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  1. The rising interest in 3D-printing of concrete structures for use in marine environments requires development of concrete mixtures with adequate mechanical and durability characteristics. The incorporation of alternative cementitious materials, combined with careful selection of printing parameters has emerged as an effective way of controlling not only the fresh properties and printability of mixtures, but also their mechanical and durability properties. This paper presents the results of various durability related tests performed on 3D-printed mortars, including density, porosity, rate of water absorption and resistance to chloride penetration. Results of these tests indicate that the performance of mortar elements 3D-printed using controlled overlap process was similar to the performance of conventionally cast mortar elements with the same composition. Moreover, the results of the chloride transport related tests obtained from all specimens evaluated during the course of the study indicate low chloride ion penetrability, thus re-affirming that combination of the proposed material and 3D-printing method of fabrication have a potential for producing structural elements for applications in marine environments.
    Free, publicly-accessible full text available June 25, 2023
  2. Abstract

    Phase Transforming Cellular Materials (PXCMs) are periodic cellular materials whose unit cells exhibit multiple stable or meta-stable configurations. Transitions between the various (meta-) stable configurations at the unit cell level enable these materials to exhibit reusable solid state energy dissipation. This energy dissipation arises from the storage and non-equilibrium release of strain energy accompanying the limit point traversals underlying these transitions. The material deformation is fully recoverable, and thus the material can be reused to absorb and dissipate energy multiple times. In this work, we present two designs for functionally two-dimensional PXCMs: theS-typewith four axes of reflectional symmetry based on a square motif and, theT-typewith six axes of symmetry based on a triangular motif. We employ experiments and simulations to understand the various mechanisms that are triggered under multiaxial loading conditions. Our numerical and experimental results indicate that these materials exhibit similar solid state energy dissipation for loads applied along the various axes of reflectional symmetry of the material. The specific energy dissipation capacity of theT-typeis slightly greater and less sensitive to the loading direction than theS-typeunder the most of loading directions. However, both types of material are shown to be very effective in dissipating energy.

  3. Abstract

    The measurement of local mechanical properties of living cells by nano/micro indentation relies on the foundational assumption of locally isotropic cellular deformation. As a consequence of assumed isotropy, the cell membrane and underlying cytoskeleton are expected to locally deform axisymmetrically when indented by a spherical tip. Here, we directly observe the local geometry of deformation of membrane and cytoskeleton of different living adherent cells during nanoindentation with the integrated Atomic Force (AFM) and spinning disk confocal (SDC) microscope. We show that the presence of the perinuclear actin cap (apical stress fibers), such as those encountered in cells subject to physiological forces, causes a strongly non-axisymmetric membrane deformation during indentation reflecting local mechanical anisotropy. In contrast, axisymmetric membrane deformation reflecting mechanical isotropy was found in cells without actin cap: cancerous cells MDA-MB-231, which naturally lack the actin cap, and NIH 3T3 cells in which the actin cap is disrupted by latrunculin A. Careful studies were undertaken to quantify the effect of the live cell fluorescent stains on the measured mechanical properties. Using finite element computations and the numerical analysis, we explored the capability of one of the simplest anisotropic models – transverse isotropy model with three local mechanical parameters (longitudinalmore »and transverse modulus and planar shear modulus) – to capture the observed non-axisymmetric deformation. These results help identifying which cell types are likely to exhibit non-isotropic properties, how to measure and quantify cellular deformation during AFM indentation using live cell stains and SDC, and suggest modelling guidelines to recover quantitative estimates of the mechanical properties of living cells.

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