Master Thesis - OUFTI-1
Master Thesis - OUFTI-1
Master Thesis - OUFTI-1
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Figure 4.18: MAC matrix using the simple method<br />
It can be immediately noted that these results are not good because only two modes<br />
of the card are found by the model.<br />
This great dierence between the results from the model and the ones obtained by<br />
experimental test, can be explained by several facts:<br />
• Firstly, the boundary conditions are not fully "free-free" in the experimental set-up<br />
(this type of boundary conditions is impossible to reproduce in reality owing to the<br />
gravity). This could bring some unknowns about these boundary conditions which<br />
are not taken into account in the FE model. This fact could lead to dierent dynamic<br />
responses of the PCB.<br />
• Then, the choice of hammer and/or tip could be not appropriate to our case. And, if<br />
the structure is not well excited, its dynamic response can not be measured accurately.<br />
• Finally, owing to the restricted dimensions of the studied structure, the exact location<br />
of measurement points is uncertain. Any error in this location could lead to a<br />
comparison between two points (the measurement point and its "equivalent" from<br />
the FE model) that have fundamentally dierent displacements.<br />
But, for our study, the results obtained are sucient and so, an other test will not be<br />
performed.<br />
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