Effect of Carbon Nanofiber Clustering on the Micromechanical Properties of a Cement Paste

The use of carbon nanofibers (CNFs) in cement systems has received significant interest over the last decade due to their nanoscale reinforcing potential. However, despite many reports on the formation of localized CNF clusters, their effect on the cement paste micromechanical properties and relation to the mechanical response at the macroscopic scale are still not fully understood. In this study, grid nanoindentation coupled with scanning electron microscopy and energy dispersive spectroscopy was used to determine the local elastic indentation modulus and hardness of a portland cement paste containing 0.2% CNFs with sub-micro and microscale CNF clusters. The presence of low stiffness and porous assemblage of phases (modulus of 15–25 GPa) was identified in the cement paste with CNFs and was attributed primarily to the interfacial zone surrounding the CNF clusters. The CNFs favored the formation of higher modulus C–S–H phases (>30 GPa) in the bulk paste at the expense of the lower stiffness C–S–H. Nanoindentation results combined with a microscale–macroscale upscaling homogenization method further revealed an elastic modulus of the CNF clusters in the range from 18 to 21 GPa, indicating that the CNF clusters acted as compliant inclusions relative to the cement paste.

Determination of the Effects of Superheated Steam on Microstructure and Micromechanical Properties of Bamboo Cell Walls Using Quasi-Static Nanoindentation

In this paper, quasi-static nanoindentation was applied for investigating the influence of superheated steam on microstructure and micromechanical properties of Moso bamboo cell walls. The changes of mico-morphology, chemical composition, cellulose crystallinity index, micro-mechanical properties of bamboo were analyzed via scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and nanoindentation. As expected, the content of hemicellulose and cellulose showed a downward trend, whereas the relative lignin content increased. Elastic modulus and hardness of the cell wall increased compared with that of the untreated sample. The elastic modulus and hardness of bamboo increased from 11.5 GPa to 19.5 GPa and from 0.35 GPa to 0.59 GPa. Furthermore, results showed that the creep resistance positively correlated to treatment severity.

The Evolution of Micromechanical Properties for Zr-Based Metallic Glass Induced by Laser Shock Peening

The micromechanical properties of Zr-based metallic glass (MG) induced by laser shock peening (LSP) were studied through the use of nanoindentation. The serrations in representative load-displacement (P-h) curves exhibited a transformation from stairstep-like to ripple-shaped from untreated zone to shock region, which implied an increase in plastic deformation ability of material after LSP. Significant hardening was also observed in the impact zone, which can be attributed to the effect of compressive residual stress. Both increase in hardness and plastic deformation ability in shock region indicate the excellent effect of LSP on the micromechanical properties of investigated Zr-based MG, which provide a new way to study the deformation mechanism in metallic glasses and a further understanding of plasticization.

Baseline Stiffness Modulates the Non-Linear Response to Stretch of the Extracellular Matrix in Pulmonary Fibrosis

Pulmonary fibrosis (PF) is a progressive disease that disrupts the mechanical homeostasis of the lung extracellular matrix (ECM). These effects are particularly relevant in the lung context, given the dynamic nature of cyclic stretch that the ECM is continuously subjected to during breathing. This work uses an in vivo model of pulmonary fibrosis to characterize the macro- and micromechanical properties of lung ECM subjected to stretch. To that aim, we have compared the micromechanical properties of fibrotic ECM in baseline and under stretch conditions, using a novel combination of Atomic Force Microscopy (AFM) and a stretchable membrane-based chip. At the macroscale, fibrotic ECM displayed strain-hardening, with a stiffness one order of magnitude higher than its healthy counterpart. Conversely, at the microscale, we found a switch in the stretch-induced mechanical behaviour of the lung ECM from strain-hardening at physiological ECM stiffnesses to strain-softening at fibrotic ECM stiffnesses. Similarly, we observed solidification of healthy ECM versus fluidization of fibrotic ECM in response to stretch. Our results suggest that the mechanical behaviour of fibrotic ECM under stretch involves a potential built-in mechanotransduction mechanism that may slow down the progression of PF by steering resident fibroblasts away from a pro-fibrotic profile.