Research On Ultrasonic Evaluation Method Of Pore Content Of Quartz Fiber Composites

RTM quartz fiber composite material has the advantages of low cost,fast forming speed,high strength and modulus,heat resistance,low dielectric constant and small tangent loss.It has been widely used in aerospace,military,biomedical engineering and other fields.The pore micro defects are unavoidable in the process of material forming,and the mechanical properties of the composites were affected.Therefore,the non-destructive evaluation of pore micro defects has become a hotspot.At present,the ultrasonic method is mainly used to evaluate the pore content.Aiming at the non-destructive evaluation of the pore content of RTM quartz fiber composite,this paper studies the effect of forming process parameters on the pore content and the ultrasonic evaluation method of pore content.Firstly,the composite materials with different pore contents are obtained by changing the resin injection pressure,sample thickness and resin injection temperature during the molding process of RTM quartz fiber / epoxy resin composites.Secondly,the pore content and mechanical properties of RTM quartz / epoxy composites are measured,and the effects of RTM molding parameters on the pore content of the composites and the effect of pore content on the mechanical properties are investigated.Finally,The void content of RTM quartz fiber composites with different resin matrix is evaluated by sound velocity,acoustic attenuation coefficient and relative nonlinear coefficient,and an improved method of sound velocity and sound attenuation coefficient is proposed for quartz / phenolic composites with large pore volume and large attenuation.The results show that the forming parameters of RTM affect the formation of porosity defects,and the pore content decreases with the increase of resin injection pressure.When the injection pressure is 0.6MPa,the pore content of composites increase with the increase of temperature.The flexural strength and compressive strength of the composites decrease with the increase of pore content.When the pore content changes within 1%,the velocity of sound does not change with the pore content regularly,while the ultrasonic attenuation coefficient and the relative nonlinear coefficient are monotonically increasing with the pore content,which can be used to evaluate the pore content of quartz fiber composites.Compared with the ultrasonic attenuation coefficient,the relative nonlinear coefficient is more sensitive to the pore defects.