Robust Project. Deliverables D.3.4 New lightweight mounting block by joq12180

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									                                Robust Project.

                              Deliverables D.3.4

                     New lightweight mounting block.

                      Natural frequencies measure




Author: Marco Anghileri
Dipartimento di Ingegneria Aerospaziale - Politecnico di Milano
34, via La Masa
tel: 02 23998316
fax: 02 23998334
e-mail: anghileri@aero.polimi.it


Milano, 26.11.2004
Robust WP3




       INTRODUCTION                          3

       FIRST MOUNTING.                       3

         Frequency analysis:                 5


       NEW MOUNTING                          7

         Data analysis                       9




Marco Anghileri
                               Page 2 / 11
Robust WP3


Introduction

       To better understand the results of the test carried at TRL on November 17
2004 we performed some basic experiments installing the composite mounting block
on a Peugeot 106 tunnel to reproduce the resonance problems shown by TRL data.
       In this report a preliminary analysis of these tests is reported.


First mounting.

        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.
       In the following figures the test setup is reported:




Figure 1: Test procedure




Marco Anghileri
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Robust WP3




Figure 2 Test procedure




Marco Anghileri
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Robust WP3




Figure 3 Test procedure



Frequency analysis:
        During these tests 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.
        In the following figure the results of one of the test is reported. We conducted
10 tests with the same results.




Marco Anghileri
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Robust WP3


                   5
                                                                                                      acc 1
                                                                                                      acc 2
                   4                                                                                  acc 3


                   3


                   2


                   1


                   0


                   -1


                   -2


                   -3


                   -4


                   -5
                        0        0.5             1            1.5             2           2.5                  3
                                                                                                               4
                                                                                                        x 10


Figure 4: Accelerometer time history.


                                                     spectrum power density
                   1


                  0.9


                  0.8


                  0.7


                  0.6


                  0.5


                  0.4


                  0.3


                  0.2


                  0.1


                   0
                        0   20         40   60       80       100      120        140   160     180           200




Figure 5: spectrum x direction




Marco Anghileri
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Robust WP3

                                             spectrum power density
                   1


                  0.9


                  0.8


                  0.7


                  0.6


                  0.5


                  0.4


                  0.3


                  0.2


                  0.1


                   0
                        0   20   40   60     80       100      120    140   160   180   200




Figure 6: spectrum y direction

This figure shows these important results:
    1. The behaviour shown during TRL tests has been reproduced even if the
       resonance frequency is at 85 hz
    2. 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.

New mounting

        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. In the
following photos this new fixture is shown




Marco Anghileri
                                      Page 7 / 11
Robust WP3




Figure 7 New mouting




Figure 8 New mounting




Marco Anghileri
                        Page 8 / 11
Robust WP3

Data analysis
      With the above shown new fixture the same tests described before have
been performed. In the following images are reported the results of them:


                  3
                                                                       acc 1
                                                                       acc 2
                                                                       acc 3

                  2




                  1




                  0




                  -1




                  -2




                  -3
                       0       0.5         1           1.5   2   2.5            3
                                                                                4
                                                                         x 10


Figure 9:8 bolts accelerometers time history




Marco Anghileri
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Robust WP3

                                        spectrum power density
          1


        0.9


        0.8


        0.7


        0.6


        0.5


        0.4


        0.3


        0.2


        0.1


          0
              0    20       40    60    80       100      120      140     160    180    200




Figure 10 Spectrum x direction




                                                  spectrum power density
                   1


                  0.9


                  0.8


                  0.7


                  0.6


                  0.5


                  0.4


                  0.3


                  0.2


                  0.1


                   0
                        0    20    40    60        80       100     120     140    160    180   200




Figure 11 Spectrum y direction


Marco Anghileri
                                        Page 10 / 11
Robust WP3

      These results show that this modification strongly modify the frequency
response.
       Comments:
        With this modification 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. Further tests will be performed using also the
metal plate between the carbon fiber and the bolts.




Marco Anghileri
                                     Page 11 / 11

								
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