Marco Anghileri Dipartimento di Ingegneria Aerospaziale Politecnico di Milano Italy Robust: “Road Upgrade of Standards” GRD Second year meeting. Copenhagen March 1 – WP3: “ Instrumentation and measurement”

Robust. GRD /35Second year. Copenhagen 1/3/2005 Composite mounting block activity report. Composite mounting design and construction. Test at TRL. Tests at Polimi. Discussion

Robust. GRD /35Second year. Copenhagen 1/3/2005 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.

Robust. GRD /35Second year. Copenhagen 1/3/2005 Composite mounting block Requirements: –Weight (about 400 g). –Shape (similar to Lier structure) –Strength (able to sustain several crash test). 10 blocks produced.

Robust. GRD /35Second year. Copenhagen 1/3/2005 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 Aluminium or steel plate

Robust. GRD /35Second year. Copenhagen 1/3/2005 TRL TB11 test Test was performed at TRL on Nov –Ford Fiesta: –Weigth 900 kg. –Impact angle 20° –Speed 102 km/h.

Robust. GRD /35Second year. Copenhagen 1/3/2005 TRL TB11 test results. 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

Robust. GRD /35Second year. Copenhagen 1/3/2005 TRL TB11 results 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.

Robust. GRD /35Second year. Copenhagen 1/3/2005 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).

Robust. GRD /35Second year. Copenhagen 1/3/2005 TRL TB11 results 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:

Robust. GRD /35Second year. Copenhagen 1/3/2005 TRL TB11 results.

Robust. GRD /35Second year. Copenhagen 1/3/2005 TRL TB11 results 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.

Robust. GRD /35Second year. Copenhagen 1/3/2005 TRL TB11 results Severity indices ASIThivPhd Tunnel (t=.2531)11.7 Composite (t=.2883)31.2 –The standard correction should be applied for the different location.

Robust. GRD /35Second year. Copenhagen 1/3/2005 TRL TB11 conclusion. 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.

Robust. GRD /35Second year. Copenhagen 1/3/2005 Composite mounting fixing. To better understand the results of the test carried at TRL on November 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.

Robust. GRD /35Second year. Copenhagen 1/3/2005 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

Robust. GRD /35Second year. Copenhagen 1/3/2005 Composite mounting fixing.

Robust. GRD /35Second year. Copenhagen 1/3/2005 Composite mounting fixing.

Robust. GRD /35Second year. Copenhagen 1/3/2005 Composite mounting fixing. 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.

Robust. GRD /35Second year. Copenhagen 1/3/2005 Composite mounting fixing. 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.

Robust. GRD /35Second year. Copenhagen 1/3/2005 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.

Robust. GRD /35Second year. Copenhagen 1/3/2005 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.

Robust. GRD /35Second year. Copenhagen 1/3/2005 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.

Robust. GRD /35Second year. Copenhagen 1/3/2005 Deceleration tests. Aluminium mounting block structure: –Simple shape, same dimensions as composite structure. –Weigth: 4.7 kg Two series of tests. –Car installed with two directions respect to the applied acceleration. 70° 20° Imposed acceleration Car Sled

Robust. GRD /35Second year. Copenhagen 1/3/2005 Deceleration tests.

Robust. GRD /35Second year. Copenhagen 1/3/2005 Deceleration tests.

Robust. GRD /35Second year. Copenhagen 1/3/2005 Deceleration tests Performed 12 tests: –3 tests 20° aluminium mounting –3 tests 20° composite mounting –3 tests 70° aluminium mounting –3 tests 70° composite mounting 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.

Robust. GRD /35Second year. Copenhagen 1/3/2005 Deceleration tests

Robust. GRD /35Second year. Copenhagen 1/3/2005 Deceleration tests. Results Imposed acceleration time histories properly reconstructed by local measures.

Robust. GRD /35Second year. Copenhagen 1/3/2005 Deceleration tests. Results. Frequency response: –Y direction much more sensible (70° impact). –Differences also at lower frequencies

Robust. GRD /35Second year. Copenhagen 1/3/2005 Deceleration tests. Results. Accelerations measured on composite mounting block have always: –lower oscillation amplitude –higher natural frequency

Robust. GRD /35Second year. Copenhagen 1/3/2005 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.

Robust. GRD /35Second year. Copenhagen 1/3/2005 Severity indices. ASI Max difference measured between ASI measures is 0.1

Robust. GRD /35Second year. Copenhagen 1/3/2005 Severity indices. ASI Less differences with filtered ASI

Robust. GRD /35Second year. Copenhagen 1/3/2005 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 Autostrade will test next week the N2 barrier with the composite block