In-situ AFM Experiments with Discontinuous DIC Applied to Damage Identification in Biomaterials

Abstract

Natural materials (e.g. nacre, bone, and spider silk) exhibit unique and outstanding mechanical properties. This performance is due to highly evolved hierarchical designs. Building a comprehensive understanding of the multi-scale mechanisms that enable this performance represents a critical step toward realizing strong and tough bio-inspired materials. This paper details a multi-scale experimental investigation into the toughening mechanisms in natural nacre. By applying extended digital image correlation and other image processing techniques, quantitative information is extracted from otherwise prodominantly qualitative experiments. In situ three point bending fracture tests are performed to identify and quantify the toughening mechanisms involved during the fracture of natural nacre across multiple length scales. At the macro and micro scales, fracture tests performed in situ with a macro lens and optical microscope enable observation of spreading of damage outward from the crack tip. This spreading is quantified using an iso-contour technique to assess material toughness. At the nanoscale, fracture tests are performed in situ an atomic force microscope to link the larger-scale damage spreading to sliding within the tabletbased microstructure. To quantify the magnitude of sliding and its distribution, images from the in situ AFM fracture tests are analyzed using new algorithms based on digital image correlation techniques which allow for discontinuous displacement fields. Ultimately, this comprehensive methodology provides a framework for broad experimental investigations into the failure mechanisms of bio-and bioinspired materials.

AFM Identification of Beetle Exocuticle: Bouligand Structure and Nanofiber Anisotropic Elastic Properties

“…For instance, studies performed on abalone nacre revealed that the material exhibits a toughness similar to aluminum even when it contains 95% calcite, a ceramic . Espinosa and co‐workers showed that such toughness arises from a millimeter size process zone consisting of tablets sliding without pullout . Recent developments in advanced manufacturing such as freeze casting and 3D printing have made possible the direct translation of the elegant architectures from natural materials to artificial materials and structures.…”

Imaging Inelastic Fracture Processes in Biomimetic Nanocomposites and Nacre by Laser Speckle for Better Toughness

“…The plot shows a short development phase during which the process zone attains its final width of ≈0.4 mm. Previously, the process zone of nacre has been studied by observing the whitening zone at the crack tip that provides clear indication of platelet sliding taking place . Therefore, the speckle imaging can be compared against the traditional method for verification.…”

Revealing extraordinary tensile plasticity in layered Ti-Al metal composite

“…Small scratches of specimen surface were artificially made by mechanically polishing the surface using the 4000-grit sandpaper. The difference in the positions of small scratches on surface of sample before and after deformation was used to quantify the local strain38. Additionally, the strain distributions were analyzed using the VIC-2D software.…”