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

Abstract

The fracture toughness of Al2124/Al2124zSiC bimaterials is affected by thermal residual stresses, elastic/plastic mismatch, precrack tip position, and failure mechanism. When the precrack tip is in the Al2124 side, final catastrophic failure occurs when ductile fracture of the Al2124 layer between the precrack tip and the composite side takes place, followed by fracture of the composite layer. For a precrack tip 2 . 0 mm from the interface, K Q (5%) values are lower than the 'Al2124 only' value due to the near crack tip tensile residual stresses and higher stress triaxiality within the Al alloy ligament. At 0 . 5 mm from the interface, K Q (5%) values increase and are usually as high as the 'Al2124 only' value due to the stronger shielding of the elastic/plastic mismatch. If the precrack tip is 2 . 0 mm from the interface, K crit values of the bimaterial are higher than the 'Al2124 only' value and this is deduced to be due to the elastic/plastic mismatch shielding. At 0 . 5 mm from the interface, K crit values are reduced because both the near tip tensile residual stress is higher and stress triaxiality levels of the ductile ligament are higher, although the elastic/plastic mismatch shielding is also higher at this position.MST/6011

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).…”

Fatigue behaviour of friction stir welded AA2024‐T3 alloy: longitudinal and transverse crack growth

“…On the other hand, compressive residual stresses reduce the fatigue crack growth rate (FCGR) by decreasing the effective stress ratio. Additionally, residual stresses were found to affect initiation fracture toughness values ( K C ) of aluminium alloys 6,7 …”

“…Additionally, residual stresses were found to affect initiation fracture toughness values (K C ) of aluminium alloys. 6,7 Transverse cracks present an even more complex situation, inasmuch as the defect propagates from the parent material towards the weld region. The crack tip intersects different microstructures and distinct intrinsic fatigue cracking behaviours can be expected.…”