Ductile fracture studies in an Al-4% Cu alloy

• Main Author: Belcher, W. P. A.
• Published: University of Cambridge 1979
• Subjects: 669
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596529

An Al-4% Cu alloy has been heat treated to produce a series of precipitate dispersions in which a wide range of particle variables could be considered with respect to the mechanisms associated with ductile fracture. Void initiation studies were performed on dispersions deformed by rolling or in tension. Θ particles initiated voids by particle cracking, the extent of which increased with increasing strain and was inversely proportional to the deformation temperature. Particle shear and tensile fracture mechanisms operated, the former a result of slip line/particle intersections, the latter predominantly an effect of fibre loading tensile stress. The change from Θ particle cracking to Θ ' deformation with matrix strain was associated with a change of particle nature, size and coherency, and resulted because dislocations were able to shear Θ ' precipitates. Results suggest that particle shear is more effectively controlled by particle nature than interface coherency. Void initiation by particle/matrix interface decohesion at Θ or Θ ' particles was not observed in the absence of a propagating ductile crack or behind any fracture surface. The effect of precipitate variables on the overall ductile fracture process was assessed by correlating precipitate and fracture surface dimple spacings for each particle dispersion. A critical precipitate size criterion for void initiation at Θ ' particles by interface decohesion was suggested. For precipitates larger than this critical size, void initiation by interface decohesion at particles ahead of a propagating ductile crack was proposed to explain the observed involvement of particles in ductile fracture irrespective of their size, shape, coherency, nature, orientation, structure and cracking or deformation characteristics. The stress concentration requirement for interface decohesion suggests the relevance of an interfacial stress criterion for ductile fracture, and the importance of large particle cracking in initiating the ductile crack.