Determination of interface fracture properties by micro- and macro-scale experiments in nacre-like alumina

Abstract

The mechanical properties of brick-and-mortar composites depend on their interface fracture properties, which have not been evaluated to date, preventing a rational optimization of the microstructure and of the resulting mechanical properties. Micro-(cantilever) and macro-scale (Single Edge Notched Bending) tests on nacre-like alumina both result in crack initiation at the interface between the platelets. We assess crack initiation and predict the failure force by means of 2D and 3D finite element simulations employing the same fracture modeling approach at both scales, namely the coupled criterion. The interface fracture properties are determined by means of inverse identification based on both micro-and macro-scale experiments. The interface exhibits typical values of 625 MPa tensile strength and 1.9 J/m 2 toughness. The forces at crack initiation predicted employing these parameters are in good agreement with the forces measured experimentally for both micro-and macro-scale tests. The quantitative determination of the interface fracture properties should help the design and optimization of this class of brick-and-mortar materials.

Toughening mechanisms in nacre-like alumina revealed by in-situ imaging of stress

“…Fluorescence maps revealed important stress gradients near the tip of the notch, with variations of up to 300 MPa in a few micrometers. This is lower than the strength of platelets around 1 GPa (Doitrand et al, 2020;Feilden et al, 2017), but higher than the yield strength of aluminosilicate glasses used as mortar along the interfaces (Bouville et al, 2014;Saad et al, 2020), with values lower than 100 MPa (Sheikh et al, 2019). Even if a calculation of local stresses considers hydrostatic stresses and is based on the hypothesis of isotropy in piezospectroscopic coefficient (thereby not capturing the texture of this material), the stress values are coherent.…”

Toughening mechanisms in nacre-like alumina revealed by in-situ imaging of stress

“…Fluorescence maps revealed important stress gradients near the tip of the notch, with variations of up to 300 MPa in a few micrometers. This is lower than the strength of platelets around 1 GPa (Doitrand et al, 2020;Feilden et al, 2017), but higher than the yield strength of aluminosilicate glasses used as mortar along the interfaces (Bouville et al, 2014;Saad et al, 2020), with values lower than 100 MPa (Sheikh et al, 2019). Even if a calculation of local stresses considers hydrostatic stresses and is based on the hypothesis of isotropy in piezospectroscopic coefficient (thereby not capturing the texture of this material), the stress values are coherent.…”

Finite fracture Mechanics at the micro-scale. Application to bending tests of micro cantilever beams

“…It is important to highlight that this incremental form is the foundation of FFM, since it assumes the instantaneous formation of cracks of finite size [16][17][18][19]. Moreover, in the case of the CC this instantaneous crack onset is not an assumption but the consequence of the two inequalities ( 6) and (7) as shown in [18]. To sum up, the crack nucleation is predicted by the CC using two necessary and together sufficient conditions…”

“…Furthermore, the nuclear industry is also in demand for a better knowledge of the behaviour of fuels such as UO2 in pressurized water reactors [5,6]. It is also important to highlight the tendency to mimic natural materials like mother-of-pearl to create nacre-like inorganic materials [7,8].…”