Self-healing of damaged particulate materials through sintering

Particulate materials loaded under uniaxial compression and tension are studied using the discrete element method. Self-healing of the damaged samples is activated through sintering, a process that effectively increases the contact adhesion (i.e. the tensile strength) between particles. The initial sample is prepared from spherical particles by applying high (isotropic) pressure, where particles in contact deform plastically and adhere to each other due to increased van der Waals forces. The result of this pressure-sintering is a solid sample from which the stress is released before uniaxial tension or compression is applied. Damage occurs microscopically through loss of contacts and thus loss of adhesion. In order to self-heal (part of) this damage, the system is sintered again, so that the adhesion at existing contacts in the damaged sample becomes stronger than originally. The stress-strain curves for the mechanically loaded samples are characterised by a peak-strength followed by a softening branch. Self-healing of an originally weak sample, up to a strong adhesion level, leads to qualitatively different stress-strain behaviour, dependent on the strain at which self-healing is applied. Interestingly, the response of the weak self-healed material is bounded by the damage response of the strong material. For an optimal self-healing of the particulate material, it is preferable to initiate the healing mechanism during the early stage of damage development, before the peak-strength is reached.