Characterization In Situ For Acoustic Emission And Tensile Mechanics Of Fiber Bundle At Breaking

Compared to the single fiber tensile test, fiber bundle tensile test is a rapid and convenient method for fiber mechanical testing. It has smaller variation, fewer testing times and could provide more information, so it plays a significant role in fiber testing. However, only through the fiber bundle tensile test, the strength distribution of single fiber is beyond measure, and the elongation distribution of single fiber is only theoretical calculated.When Fiber bundle is stretched to fracture, discontinuous audio acoustic emission can be heard. The acoustic emission is generated by the conversion of part of the elastic potential energy coming from the stress deformation of fiber. Therefore, for one, there must be a relationship between the mechanical properties of fracture point of fiber and the acoustic emission. For another, each acoustic emission and single fiber fracture is one-to-one correspondence in time, so it can make a real-time measurement of fiber bundle in the time domain. Based on the acoustic emission spectrum in fracture of fiber bundle, the purpose is to measure the fiber bundle fracture strain and fracture stress accurately, and to realize the measurement and characterization in situ of acoustic emission and tensile mechanics of fiber bundle at breaking.Combined with the principle of fiber bundle tensile test and acoustic emission test, the sound module of the existing TMT-InFiBTensor is designed. Based on the thoughts of virtual instrument, the collection of voice signal in Lab VIEW environment by using common sound card, wavelet noise reduction and waveform parameter extraction with the MATLAB Script node are realized.Test with wool and ramie fiber bundle, respectively. In order to find out the number of fracture fibers at a certain time or elongation in bundle fiber tensile test accurately, a method based on wavelet transform and waveform analysis id proposed to distinguish the fracture acoustic signal from the noise. De-noising effects of different waveform parameters are compared, and new complex parameter M and X are presented, the experimental results verify that the M and X critical value can identify the fracture fiber accurately, the error rate are less than5%.According to the fracture acoustic emission wave time, the fracture elongation distribution of wool and ramie fiber bundle are calculated respectively. And the computation of fracture elongation distribution has reliability, and the results of wool have good consistency with the front part of single fiber fracture elongation distribution curve based on stress-strain curve, and the two distribution curves have strongly consistent characteristicsin in tiny fluctuation of minute random.Through the combined test of wool and ramie single fiber, there is a good linear relationship between fiber breaking strength and fracture energy of acoustic emission. So it can be used to estimate fiber breaking strength through the single fiber fracture acoustic signal energy. The experimental results show that the strength distribution of wool and ramie fiber bundle calculated by the method above are very similar with the result from real measurement, and the average fracture strength are close to experience value. So the estimated results can be reference value and have certain practical significance.