Mechanical Properties with High Temperature and the Microstructure of Carbon/Phenolic Ablative Composites

Carbon fiber reinforced phenolic based composites were prepared by laminating molding. The variation in mechanical characteristics of composites was evaluated with heating temperature and procedure. The microstructures of composites at different temperatures were observed by optical microscope and scanning electron microscope, respectively. The results showed that the main weight loss range of carbon/phenolic is from 300 to 800 ℃, before 700 ℃ the weight loss was resulted from pyrolysis and after that the weight loss was mainly by oxidation in the fiber phase; with the heat treatment temperature rising, the bonding at the interface of carbon fibers and resin matrix weakened; in the pyrolysis temperature range, the interlaminar shear strength（ILSS） of carbon/phenolic showed a rapid drop with temperature rising, and then decrease in the rate of ILSS became relatively slower; the fiber oxidation had little influence on the ILSS.

Strain-rate Sensitivity of Aluminum 2024-T6/TiB_2 Composites and Aluminum 2024-T6

Strain-rate sensitivities of 55vol%-65vol% aluminum 2024-T6/TiB2 composites and the corresponding aluminum 2024-T6 matrix were investigated using split Hopkinson pressure bar method. The experimental results showed that 55vol%-65vol% aluminum 2024-T6/TiB2 composites exhibited significant strain-rate sensitivities, which were three times higher than the strain-rate sensitivity of the aluminum 2024-T6 matrix. The strain-rate sensitivity of the aluminum 2024-T6 matrix composites rose obviously with increasing reinforcement content（up to 60%）, which agreed with that from the previous researches. But it decreased as the ceramic reinforcement content reached 65%. After high strain rates compression, a large number of dislocations and micro-cracks were found inside the matrix and the Ti B2 particles, respectively. These micro-cracks can accelerate the brittle fracture of the composites. The aluminum 2024-T6/Ti B2 composites showed various fracture characteristics and shear instability was the predominant failure mechanism under dynamic loading.

Enhanced mechanical properties in Al/diamond composites by Si addition

Diamond particles reinforced aluminum–silicon matrix composites,abbreviated as Al（Si）/diamond composites,were fabricated by squeeze casting.The effect of Si content on the microstructure and mechanical properties of the composites were investigated.The mechanical properties are found to increase monotonically with Si content increasing up to 7.0 wt%.The Al-7.0 wt% Si/diamond composite exhibits tensile strength of 78 MPa,bending strength of 230 MPa,and compressive strength of426 MPa.Al–Si eutectic phases are shown to connect with Al matrix and diamond particles tightly,which is responsible for the enhancement of mechanical properties in the Al（Si）/diamond composites.