Phase-field modelling of failure in ceramics with multiscale porosity

TL;DR

This paper develops a phase-field finite element model to analyze how multiscale porosity affects failure mechanisms in ceramics, inspired by biological materials like bone and wood, to guide the design of bio-mimetic artificial materials.

Contribution

It introduces a multiscale porosity model using phase-field fracture simulation to understand failure in ceramics, bridging biological insights and artificial material design.

Findings

Small voids promote damage nucleation and crack bridging.

Macro-pores influence fracture propagation and overall response.

Multiscale porosity plays a critical role in failure mechanisms.

Abstract

Many stiff biological materials exhibiting outstanding compressive strength/weight ratio are characterized by high porosity, spanning different size-scales, typical examples being bone and wood. A successful bio-mimicking of these materials is provided by a recently-obtained apatite, directly produced through a biomorphic transformation of natural wood and thus inheriting its highly hierarchical structure. This unique apatite (but also wood and bone) is characterized by two major distinct populations of differently-sized cylindrical voids, a porosity shown in the present paper to influence failure, both in terms of damage growth and fracture nucleation and propagation. This statement follows from failure analysis, developed through in-silico generation of artificial samples (reproducing the two-scale porosity of the material) and subsequent finite element modelling of damage, implemented with phase-field treatment for fracture growth. It is found that small voids promote damage nucleation and enhance bridging of macro-pores by micro-crack formation, while macro-pores influence the overall material response and drive the propagation of large fractures. Our results explain the important role of multiscale porosity characterizing stiff biological materials and lead to a new design paradigm, by introducing an in-silico tool to implement bio-mimicking in new artificial materials with brittle behaviour, such as carbide or ceramic foams.