Damage Monitoring And Evaluation Of Anti-oxidized Carbon-carbon Composites Based On Electrical Resistance Method

Carbon fiber reinforced carbon(C/C)composites have excellent high temperature mechanical properties.Multi-matrix C/C composites have superior high temperature and ablation resistance based on C/C composites.Anti-oxidized carbon-carbon composites is a typical multi-matrix C/C composite material,which has broad development prospects in the aerospace field.However,as the material is used,damage will continue to occur.Most non-destructive testing techniques are extremely difficult to achieve real-time monitoring of material damage.The electrical resistance method is a kind of damage assessment method that can be observed in real time and is easy to operate.First of all,the conduction mechanism of composite materials was summarized,and the theoretical model of resistance change rate-strain was derived,which provided theoretical support for subsequent experimental data analysis.After that,an acoustic/force/electric joint experimental platform was designed at room temperature.The electrode connection mode,resistance measurement mode and experimental rate were selected,and the test specimen was pretreated to meet the experimental requirements.Secondly,The monotonic stretching,tensile loading and unloading mechanical experiments of Anti-oxidized carbon-carbon composite materials on the acoustic/ force/electric combined experimental platform were carried out.At the same time,the acoustic emission technology and the electric resistance method were used to detect the mechanical experiment process in real time.The characteristic parameters of the acoustic emission signal were extracted and clustered,and two kinds of signal characteristic parameters were obtained.Combined with the fracture microscopic scanning,two types of signals were analyzed to represent the damage modes of matrix crack and fiber bundle fracture.It was concluded that the initial stress and saturation stress of the Anti-oxidized carbon-carbon composites matrix were respectively 10 MPa and 90 MPa.CoMParing the characteristics of resistance change,it is found that the resistivity of the matrix cracks rises slowly,the resistivity of the fiber bundle breaks increases sharply,and the resistance change rate-strain model is fitted.The results are good,which proves that the model has certain reference.Finally,a thermal/force/electric joint experimental platform was designed.For the special nature of high temperature environment,the fixture structure,wire material,insulation measures and lead method were specially selected and treated.The tendency of the material resistance to change with temperature was tested under the condition that the material itself did not apply a load.It is proved that Anti-oxidized carbon-carbon composites is a negative temperature coefficient(NTC)material,that is,the material resistance of the material decreases with increasing temperature,and the resistance returns to the initial level after cooling.The resistance damage detection of the Anti-oxidized carbon-carbon composites under monotonic stretching at 600 ° C and 1000 ° C was completed.Different damage mode were obtained.It shows that the electrical resistance method is achievable in the field of nondestructive testing in the future.