[PPT] - Robust: Road Upgrade of Standards GRD1-2002-70021 Testing PowerPoint Presentation

SLIDE 1

Marco Anghileri Dipartim ento di I ngegneria Aerospaziale Politecnico di Milano I taly

Robust: “Road Upgrade of Standards” GRD1-2002-70021 Testing procedures and severity indices evaluation.

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Scope of the activities. Scope of the activities.

To harmonise the measurement

practice in the European laboratories and remove possible discrepancies from different transducer and test set-up.

Part of the consideration already

presented by Lier.

Fields:

– Experimental – Analytical

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Contribution. Contribution.

1. Statistical analysis of already

performed tests.

2. Severity indices definition.
3. Data acquisition and severity indices

evaluation.

4. Instrumentation mounting.

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Statistical analysis of already Statistical analysis of already performed tests. performed tests.

Analysis of existing data obtained form

European laboratories to investigate possible correlation betw een severity indices.

Analysis of existing data obtained form

European laboratories to investigate differences betw een tests houses

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Data base. Data base.

From European laboratories a set of 174 data of

TB11 full scale crash tests have been obtained containing the follow ing information:

– year of test – vehicle make – vehicle test mass – data sample rate – actual speed and angle – barrier dynamic deflection – ASI – THIV/PHD

Data w ere received from 7 Laboratories. Of 174

TB11 tests, 111 w ere successful and 63

unsuccessful. Some tests have been received

w ithout PHD data.

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THIV-ASI THIV-ASI

This graph show s a fair correlation betw een

ASI and THIV indices. Correlation factor of 0.7451

Correlation THIV- ASI (All data except singular points) y = 25.033x0.4983 R2 = 0.7451 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.00 0.5 1 1.5 2 2.5 ASI T H IV

THIV/ASI-Re Pow er (THIV/ASI-Re)

0.4989

25.033 THIV ASI = ฀

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Thiv-Asi different labs. Thiv-Asi different labs.

Correlation THIV/ASI

0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 0.00 0.50 1.00 1.50 2.00 2.50 3.00 ASI THIV Lab1 Lab 2 Lab 3 Lab 4 Lab 5

y = 23.6 ASI^0.4899 5 y = 25.1 ASI^0.5596 4 y = 24.8 ASI^0.545 3 y = 24.0 ASI^0.3305 2 y = 26.9 ASI^0.4305 1 y = 25.0 ASI^0.4983 ALL

Corr. function

Lab

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THIV-PHD PHD-ASI THIV-PHD PHD-ASI

no correlation

betw een PHD and THIV or ASI

THIV-PHD correlation

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.00 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 PHD [g] THIV [km/h]

PHD-ASI correlation

0.5 1 1.5 2 2.5 3 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 PHD [g] ASI

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ASI-DD THIV-DD PHD-DD ASI-DD THIV-DD PHD-DD

PHD: no

correlation.

THIV-DD ASI_DD:

w eak correlations

ASI-dynamic deflection y = 1.4448e0.683x- R20.5653 = 0.00 0.40 0.80 1.20 1.60 2.00 0.00 0.50 1.00 1.50 2.00 Dynamic deflexion ASI ASI-DD

Espo. (ASI-DD)

THIV - Dyn. deflexion

y = 30.631e

0.3764x-

R

20.5591 =

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 0.00 0.50 1.00 1.50 2.00 Dynamic deflexion THIV THIV-DD

Espo. (THIV-DD)

PHD - Dynamic deflection y = 16.719e

0.6093x-

R

20.2336 =

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 0.00 0.50 1.00 1.50 2.00 Dynamic deflexion PHD PHD-DD

Espo. (PHD-DD)

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Different Labs Different Labs

ASI-dynamic deflection

0.00 0.50 1.00 1.50 2.00 2.50 3.00 0.00 0.50 1.00 1.50 2.00 Dynamic deflection [m] ASi Lab 1 Lab 2 Lab 3 Lab 4 Lab 5

THIV-dynamic deflection

0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 0.00 0.50 1.00 1.50 2.00 Dynamic deflection [m] THIV [km/h] Lab 1 Lab 2 Lab 3 Lab 4 Lab 5

y = 1.4716e-0.8779x 5 y = 1.6442e-0.9867x 4 y = 1.3841e-0.6902x 3 y = 1.4973e-0.6099x 2 y = 1.2829e-0.5836x 1 y = 1.4448e-0.683x All

Corr. Function

Lab y = 27.801e-0.3747x 5 y = 29.923e-0.4634x 4 y = 27.476e-0.2846x 3 y = 32.141e-0.4018x 2 y = 32.827e-0.5464x 1 y = 30.631e-0.3764x All

Corr. Function

Lab

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Results of statistical analysis. Results of statistical analysis.

These results show that there is a limited

correlation betw een severity indices.

Reason: from the scientific point of view , ASI, THIV

and PHD are different things.

The main differences betw een these severity

indices are:

– ASI is using three components of acceleration w hile THIV- PHD use a planar motion w here the z acceleration component is not used. – THIV – PHD use a critical time that corresponds to the time w here the theoretical head impact against the conventional box representing the vehicle interior. – THIV is affected also by the yaw motion w hile ASI does not take into account this measure into account.

Test houses have similar tendencies.

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Severity indices definition. Severity indices definition.

EN 1317 requires, to evaluate barrier

performance, to measure the follow ing severity indices: ASI THIV / (PHD)

Based on acceleration measured during

the certification test on the vehicle CG.

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ASI. Acceleration Severity Index
ASI. Acceleration Severity Index

– “The index ASI is intended to give a measure of the severity of the vehicle motion for a person seated in the proximity

f point P (CG) during an impact.”

– Steps:

Measure three acceleration components of

vehicle CG according w ith CFC180.

Apply a 50 ms moving average on these

acceleration.

Evaluate Asi as:

2 2 2 lim lim lim

( )

y z x x y z

a a a ASI t a a a ⎛ ⎞ ⎛ ⎞ ⎛ ⎞ = + + ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ ⎝ ⎠

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ASI. Acceleration Severity Index.
ASI. Acceleration Severity Index.
Where:

– “Are obtained from the human body tolerances limits.”

ASI is the maximum value of ASI(t).
“The average in equation (of ASI) is actually a

low pass filter, taking into account the fact that vehicle accelerations can be transmitted to the

ccupant body through relatively soft contacts,

w hich cannot pass the highest frequencies.”

The equation (of ASI) is the simplest possible

interaction equation of three variables x, y and z.

The limit accelerations are interpreted as the

values below w hich passenger risk is very small (light injures if any).”

lim lim lim

12 9 10

x y z

a g a g a g = = =

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Moving average Moving average

Asi and Phd evaluation requires moving

average techniques:

– ASI 50ms – PHD 10ms (NCHRP-350 ORA 10 ms) – The original idea w as to have a w indow to

bserve the acceleration time histories.
Questions:

– Is moving average a true filter? – Can moving average give w rong information?

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Filtering Filtering

Signal processing (analog, digital or

mechanical) to:

– Eliminate noise or oscillation – Amplify frequencies – Avoid problems (example: aliasing)

Attenuation:

10

20log Out Db In ⎛ ⎞ = ⎜ ⎟ ⎝ ⎠

Filter Input signal Output signal

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Typical low -pass filter frequency Typical low -pass filter frequency response response

1 0 1 0

1

1 0

2

1 0

3

1 0

4

4 0 0
3 5 0
3 0 0
2 5 0
2 0 0
1 5 0
1 0 0
5 0

fre q [H z] Ampiezza [Db] F iltro B utte rw o rth

20 db means

Output=0.1* Input

The moving average is a filter in the sense that

it modifies the original signal.

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50 ms moving average – 50 ms moving average – standard standard filtering gain. filtering gain.

Gain=output/input

moving average over 50 ms

0.3
0.2
0.1

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 50 1 00 1 50 200 frequency [Hz] 20 40 60 80 100 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 freq [Hz] Gain Butterworth filter

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50 ms moving average – 50 ms moving average – standard standard filtering attenuation. filtering attenuation.

Comparison w ith a CFC shaped filter

10 10

1

10

2

10

3

10

4

350
300
250
200
150
100
50

freq [Hz] Amplitude [Db] Moving average Filter

20 40 60 80 100

350
300
250
200
150
100
50

50 100 freq [Hz] Amplitude [Db] Moving average

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Moving average does not Moving average does not preserve energy. preserve energy.

Velocity evaluation w ith:

– Original signal – Filtered signal (Butterw orth) – Moving Average

0.2 0.4 0.6 0.8 1

2
1.5
1
0.5

0.5 1 Velocity evaluation time velocity Moving average Original signal Filtered signal

0.2 0.4 0.6 0.8 1 1.2 1.4

1.4
1.2
1
0.8
0.6
0.4
0.2

0.2 0.4 0.6 Velocity evaluation time velocity Moving average Original signal Filtered signal

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Moving average sensitivity to noise. Moving average sensitivity to noise.

Different acceleration noises:
Constant amplitude acceleration for different

frequencies.

Constant energy (same velocity), the

amplitude is modified w ith frequencies.

– How these noises are seen by the moving average and a “correct” filter.

“Correct” = equivalent filter:

– 10 hz tw o poles Butterw orth “forw ard- backw ard” (four total poles) to avoid time shift.

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Noise influence on ASI w ith moving Noise influence on ASI w ith moving average average

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Is this a real problem? Is this a real problem?

To verify the presence of this problem:

– Test cases obtained from some standard crash tests.

For each test case:

– Acceleration time-history. – Frequency spectrum. – Evaluation of ASI w ith moving average. – Evaluation of ASI w ith “correct” filter.

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Example. Example.

0.2 0.4 0.6 0.8 1

50
40
30
20
10

10 20 30 TEST 3: accelerazione X time [s] g 50 100 150 200 1000 2000 3000 4000 5000 6000 Spettro TEST 3: accelerazione X 0.2 0.4 0.6 0.8 1

20
15
10
5

5 10 15 20 TEST 3: accelerazione Y time [s] g 50 100 150 200 250 300 1000 2000 3000 4000 5000 6000 7000 Spettro TEST 3: accelerazione Y 0.2 0.4 0.6 0.8 1

15
10
5

5 10 15 TEST 3: accelerazione Z time [s] g 50 100 150 200 250 300 1000 2000 3000 4000 5000 6000 7000 Spettro TEST 3: accelerazione X

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0.2 0.4 0.6 0.8 1

16
14
12
10
8
6
4
2

2 time [s] g TEST 3:Confronto tra media mobile e filtraggio. Componente X Media mobile Filtro 0.2 0.4 0.6 0.8 1

2
1.5
1
0.5

0.5 1 1.5 2 2.5 time [s] g TEST 3:Confronto tra media mobile e filtraggio. Componente Y Media mobile Filtro

0.2 0.4 0.6 0.8 1

1.5
1
0.5

0.5 1 1.5 2 2.5 3 time [s] g TEST 3:Confronto tra media mobile e filtraggio. Componente Z Media mobile Filtro

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Moving average Moving average

The modification of original signals

driven by the moving average has been demonstrated but:

Is this strange behavior of moving

average desired by the original designer

f ASI?
Or w as simply not observed?

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History of ASI. History of ASI.

I.Laker: “ A short summary of three

vehicle Impact Severity Measure- ASI THIV/PHD NCHRP 230” 1991.

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ASI History. ASI History.

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ASI History ASI History

1955 Stapp

tests.

1969 Limits in

3 direction

1971 moving

average.

1972

Ellipsoidal Envelope from US Air force documents

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Acceleration time histories. Acceleration time histories.

– Aeronautical deceleration:

Source: Us Army “Aircraft

Crash Survival Design Guide”.

Single peak: from 15 to 30 g
Time duration from 0.1 to

0.15 s

– Safety barrier deceleration.

0.2 0.4 0.6 0.8 1

15
10
5

5 10 TEST 1: accelerazione X time [s] g

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ASI History ASI History

The origin of ASI calculation procedure w as based on

research on the injury assessment of vehicle and aircraft occupants in phenomena such as re-entry space capsule impacts and combat airplane maneuvers.

These phenomena have limited or no oscillations

throughout the event.

For this reason, computing an average over a period of

50 ms w as used to obtain an average value to be compared w ith the tolerable limits.

Impacts against road restraint systems generally have a

duration much greater than 50 milliseconds, and show strong oscillations at different frequencies.

The 50 ms moving average w hen applied over such

longer acceleration pulses becomes a low -pass filter, but it does not behave like filters used conventionally for crash analysis.

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ASI modification. ASI modification.

To avoid the problem related to the

moving average a standard filtering technique should be used.

Which filter?
Which cut off frequency?

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Asi modification w ith different Asi modification w ith different “correct” filtering cut off frequency. “correct” filtering cut off frequency. Test 3 Test 3

hz Modified ASI 10.0 1.0915 15.0 1.2009 20.0 1.2181 25.0 1.2705 30.0 1.3876

5 10 15 20 25 30 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Influence of different cut off filtering on Test 4 modified ASI. frequency [hz] ASI Original ASI Modified ASI

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Modification of ASI formulation. Modification of ASI formulation.

126 tests analyzed

– 65 from Autostrade – 17 from Lier – 20 from TRL – 16 from Italian producers – 8 from Round Robin

Evaluation of ASI using filtering instead
f moving average.

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Filtered ASI Filtered ASI

Raw data have been filtered w ith CFC180 and

a new ASI technique has been applied avoiding moving average and using:

2 poles Butterw orth forw ard – backw ard (to

avoid time shift) filter. 4 total poles.

Cut off frequencies tested:

10 – 12 – 14 – 16 – 18 – 20 hz

The final cut off frequency has been identified

as the one w ith the better correlation w ith the standard ASI formula. The idea is to avoid, if possible, modification of the current limits for the ASI formula.

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Filtered ASI results Filtered ASI results

0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2

ASI standard ASI filtered

asi 10 Hz 12 hz 14 hz 16 hz 18 hz 20 hz Lineare (asi) Lineare (18 hz) Lineare (20 hz) Lineare (14 hz) Lineare (12 hz) Lineare (10 Hz) Lineare (16 hz)

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Filtered ASI. Filtered ASI.

Best correlation (not in all the domain):

– 12 hz cutoff frequency. – 2 pole forw ard-backw ard Butterw orth filter. (4 resultant poles)

0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2

ASI standard ASI filtered

asi 12 hz Lineare (asi) Lineare (12 hz)

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Filtered ASI. Filtered ASI.

Comparison w ith original ASI values:

– Up to 1 small modification (for some tests new ASI value is higher than the standard value) – From 1 to 1.5 global decrease if compared to standard ASI. – For higher ASI value a slightly decrease of the new value. – Cut off frequency must carefully considered.

Moving average effect cancelled.
Less sensible to noise.

10 10

1

10

2

10

3

10

4

350
300
250
200
150
100
50

freq [Hz] Amplitude [Db] Moving average Filter R2 = 0.9668 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 ASI standard ASI filtered asi 12 hz Lineare (asi) Potenza (12 hz)

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Data acquisition and severity Data acquisition and severity indices evaluation (experimental). indices evaluation (experimental).

Round Robin 1: TB11 tests, same new

car (Peugeot 106), same concrete rigid barrier in all the labs. Only, transducers, data acquisition system and softw are is different.

Round Robin 2: TB11 tests, different

cars (each lab uses ow n standard car), same concrete rigid barrier.

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Round Robin Round Robin

A first analysis show a large scatter betw een

labs and strong differences betw een different indices evaluation of the same signals.

Some of the differences came from different

testing procedures. Some other from softw are and data acquisition.

To better understand this problem a first analysis

found as a key point the offset evaluation that can produce strong influences on THIV value and medium influences on ASI and PHD.

Med max % min % Asi 1.86 0.05 2.83

0.03 -1.48

THIV 32.89 1.31 3.98

0.49
1.5

PHD 14.15 3.55 25.1

2.75 -19.4

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Offset removal. Offset removal.

Offset is usually evaluated obtaining the mean

value of that channel for some milliseconds before the impact. The number of milliseconds used as w ell as the precise impacting point sample evaluation can produce different offset results on the same signal.

Acceleration time histories just before the

impact can contain oscillations transmitted from ground and (mainly for pushed or pulled car systems) the release of the car induces movements of the vehicle that can influence

ffset evaluation.
For this reason the evaluation of zero-level

should be better defined and improved.

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Offset removal. Offset removal.

Oscillation w ith amplitude of about 1 g are present

before the impact being the mean value zero but can be understood that a different offset w indow or a real vehicle acceleration can strongly influence the output.

A different offset evaluation of .5 g on each channel can

produces a delta in ASI of about 0.1 and in THIV of 1.74 km/h.

Drift of signals during the preparation must be taken

into account to find a better solution.

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

2
1.5
1
0.5

0.5 1 1.5 accelerazione y

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Softw are influence. Softw are influence.

To investigate the influence of different

softw are a benchmark file has been produced w here the different offset evaluation procedures w ould not generate influences.

This signal is simply one of the original

signals w here the impacting point has been defined and all data before this point are equal to 0.

With this file the influence of offset

removal has been avoided.

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Softw are influence. Softw are influence.

Can be seen that the different softw are used

evaluate indices w ith scatter that should not be present. Conclusion to this point is that a validated and common softw are should be used to evaluate severity indices .

ASI t (s) THIV t (s) PHD t (s) 1.84 32.43 0.0766 12.15 0.1369 1.84 0.0097 32.45 0.0766 11.88 0.1370 1.84 0.0099 32.49 0.0767 12.15 0.1370 1.84 0.1148 32.43 0.1566 13.69 0.2220 1.84 0.0098 32.4 0.0779 11.9 0.1370 BENCH DATA L1 L2 L3 L4 TRAP

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Accelerometer mounting Accelerometer mounting

The structure of the floor of a car is

made of thin plates that, during the test, produces vibrations.

These vibrations can be affected by the

mass of the structure used to install the accelerometers in the proper position.

The severity indices can be affected by

the structure used to install the accelerometers.

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0.0E+00 2.0E-01 4.0E-01 6.0E-01 8.0E-01 1.0E+00 1.2E+00 20 40 60 80 100 120 140 160 180 200

Frequenza [hz] Ampiezza

Serie1 Serie3 Serie4 Serie6 Serie7 Serie9 Serie15

Different mounting block natural Different mounting block natural frequencies frequencies

First natural frequencies located betw een 10 and 15

hz.

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Results Results

These frequencies are low er that the

target design ones (about 30 hz).

15 hz is a frequency not modified by the

moving average.

– This frequency can influence severity indices

Mounting block influence:

– w eight of the block in general decreases the first frequency.

Mounting block should be described

inside the standards.

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Composite mounting block Composite mounting block

To demonstrate the influence of the mass a

composite mounting block has been designed.

Structure:

– Carbon fiber /nomex structure. – Glass fiber plates to be easily machined to fix the structure to the car and install accelerometers. – 8 blocks produced.

Some tests houses used this structure to verify

the influence on the final results.

The idea is not to suggest the use of this

structure but to demonstrate how can affect the results.

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Composite mounting fixing. Composite mounting fixing.

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Deceleration tests. Deceleration tests.

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Deceleration tests. Results. Deceleration tests. Results.

Frequency response:

– Strong differences betw een different mounting blocks – Differences also at low er frequencies

20 40 60 80 100 1000 2000 3000 4000 5000 6000 7000 8000 spectrum power density. y direction. 70° impact Aluminium Composite

2 4 6 8 10 12 14 1000 2000 3000 4000 5000 6000 7000 spectrum power density. y direction. 70° impact Aluminium Composite

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Conclusion. Conclusion.

Validated softw are should be used

during certification tests.

A precise procedure to evaluate the
ffset value must be inserted in EN

1317

Mounting block structure can influence

the acceleration time histories.

EN 1317 should describe the technical

requirements to avoid this kind of influences on the results.

SLIDE 53

53 /77 Bruxelles 30/05/2006

Robust. GRD1-2002-70021