Advanced Estimation of Compressive Strength and Fracture Behavior in Ceramic Honeycombs by Polarimetry Measurements of Similar Epoxy Resin Honeycombs

Abstract

Finding a non-destructive characterization method for cellular ceramics’ compressive strength and fracture behavior has been a challenge for material scientists for years. However, for transparent materials, internal stresses can be determined by the non-destructive photoelastic measurements. We propose a novel approach to correlate the photoelastic stresses of polymer (epoxy resin) prototypes with the mechanical properties of ceramics (alumina). Regular and inverse epoxy honeycombs were 3D-printed via stereolithography with varying structure angles from −35° to 35°, with negative angles forming an auxetic and positive hexagonal lattice. Photoelastic measurements under mechanical loading revealed regions of excess stress, which directly corresponded to the initial fracture points of the ceramic honeycombs. These honeycombs were made by a combination of 3D printing and transfer molding from alumina. The photoelastic stress distribution was much more homogeneous for angles of a smaller magnitude, which led to highly increased compressive strengths of up to 446 ± 156 MPa at 0°. By adapting the geometric structural model from Gibson and Ashby, we showed that we could use a non-destructive technique to determine the compressive strength of alumina honeycombs from the median photoelastic stress measured on similar epoxy honeycomb structures.

Relation between Structure, Mechanical and Piezoelectric Properties in Cellular Ceramic Auxetic and Honeycomb Structures

“…The evolution of the surface stress with increasing θ angle shows, on the one hand, a more homogeneous stress distribution in the auxetic region and, on the other hand, higher absolute stress in the honeycomb area. This also correlates with the fracture behavior of ceramic honeycombs, as described by Köllner et al [20] Thus, the honeycomb specimen mainly exhibited the fracture in the center of the upper strut, which is consistent with the stress-exceeded point of this FEM simulation. Furthermore, this simulation indicates or explains that auxetic structures achieve higher strength values than honeycomb structures.…”

“…The issue has already been observed on alumina auxetic and honeycomb structures, where this effect was due to the different mechanical stress modes between auxetic and honeycomb specimens. [ 20 ] Especially the stress‐excessive points showed compressive stresses in the auxetic case and tensile stresses in the honeycomb case, which lead to higher strength for the auxetic specimens. [ 20,49,50 ] …”

“…[ 20 ] Especially the stress‐excessive points showed compressive stresses in the auxetic case and tensile stresses in the honeycomb case, which lead to higher strength for the auxetic specimens. [ 20,49,50 ] …”

“…2.1. Fabrication Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3 (BCZT) cellular structures were produced via an injection molding technique, described in detail in the study by Köllner et al [20] The auxetic and honeycomb unit cell is shown in Figure 1. All samples had a constant strut thickness t of 0.8 mm, height Y of 5.66 mm, width h of 4.92 mm, and depth T of 2.00 mm.…”

“…Honeycombs represent a subgroup of cellular ceramics, in which the mechanical and piezoelectric properties are strongly controlled by geometrical parameters and less by the porosity itself. [20,21] Using auxetic PZT lattices (inverse honeycombs), Fey et al have already shown that despite a porous structure, higher piezoelectric coefficients and strain amplification can be achieved compared to the bulk material. [22] Furthermore, Tang et al demonstrated improved piezoelectric properties with an auxetic metamaterial.…”