Tutorial - Crash Bumper Analysis - Altair University

Copyright © 2013 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Copyright © 2013 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.

Tutorial - Crash Bumper Analysis


Why Crash Analysis?

To find deformation, stress, and energy absorbing capacity of various

structural components of a vehicle hitting a stationary or moving object.

The component is said to be crashworthy (safe) if it meets the plastic strain and

energy targets.

Bumper is one of the components which is used to protect passengers

from front and rear collision.

Bumper crash tests are necessary for instance to calculate the energy

absorption of this component during a crash.


Agenda

Geometry meshing with HyperMesh

Mesh preparations and modifications with HyperCrash

Material creation and assignment

Property creation and assignment

Welding

Mirror to full model

Global contact definition

Load case creation

Model check

Start of simulation


Agenda





Welding



Load case creation

Model check

Start of simulation


Mesh preferences for crash analysis

For crash analysis the preferred element type is hexa over tetra when

using 3D elements, shell elements are used for 2D modeling (as in

the case of this analysis). Follow the mesh flow line requirement and

avoid rotating quads, or diamond element formation.

Constant mesh size is preferred over variable mesh size.

Make sure the element quality matches requirements. Checking

element quality is a good practice.

Element characteristic lengths should allow a reasonable initial time

step.


Mesh preferences for crash analysis

We recommend to also view the

video series by Paul du Bois

(available on the Academic Blog)

http://www.altairuniversity.com/2013/03/01/some-

principles-of-explicit-finite-element-analysis-by-paul-du-

bois-and-altair-engineering-inc-videos/

http://www.altairuniversity.com/2013/03/01/some-principles-of-explicit-finite-element-analysis-by-paul-du-bois-and-altair-engineering-inc-videos/
































Meshing

Start HyperMesh 12.0, select RADIOSS Block user profile

Select

RADIOSS

Block 110

from User

Profiles


Meshing

Open the .hm file

Open

Bumper_System_2012_A.hm


Meshing

Check and configure element type

Go to

2Delement types


Meshing

Configure element type

Select

2D&3D

Set to:

SHELL 3N &

SHELL 4N

Click

return


Meshing

2D Automesh

Go to

automesh

from the 2D

page


Meshing

Mesh geometry with 2D elements using „automesh“ panel

Change the

entitiy selector to

surfaces, double

click and select

all, set element

size to10 mm


Meshing

Export the mesh as a RADIOSS (BLOCK) deck

Export mesh


Agenda





Welding



Load case creation

Model check

Start of simulation


Mesh modifications

Start HyperCrash 12.0 and configure.

Set Working directory

to a suitable location

Choose

RADIOSS V11

Unit system on

kN mm ms kg

Switch GUI to new and

start Hypercrash


Mesh modifications

Import of the Mesh/Model

Import of a

RADIOSS mesh


Mesh modifications

Import of the Mesh/Model

Accept the

transformation of

the unit system


Mesh modifications

Create new assemblies and sort the parts Mark one part

<left click>

Open the

submenu with

<right click>

Choose New

Assembly to

create a new:

BUMPER_BEAM

Repeat the whole

step and name it:

CRASH_BOX_LHS


Mesh preparations and modifications

Create new assemblies and sort the parts

Activate part

selection with box

Select the

BUMPER_BEAM

parts with a box

- Parts will be

selected in tree

Pull the marked

parts with the

<middle mouse

button> to the

assembly

BUMPER_BEAM


Mesh modifications

Create new assemblies and sort the parts

- Activate simple part

selection

- Pick both

CRASH_BOX parts

- Confirm the

selection with yes

- Parts are

selected in the

tree now

Pull the Parts into

the assembly

CRASH_BOX_LH

S using the

<middle mouse

button>


Mesh modifications

Equivalence unconnected nodes

Mesh Editing

Node Modify

Select the parts of

the

BUMPER_BEAM

in the tree


Why equivalence?

To ensure connectivity between the elements, you need to equivalence any

coincident nodes in the model. The equivalence operation identifies any

location where two or more nodes exist within the specified search tolerance.

During equivalence, one of the nodes is retained and any element definitions

referencing the other nodes are re-defined to use the retained node.


Mesh modifications


Add selected parts

of Tree

- Nodes of the

BUMPER_BEAM

are highlighted

Activate Set 1


Mesh modifications


Activate „Set 2“

Add selected parts

of Tree

Nodes of the

BUMPER_BEAM

are highlighted

again

Gap search: 1mm


Mesh modifications


Click on See

node(s) to merge

Now you can see,

which nodes

(highlighted in red)

will be equivalenced

(arrows show the

direction of merging)

Conclude by

clicking Save.

Changes will be

saved in model

and NOT on disk

(HyperCrash does

not have its own

file format)




Switch to Tree

and choose the

first part of

CRASH_BOX_LH

S

To isolate the

selected part(s),

click Isolate Tree

Selection


Mesh modifications


You can change the

view with Display

mode, switch here

to Shaded with

Lines

The perspective

can be switched on

or off by pressing

the key „P“

Zoom to bad-

connected flanges

(using scroll-wheel)


Mesh modifications


Measure the

distance between

these two nodes

(longest distance)

The results appear in

the Message area

Click cancel to close

it


Mesh modifications


Connect each set of

nodes (you have to

confirm with enter

every time)

Go to Mesh Editing

Node Modify“

To finish this step,

press Close


Mesh modifications


Go to Mesh

EditingMove

and select the

suitable nodes

Problem: deformed

mesh

Finish the selection

with Yes


Mesh modifications


Movement plane

Left click on the red

node and pull till you

find a visually

improved mesh

Finish with Yes

Mesh is now

perpendicular


Mesh modifications


Switch to Tree and

choose the second

part of

CRASH_BOX_LH

S

To isolate this

part, click

Isolate Tree

Selection


Mesh modifications


Measure

maximum

distance (in this

case: 1.9999)

Finish Measuring

by clicking

Cancel

Merging occurs

automatically




Go to Merge multi

Then click on Set

1, and click on

add selected part

of Tree, repeat the

same for set 2

input gap search

2mm and click

See to visualize

confirm with save

and Close

afterwards


Mesh modifications

Global depenetration

Show all using

Display All (or

CTRL+S) and

zoom in with Fit

Model (or

CTRL+R)

Menu LoadCase

Contact Interface


What are penetrations and intersections?

Penetration is defined as the overlap of the material thickness of shell

elements, while Intersection is defined as elements that actually pass

completely through one another

All models and especially impact models should be checked for

penetrations and intersections and depenetrated to ensure the

integrity of the model

Penetrations adversely affects results and should be removed


Mesh modifications


Create a new

object Multi

usage (Type 7)


Mesh modifications


Activate Self

Impact checkbox

for autocontact

Add selected

parts by box


Mesh modifications


Input „1“ at Min. gap

for impact

activ.(check next

slide for Gap input

options).

Save and Close


Intersection-penetration check

HyperCrash checks for intersections and penetrations. The list of

intersecting nodes is displayed at the bottom of the menu.

To find and to correct the penetrations use the “variable gap” or a

“constant gap” option.

1.The variable gap option (if "Gap_interface" = "variable")

searches and corrects the penetrations taking into account the

actual thickness' of the plates (coming from the PID).

2.The constant gap option (if a value for "Gap_interface" is

entered) uses a (user-defined) fixed value to search and correct

the penetrations (the value can be the gap of the interface, for

instance).


Mesh modifications


Menu: Quality

Check All Solver

Contact Interfaces

VERY IMPORTANT

and USEFUL

FUNCTION !!!

Use it as often as

you modify

mesh/model


Mesh modifications


Searching for

Intersections and

Penetrations (if some

found, the number

will be displayed).

After selecting

intersection from list,

it will be shown

highlighted in a

transparent model

Zoom to it as near

as necessary

Isolate Crashbox

1. Correct

INTERSECTIONS

(because it’s more

difficult)


Mesh modifications


- With Move nodes

1 by 1 move the

intersection node

away

- Afterwards confirm

two times with Yes

and Close.


Mesh modifications

Global depenetration (it is strongly recommended to remove the intersections before

removing the penetrations)

Recheck for

Intersections and

Penetrations

(Quality Check All

Solver Contact

Interfaces)

- There shouldn‘t be

any intersections,

now.

Assign all

penetrations and

display all

2.Correct

Penetrations

(very easy)


Mesh modifications


Select the parts

which are not

allowed to be

modified (Fixed

parts).

Depenetrate auto


Mesh modifications


LoadCase

Contact Interface


Mesh modifications

Global depenetration: delete temporary contact interface

Select Contact and

Delete selected

item(s)

Close


Agenda





Welding



Load case creation

Model check

Start of simulation



Crashbox Material (Steel) generic DP600

Model Material

Pick this Crashbox

Parts from the

Tree




Creates a new

object Elasto-

plastic

Johnson_Cook

(LAW 2)


Why Johnson_Cook (LAW 2)?

This is an elasto-plastic material which includes strain rates and

temperature effects (stress vs plastic strain law)

The yield stress is converted into true stress

In this law the material behaves as linear elastic when the equivalent

stress is lower than the yield stress. For higher stress values the

material behavior is plastic.

Note: find a summary on true

stress – strain vs. enginering

stress – strain in the Student

Guide (Chapter 13.4)



Include picked

parts and select

both parts of the

Crash Box

Yes to confirm





Click Save



Bumper Beam Material (Steel) generic DP1000

Creates a new

object Elasto-

plastic

Johnson_Cook

(LAW 2)




Go to Tree

Choose all parts of

the

BUMPER_BEAM

and turn back to

Material




Add selected parts

of Tree




Add simple Failure

criteria

(deletion at

equivalent plastic

strain of 30%)

Finish this with

Save


Agenda





Welding



Load case creation

Model check

Start of simulation



Crashbox Shell element definition (thickness = 2.2 mm ) and assignment

Select Crash Box

parts out of the tree




Model Property

Creates a new

object Surface

Shell (1)




Add Selected Parts

of Tree




Save to finish input

Best choice

for crash



Bumper Shell element definition (thickness = 1.8 mm ) and assignment

Creates a new

object Surface

Shell (1)




Use Include picked

parts to select the

front and horizontal

parts in the middle of

the Bumper_Beam

(not the rear Bumper

Beam sheet)

Confirm with Yes




End with Save


Why QEPH shell formulation?

QEPH (Quadrilateral ElastoPlastic Physical Hourglass Control) element

With one-point integration formulation, if the non-constant part follows exactly

the state of constant part for the case of elasto-plastic calculation, the

plasticity will be under-estimated due to the fact that the constant equivalent

stress is often the smallest one in the element and element will be stiffer.

Therefore, QEPH, defining a yield criterion for the non-constant part seems to

be a good ideal to overcome this drawback.

QEPH shells are more accurate for elastic or elasto-plastic loads, whatever

the loading type - quasi-static or dynamic.

QEPH shells will give better results if the mesh is fine enough. It is not

recommended for coarse mesh.




Creates a new

object Surface

Shell (1)




With Include

picked parts

select

Bumper_Beam

Rear part

Finish with

Yes




End with Save


Why use 5 integration points in the thickness

of shell elements?

In case of an elastic behavior, one gets the exact solution from three

integration points – that is to say that the bending moments are exactly

integrated through the thickness of the shell – and it is not necessary to use

more integration points.

In case of a plastic behavior, the bending moments are not integrated

exactly. Using more integration points, the solution becomes more accurate;

so it is recommended to use five integration points.



Shell element definition and assignment

Plausibility check:

Are all properties

created and

assigned ?

End property menu

with Close


Agenda





Welding (SPOTWELDS)



Load case creation

Model check

Start of simulation


SPOTWELDS

Connection of Crash-Box upper with Bumper-beam

Rotate the model

to see its rear

parts

Choose

Connections

Spotweld Create


SPOTWELDS

Connection of Crash-Box upper with Bumperbeam

Include picked parts

Select both parts

(bumper rear and

crash box upper).

Selected parts

are highlighted in

red

Confirm selection

with Yes


SPOTWELDS


Pick a point and

see spotweld and

click on marked

elements to give the

Spotwelds the right

position

Every Spotweld has

to be confirmed with

Enter

Save to save the

spotwelds in the

model

Cancel

Now repeat the same steps with the lower part of the Crash Box)


SPOTWELDS


Choose Include

picked parts

Pick both

Crash-Box parts

(crash-box

upper and crash

box lower)

Validate with Yes


SPOTWELDS


Line and type in 30

for the Pitch length

(distance between

spotwelds)

Click at Beginning-

Point and End-Point

for SPOTWELD line

Confirm with Save.

Follow the same

procedure at the

other side


SPOTWELDS


Spotwelds are mesh

independent. These

are modeled using

spirng elements with

both sides of the

spring linked with

mesh using tied

interface.


Agenda





Welding (SPOTWELDS)



Load case creation

Model check

Start of simulation


Mirror preperation

Save your model (“File” “Export” „RADIOSS…“)

Open the saved location and delete the *.M00 file

Import the ..000.rad file back in HyperCrash to mirror.

In order to mirror elements and spotwelds, follow the below:



Duplicate all parts with all options

Select: Mesh Editing

Part Duplicate

Mark the highest

model hirarchy



Duplicate all parts with all options

Mirror

Include selected

parts of Tree

Apply Mirror

Save and Close

Mesh + all options



Equivalence at mid/mirror plane

Attention:

Nodes at the

midplane ar NOT

equivalenced

already!

New assembly:

Duplicated Parts

was created




Mesh Editing

Node Modify

Select the new

(duplicated)

BUMPER BEAM

from the tree




Add selected parts

of Tree

Merge multi

Nodes of the new

(duplicated)

bumper are

highlighted

Switch back to the

tree selection




Switch back to

Mesh Editing

Select the old

BUMPER BEAM




Add selected parts

of Tree (Nodes of

the original

BUMPER BEAMS

are highlighted)

Select Set 2

Type „1“ in gap

search to merge




Click See node(s)

to merge

and rotate graphics

area to verify the

nodes to merge

Click Save to

confirm

Close




Connections

Spotweld Extract

from Model




Connections

Spotweld Modify




Use

Select/Unselect all

spotweld(s) to

select all spotwelds

of the list

Display all

spotwelds using the

tool See selected

spotweld(s)

All O.k.?

Then go for

close


Agenda





Welding (SPOTWELDS)



Load case creation

Model check

Start of simulation


Global Contact Definition

Interface properties for penalty contact definition

Choose highest

level in Tree to

select all (shell

meshed) parts

LoadCase

Contact

Interfaces

Create/Modify




Creates a new

object Multi

usage (Type 7)


Why type 7? What is interface gap?

This interface simulates the most general type of contacts and impacts

Impacts occur between a master surface and a set of slave nodes.

All limitations encountered with interface types 3, 4 and 5 are solved with this

interface.

It is a fast search algorithm without limitations.

Interfaces have a gap that determines when contact between two segments

occurs. This gap is user defined, but some interfaces will calculate an

automatic default gap.




Activate

Self-Impact

Add selected parts

of Tree (all shell

parts should be

selected




End with Save

and Close


What is coulomb`s friction law?

Type 7 interface allows sliding between contact surfaces. Coulomb friction

between the surfaces is modelled.

Coulomb’s friction law is a classic friction law which states that frictional force

= coeff of friction*force acting on the object [Ff= µ*F]. Example - a block

sliding on an inclined plane.

It states that the Kinetic friction is independent of the sliding velocity.

The Coulomb approximation mathematically follows from the assumptions

that surfaces are in atomically close contact only over a small fraction of their

overall area, that this contact area is proportional to the normal force

(until saturation, which takes place when all area is in atomic contact), and

that frictional force is proportional to the applied normal force, independently

of the contact area .


Agenda





Welding (SPOTWELDS)



Load case creation

Model check

Start of simulation


Load case creation

Create rigid body

Switch to XY View

Press the „P“ key

to turn off the

perspective!


What is a rigid body?

A rigid body is an idealization of a solid body in which deformation is

neglected. In other words, the distance between any two given points of a

rigid body remains constant in time regardless of the external forces exerted

on it.

Rigid body elements are used to

- impose equal displacement to a set of nodes;

- model rigid connections and pin-joints;

- enforce symmetry;

- model transitions, connections, spot-welds, seam-welds between non-

matching (dissimilar) meshes;

- distribute concentrated loads/masses to a set of nodes


Load case creation

Create Rigid body

Mesh Editing

Rigid Body

Create


Load case creation

Create Rigid body

Name RigidBody

and Ok

Add nodes by box

selection and pull

a box over the last

row of crashbox

nodes


Load case creation

Define vehicle mass component to partially take into account the inertia

properties and mass of the missing parts of the vehicle Adjust

Properties of

rigid body:

Save and

Close


Load case creation

Define vehicle mass component to partially take into account the inertia

properties and mass of the missing parts of the vehicle Display Graphic

Objects On/Off

Rigid Bodies.

To simplify the

model, several of

the components are

not modelled to

save time and cost.

Instead they were

represented as a

point mass and rigid

bodies.


Load case creation

Rigid body – Boundary Condition definition

LoadCase

Boundary

Conditions

Create


What is a boundary condition?

A boundary condition is simply the load applied to the system.

Boundary conditions are an approximation of the actual physical conditions

the system experiences and should match reality as closely as possible.

Boundary conditions include forces, imposed velocities and accelerations,

pressure loads, constraints on the movement of certain nodes, etc.


Load case creation

Rigid body – Boundary Condition definition

Name this

boundary condition

Ok

Add/Remove nodes

by picking and

select the Master

Node of the

RigidBody

Select all degrees

of freedom except

the translation to

x(Tx)

Save


Why Translation to TX not chosen?

In this case the boundary condition being created is to constraint he

movement of the component in unwanted directions.

We do not constrain movement in the TX direction or Translation in the X

direction, because we need the bumper to move in this direction for our

simulation, this also reflects the reality of its movement.


Load case creation

Boundary Condition definition

Display Graphic

Objects

On/Off Boundary

Conditions.


Load case creation

Gravity Load

LoadCase

Gravity Load


Load case creation

Gravity Load

Give name and

Ok

Record data:

t = 0

9.81e-3

t = 100

9.81e-3

Save

Define time function


Load case creation

Gravity Load

Choose Add all

nodes

Pick „Z“ as

direction

„-1“ for the negative

„Z“-direction

Save and Close


Load case creation

Gravity Load

Display Graphic

Objects On/Off

Gravity


Load case creation

Initial velocity definition

LoadCase Initial

Velocities


Load case creation


Name and „Ok“

Add all nodes

„-5“ (m/s) in X-

direction

Save and Close


Load case creation


Display Graphic

Objects

On/Off Initial

velocities


Load case creation

Rigid Wall definition

LoadCase

Rigid Wall

Create


What is a rigid wall?

A rigid wall is a nodal constraint applied to a set of slave nodes in order to

avoid the node penetration to the wall. If contact is detected, then the slave

node acceleration and velocity are modified.

Mainly to constrain movement of a moving body after impact, We will be using

a cylindrical wall.

An infinite cylindrical wall is a cylinder which extends to infinity. It is defined

with two points (or one point and one node) and a diameter. Note that contact

is only possible from outside the cylindrical wall.


Load case creation

Rigid Wall definition

Select Rigid wall

type Cylinder

Take over the

properties

See, Save and

Close


Load case creation

Definition of Accelerometer for post processing

Data History

Accelerometer

Create

The accelerometer

option computes a

filtered acceleration

in the output system


Load case creation


Name „Ok“

Select with Pick

nodes to add one

node to be defined

as accelerometer

Cut off frequency of

1.650 (=1650 Hz)

equates:

CFC1000 filtering

Save and Close


Load case creation


Data History

Section Create


Load case creation


Type Name Ok

Select both

Crashbox parts

using Include

picked Parts

Conclude with Yes


Load case creation


Define section

plane with 3

nodes

Adjust with shells

and nodes

correct the

section plane


Load case creation


Type the name

Ok

Before: Afterwards:

Save


Agenda





Welding (SPOTWELDS)



Load case creation

Model check

Start of simulation


Model Check

Clean model

Mesh Editing

Clean


Model Check

Clean model

Clean and Close

Review the

checkboxes


Model Check

Interface Checker

Quality Check All

Solver Contact

Interfaces


Model Check

Interface Checker

Results should

look like:

0 Intersections

and

0 Penetrations

Penetrations (not

Intersections) can

be dissolved

automatically by:

Depenetrate auto

Close


Model Check

Model Checker

MOST important

Function (ALWAYS

to use before the

export of the

model):

The Model

Checker


Model Check

Model Checker

Most Warnings can

be ignored or be

resolved

automatically.

(Beware of Errors

Must be solved)

Close


Agenda





Welding (SPOTWELDS)



Load case creation

Model check

Start of simulation


Simulation

RADIOSS (BLOCK) is the solver used for solving non-linear implicit and

explicit problems.

HyperCrash/RADIOSS essentially writes out starter file and Engine file.

Engine files are used to set up the model, including termination times, output

requests, and other checks that control the execution of the job.

Starter file contains actual model definition. Engine file executes the actual

computation.


Simulation parameters

Control Card

Model Control

Card


Simulation Parameters

Control Card

take required

settings



Make sure to save every setting before

you move to the next Control Card

Defines the time for running

Writes animation files at a time frequency

of 5 and the start time is 0

Writes a time history file. the time at which

the time history file begins.


Generates animation file which contains

element data for specified results (Energy

desity, hourglass energy, etc…)

Writes nodal scalar data (mass, inertia,etc)

Writes vector data (velocity, acceleration, etc..



Export model

Export Model

Select File

Export

RADIOSS…


Export model

Export Model

Choose path…

Give file

name…


Export model

Create/export starter file with model (_0000.rad)

Possibility to write

comments and/or

model evolution

into model file

(Start with „#“ at

beginning of every

row for comment)

Save Model


Start RADIOSS

Start model

START

Programme

Altair…

RADIOSS


Start RADIOSS

Start model

Select working

directory

Choose:

RADIOSS

Version

(Starter and/or

Engine)

Number of

CPUs

Run


Start RADIOSS

Start model

RADIOSS Starter

announces:

0 ERROR(S)

0 WARNING(S)

RADIOSS Engine

starts the

simulation and

writes Animation

files


Post processing

Model post processing with HyperView

Open animation

files (also during

simulation

possible)

With Load Model

Play animation

Documents

Tutorial - Crash Bumper Analysis - Altair University