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The objective of this work is to propose the identification of the local mechanical properties of a orthotropic composite by non-destructive technique using the wave propagation.
In the general case of an isotropic plate subjected to an excitation, the motion of any point (x, y) can be expressed from the flexural rigidity, the geometry of the plate and the input sollicitation. At first, from this expression, the RIFF method (Inverse Filtered Windowed Resolution)Force Analysis Technique (also known as RIFF method) can identify the sources of the vibration from the measurement of the local motion field and the properties of the plates without considering the boundary conditions. Thereafter, focusing on unsolicited areas, and considering the fact that neither the boundary conditions nor the nature of the vibration are part of the equation of the problem, the bending stiffness and damping can be determined only from a displacement field obtained experimentally.
The work presented in this paper is the extension of this technique to an orthotropic material by introducing the main directions of the fibers.
The material of this study is composed of uni-directionnal glass fibers impregnated by a polyester resin using a LRI process. Two panels were produced: the first one is pure uni-directionnal (huge difference between the longitudinaland transversal rigidities) and the second is balanced (where the rigidities are equivalent in 0 ° and 90 °). The objective of this paper is to show the relevance of the technique to differentiate rigidities in both directions.
The experimental apparatus consists of an excitation system injecting a SHIRP chirp signal in the structure and a measurement system composed of a scanning laser vibrometer multipoint. The transverse displacement is then measured in a 200mm x 400mm field with a total of 1000 measuring points uniformly distributed over the surface. The global bandwiht bandwidth of the study is fixed from 0hz Hz to 3kHz.
The first results are quite encougaging even if the frequencies below 500Hz are difficult to explaneexplain. For the unidirecitonnal uni-directional composite, the difference between the values in the two directions is very marked. While in the case of balanced composite, rigidities are of the same order of magnitude.
The current work is the understanding of the phenomena that disturb the results at certain frequencies. Finally, a particular attention is given to achieve the expression of Young's moduli and absorption coefficients.
