Basic steps in impact analysis using LS-DYNA

LS-DYNA can be a great software when doing the explicit analysis or the analysis that happen in fraction of a seconds. These type of analysis involve high impact rate or high strain rate.

LS-DYNA workflow for impact analysis

Everything in LS-DYNA is created as the cards that are represented as the keywords. These keywords represents from geometry, materials to boundary conditions, results and studies.

There are few basic steps that are common in all the dynamic analysis :

• Creating the geometry: The geometry is created using the built-in mesh options or by importing the geometry from CAD software.
• Defining the element type and size: This is done by creating the Section cards. Using this, you can define different mesh parameters of the domains.
• Defining the material: To create the materials, you need to select the Material cards. There are more than hundreds of material models defined within the LS-DYNA.
• Assigning the materials and sections to the parts: Once the material cards and the mesh parameters are defined, now it is the time to assign these values to the domains.
• Assigning the boundary conditions and loading: There are many ways to define the boundary conditions that vary based on the type of the boundaries. Mostly, the Create Entity tab. This provides options to restrains motions along multiple DOFs or to directly implement predefined constraints like welds, riveting, rigid body.
• Defining the velocity of projectile: No dynamic analysis is complete without defining a proper projectile velocity. The velocity is defined in many ways, but commonly Initial card is used to define them.
• Defining the type of contact: One of the most crucial step in the analysis is defining the contacts where there is relative motion between the bodies. This is done using the Contact cards present in LS-DYNA.
• Defining the termination time: Keeping termination (simulation) time too long can increase your computation cost and keeping too low can leave you without complete simulation result. The termination time can defined using the Control cards. In general you can estimate the simulation time by calculating the time travelled by projectile to pass the body.
• Defining the outputs: What data you want to retrieve from the study is defined using the Database cards, this includes the plots, charts, history and tables.

There are hundreds and thousands of problem specific cards present in LS-DYNA. That govern the behavior of material under loading and the response it is generating.

This includes Control cards for defining the energies that needs to be conserved, EOS cards to define the equation of state of various materials etc.

References

• Hypermesh LS Dyna Analysis [SPH Tutorial] - YouTube

• LS-DYNA TUTORIAL 1: Ball Impact on a Plate - YouTube

• Manuals — Welcome to the LS-DYNA support site