Evaluation of stresses in carbon fiber composites for aerospace applications employing LCR waves and ultrasonic arrays

Abstract

Aircraft components must be monitored continuously to allow the safe operation of the aircrafts. The inspection of mechanical stress state is of paramount importance to ensure such safety. Nondestructive techniques for evaluating stresses are the most suitable for components that cannot be replaced or removed from the operating site. Among the non-destructive techniques, those which are based on the acoustoelasticity stand out for their simplicity and low cost. The acoustoelastic theory relates the variation of the elastic wave speed with the change of the stress in the material. For measuring from the surface, the most sensitive technique is based on Longitudinal Critically refracted waves (LCR). However, not only the stress influences the wave velocity, but also the uniformity of materials inspected, and other factors, such as temperature. Non uniformity is a problem particularly important for the inspection of structural composites, because such variation can lead to changes in the wave speed. The objective of this research project is to evaluate the variation of propagation speed of LCR waves in carbon/epoxy composites, aiming to correlate its variation to the applied stress. The evaluation of non-uniformity shall be performed using ultrasonic arrays and the TFM technique (Total Focusing Method). As a result of this project, it is expected to develop a nondestructive method for stress measurements that provide safer, more reliable, and economically viable inspections. As additional results it is expected to submit papers to scientific journals and conferences in the area, the graduation of students, and the generation of patents on innovative aspects of the technique developed. (AU)