Fabrication And Properties Of SiO_2f/PI Composites Based On Liquid Phase Impregnation Technology

With the continuous development of long-range strike and precision guidance technology,high-performance composite materials with high strength,high toughness,good electromagnetic wave permeability and high temperature resistance have become the key materials for technological innovation.Base on the application of high-temperature radome and the wave-transmitting composites for high temperature resistant,the two-dimensional and three-dimensional quartz fiber fabric reinforced polyimide composites(2D-SiO_2f/PI,3D-SiO_2f/PI)were prepared.The mechanical properties,dielectric properties and high temperature resistant performance of the materials were systematically investigated,and the relationship between the stitch density and material properties was also further studied.The 2D-SiO_2f/PI composite was formed through vacuum-assisted impregnation and then prepared by hot pressing process.The microstructure,mechanical property and dielectric property of the material were characterized by a series of technologies.Compared with the quartz fiber pretreated at 600°C in air,the quartz fiber pretreated by acetone immersion showed higher tensile strength and its reinforced composite has much higher mechanical properties.The porosity of 2D-SiO_2f/PI composite is 0.14%,the in-situ modulus of the matrix and fibers are 4.7±0.2GPa and 64.7±3.0GPa,respectively.The interfacial shear strength of composite is 93.24±1.97MPa.The average dielectric constant is 3.347 and the average loss tangent is 0.012 in 8～12GHz.The bending strength and bending modulus of composite is 591.9±4.6MPa and18.3±1.5GPa,respectively.The interlaminar fracture toughness is 1.18±0.38kJ/m²,which shows poor resistance to delamination.After heat-treated at 500°C for 1000s,the interior of the composite appears obviously delamination damage with weight loss of1.4%,the average dielectric constant is reduced to 2.984 and the average loss tangent is0.011 in 8～12GHz.The bending properties of the composite at 500°Care significantlydecreased,with bending strength 78.5±5.6MPa（retention of 13.26%）and bending modulus7.83±1.61GPa（retention of 42.72%）.Aiming to overcome the weakness of poor resistance to delamination,the3D-SiO_2f/PI composite was prepared using stitching technology,and the relationship between the stitching density and the material properties was studied.The porosities of3D-SiO_2f/PI composite with different stitching density are all below 2%,and the dielectric constants are about 3.4 and the average loss tangents are 0.01～0.02 in8～12GHz.The flexural strength of the composite with the stitching density of3mm×3mm was 483.64±50.66MPa and the flexural modulus is 18.21±0.80GPa.The bending strength and modulus of the stitched composites decreased lightly（the reduction rate was within 23%）,while the interlaminar fracture toughness of composite with stitching density of 3mm×3mm was improved with an increase of 4 times（6.08±0.39kJ/m²）.After 1000s treatment at 500°C,the delamination of 3D-SiO_2f/PI composites with different stitching densities was slowed down.The average dielectric constant was about 3.2～3.4,and the average dielectric loss was 0.02～0.03.The retention rate of real-time bending strength at 500°C of composites with different stitching densities was improved,and the retention rate of composites with stitching density of3mm×3mm increased to 20.74%.The stitching process effectively improves the real-time high-temperature mechanical properties of the composite material and improves the reliability of the composite structure and performance.