Damage Characteristics Analysis Of T700 Carbon Fiber Composite Based On Modal Acoustic Emission

Carbon fiber composite materials have high specific strength,high specific stiffness,corrosion resistance,high temperature resistance and other excellent physical and chemical properties,and are widely used in scientific research with a high proportion of science and technology.Although composite materials have the above advantages,due to long-term operation of composite materials in high load and corrosive environments,such as fatigue,creep,mechanical damage and other factors,it may cause visually invisible internal damage,resulting in macroscopic composite materials.The decrease in mechanical properties and the decrease in the residual properties of the material have an impact on the usability and reliability of the material.In the process of defects,carbon fiber composites produce acoustic emission signals due to matrix cracking and fiber breakage.In summary,it is very important to study the acoustic emission characteristics,damage detection and evaluation methods of carbon fiber composites.In this paper,the modal analysis of the acoustic emission signals generated by the typical surface source of the 7075-T6 aluminum plate and the side burst type and continuous type is carried out,and the typical sound source Lamb wave is combined with the dispersion curve of the 7075-T6 aluminum plate.Modal recognition,and the spectrum and modal characteristics during the propagation of typical sound source signals are studied.Tensile tests were carried out on T700SC-12000-50 C carbon fiber composite fiber filaments and resin matrix to cause fracture damage.Acoustic emission methods are used to acquire signals for damages occurring during the experimental process.The acoustic emission signal is subjected to parametric analysis and the waveform is extracted for waveform analysis,and the modal analysis of the spread wave and the bending wave is performed by modal acoustic emission means.The characteristics of several typical damage modal acoustic emission signals are analyzed.The acoustic emission signal generated by fiber breakage is determined to be a low-order spread wave signal,which is different from other damages.The results show that the method of modal acoustic emission is effective for analyzing the damage degree of fiber breakage of carbon fiber composites.The potential energy energy calibration experiment was carried out.The gravitational potential energy of the metal ball was released to impact the aluminum alloy plate to generate an acoustic emission signal,and the energy of the extended wave in the acoustic emission signal generated by the impact was calculated.The Polynomial curve was finally fitted.The relationship between the potential energy and the energy of the spread wave in the acoustic emission signal is determined,and the energy coefficient k is solved.In the typical damage form of carbon fiber composites,the fracture of fiber filaments and fiber bundles is the most influential form of damage to the structural integrity of composite specimens and containers.In general,it is not uncommon for a single fiber to break.Generally,a fiber bundle composed of a plurality of fibers is simultaneously broken.Because the composite material is opaque and the fiber diameter is small,it is difficult to directly prove that fiber breakage has occurred in the composite test piece or container.In this chapter,the relationship between the energy of the acoustic emission signal and the energy released by the fiber bundle breakage is established,and a method for judging the number of fiber bundle breaks is summarized.