DT2MS negative?

The difference between using a positive or negative number for DT2MS in *CONTROL_TIMESTEP is as follows: Negative: Mass is added to only those elements whose timestep would otherwise be less than TSSF*abs(DT2MS) . When mass scaling is appropriate, I recommend this method.

What is DT2MS in LS-DYNA?

When DT2MS is less than zero, LS-DYNA adds mass of each element whose timestep is below abs(DT2MS) such that the element’s updated DT is equal to abs(DT2MS). When DT2MS is greater than zero, LS-DYNA adds mass to elements whose DT is below abs(DT2MS) and “removes” mass from elements whose DT is greater than zero.

What is mass scaling in LS Dyna?

Mass-scaling refers to a technique whereby nonphysical mass is added to a structure in order to achieve a larger explicit timestep. Anytime you add nonphysical mass to increase the timestep in a dynamicanalysis, you affect the results (think of F=m*a ).

What is NaN error in LS Dyna?

Velocities reported as NaN (Not a Number) indicate that the analysis has gone unstable for any number of reasons. Tracking the root cause of NaNs reported late in the calculation can be difficult.

What is element formulation in LS Dyna?

All shell elements include membrane, bending and shear deformation. The default Belytschko-Tsay formulation is the most economical and should be used unless features particular to other formulations are required e.g.: Hughes Liu: can o set the mid-plane of the element away from the nodes.

How do I reduce my hourglass energy in LS-DYNA?

LS-DYNA has various algorithms for inhibiting hourglass modes. The default algorithm ( type 1 ), while the cheapest, is generally not the most effective algorithm. A way to entirely eliminate hourglass concerns is to switch to element formulations with fully-integrated or selectively reduced ( S/R ) integration.

What does Hourglassing mean?

Hourglassing definition (1) Staring at a computer screen waiting for a task to be completed. See hourglass.

How do you avoid negative volume in LS-DYNA?

What is mass scaling in LS-DYNA?

How do you stop Hourglassing?

A way to entirely eliminate hourglass concerns is to switch to element formulations with fully-integrated or selectively reduced ( S/R ) integration. There can be a downside to this approach. For example, type 2 solids are much more expensive than the single point default solid.