||The thesis aims to investigate the mechanical behavior and properties of a centrally notched hybrid Magnesium/Carbon-Fiber/PEEK laminate at elevated temperature. The high performance hybrid composite laminates of 0.5mm Magnesium sheets sandwiched by Carbon-Fiber/PEEK (APC-2) guasi-isotropic and cross-ply laminates were fabricated. The Magnesium sheets were polished and cleaned by acetone, then underwent the surface treatment by CrO3-base solvent etchants, cured by the improved diaphragm curing process. The finished laminates were cut into the specimen than drilled a 4mm diameter hole in the center of specimen.|
At first, the ultimate strength, stiffness and stress-strain diagram were obtained due to static tension tests at elevated temperature, such as 25°C(RT), 75°C, 100°C, 125°C, and 150°C. Compare of them, the notched quasi-isotropic ones drop almost 50% in strength, and the notched cross-ply ones are half of unnotched ones. The two lay-up notched specimens are slightly below the unnotched ones in stiffness. The strength of the specimens are decrease as temperature rise. As the temperature rise the stiffness of quasi-isotropic ones drop, but it just change little in cross-ply ones.
Then the notched specimen fatigue life and load-cycle (P-N) curves were obtained by tension-tension fatigue test. The P-N curves were adopt to prevent the stress concretion of the notched specimen. Consider the same loading, notched specimens has worse fatigue behavior, but in the same load ratio, the normalized P-N curves of the unnotched ones were below the notched ones means notched ones has better fatigue behavior.
Recording the specimen image by video camera during the testing process, the cracks at the edge of hole were found. However delamination was not found. Necking was observed in quasi-isotropic specimens, but not in cross-ply. Observed by optical microscopy, the improved surface treatment will decrease the probability of delamination from 20% to less than 10% after hot press.