Structural characterization of tie-rods by means of dynamic testing and Genetic Algorithms

Identification procedures based on dynamic testing have been extensively used to characterize tie-rods in a nondestructive manner. In general, the Young modulus of the rod, the applied tensile load, and the rotational stiffness of both the restraints are the sought parameters. To date, a procedure capable to identify all the above mentioned parameters has not been developed. In this work a strategy based on dynamic testing, added masses and Genetic Algorithms (GAs) is proposed. The framework estimates the unknowns by minimizing an objective function based on the discrepancy between the experimental and the numerical frequencies of vibration. Numerically, the frequencies are predicted for a given set of the sought parameters by a finite element based formulation. It is shown that by exploiting only few experimental frequencies of the tie-rod (principal system) along with those of some modified systems (dummy systems), that can be simply obtained from the principal system by adding a concentrated mass at a specific position along the rod, all the target parameters can be identified, even in the case of different rotational stiffnesses at the ends.