Study On Tensile Deformation And Progressive Damage Of Carbon Fiber Three Dimensional Braided Composites

Carbon fiber three-dimensional weaving composite materials in the aerospace,automotive and industrial engineering fields,the inevitable application of impact and collision damage,and then affect the mechanical properties of composite materials and the incidence of potential safety hazards.Therefore,the in-depth understanding of the mechanism of the damage evolution of carbon fiber composites is of great significance for its safe service and prolonged service life.It can also provide structural optimization design and high-performance composite material production.Therefore,this paper uses the Digital Image Correlation(DIC)method and Acoustic Emission(AE)technology combined with the K-means clustering algorithm to stretch,indent and compress the carbon fiber plain-woven composites.Based on the evolution law of damage,the characteristics of AE behaviors,K-means clustering results and changes of local micro-deformation field during the three-dimensional woven and three-dimensional four-directional braided composites were studied in depth.Based on the macroscopic and microscopic changes in the morphology of the composite material and the research results in the field,the correlation between the specific failure AE signal and the damage mechanism was established.In addition,according to the time-domain characteristics of the AE signal in the process of composite material failure,the sentinel function and B value processing method of AE signal are used to respectively perform the failure criteria for the damage history and thoroughly explain the dynamic evolution process in the composite material destruction process.Experimental results show:(1)The relative parameters such as AE relative energy,cumulative number of impacts,and amplitude during the damage process of carbon fiber composite material reflect the internal damage evolution process of the composite material;there are many high duration,high amplitude AE signals near the critical point of composite material failure.,and the cumulative number of impacts increased significantly.(2)When the quasi-static indentation load is small,the surface of the plain-woven braided composite has a small surface damage area and little effect on its residual compressive strength.When the indentation load reaches 40 kN,the indentation damage results in a large number of layers and fibers in the composite.Breakage and local area damage penetration,and the actual damage conditions lead to a significant decline in the residual compressive strength of the composite,and the fracture form changes from complex failure mode to brittle fracture.(3)The AE damage evolution rules of plain weave composites,3D woven composites and 3D braided composites are different,but the clustering results of AE signals are similar.Compared with the peak amplitude of AE,the frequency distribution shows superiority in feature recognition of the damage source of composite materials.Based on the research results in this field,frequency distribution ranges of different damage modes are established: 0-50 kHz low-frequency AE signals corresponding to the matrix cracking;50-150 kHz of AE signal corresponding to fiber/matrix debonding;250-600 kHz high frequency AE signal corresponding to fiber breakage.(4)According to the dynamic relationship between instantaneous mechanical energy of composite materials and AE energy,the information of damage pattern evolution under different load levels can be effectively obtained,and the signal processing method for exploring the damage evolution law of composite materials is simplified;the time domain distribution of b value of AE signal is changed.It is possible to effectively extract the appearance of internal cracks in the specimen and determine the level of the load that is about to expand unstably.(5)In the plain weave composites and the three-dimensional woven composites,the strain field at the surface of the specimen changes more uniformly at low strain levels.As the average strain level increases,random local strain concentration points appear;for three-dimensional braided composite materials in the surface strain field,at the low average strain level,the strain concentration point first appears in the yarn interweaving area,and along with the increase of the average strain level,the high strain area develops along the transverse and longitudinal direction of the yarn and finally forms the braided yarn.It is a saw-tooth strain concentration belt of the loaded body.