Study on the macro- and micro-mechanical properties of quartz fiber reinforced polyimide resin matrix composite after thermal aging

In this work, the polyimide resin (YH-550) with high glass transition temperature (similar to 403 degrees C) was selected as the matrix, and the quartz fiber reinforced polyimide resin matrix (SiO2f/PI) composite was prepared by prepreg hot pressing method. In order to obtain the evolution mechanism of macro-and micro-mechanical properties of the SiO2f/PI composite after thermal aging, the composite was first subjected to thermal aging at 250 degrees C and 350 degrees C for 100 h (SiO2f/PI-250 degrees C, SiO2f/PI-350 degrees C) in air, respectively. And then the as-received SiO2f/PI, SiO2f/PI-250 degrees C and SiO2f/PI-350 degrees C composite was tested by SEM, macro-mechanics, nano-mechanics and XPS. Thus, the macro-and micro-mechanical properties of the SiO2f/PI composite were constructed. The results show that the SiO2f/PI-250 degrees C composite still has excellent mechanical properties. However, the flexural strength of SiO2f/PI-350 degrees C composite decreases remarkably (similar to 227.7 MPa). The in-situ modulus of fiber and matrix in as-received SiO2f/PI, SiO2f/PI-250 degrees C and SiO2f/PI-350 degrees C composite do not change significantly, but interfacial shear strength (IFSS) changes greatly, which are 106.7 +/- 2.0 MPa, 97.0 +/- 8.3 MPa and 14.7 +/- 0.7 MPa, respectively. Based on the basic mechanical theory of composites, it is concluded that the decrease of IFSS is the fundamental reason for mechanical properties degradation of SiO2f/PI-350 degrees C composite, and the interface evolution mechanism of the composite was discussed.