The Ultrasonic Non-Destructive Test On The Porosity Of The Carbon Fiber Reinforced Polymer Matrix Composite

In recent years, the Carbon Fiber Reinforced Polymer(CFRP) have been widely used in the fields which is strictly for density, stiffness, weight and fatigue properties and in the occasions that are in need of high temperature and high chemical stability for its outstanding ratia-strength and ratia-modulus of elasticity. Especially in the fields of aviation, ships and nuclear energy, the ratio of CFRP is increasingly high and its development is very rapid. We can predict that the day when widely using it is not too distant and its prospects are greatly extensive.Because of its special forming process, a quantity tiny pore often exists in CFRP more or less. The interlaminar shear strength and flexural strength of CFRP will be influenced seriously and its life will be reduced, when the content of pore is beyond a certain limitation. Consequently, we generally make use of the Nondestructive Testing to detect the content of pore (namely porosity) to ensure that use the CFRP is used safely. The Ultrasonic Non-destructive Testing becomes one of the most important methods which is used to detect porosity of CFRP because of its unique advantages.Based on the using of the method of ultrasonic attenuation and acoustic impedance respectively, some investigations are developed on the CFRP which are formed by hand-paste and hot pressing, and own a porosity over 0.03% to 4.96%. By the theory analysis and experiment verification, a corresponding model is set up at the end. The primary content of this paper is as follows:The CFRP whose fiber is arrayed unidirectionally are made by hand-paste and hot pressing process. By studying a large amount of literature, the experiment program is made and the model is tried to set up. After many experiments, a flat probe with a central frequency of 5MHz is fixed. The ultrasonic C scan process is chose to select the uniform region of porosity. The signal only from the region is collected and processed to achieve the attenuation coefficient and the acoustic impedance of the sample. Then by combining the acoustic parameters with the porosity of specimen which is gained by destroying such as metallographic analysis, a test model was obtained. For the method of ultrasonic attenuation, the relation between the attenuation coefficient a and the porosity P is:α=1.65+1.78P, when 0.03%≤P≤0.5% andα=2.5+0.15P~2, when 0:5%≤P≤4.96%. For the method of acoustic impedance, the relation between the acoustic impedance Z_c and the porosity P is: Z_c=18.48P~2-349.53P+4794.30, when 0.6%≤P≤3.8%.When verifying the acoustic attenuation method and acoustic impedance method with sample whose porosity over 0.03% to 2.21%, we find that the error of porosity measurements in acoustic impedance method is less 0.08% than that in acoustic attenuation method . we can make use of the two method together when detect the porosity ultrasonic examination to verify the detection result each other. Otherwise, when the porosity is obtained by metallography, the expansion uncertainty of result U is 0.20% which is based on the synthesis uncertainty u_c=0.10% and the containing factor k=2. The confidence level of uncertainty is approximately 95%. This uncertainty can reflect the uncertainty level used in this research when detect porosity by metallography.