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Background: Compression experiments are widely used to study the mechanical properties of materials at micro- and nanoscale. However, the conventional engineering stress measurement method used in these experiments neglects to account for the alterations in the material's shape during loading. This can lead to inaccurate stress values and potentially misleading conclusions about the material's mechanical behavior, especially in the case of localized deformation. Objective: Our goal is to calculate true stress in cases of localized plastic deformation from standard experimental data (displacement-force curve, aspect ratio, shear band angle and elastic strain limit). Methods: We use a simple mechanical-geometrical approach based on reasonable physical assumptions to get analytic formulas of true stress and eliminating the need for finite element computations. Furthermore, in numerical simulations of pillar compression, the formula-based true stress demonstrates strong alignment with the theoretical true stress. Results: We propose analytic formulas for calculating true stress in cases of localized plastic deformation commonly encountered in experimental settings for a single band oriented in arbitrary directions with respect to the vertical axis of the pillar. Conclusions: The true stress computed with the proposed formulas provides a more precise interpretation of experimental results and can serve as a valuable and simple tool in material design and characterization. [ABSTRACT FROM AUTHOR]

In the contemporary era, the enhancement of wearable capacitive sensors is achieved through the utilization of polymeric micropillars as filler materials between electrode plates. To gain a deeper understanding of the dynamic response of the system, nonlinear coupled governing equations of a circular microplate motion resting on an array of polymeric micropillars have been derived. These equations are used to model the system's behavior. In addition, the squeezing motion of the micro-pillars is characterized using the incompressible Neo-Hookean model. Both static and dynamic responses, including transient and steady-state solutions, are investigated in detail by discretizing over spatial coordinates using a weak formulation approach. A frequency response analysis is conducted using a continuation-based method. This entails expanding the steady-state solution using a Fourier transform and employing the energy balance principle. The unknown coefficients of the expansion series are calculated using a gradient descent-based learning approach that is physically motivated. Furthermore, a dynamic step size strategy for frequency increments is employed to effectively follow the solution path. This strategy is implemented via the ARC length method. In this study, we examine the impact of varying PDMS (polydimethylsiloxane) hydrogel mechanical and geometrical configurations. It can be reasonably concluded that the mechanical properties of the pillars and the geometrical configuration of the circular plate and micropillars have a significant impact on the maximum tolerable pressure, fast transient response, and frequency response analysis. [ABSTRACT FROM AUTHOR]

Abstract In the contemporary era, the enhancement of wearable capacitive sensors is achieved through the utilization of polymeric micropillars as filler materials between electrode plates. To gain a deeper understanding of the dynamic response of the system, nonlinear coupled governing equations of a circular microplate motion resting on an array of polymeric micropillars have been derived. These equations are used to model the system’s behavior. In addition, the squeezing motion of the micro-pillars is characterized using the incompressible Neo-Hookean model. Both static and dynamic responses, including transient and steady-state solutions, are investigated in detail by discretizing over spatial coordinates using a weak formulation approach. A frequency response analysis is conducted using a continuation-based method. This entails expanding the steady-state solution using a Fourier transform and employing the energy balance principle. The unknown coefficients of the expansion series are calculated using a gradient descent-based learning approach that is physically motivated. Furthermore, a dynamic step size strategy for frequency increments is employed to effectively follow the solution path. This strategy is implemented via the ARC length method. In this study, we examine the impact of varying PDMS (polydimethylsiloxane) hydrogel mechanical and geometrical configurations. It can be reasonably concluded that the mechanical properties of the pillars and the geometrical configuration of the circular plate and micropillars have a significant impact on the maximum tolerable pressure, fast transient response, and frequency response analysis.

Additive manufacturing makes fabricating titanium alloy components directly into their near-net shapes possible, reducing the need for machining. However, post-additive manufacturing machining becomes necessary for immediate design adjustments, dimension alterations, and surface quality enhancement. The inherent thermal effects during additive manufacturing make machining challenging due to altered mechanical properties from their wrought counterpart, including increased strength and hardness with reduced ductility. Textured cutting tools are being widely used to enhance the machinability of superalloys. In this work, micro-pillar type textures, created using Reverse Micro Electrical Discharge Machining (RμEDM) on tungsten carbide inserts, aimed to explore machinability in turning operations on selective laser melted (SLM) titanium alloy. The study investigates micro-pillar interaction with SLM Ti6Al4V in chip behavior, tool morphology, cutting forces, and surface roughness under various cutting fluid strategies. Under Minimum Quantity Lubrication (MQL), textured tools show significant improvements, producing untangled chips with reduced curl radius. A considerable decrease of 38 % in the tool/chip contact area indicates a substantial reduction in the seizure zone, hence a decline in the temperature rise of the cutting tool. Dry conditions show a 20.4 % reduction in flank wear width, suggesting prolonged cutting-edge sharpness due to tool texturing. In MQL conditions, a maximum 28.9 % reduction in feed force is observed, indicating improved frictional conditions at the interface. Additionally, a 10.4 % improvement in surface finish is achieved. The work is summarized by claiming micro-pillar textured tools enhance the machinability of additively manufactured Ti6Al4V demonstrated through improvements in titanium adhesion, cutting-edge sharpness, feed force, and surface finish, particularly MQL conditions. [Display omitted] • Fabrication of novel micro-pillar textures on tungsten carbide inserts using RμEDM. • Machining under dry, compressed air, minimum quantity lubrication, and wet conditions. • Investigation of forces, surface roughness, tool wear, and chip morphology is performed. • Enhanced machinability of SLM Ti6Al4V due to micro-texturing of the rake face. • Reduced tool-chip contact and enhanced CF penetration are witnessed in textured tools. [ABSTRACT FROM AUTHOR]

Graphical Abstract

Microglia are the resident macrophages of the central nervous system and contribute to maintaining brain's homeostasis. Current 2D "petri-dish" in vitro cell culturing platforms employed for microglia, are unrepresentative of the softness or topography of native brain tissue. This often contributes to changes in microglial morphology, exhibiting an amoeboid phenotype that considerably differs from the homeostatic ramified phenotype in healthy brain tissue. To overcome this problem, multi-scale engineered polymeric microenvironments are developed and tested for the first time with primary microglia derived from adult rhesus macaques. In particular, biomimetic 2.5D micro- and nano-pillar arrays (diameters = 0.29-1.06 µm), featuring low effective shear moduli (0.25-14.63 MPa), and 3D micro-cages (volume = 24 × 24 × 24 to 49 × 49 × 49 μm 3 ) with and without micro- and nano-pillar decorations (pillar diameters = 0.24-1 µm) were fabricated using two-photon polymerization (2PP). Compared to microglia cultured on flat substrates, cells growing on the pillar arrays exhibit an increased expression of the ramified phenotype and a higher number of primary branches per ramified cell. The interaction between the cells and the micro-pillar-decorated cages enables a more homogenous 3D cell colonization compared to the undecorated ones. The results pave the way for the development of improved primary microglia in vitro models to study these cells in both healthy and diseased conditions., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Sharaf, Roos, Timmerman, Kremers, Bajramovic and Accardo.)

To explore the deformation mechanism of α-Ti with high oxygen doping, micro-pillars of single crystal with orientations of near 0°, 45°, and 90° inclined to c -axis were fabricated via focused ion beam (FIB) milling from a high oxygen content commercial purity Ti (CP–Ti). The micro-pillars were loaded under quasi-static compression. Post-mortem analysis reveals that only prismatic slip activated for 45° and 90° oriented samples with their critical resolved shear stress (CRSS) values of about 457 MPa and 596 MPa, and only {10–11}< c + a > the first-order pyramidal slip activated on the 0° sample with a CRSS of around 1019 MPa. The results suggest that the oxygen addition remarkably reduces the CRSS ratio between non-prismatic and prismatic slips of α-Ti. In addition, the results indicate that the Schmid law may not be applicable for α-Ti single crystal at micro-size level. [ABSTRACT FROM AUTHOR]