High-throughput screening the micro-mechanical properties of polyimide matrix composites at elevated temperatures

In this work, a novel high-throughput methodology based on combinations of nanoindentation, indentation creep and push-in methods, is proposed to measure in-situ the micro-mechanical properties of typical polymer matrix composites at a wide temperature range. The Young's modulus and strain rate sensitivity of a polyimide matrix and the interfacial shear strength in a quartz fiber reinforced polyimide matrix composite are measured at 25–350 °C for the first time. The results highlight a linear softening of the polyimide matrix at high temperatures, which is evidenced by the approximate linear decrease of Young's modulus from ≈5.0 GPa at 25 °C to ≈1.1 GPa at 350 °C. In comparison, the strain rate sensitivity of the polyimide matrix is increased, from ≈0.032 at 25 °C to ≈0.062 at 350 °C. This evidences a stronger visco-plasticity of polyimide at higher temperatures. The shear strength of the fiber/matrix interface is also temperature dependent. As the testing temperature increases from 25 to 300 °C, the shear strength is decreased from ≈147 MPa to ≈40 MPa. Specially, the interfacial strength is extremely low at 350 °C (≈4 MPa), evidencing a failure of the composite at this temperature.