Acoustic-Optical-Thermal Detection Of Damage Evolution Behavior Of Carbon Fiber Reinforced Composites

Carbon fiber reinforced composites with high strength and modulus as well as the design of excellent properties,are widely used in various fields.However,in the process of long-term service,carbon fiber reinforced composites may be damaged by stretching and bending load.It is of great significance to study the damage evolution and failure analysis processes,which can provide the basis for its health testing.Carbon nanotubes have good mechanical properties,and the combination with carbon nanotubes and other nanomaterials is of great significance for the expansion of their applications.In order to improve the properties of planar two-dimensional carbon fiber reinforced composites,3D braiding technology is adopted to obtain 3D braided prefabricated parts.Because of its excellent mechanical properties,it has a wide application prospect.In this paper,acoustic emission nondestructive detection technology was used to monitor the damage process of carbon fiber reinforced composite samples in real time,and the AE data were post-processed by means clustering and fuzzy clustering analysis.Digital image correlation and acoustic emission techniques were used to monitor and analyze the damage process of carbon fiber reinforced composite samples from the inside and outside.In addition,the infrared thermal imaging detection technology,combined with acoustic emission technology and digital image correlation method,was used to analyze the three aspects of sound-light-heat,and the internal characteristics and fracture damage morphology of the composite material specimen were observed through microscopic CT.The results indicate that:(1)During the tensile damage evolution process of open-hole carbon fiber reinforced composite laminates with/without carbon nanotubes,the addition of carbon nanotubes can reduce the stress concentration,improve the strength and interfacial fracture stiffness of composite laminates,and prevent the development of micro cracks.Acoustic emission signals were concentrated in three areas: 23-74 k Hz(matrix cracking),82-120 k Hz(fiber pull out and delamination),120-190 k Hz(fiber breakage).(2)In the bending experiments of carbon nanotubes with different off-axis angles,the maximum load and stiffness of the laminates decreased with the increase of off-axis angles.Three key points(linear growth point,maximum load point and failure point)were selected to study the progressive damage process of composite materials.The existence of Kaiser effect was observed.With the increase of off-axis angle,damage degree of elastic-plastic matrix and maximum load that can be sustained are increased.(3)In the process of tensile loading of specimens with different off-axis angles,the stiffness decreases with the increase of off-axis angles.When the off-axis angle is 0o,the initial stress of the fibers increases,and the brittle fracture characteristics are obvious.Because of the symmetrical structure,the tensile strength of the composite specimen with 45o off-axis angle is increased by 23.65% compared with that with 30o off-axis angle.(4)In the process of tensile loading,acoustic emission signals can be divided into three categories(matrix fracture,fiber/matrix debonding,fiber fracture)for different volume fraction of 3D braided carbon fiber composite material.Under the same tensile load increment,the displacement field in the loading direction decreases with the increase of the volume fraction,and the maximum failure temperature increases slightly.