Nessun titolo diapositivaWP3: “Instrumentation and measurement”
Robust. GRD1-2002-70021
Test at TRL.
Tests at Polimi.
Robust. GRD1-2002-70021
Scope of this activity
Acceleration recorded on CG contains components introduced by the oscillation of the floor.
The structure of the accelerometers mounting block can modify these frequencies shifting them at lower regions where our severity indices work.
To investigate the influence on the acceleration time histories of mounting block mass, a carbon fiber mounting block has been designed constructed and used during a TB11 test and several deceleration tests.
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
Strength (able to sustain several crash test).
10 blocks produced.
Robust. GRD1-2002-70021
TRL TB11 test
TRL performed a Round Robin II test installing the new structure.
The fixing to the floor structure was obtained with 4 bolts
upper plate to fix accelerometers
White Fiberglass plates
lower fiberglass plate to fix the structure to the car
4 Bolts
Car floor
Robust. GRD1-2002-70021
Ford Fiesta:
Robust. GRD1-2002-70021
Structural behaviour:
The structure of the mounting did not show any damage during the test.
Frequency behaviour:
Not satisfactory. Presence of oscillation.
A first numerical acitivty has been conducted to investigate these problems
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
Frequency analysis:
During the test two set of accelerometers have been mounted on the car. The first on the new mounting and the second on the floor of the car.
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
TRL TB11 results
The frequency content at lower frequency (below 20 hz) is lower for the new mounting than for the second set of accelerometers.
The frequency content at higher frequency is lower for the new mounting than for the second set of accelerometers.
The new mounting block shows a strong resonance peak at 50 hz (any contribution from AC supply has been excluded).
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
Time analisys:
Time analysis shows that acceleration measured on the new mounting are always lower than the acceleration measured on the second set. Different accelerometers location should be taken into account. This is clearly shown in the following figures with unfiltered results:
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
Robust. GRD1-2002-70021
Same behaviour if a 20 hz filtering is applied.
Accelerations time history measured on the tunnel does not show the typical second peak related to the impact of the rear part of the vehicle while composite acceleration shows this second impact. A correction should be applied for the different location.
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
 
Robust. GRD1-2002-70021
The previous results show interesting aspects that should be further investigated.
Preliminary analysis showed a basic success but the mechanical noise affecting acceleration measurement must be investigated and eliminated.
A new activity was planned at Polimi to investigate this problem.
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
Composite mounting fixing.
To better understand the results of the test carried at TRL on November 17 2004 some basic experiments has been performed.
The composite mounting block has been installed on a Peugeot 106 tunnel to reproduce the resonance problems shown by TRL data.
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
Composite mounting fixing.
A first series of tests have been conducted using the installation procedures agreed by the consortium. The structure has been fixed on the tunnel of the vehicle using 4 bolts (8 mm diameter).
To measure the frequency behaviour a standard technique for modal analysis has been adopted impacting the structure with a small hammer and measuring the output with piezoelectric accelerometers with high sensitivity
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
Robust. GRD1-2002-70021
Robust. GRD1-2002-70021
A triaxial accelerometer has been installed on the structure.
The output of these accelerometers, together with the spectrum response showed a behaviour similar to the one seen at TRL even if the main frequency is here at about 85 hz.
The difference between this frequency and the one measured at TRL (50 hz) is probably due to the different placement of the structure and the presence, at TRL, of the heavy structure used to release the cable that lowers all the natural frequency increasing the mass of the adjacent structure.
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
This figures show these important results:
The behaviour shown during TRL tests has been reproduced even if the resonance frequency is at 85 hz
This is the only frequency present and if we are able to shift this frequency where severity indices don’t work all the possible concerns related with these oscillation are removed.
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
Composite mounting new fixing.
To overcome the above shown problem we simply added four more bolts and introduced spacers to fix the structure on a wider part of the floor.
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
Composite mounting new fixing.
The first natural frequency of the system is above 105 hz (y direction) ad 140 Hz (x direction) . These frequencies are far from the relevant for the severity indices evaluation.
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
Deceleration tests.
Having solved the problems related to the mechanical oscillation a new activity started installing the car on the deceleration sled at Polimi.
Purpose:
To apply known deceleration triangular pulses comparing measures obtained with the composite structure and an aluminium structure.
Same pulse to different mounting structures.
To have results avoiding any cotribution from barrier, ground condition or suspension system.
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
Weigth: 4.7 kg
Car installed with two directions respect to the applied acceleration.
20°
Robust. GRD1-2002-70021
Robust. GRD1-2002-70021
Robust. GRD1-2002-70021
Acceleration pulses:
Peaks: 5 to 25 g (imposed ASI from .45 to 1.9)
Rise time: 0.1 to 0.15 s.
Data analisys not completed but interesting results.
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
Robust. GRD1-2002-70021
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
Differences also at lower frequencies
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
lower oscillation amplitude
higher natural frequency
Robust. GRD1-2002-70021
Severity indices. ASI
No differences during first part of the deceleration pulse due to the strong slope of the acceleration pulse.
After the peak differences between mounting blocks is relevant.
Better agreement between sled and mounting with composite solution.
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
Politecnico di Milano - “Analisi numeriche”
Robust. GRD1-2002-70021
Robust. GRD1-2002-70021
Composite mounting block. Conclusion
The activity showed the influence of the mass of the mounting block on the results.
Ferquency response can be modified with a light structure.
The composite solution could be not the proper solution but some specification on the frequecy response should be added to EN 1317.
Autostrade will test next week the N2 barrier with the composite block
Politecnico di Milano - “Analisi numeriche”
TRAINING A/C
Aluminium
Composite
1.6
1.8
2
2.2
2.4
2.6
-25
-20
-15
-10
-5
0
5
10
15
20
25
Aluminium
Composite
2
2.2
2.4
2.6
2.8
3
-20
-15
-10
-5
0
5
10
15
20
25
2
2.5
3
3.5
4
4.5
1.95
2
2.05
2.1
2.15
2.2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8