a) Stress state in the vicinity of a planar crack as it approaches a spherical inclusion embedded in a linearly elastic matrix and subjected to a remote tensile loading perpendicular to the fracture plane. The left and right figures correspond to an inclusion three times stiffer (E* = E_sphere/E_matrix = 3) and three times more compliant (E* = ¹/₃) than the surrounding matrix, respectively. The Poisson's ratios of the sphere and matrix are equal (0.30).

b) A time sequence of video images shows the rupture of a microcapsule and the release of the healing agent. A red dye was added for visualization. The elapsed time from the left to right image is ¹/₁₅ s. Scale bar, 0.25 mm.
(See also: Video of crack propagates and heals in a piece of polymer -- QuickTime, 427Kb.)

c) A scanning electron microscope image shows the fracture plane of a self-healing material with a ruptured urea-formaldehyde microcapsule in a thermosetting matrix.
(See also: Video of crack propagates and heals in a piece of polymer --QuickTime, 427Kb.)