Self-healing of damaged particulate materials through sintering

Abstract

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.

Keywords:

• DEM simulation
• sintering contact model
• micro-macro relations
• tensile and compressive tests
• self healing materials

Acknowledgements

The authors acknowledge the financial support from the Delft Centre for Materials (DCMat) in the form of project TCO501, “Modelling of repeated self-healing processes in materials”. Furthermore, the helpful discussions with Prof. S. van der Zwaag (Delft University of Technology) on self-healing materials, Dr. W.G. Sloof (Delft University of Technology) on thermal-barrier coating systems and Dr. L. Brendel (University Essen-Duisburg) on particle contact laws are gratefully acknowledged.