While converting true-stress vs true-strain curve into effective stress vs effective plastic strain, the removal of elastic strains can be based on a constant or varying strain value. For relatively small hardening, both methods should yield identical plastic strains but significant hardening, using an instantaneous elastic strain as opposed to a constant elastic strain is…
In an earlier post on simulation based product design we saw that in many cases a large portion of effort early on in the design cycle is usually spent on determining the best practices to simulate a physical event. We can speed up such simulations by the discrete variable support in LS-OPT version 3.1. An…
Here is a simple way to prescribe sinusoidal motion using *DEFINE_CURVE_FUNCTION. *PARAMETER ramp, 10.0 rfreq, 600 rshift, 0.0 *DEFINE_CURVE_FUNCTION curve_id &*sin(&freq*TIME+&shift) The parameter “amp” is the amplitude, “freq” is the frequency of the oscillation (2PI/T, T is the time period), and “shift” is the phase shift. TIME is the simulation time that will be replaced…
There are three different ways to model unloading behavior when using material model MAT_083. They are graphically depicted below (these figures may appear in the next release of the LS-DYNA keyword and theory manual). Option 1 – Default (Click image to enlarge) In the default option (1), HU=0, and the table is positive which then…
A short presentation on the Explicit and Implicit time integration schemes which I use in my advanced LS-DYNA class is included here. Its a evolving document but the latest version is available for download. Time Integration (PDF, 346 Kb) Note: Fixed the corrupted PDF file. Sorry for the inconvenience.
LS-DYNA allows several ways to model of stress relaxation often seen in viscoelastic materials when subjected to a sudden constant strain. The methods to model the stress relaxation is briefly discussed here. 1. Curve Input When using MAT_GENERAL_VISCOELASTIC material model, one can directly input the time log dependence of the relaxation modulus using LCID parameter.…
A modified version of the NHTSA finite element model of the USSID is now available at no charge. LSTC USSID version 1.0 (LSTC FTP site) LSTC USSID
SPH is now widely used in several high strain-rate and large-deformation problems which may otherwise be difficult to simulate when using traditional mesh based approaches. LS-DYNA allows mesh-based and mesh-free techniques such as SPH to exist and interact in one simulation allowing users to take advantage of both procedures. The interaction or coupling between the…
Interface component analysis is a unique feature that helps to speed design variation studies for non-structural components using a model fragment of the full system model. It works by first storing the displacement time history of user-defined nodes to a disk on a file system. The stored file is a binary file and its name…
A powerful feature of LS-DYNA v970 and beyond that has yet to gain widespread popularity is the *CASE keyword. Here are two examples to highlight the use of *CASE. Sequential and Independent Simulations Ex: Head Impact (FMVSS 201) *keyword $ $ Impact 1 $ *case_begin_1 *title position 1 impact *include vehicle_model.i *include head_position_1.i *case_end_1 $…
