Finite ElementCrash & Impact Analysis

LS-DYNA Project

Ran Wang

2016/4/7

Project

Wang Ran, University of Windsor 04/07/2016

Contents

1 Introduction 2

2 Problems observed 22.1 Contact Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.2 Hourglass control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.3 Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3 Method to improve 53.1 Aiding new contact definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63.2 Hourglass control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.3 Energy balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4 50 percent offset crash test 12

5 Head injury criteria 135.1 Full wall crush . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135.2 Half wall crush . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Course Project Page 1 / 14

1 Introduction

In this project, a crush simulation has been set up but there are some improvements needed to be done inorder to enhance the simulation quality.

2 Problems observed

2.1 Contact Problem

There are three contact parts penetrate with its counterparts during the crush.

1. Legs with legs

Figure 1: Penetration between legs

2. Hands with the front window

Figure 2: Penetration between hands and windows

3. Legs with cabin


Figure 3: Penetration between legs with cabin

4. Belt normal

Figure 4: Penetration between belts

I also check the normals of the belt and I find that some normal directions are not right.

Figure 5: Belt normals

2.2 Hourglass control

Because of the coarse mesh, some parts of the car has unreasonable deformations. Following figure showsdeformation of the radiator-MTG at 140 msec.


Figure 6: Unreasonable deformation

The simulations are always terminated because of the elements of this part. Following is the hourglassenergy.

Figure 7: hourglass energy of part 3016

From this figure, there is negative hourglass energy which is not reasonable.

2.3 Energy

The energy balance of the rigid wall does not make sense.

Figure 8: Original energy balance of the rigid wall

From the figure 4, the energy balance starts to become unusual after 60s in the simulation. The slidingenergy start to decrease and become negative. There must be something can be done to improve this issue.


3 Method to improve

First of all, it needs to careful check the contact definition in this model. Following is the first of theoriginal contact define given by professor.

1. SINGLE_SURFACE contact

*CONTACT_AUTOMATIC_SINGLE_SURFACE

$# SSID MSID SSTYP MSTYP SBOXID MBOXID SPR MPR

8011 0 2 5 0 0 0 0

$# FS FD DC VC VDC PENCHK BT DT

0. 0. 0. 0. 0. 0 0. 0.

$# SFS SFM SST MST SFST SFMT FSF VSF

0.1 0. 0. 0. 0. 0. 0. 0.

$# SOFT SOFSCL LCIDAB MAXPAR EDGE DEPTH BSORT FRCFRQ

2. 0. 0. 0. 1. 0. 0. 0.

$# PENMAX THKOPT SNLOG ISYM I2D3D SLDTHK SLDSTF

0. 0 0 0 0 0. 0.

Focus on this line:



8011 0 2 5 0 0 0 0

SSID 8011 includes all the part of the car except some part ID and these part can be visualized as thefollowing figure.

Figure 9: SINGLE_SURFACE contact slaves excluding parts

MSID is equal to 0. This means that including all other part.

2. Contact between dummy and some parts of the car

The k-word is shown in the following.

*CONTACT_GEBOD_LOWER_TORSO

$ DID SSID SSTYP SF DF CF INTORD

1 20 2 1.0 20.0 0.3 2


$ BT DT SO

0.0 1.0E+20 0

SSID is 20, and it can be visualized as following:

Figure 10: Slave parts(contact between dummy and some parts of the car)

As you can see, the penetrations mainly occur between the dummy and this part of the car. Someimprovements will be done in this part.

3.1 Aiding new contact definitions

1. Leg with leg

A new contact has been defined in the following k-word:


*CONTACT_AUTOMATIC_SURFACE_SURFACE


8012 8013 2 2 0 0 0 0


0. 0. 0. 0. 0. 0 0. 0.


0.1 0. 0. 0. 0. 0. 0. 0.


2. 0. 0. 0. 1. 0. 0. 0.


0. 0 0 0 0 0. 0.

The part represented by SSID and MSID can be visualized as:

Figure 11: Slave and master parts(A new contact between the right leg and the left leg)

2. Arm with arm

Using the same k words, I also define the contact between the left arm with the right arm.

Figure 12: Slave and master parts(A new contact between the right arm and the left arm)



8014 8015 2 2 0 0 0 0


3. Hands with the front window

Again, using the same method, we can define contact between hands with the window.

Figure 13: Slave and master parts(A new contact between the hand and the window)

4. Legs with cabin

Again, using the same method, we can define contact between feet with the cabin.

Figure 14: Slave and master parts(A new contact between the feet and the cabin)

After done those new contact definitions, the penetrations disappear.

5. Belt

Firstly, I invert all the normals.


Figure 15: After invert normals

I also define a new contact between belt and the dummy.

*SET_PART

$# SID DA1 DA2 DA3 DA4

8020 0. 0. 0. 0.

$# PID1 PID2 PID3 PID4 PID5 PID6 PID7 PID8

3063 3064 3065 3066 3080

$##BeltGeobody_Upper



8020 2999 2 3 0 0 0 0


0 0 0. 0. 20. 0 0. 0.


1 1 0. 0. 0. 0. 0. 0.


1. 0. 0. 0. 2. 0. 0. 0.


0. 0 0 0 0 0. 0.

The belt it self may also contact with itself. So a sing-surface contact is also defined for the belt.

$##BeltSelf



2999 0 3 5 0 0 0 0


0 0 0. 0. 20. 0 0. 0.


1 1. 0. 0. 0. 0. 0. 0.



1. 0. 0. 0. 2. 0. 0. 0.


0. 0 0 0 0 0. 0.

3.2 Hourglass control

Because we can not change the mesh of the part. There are two ways to improve hourglass. The first oneis using hourglass control card for a specific part. The second one is using full integration element.

*HOURGLASS

$# HGID IHQ QM IBQ Q1 Q2 QB/VDC QW

1 5

*PART

$# HEADING

SHELL: RADIATOR-MTG

$# PID SECID MID EOSID HGID GRAV ADPOPT TMID

3016 3016 3016 0 1 0 0 0

The second way is to use different element formulation.

*SECTION_SHELL

$# SECID ELFORM SHRF NIP PROPT QR ICOMP

3016 2 0. 3. 0. 0. 0

$# T1 T2 T3 T4 MAREA

1.1 1.1 1.1 1.1 0.

ELFORM 2 is Belytschko-Tsay formulation. I choose another one: ELFORM 16(full integrated shellelement). Following is the result.

*SECTION_SHELL

$# SECID ELFORM SHRF NIP PROPT QR ICOMP

3016 16 0. 3. 0. 0. 0

$# T1 T2 T3 T4 MAREA

1.1 1.1 1.1 1.1 0.

Figure 16: After define hourglass control and change element formulation. Part 3016 at 140 msec


Figure 17: After define hourglass control and change element formulation. Hourglass energy of part 3016

3.3 Energy balance

By carefully checking key word from the professor, I find this part is interesting:



8011 0 2 5 0 0 0 0


0. 0. 0. 0. 0. 0 0. 0.


0.1 0. 0. 0. 0. 0. 0. 0.


2. 0. 0. 0. 1. 0. 0. 0.


0. 0 0 0 0 0. 0.

Especially this line:


2. 0. 0. 0. 1. 0. 0. 0.

This is the key word manual(May 2007 Version 971) on page 394.

Figure 18: key word manual(May 2007 Version 971) on page 394

There is no variable called EDGE. Instead, it means SBOPT(Segment-base contact options) when


SOFT=2. When this variable is set as 1, it means this is a pinball edge-edge contact, which is not rec-ommended by user’s manual. I change it to 2(assume planner segments). After running the simulationagain, I get a new energy balance curve which is much better than the previous one. The sliding energyalmost remains zero.

Figure 19: Inprove Energy balance

4 50 percent offset crash test

This test can be achieved by changing the definition of the rigid wall. The k words are shown in thefollowing:

*RIGIDWALL_PLANAR_FINITE

$# NSID NSIDEX BOXID OFFSET

0 0 1 0.

$# XT YT ZT XH YH ZH FRIC

4700. 0. 0. 0. 0. 0. 0.3

$# XHEV YHEV ZHEV LENL LENM

0 0 4700 5000 5000

The half wall can be visualized as:

Figure 20: Half Wall

Following figure is the energy balance of the half wall crash.


Figure 21: energy balance of the half wall crash

5 Head injury criteria

"TheHead Injury Criterion (HIC) is ameasure of the likelihood of head injury arising from an impact. TheHIC can be used to assess safety related to vehicles, personal protective gear, and sport equipment."(FromWikipedia). According to the Insurance Institute for Highway Safety, head injury risk is evaluated mainlyon the basis of head injury criterion. A value of 1000 is the critical point.

5.1 Full wall crush

Node ID 125357 is the top node on the head. It has been used to determine the head injury criterion.

Figure 22: HIC

The HIC value of the first simulation is 846.8.


5.2 Half wall crush

Figure 23: HIC

The HIC value of the second simulation(half wall)is 734.1. From the comparison between the full wallcrash and the half wall crash, it is clear that both of the HIC value is under the safe line(1000). However,the full wall crash has a higher HIC value than the half wall crash.


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