initial stress with interface_springback_lsdyna
changp...@ltu.se
James M. Kennedy
Dear Changping,
Much of this has been drawn from the very nice shared notes by Jim Day in the following, regarding several preload approaches:
http://ftp.lstc.com/anonymous/outgoing/jday/bolt_preload3.pdf
http://ftp.lstc.com/anonymous/outgoing/support/FAQ_docs/preload.pdf
The specific manner in which a preload application via dynamic relaxation is made effects the preload transition to the transient analysis phase. An internal load need not be sustained to maintain equilibrium after equilibrium is established in the preload phase; example, *INITIAL_STRESS_SECTION. An external load needs to be sustained to maintain equilibrium of the preloaded phase; examples, *LOAD_THERMAL or *LOAD_BODY (gravity).
Five different preload options are discussed which use *INITIAL_STRESS_SECTION (the bolt stress is specified directly in these preload options):
1. Explicit Dynamic Relaxation (ExpDR)
2. Implicit Dynamic Relaxation (ImpDR) - IDRFLG=5/6
3. Transient Explicit with Mass Damping
4. Transient Implicit/Explicit Single Switch
5. Two Separate Analyses - dynain mods in Transient Explicit
-------------------------------------------
5. Two Separate Analyses - dynain mods in Transient Explicit
Make an implicit (or explicit) simulation of the preload. In the input deck specify *INTERFACE_SPRINGBACK_LSDYNA. This creates an ASCII file called dynain when the simulation is finished. The dynain file contains keyword commands describing the deformed geometry, stresses, and plastic strains. Merge these commands into the original deck, deselect the implicit cards, modify the loads, and run a second, explicit simulation.
The dynain file does not include contact forces nor does it contain nodal velocities. Thus these quantities from the preload analysis do not carry over to the second analysis.
a. Analysis #1 - Preload
*CONTROL_TERMINATION
$# endtim endcyc dtmin endeng endmas
2.000000 0 0.000 0.000 0.000
*CONTROL_IMPLICIT_GENERAL
$# imflag dt0 imform nsbs igs cnstn form zero_v
$ 0 1.000E-1
$ 0 1.000E-2
0 2.000E-3
*CONTROL_IMPLICIT_DYNAMICS
$# imass gamma beta tdybir tdydth tdybur irate
$ 0 0.5 0.25 0.01.00000E281.00000E28 0
1 0.5 0.25 0.01.00000E281.00000E28 0
*CONTROL_IMPLICIT_AUTO
$# iauto iteopt itewin dtmin dtmax dtexp kfail kcycle
0 11 5
$ 1 11 5
*INTERFACE_SPRINGBACK_LSDYNA
$# This creates an ASCII file called dynain when the simulation is finished.
*INITIAL_STRESS_SECTION
$# *INITIAL_STRESS_SECTION will preload a cross-section of solid elements to
$# a prescribed stress value.
$# issid csid lcid psid vid
13 13 2 213 0
14 14 2 214 0
*DEFINE_CURVE_TITLE
$# The preload condition described by implicit solver in this option (Two
$# Separate Analyses) is invoked by setting parameter SIDR in a load curve to 0.
$#
$# Ramp the load during preload phase and then hold load constant until solution
$# converges. Make sure convergence occurs after 100% of preload is applied.
$#
$# The preload stress is just intended to bring the model into a state of pre-
$# load equilibrium. Once that equilibrium is established, it's not necessary
$# to prescribe that stress any longer.
Bolt_Stress
$# lcid sidr sfa sfo offa offo dattyp
2 0 1.000000 1.000000 0.000 0.000 0
$# a1 o1
0.000 0.000
1.000000 218.500
2.000000 218.500
b. Analysis #2 - Initial Velocity
Data added/modified from dynain file of preload analysis:
*NODE (deformed configuration)
*INITIAL_STRESS_SOLID
*INITIAL_STRAIN_SOLID
*CONTROL_TERMINATION
$# endtim endcyc dtmin endeng endmas
2.000000 0 0.000 0.000 0.000
*INITIAL_VELOCITY_GENERATION
$# Apply transient loads AFTER preload is established. Use zero birth time.
$#nsid/pid styp omega vx vy vz ivatn icid
999 3 0.000 175.00000 0.000 0.000 0 4
$# xc yc zc nx ny nz phase iridid
0.000 0.000 0.000 0.000 0.000 0.000 0 0
*INITIAL_VELOCITY_GENERATION_START_TIME
$# Use *INITIAL_VELOCITY_GENERATION_START_TIME for problems whose transient
$# response is driven by initial velocity. For this option, this is zero.
$# stime
0.000001
*DEFINE_COORDINATE_NODES_TITLE
Local_Coordinate_System for impacting part assigned initial velocity
$# cid n1 n2 n3 flag dir
4 5000002 5000001 5000003 0X
Unfortunately, as I understand it, the internal energies of the bolt assembly components are not saved during the solver switch in the two separate analyses. Thus, this result checking (bolt assembly components) cannot be done easily at the analysis switch. However, the stresses in the bolt assembly components, at time=0.0, of the initial velocity analysis seem to match those at the end time of the preload analysis.
Sincerely,
James M. Kennedy
KBS2 Inc.
November 4, 2021
--
You received this message because you are subscribed to the Google Groups "LS-DYNA2" group.
To unsubscribe from this group and stop receiving emails from it, send an email to ls-dyna2+u...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/ls-dyna2/0d76d37d-ad02-4d90-93d6-e065534a4b46n%40googlegroups.com.