Ultrasonic characterization of fiber-reinforced polymeric (FRP) composites.

摘要

The focus of this research is to determine quantitative methods for the characterization of fiber reinforced polymeric (FRP) composites. The FRP materials used in this study are glass reinforced vinylester and polyester composites manufactured by the pultrusion process. Various forms of structural members (plates, I-, angle, channel shape section among others) are used. This transversely isotropic material possesses five independent elastic constants, from which the engineering constants can be calculated.;Three separate ultrasonic techniques are to determine the engineering constants of the FRP materials. The first of these ultrasonic techniques implements a combination of contact piezoelectric transducers and immersion transducers. The results from the nondestructive immersion technique are compared to results from destructive mechanical tests on the exact same specimens. This immersion set-up is also used to observe spatial variation of engineering constants over a single specimen; the change in these constants is observed along, as well as perpendicular to, the pultrusion (fiber) direction.;The remaining two ultrasonic techniques were developed specifically for this research; both of these techniques implemented a combination of contact piezoelectric transducers and optical generation and detection of ultrasound. One of these techniques uses the optical techniques to generate and detect three surface acoustic waves traveling in specific directions on specific specimen surfaces. Results from this technique are compared to the immersion technique. The last methodology implements the optical generation and detection of a single surface acoustic wave, traveling in the pultrusion direction. This technique has the benefit that it can be performed when access to only a single side of the specimen may be obtained. The results of this technique are compared to results from the immersion technique on the exact same specimens.;The ultrasonic techniques provide quantitative methods for measuring the engineering constants of FRP materials. They provide local measurements of engineering constants, which allows for the evaluation of specimens with geometries that do not allow mechanical testing. These nondestructive point detection techniques exhibit great potential for the in service monitoring of FRP structures.