The fluid-structure interaction and the fluid flow are studied in cases of a fuel tank sloshing and overturning. A
bi-phase liquid-gas material with an ALE formulation is used to define the interaction between water and air in the
fuel tank.
The purpose of this example is to study the energy propagation and the momentum transfer through several bodies, initially
in contact with each other, subjected to multiple impact. The process of collision and the energetic behavior upon
impact are described using a 3-dimensional mode.
The impact and rebound between balls on a small billiard table is studied. This example deals with the problem of
defining interfaces and transmitting momentum between the balls.
After a quasi-static pre-loading using gravity, a dummy cyclist rides along a plane, then jumps down onto a lower
plane. Sensors are used to simulate the scenario in terms of time.
The problem of a dummy positioning on the seat before a crash analysis is the quasi-static loading which can be resolved
by either Radioss explicit or Radioss implicit solvers.
The crashing of a box beam against a rigid wall is a typical and famous example of simulation in dynamic transient
problems. The purpose for this example is to study the mesh influence on simulation results when several kinds of
shell elements are used.
A square plane subjected to in-plane and out-of-plane static loading is a simple element test. It allows you to highlight
element formulation for elastic and elasto-plastic cases. The under-integrated quadrilateral shells are compared with
the fully-integrated BATOZ shells. The triangles are also studied.
The modeling of a camshaft, which takes the engine's rotary motion and translates it into linear motion for operating
the intake and exhaust valves, is studied.
The ditching of an object into a pool of water is studied using SPH and ALE approaches. The simulation results are
compared to the experimental data and to the analytical results.
A rubber ring resting on a flat rigid surface is pushed down by a circular roller to produce self-contact on the inside
surface of the ring. Then the roller is simultaneously rolled and translated so that crushed ring rolls along the
flat surface.
Polynomial EOS is used to model perfect gas. Pressure or energy can be absolute values or relative. Material LAW6
(/MAT/HYDRO) is used to build material cards for each of these cases.
Separate the whole model into master domain and sub-domain and solve each one with its own timestep. The new Multi-Domain
Single Input Format makes the sub-domain part definition with the /SUBDOMAIN keyword.
The Cylinder Expansion Test is an experimental test used to characterize the adiabatic expansion of detonation products.
It allows determining JWL EOS parameters.
The aim of this example is to introduce /INIVOL for initial volume fractions of different materials in multi-material ALE elements, /SURF/PLANE for infinite plane, and fluid structure interaction (FSI) with a Lagrange container.
A heat source moved on one plate. Heat exchanged between a heatsource and a plate through contact, also between a
plate and theatmosphere (water) through convective flux.
Impacts of rotating structures usually happen while the structure is rotating at a steady state. When the structure is
rotating at very high speeds, it is necessary to include the centrifugal force field acting on the structure to correctly
account for the initial stresses in the structure due to rotation.
Failure criteria defined in material LAW2 and LAW27.
In Radioss, one simple way to define material failure is
by defining a failure strain in the material definition. In this example, a maximum
plastic strain is defined in LAW2 and compared to LAW27 which uses a
damage model based on strain. A model with one shell element is used to understand
the failure definition. In a second model a metallic thick plate is perforated by a
rigid sphere.
A one shell element is used to demonstrate the failure model.
The material undergoes an isotropic elasto-plastic behavior which can be reproduced
by a Johnson-Cook model.
Material properties are:
Young's modulus
71000
Poisson's ratio
0.3
Density
2.8 x 10-3 g/mm3
Yield stress
290
Hardening parameter
562.3
Hardening exponent
0.63
Maximum stress
425
The maximum stress and the failure plastic strain are considered in the failure
modeling section. The strain rate effect is not taken into account in this example.
Although LAW2 and LAW27 both use a Johnson-Cook material model for elasto-plastic
behavior, the failure definition included in the material law is different.
LAW2: Use Plastic Strain for Failure
In LAW2, the maximum plastic strain used for element failure. This means the shell element is
deleted once it reaches the maximum plastic strain defined in the model. Unlike
LAW27, there is no damage before failure and the failure can occur in both tension
and compression.
LAW27: Use a Damage Model
LAW27 is used to simulate material damage using a Johnson-Cook plasticity law. A
damage model is incorporated into the material law to take into account the damage
evolution where stress decreases up to element rupture. When using the material
failure included in LAW27, the failure and damage occur only in tension and not
compression.
The damage parameters in the principal direction are .
; ;
When the principal strain reaches , the material damage starts, based on the damage
face and , which are given by:(1)
In directions, .
The stress is then reduced using the damage parameter, .
The damage factor in the first principal direction is a function of principal
strain:(2)
Results
One Element Shell Model
In order to show the difference between LAW2 and LAW27, uniaxial and eqibiaxial loads
are applied to a one element shell model.
Test 1: Uniaxial test
With
In LAW27, are total strain.
In LAW2, is plastic strain.
In one shell element set:
In LAW27,
In LAW2,
So that element deleted at same strain.(3)
Although the element is deleted at same strain
the internal energy at failure is different for LAW2 and LAW27, due to
the difference the failure treatment.
Test 2: Equibiaxial test
The failure strain values from the uniaxial test
are used in a equibiaxial test.
In LAW27,
In LAW2,
In biaxial loading, the element deletion is different for LAW2
and LAW27, due to different failure treatment in LAW2 and LAW27. In
LAW2, the element is deleted when is reached in the element. The change in
plastic strain is:(4)
In LAW27, the element is deleted when the strain in each principal direction exceeds . The first principal strain in LAW27
is:(5)
The second principal strain is calculated in a similar manner.
Plate Impact Model
If the previous failure strains definitions in a plate example is used, the results
are also different.
The previous one element biaxial tension test showed the differences in LAW2 and
LAW27 in tension. Since LAW27 does not fail in compression, but LAW2 does fail in
compression, this causes a difference in the plate example shown in Figure 7.
Note: The property option Istrain =1 must be defined, so that the strains are calculated and
output for post-processing. This can be defined for all shell elements using
/DEF_SHELL.
During the simulation, time of element failure is written to the Engine output file
runname_0001.out.
For LAW2, the message is: RUPTURE OF SHELL ELEMENT NUMBER
#
For LAW27, the message is: TOTAL ELEMENT TENSION FAILURE, ELEMENT
#
Conclusion
Although LAW2 and LAW27 both use Johnson-Cook to describe elasto-plastic behavior, they use
different failure treatment. LAW2 checks with plastic strain and LAW27 checks with
principal strain. LAW27 uses damage parameter d
to produce linear failure; which makes it difficult to get the same failure behavior
between them.