Automated 3D assembly of periodic alumina‐epoxy composite structures

Abstract

Modular composites with a 3D periodic structure, consisting of a major brittle inorganic phase (building blocks) and a minor viscoelastic organic matrix, offer great potentials for improved fracture toughness and failure probability in polymer‐ceramic composites. Alumina building blocks with dimensions of 1500 μm were assembled by a novel placing system equipped with an automatic optical inspection (AOI) system. The AOI system coupled with shape recognition enables simultaneous dimensional characterization, tolerance sorting, and flexible placing of different shaped building blocks. 3D periodic structures with cubic, monoclinic, and triclinic unit cells were fabricated by high accuracy placing of cubic building blocks enabling near‐net shape manufacturing. The placing precision of the assembled structures was determined by μCT to have a maximum deviation of ±78 μm. The structures were afterward infiltrated with a soft epoxy resin to fabricate epoxy‐alumina composites. The brick‐and‐mortar like building block arrangements of the monoclinic and triclinic structures exhibited improved bending strength, fracture toughness, and failure probability compared to monolithic epoxy, due to crack deflection and pull‐out toughening mechanisms. A maximum bending strength of 35.1 ± 7.5 MPa, a work‐of‐fracture of 814.7 ± 255.1 J/m² and a calculated fracture toughness of 4.8 ± 0.8 MPam for the triclinic structures was achieved.

Injection Molding of 3-3 Hydroxyapatite Composites

“…The pore former containing HAp-feedstocks were homogenized for an additional mixing time of 12 h before molding. The casting molds were manufactured utilizing a negative replica technique [29,38]. Positive polymer preforms were 3D-printed with a z-resolution of 30 µm with a SLA 3D-printer (Digitalwax ® 028J, DWS S.r.l., Thiene, VI, Italy) and afterwards molded with a PDMS elastomer (Elastosil M 4643 A/B, Wacker Chemie AG, München, Germany).…”

Hierarchical Surface Texturing of Hydroxyapatite Ceramics: Influence on the Adhesive Bonding Strength of Polymeric Polycaprolactone

“…Surface-textured HAp ceramics with sub-millimeter periodic macro-texturing were fabricated by a micro transfer-molding technique, whose process steps are described in detail in [ 37 , 38 , 39 ]. Four different types of surface textures with an identical structuring depth of 500 µm (equal to an amplitude of ψ z /2 = 250 µm) and identical structuring spacing (or wavelength) of λ x = 550 µm were generated using open source software blender (v. 2.82a, Stichting Blender Foundation, Amsterdam, The Netherlands).…”

“…In this work, we therefore present the fabrication of hierarchical surface-textured HAp ceramics. Four types of computer-aided designed, periodic macro-surface textures (sub-millimeter scale) were manufactured by utilizing a micro-transfer molding technique published earlier [ 37 , 38 , 39 ]. A random surface roughening was introduced on a micron to nanometer scale by a subsequent acid etching.…”

Porous TaCx ISOL target materials from mould-casted Ta4AlC3

“…As the starting powder particles might be slightly oxidized, they could carry hydrophilic surface groups that are incompatible with a hydrophobic paraffin binder, causing agglomeration and inhomogeneous dispersion. This was avoided by hydrophobization of the Ta4AlC3 powder by means of electrosteric stabilization using stearic acid as surfactant, a technique often used to obtain low-viscosity ceramic slurries [23,24,29,30]. Ta4AlC3 and 0.15 wt% stearic acid (Grade I, ≥98.5%, Sigma-Aldrich, USA) were mixed on a low-energy rotatory mixer in n-hexane with 20 wt% Ta4AlC3 powder for 12 h.…”

“…The present study proposes a processing route based on the mould casting of a master feedstock made of wax, a pore former, and Ta4AlC3 MAX phase precursor powder. The combination of mould casting with sacrificial templating is a processing technology that has been reported for different material systems as capable of producing complex 3D geometries with precisely tailored material microstructures [19][20][21][22][23][24]. This near-net shape manufacturing technology allows the control of the total porosity and pore size distribution of the produced materials by changing the amount, shape and size of the utilized pore formers.…”