The mechanical properties such as compressive strength and nanohardness were investigated for Pinctada margaritifera mollusk shells. The compressive strength was evaluated through a uniaxial static compression test performed along the load directions parallel and perpendicular to the shell axis, respectively, while the hardness and Young modulus were measured using nanoindentation. In order to observe the crack propagation, for the first time for such material, the in-situ X-ray microscopy (nano-XCT) imaging (together with 3D reconstruction based on the acquired images) during the indentation tests was performed. The results were compared with these obtained during the micro-indentation test done with the help of conventional Vickers indenter and subsequent scanning electron microscopy observations. The results revealed that the cracks formed during the indentation start to propagate in the calcite prism until they reach a ductile organic matrix where most of them are stopped. The obtained results confirm a strong anisotropy of both crack propagation and the mechanical strength caused by the formation of the prismatic structure in the outer layer of P. margaritifera shell.
Diatom frustules, with their diverse three-dimensional regular silica structures and nano- to micrometer dimensions, represent perfect model systems for biomimetic fabrication of materials and devices. The structure of a frustule of the diatom Didymosphenia geminata was nondestructively visualized using nano X-ray computed tomography (XCT) and transferred into a CAD file for the first time. Subsequently, this CAD file was used as the input for an engineered object, which was manufactured by applying an additive manufacturing technique (3D Selective Laser Melting, SLM) and using titanium powder. The self-similarity of the natural and the engineered objects was verified using nano and micro XCT. The biomimetic approach described in this paper is a proof-of-concept for future developments in the scaling-up of manufacturing based on special properties of microorganisms.
Laboratory transmission X-ray microscopy with a spatial resolution of about 100 nm was used to image 3D interconnect structures and failures in microchips during mechanical loading, applied by a microDouble Cantilever Beam (micro-DCB) test. High-resolution 3D image sequences based on nano X-ray computed tomography (nano-XCT) are used to visualize crack opening and propagation in fully integrated multilevel on-chip interconnect structures of integrated circuits. The nondestructive investigation of sub-micron cracks during the in-situ micro-DCB test allows one to identify the weakest layers and interfaces, to image delamination along Cu/dielectric interfaces (adhesive failure) and fracture in dielectrics (cohesive failure), as well as to evaluate the robustness of Backend-of-Line stacks against process-induced thermomechanical stress.
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