| The carbon/glass fiber composite can not only make full use of mechanical properties the two kinds of fibers,but also can reduce the reflection of the radar wave through the reasonable arrangement of carbon fiber and glass fiber,which is a kind of structure-function integrated material used in stealth fighter.The degradation of resin matrix performance and interface performance caused by the thermo-oxidation environment will affect the service life of the fighter.This paper aims to find out the change law and mechanism of properties of threedimensional orthogonal and laminated carbon/glass fiber bismaleimide composites aging at200 ? and 250 ? for various aging time.Thermo-oxidation aging had a positive effect on the stealth performance of three-dimensional orthogonal carbon/glass/bismaleimide composite(3D-CF/GF/BMI composite).During the process of thermo-oxidation aging,the surface of the composite became uneven due to the degradation of the resin matrix,which increased the diffuse reflection of electromagnetic waves on the surface and reduced the reflection of electromagnetic wave.Cranks propagation in the material provided more channels for the propagation of the electromagnetic waves in the material.Therefore,thermo-oxidation aging had a positive effect on the stealth performance of the 3D-CF/GF/BMI composite.Moreover,the diffuse reflection of electromagnetic waves of the unaged 3D-CF/GF/BMI composite lower to that of laminated carbon/glass/bismaleimide composite(LM-CF/GF/BMI composite)due to the electromagnetic transmission effect of Z-binder yarns and the microwave anechoic chamber effect of three-dimensional orthogonal structure.Thermo-oxidation aging led to the continuous degradation of fiber/matrix interface properties with the rise of aging time.The Scanning Electron Microscopy observation results showed that the amount of resin adhered to the fiber decreased with the aging time.Besides,obvious voids appeared between fibers.The results of the transverse fiber bundle tensile test showed that the interfacial strength of the carbon fiber/resin matrix is higher than that of the glass fiber/resin matrix.After aging,the interfacial strength of both composites decreased obviously,and the interfacial strength of the former was less than that of the latter.On the one hand,the thermal expansion coefficient difference between carbon fiber and resin matrix is more considerable,and more significant thermal stress will be generated at the interface during the thermo-oxidation aging process,resulting in a sharp decline in interfacial strength.On the other hand,the sizing agent on the surface of carbon fiber is easy to decompose at high temperatures,which would reduce the interface strength.The degradation of resin and the degradation of interfacial properties caused by thermooxidation aging resulted in a decrease in the mechanical properties of the two kinds of composites.During the process of thermo-oxidation aging,the crack of LM-CF/GF/BMI composite expanded along the interlayer,which caused to occur delamination failure.However,the integrated structure of the 3D-CF/GF/BMI composites enabled all fibers together to resist external forces in the case of severe degradation of resin and interfacial properties.The “modified random process model” was used to predict the bending strength of 3DCF/GF/BMI composites aged at 200? for 180 days.The prediction error was less than 10%,indicating that the model was reliable.This paper contains 36 figures,9 tables,and 126 references. |
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