Feasibility evaluation of a non-destructive estimation of material properties of FRC structures using ultrasonic guided waves
A.W. Zaal (TU Delft - Mechanical Engineering)
L Pahlavan – Mentor (TU Delft - Ship Hydromechanics and Structures)
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Abstract
Variations in the production process of fiber-reinforced composite (FRC)materials often influence the material properties of the end product more substantially than their metallic counterparts. It can be valuable for the structural performance and reliability to have a better estimation of the properties of the FRC after production. Detecting these material properties is often performed by intrusive or destructive testing, which are not desirable for in-situ applications. Samples are commonly taken from the material for mechanical testing and material characterization in the laboratory. Feasibility of a non-destructive in-situ assessment method based on ultrasonic guided waves for estimation of the material properties of FRCs, e.g. stiffness in different directions, is investigated in this research. A portable and easy-to- apply measurement system is proposed that can also be less sensitive to the environmental conditions. Point-contact transducers containing a piezoelectric material are utilized for measuring guided waves that propagate through the material. The dispersion characteristics, i.e. phase speed and group speed, of these guided waves are dependent on the layup of the fibers, thickness, and ply properties. Information about the group speed from multiple directions are extracted and compared with the group speeds obtained using a semi-analytical method. A genetic algorithm (GA) is implemented to minimize the difference between the measured and modeled group speeds and obtain the ply properties. The methodology was applied to five glass FRC laminates with different layups. In the numerically simulated case, the error in the estimated material properties turned out to be less than 12%. The coefficient of variation in the experimental results of stiffness values was also less than 20%. The results suggest that the proposed combination of point contact transducers, analysis of group speeds, and GA optimization procedure can potentially form a viable approach for in-situ assessment of material properties of FRCs.