Abstract
In this study, the relationships between toughness and laminated cracks were investigated on 8090 Al-Li system alloys. In 8090V notched specimens, total absorbed energy increases with decreasing temperature up to 142K, and then decreases at 77K. This phenomenon is closely associated with the change in the number of laminated cracks on the fracture surface. Absorbed energy for forming laminated cracks is greatest at 142K. Crack propagation energy, then, increases, which results in increasing total absorbed energy. Dynamic fracture toughness and the number of laminated cracks increase with decreasing temperature. The maximum dynamic fracture toughness value is obtained at 5K. Dynamic fracture toughness increases due to the increase in the number of laminated cracks. Modified microcrack toughening concept is introduced for explaining increasing toughness by laminated cracks. The calculating value of increasing ratio in fracture toughness between R. T. and 77K is in good agreement with the experimental value of increasing ratio in fracture toughness. This result suggests that the effect of stress release by laminated cracks near the crack tip is the main cause for increasing toughness of Al-Li system alloys at low temperature.
