Voids In RTM/textile Composites Based On Nonlinear Ultrasonic Evaluation Research

Resin Transfer Molding(RTM) as a composite material forming technology,Because of its low cost、fast forming、good quality and little pollution, has been widelyapplied in aerospace at home and abroad. However, micro void defects easily producedduring the manufacturing in RTM/textile composites, observably reduced the finalmechanical properties of composites, so it is significant to study the void defects for theapplication of RTM/textile composites.RTM/textile composites are new materials which have complicated anisotropy andmicro structures, the effect of the traditional testing methods are not ideal. In this paper,based on the characteristics of acoustic wave propagation velocity and attenuation in theRTM/textile composites, combined with the nonlinear ultrasonic principles, to putforward using the nonlinear ultrasonic method to test micro void defects in theRTM/textile composites.The test system added the filters and amplifiers, based on the finite amplitudemethod, then a set of complete experimental system is developed for nonlinearultrasonic testing. The test system comprises signal source, power amplifier, signalconditioning and receiving unit, and study on the excitation waveform、coupling、power amplifier、excitation voltage those factors, how effect the system’s responsecharacteristic.Conducting nonlinear ultrasonic testing technology to assessment void defects inRTM/textile composites experimental studies. Apply the above system to measurementdifferent pores RTM/textile composites’ nonlinear coefficients, including high-harmonicnonlinear coefficients and sub-harmonic nonlinear coefficients. Initially established therelationship between the void defects and ultrasonic nonlinear coefficients.After detections, use quality volume method to calculate the total porosity ofmaterials and use immersion medium method to calculate the open porosity of materials.Finally, use scanning electron microscope (SEM) to observe the void defects microstructures, then compares the SEM results and the nonlinear ultrasonic testing results,the results can be explained and verified mutually.