Fracture toughness of selectively reinforced Al2124 alloy: Precrack tip in the composite side

Residual Stress Evaluation of AA2024-T3 Friction Stir Welded Joints

“…effectively reduces the local K. The negative values of K rx are likely to produce strong fatigue crack growth deceleration if a crack approaches perpendicularly to the weld line, however after crossing the weld region, K rx are positive and the crack may accelerate, when compared to parent material behavior. It is important to emphasize that such analysis does not take into account the differences in plastic properties of the different regions of the weld which may cause crack retardation or acceleration depending if the crack grows into a soft-hard or hard-soft transition, respectively (Milan and Bowen, 2003, Milan and Bowen 2004aand Milan and Bowen, 2004b. Therefore, when cracks grow in welded structures the effective crack tip driving force will be ruled by a synergistic interaction of the material intrinsic behavior, residual stresses and plastic mismatch between weld regions.…”

“…On the other hand, compressive residual stresses reduce the fatigue crack growth rate by decreasing the stress intensity factor range and/or stress ratio. Additionally, residual stresses were found to affect initiation fracture toughness values of aluminum alloys Bowen, 2004a andBowen, 2004b).…”

Fracture toughness of selectively reinforced Al2124 alloy: precrack tip in the aluminium alloy side

“…Tests were performed at air and room temperature in the as pressed condition (T1 heat treatment), at a crosshead speed of 0 . 5 mm min 21 .…”

“…5 mm from the interface, K Q (5%) values increase and reach values as high as the 'Al2124 only' value (except for the Al2124/ Al2124z25%SiC(20 mm)). This suggests that as the crack tip gets closer to the interface, K Q (5%) values are increased by the increase in the shielding effect caused by the elastic/ plastic mismatch (now the plastic zone size interacts with In order to demonstrate the effects of the elastic/plastic mismatch on the crack tip driving force, an empirical bimaterial mismatch factor M was introduced in a previous work and it is given by the following equation 21 M~K Q (5%) 00 K Q (5%)zK r : : : : : : : : : : : : (1)…”

“…This crack tip blunting and deflection mechanism increases the toughness of the bimaterial at the subsequent plastic collapse. 21 The main purpose of the current paper is to assess the contributions of elastic mismatch, plastic mismatch, precrack position, and thermal residual stresses to the fracture toughness values of Al2124/Al2124zSiC bimaterials when the precrack is positioned perpendicular to the interface, in the unreinforced Al2124 side and at different distances from the interface. Its intention is to contribute to the knowledge base to expose issues that may occur in a wide range of functionally graded materials and if they are subjected to load bearing applications where failure must be avoided.…”