Study On Ultrasonic Characterization Of High Porosity Quartz Composites

RTM/ quartz textile composites are widely used in thermal protection of aerospace industry due to their excellent thermal protection,load bearing and wave transmission properties.But it usually has a very high pore content.At present,the ultrasonic characterization of porosity of composite materials is mostly focused on composite materials with porosity below 4%.Because of its high attenuation characteristics,high porosity composite materials are difficult to detect by ultrasound.However,ultrasonic characterization of high porosity composites has rarely been reported.In view of the lack of ultrasonic characterization of high porosity composites,this paper studies the porosity of high porosity composites in time domain and frequency domain by using RTM/ quartz textile composites as the research object.First,the ultrasonic characterization method in time domain is improved.Such as: sound velocity method,acoustic impedance method and sound attenuation method,so that they can detect the composite material with large thickness and high porosity.The limitations and reasons of ultrasonic characterization in porosity detection of high porosity composites are summarized.Secondly,two frequency domain ultrasonic characterization methods are used to characterize the porosity of high porosity composites.The RPR-4000 nonlinear software system is optimized to make the equipment detection process more convenient and the accuracy of detection results higher.The ultrasonic characterization of frequency domain power spectrum is compared with the ultrasonic nonlinear characterization method.The relationship between pore size and ultrasonic frequency domain characteristic parameters is established.The applicability and superiority of frequency domain ultrasonic testing in high porosity composite materials are analyzed.Next,the porosity of composite materials with unknown pore contents is predicted by using the relationship between pore size and ultrasonic frequency domain characteristic parameters.Finally,the porosity of materials was measured by a variety of non ultrasonic methods.They include water absorption density method,metallographic microscope method,ICT method and ablative density method.Verify the reliability and reliability of the ultrasonic test results.The results of the study show that.In the case of low pore content,the ultrasonic parameters in the time domain can effectively characterize the porosity of the composite,but the time domain ultrasonic characterization method is limited when the thickness of the material is more than 15% of the pore volume of 8mm;The frequency domain ultrasonic characterization method can effectively characterize and predict porosity of composite materials with high porosity,and the results are consistent.The power spectrum characterization method in frequency domain is simple,stable and sensitive.The accuracy of ultrasonic nonlinearity is relatively high;For each non ultrasonic characterization method.The consistency of porosity test results is good,which verifies the reliability of the experimental results of each ultrasonic characterization method.Among them,the industrial method CT has the highest accuracy,while the ablation density method has the best cost performance.