In any wave propagation code, such as LS-DYNA, which belongs to a family of ‘Hydro’ codes, bulk viscosity is essential to treat shocks. Smooth initial data can lead into shock discontinuities and if left untreated can result in severe instabilities. LS-DYNA has the capability (performed by default) to automatically detect the shocks and treat them…
The widely popular material model *MAT_PIECEWISE_LINEAR_PLASTICITY (MAT_024) supports various methods to include the strain-rate effects. One of the methods is the scaling of the quasi-static stress-strain curves using a load-curve, LCSR, that defines a scale-factor as a function of strain-rate. This method works by first finding the yield-stress, SIG_QUASI_STATIC, as a function of the effective…
Seatbelt constitutive model, invoked by using *MAT_SEATBELT, in LS-DYNA provides features to model the loading and unloading characteristics from a uni-axial test. Parameter LLCID provides ability to model the loading curve which allows the definition of force as a function of engineering strain. Parameter ULCID, provides ability to model the unloading curve again allowing the…
When characterizing materials such as Metals and Plastics in LS-DYNA, most constitutive models provide a yield criteria that accounts for a 3D state of stress which reduces to a uniaxial yield stress in 1D. This allows us to directly input the true stress-strain curve from a one-dimensional state of stress testing such as in uniaxial…
In several situations, simulation models (new or inherited), are quite often burderend with several expensive features that may have negligible effect on the response that is purely used for comparative numerical studies. When a large portion of any simulation model turnaround time consists of features that are irrelavant to the focued study, it is imperative…
1. Introduction Contact definitions allow the modeling of interaction between one or more parts in a simulation model and have become a necessity in any small or large deformation problem. The main objective of the contact interfaces is to eliminate any “overlapâ€? or “penetrationâ€? between the interacting surfaces and they accomplish this by first detecting…
LS-DYNA offers several ways to prescribe a motion to a rigidbody using *BOUNDARY_PRESCRIBED_MOTION keyword. To prescribe a motion to a rigidbody along a local coordinate system, LS-DYNA offers two method to accomplish this. To demonstrate the differences in these two methods, we will consider a rigidbody that has initial rotational velocity and a prescribed displacement.…
Over the years, spotweld representation for crash and NVH applications have evolved from a crude to a detailed modeling resulting in reduced pre-processing effort while greatly enhancing the accuracy of numerical models. Here is link that gives a brief overview of spotwelding process in LS-DYNA. Please note that the document is over 2 years old…
In many designs, parts are often press-fitted as part of an assembly which causes an initial stress condition that is important to consider in simulations. To induce initial stresses that occur in such press-fit conditions, one can either linearly/non-linearly scale the overlap (penetration) or the contact stiffness over a certain interval depending on the following…
When running problems using Implicit solution sheme in LS-DYNA, the default iterative non-linear solver used is the BFGS method that employs a ‘Quasi-Newton’ method in which the global stiffness matrix is reformed only every ILIMIT steps and in between these a relatively inexpensive update to the stiffness matrix is performed. This default stiffness matrix update…
