Nanoindentation of cement stone samples

The preliminary results of the studied cement samples were obtained by the nanoindentation method. It was revealed that the elastic modulus M increases in samples that contain a complex additive containing nanosized particles. The effect is also observed with the introduction of an additive containing only one type of nanoparticles (nanosilica sol SiO2 or carbon nanomaterial MCNT). The selection of the parameters of the nanoindentation method, which ensured the obtaining of the final consistent results, was performed. These results are presented by histograms of the distribution of nanoindentation points in modulus of elasticity M and hardness H and distributions in M and H in the horizontal XY plane perpendicular to the motion of the nanoindentor. The results obtained indicate that there is a change in the nanostructure of the C – S – H gel, which is compared with an increase in strength, Young’s moduli and shear, upon the introduction of SiO2 nanoparticles and MCNT nanoparticles

A new Nanoindentation Protocol for identifying the elasticity of undamaged extracellular bone tissue

\u3cp\u3eWhile the quest for understanding and even mimicking biological tissue has propelled, over the last decades, more and more experimental activities at the micro and nanoscales, the appropriate evaluation and interpretation of respective test results has remained a formidable challenge. As a contribution to tackling this challenge, we here describe a new method for identifying, from nanoindentation, the elasticity of the undamaged extracellular bone matrix. The underlying premise is that the tested bovine bone sample is either initially damaged (i.e. exhibits micro-cracks a priori) or that such micro-cracks are actually induced by the nanoindentation process itself, or both. Then, (very many) indentations may relate to either an intact material phase (which is located sufficiently far away from micro-cracks), or to differently strongly damaged material phases. Corresponding elastic phase properties are identified from the statistical evaluation of the measured indentation moduli, through representation of their histogram as a weighted sum of Gaussian distribution functions. The resulting undamaged elastic modulus of bovine femoral extracellular bone matrix amounts to 31 GPa, a value agreeing strikingly well both with direct quasi-static modulus tests performed on SEM-FIB-produced micro-pillars (Luczynski et al., 2015), and with the predictions of a widely validated micromechanics model (Morin and Hellmich, 2014). Further confidence is gained through observing typical indentation imprints under Scanning Electron Microscopy (SEM), which actually confirms the existence of the two types of micro-cracks as described above.\u3c/p\u3

Early-Age Evolution of Strength, Stiffness, and Non-Aging Creep of Concretes: Experimental Characterization and Correlation Analysis

Six different concretes are characterized during material ages between 1 and 28 days. Standard tests regarding strength and stiffness are performed 1, 3, 7, 14, and 28 days after production. Innovative three-minute-long creep tests are repeated hourly during material ages between one and seven days. The results from the standard tests are used to assess and to improve formulas of the fib Model Code 2010: the correlation formula between the 28-day values of the strength and the stiffness, and the evolution formulas describing the early-age evolution of the strength and the stiffness during the first four weeks after production. The results from the innovative tests are used to develop a correlation formula between the 28-day values of Young’s modulus and the creep modulus, and an evolution formula describing the early-age evolution of the creep modulus during the first four weeks after production. Particularly, the analyzed CEM I concretes develop stiffness and strength significantly faster than described by the formulas of the Model Code. The creep modulus of the investigated concretes evolves significantly slower than their strength and stiffness. Thus, concrete loaded at early ages is surprisingly creep active, even if the material appears to be quite mature in terms of its strength and stiffness.Austrian Research Promotion Agency (FFG

Anisotropic tissue elasticity in human lumbar vertebra, by means of a coupled ultrasound-micromechanics approach

The extremely fi ne structure of vertebral cortex challenges reliable determination of the tissue's anisotropic elasticity, which is important for the spine's load carrying patterns often causing pain in patients. As a potential remedy, we here propose a combined experimental (ultrasonic) and modeling (micromechanics) approach. Longitudinalacousticwavesaresentinlongitudinal(superior -inferior,axial)aswellastransverse(circumferential) direction through millimeter-sized samples containing thi s vertebral cortex, and corr esponding wave velocities agree very well with recently identi fi ed ‘ universal ’ compositional and acoustic characteristics (J Theor Biol 287:115,2011),whicharevalidforalargedatabasecomprisingdifferent bonesfromdifferent speciesanddifferent organs. This provides evidence that the ‘ universal ’ organization patterns inherent to all the bone tissues of the aforementioned data base also hold for vertebral bone. Con sequently, an experimentally validated model covering the mechanical effects of this organization patterns (J Theor Biol 244:597, 2007, J Theor Biol 260:230, 2009) gives access to the complete elasticity tensor of human lumbar ve rtebral bone tissue, as a valuable input for structural analyses aiming at patient-speci fi cfractureriskassessm ent, e.g. based on the Finite Element Method.Peer Reviewe