From discrete particles to solids - about sintering and self-healing (Review)

In this review, particulate materials are studied using the Discrete Element Method (DEM), where the particles keep their identity throughout. Loose particles can sinter due to time-, stress- or temperature-dependent forces. Large deformations of sintered samples will then lead to damage. Self-healing of damaged samples can be activated through resintering, a process that increases further the contact adhesion between particles. Initially, the particle-samples are prepared by applying isotropic (hydrostatic) pressure. The spherical particles deform plastically at contact and stick to each other due to strong, non-linearly increased van der Waals forces. Such pres-sure-sintering results in a solid sample with (after releasing pressure) zero conflning stress - on which uni-axial tension or compression can be applied. Damage can occur through loss of contacts and/or loss of adhesion and more damage will occur with increasing deformation. In order to trigger "self-healing at different damage levels, the mechanical loading is first stopped, second, the system is resintered (so that the adhesion at existing contacts in the damaged sample becomes stronger than originally), and third, mechanical loading is continued with the healed sample, in order to study the material properties after the healing event.