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Ductile fracture process consist of the nucleation, growth and coalescence of voids in a material during plastic deformation. It has been studied extensively in the literature but there is still no complete theory of ductile fracture that covers all three phases of the process. A critical issue is the lack of systematic experimental ways to observe the coalescence of voids.

Ductile fracture process which consist of void nucleation, growth and coalescence.

Fracture surface showing coalesced voids.

The reason for the lack of experimental results resides in:

• the statistical nature of void nucleation
• the stochastic nature of coalescence which occurs over small strain increments
• the too large number of voids on the fracture surface
• the difficulty in visualizing the voids in the bulk of the sample

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By combining a variety of new techniques, it was possible to visualise the ductile fracture process in details. Two types of model materials were fabricated. The first has a core/shell design and is made of a pure aluminum matrix reinforced in its center by Zirconia/Silica spheres. The second consists of laser drilled metallic sheets that can be diffusion bonded to obtain an embedded 3D array of holes. In-situ tensile tests are then carried out in the scanning electron microscope (SEM) and in an x-ray computed tomography set-up. The advantages of such approches are as follows:

• Void nucleation is controlled by having a uniform distribution of spherical particles.
• The nucleation event can be removed by having the laser drilled holes
• The laser holes (voids) can be presisely positioned
• The failure is controlled by having a core/shell design
• In-situ tensile tests allow better capture of the coalescence event
• Using x-ray computed tomography it is possible to visualize the ductile fracture process in the bulk