Optimization Of 2-D Random Void Model For Composite Materials And Analysis Of Effect Of Void Morphology On Acoustical Parameters

It's of great significance to establish the physics model with void compound materials in order to carry out the void content test with the method of ultrasonic attenuation. In the present physics model void compound materials were supposed to be formal medium consisting of blowholes with the same size and regular shape. But the prediction concluded from the model greatly differed from the experimental results and there was some results not easily to be explained. Based on the research results on the metallurgical statics of void morphology in the case of Carbon Fiber Reinforced Polymer and the established 2-dimensional Random Void Model resulted from the random theory of statics, in this study five parameters introduced in the establishing process of 2-dimensional RVM were analyzed and optimized:roughness factor r, autocorrelation length a and b, disturbance standard deviation s and void content P which was aimed at 15 sets of samples with porosities ranging from 0.03% to 4.62%.In addition the ultrasonic transmission process in RVM was also simulated with the method of Finite Difference Time Domain and the effect of void morphology on the ultrasonic attenuation coefficient and the ultrasonic longitudinal wave velocity was also investigated.Optimization on the 2-dimensional Random Void Model showed that void margin smoothness, the average void size of the model and the deviation between the void and the matrix were all determined by roughness factor r, autocorrelation length a and b and disturbance standard deviationε, respectively. The error between the void morphology statics of RVM and metallurgical statics of samples was less than 2% after optimizing parameters, which met the value calculation precision.For the unchanged void content, the ultrasonic attenuation coefficient affected by single morphological factor such as the shape, orientation, amount and distribution as well as multiple random characters of voids was calculated in the simulation. For the void with ellipse shape, the ultrasonic attenuation coefficient both increased with increasing size of void vertical to the ultrasonic transmission direction. Aimed at the 8 void contents ranging from 0.6 to 4.62%, it was found that the random change in void morphology would result in the fluctuation of ultrasonic attenuation coefficients and higher void content level led to larger fluctuation of ultrasonic attenuation coefficients and unusual large voids would take significant effect on the scattering attenuation coefficients after investigating the void morphology and its correlation with porosity volume fraction, ultrasonic frequency and ultrasonic scattering attenuation coefficient.Aimed at the statistics results for 15 void contents ranging from 0.03 to 4.62%,2D-RVM was established by using nine pairs of autocorrelation length a and b for each porosity and the ultrasonic longitudinal-wave velocity was simulated and calculated. The relationship between the ultrasonic longitudinal-wave velocity and the void content P, autocorrelation length a and b and autocorrelation length ratio b/a was also discussed and analyzed. Calculated results showed that the larger the void content was, the smaller the ultrasonic longitudinal-wave velocity was. With autocorrelation length a and b tending to go up, correspondingly, the acoustic velocity would slightly decrease or increase. The change of void morphology would have an effect on the longitudinal-wave velocity.