Effect Of Feature Size Research Articles

Contradictory Feature Size Effects in the Tensile Yield Strength of Cu Sheets Produced Using Different Sequences Involving Annealing, Rolling, and Grinding

The feature size effect is significant research interest in the field of microforming. It is assumed that the size effect is influenced by the material preparation process. To verify this, the feature size effects associated with the tensile yield strength of Cu sheets with thicknesses ranging from 100 to 200 μm, produced using different sequences involving annealing, rolling, and grinding, were studied. Differing feature size effects were observed in the Cu specimens, and it was confirmed that the size effect was indeed influenced by the specimen preparation sequence. The tensile yield strengths of the annealed–ground–rolled and annealed–rolled specimens increased as the specimen thicknesses decreased. However, an opposing size effect was observed in the case of the annealed–rolled–annealed, annealed–ground, and annealed–rolled–ground specimens. The reduction ratio did not alter the trend associated with the size effect, but influenced the intensity of the size effect. It is believed that the reinforcement and erosion of the surface-hardened layer introduced during rolling resulted in the contradictory results.

Inversely designed micro-textures for robust Cassie–Baxter mode of super-hydrophobicity

Abstract The robust Cassie–Baxter mode of the wetting behaviour on a micro-textured solid surface, is a key topography element yielding stable super-hydrophobicity. To meet this purpose, we propose an inverse computational design procedure for the discovery of suitable periodic micro-textures, based on three different tilings of the plane. The symmetric tiles of the lattice are regular triangles, quadrangles, and hexagons. The goal of the inverse design procedure is to achieve the robust Cassie–Baxter state, in which the liquid/vapour interface is mathematically described using the Young–Laplace equation on the lattice, and a topology optimisation approach is utilised to construct a variational problem for the inverse design procedure. Based on numerical calculations of the constructed variational problem, underlying effects are revealed for several factors, including the Bond number, duty ratio, feature size, and lattice constant. The effects of feature size and lattice constant provide approaches for compromisingly considering the robustness of the Cassie–Baxter mode and manufacturability of the inversely designed micro-textures; the effect of the lattice constant permits the scaling properties of the derived patterns, and this in turn provides an approach to avoid the elasto-capillary instability driven collapse of the micro/nanostructures in the derived micro-textures. Further, a monolithic inverse design procedure for the periodic micro-textures is proposed in the conclusions, with synthetically considering the manufacturability as well as contact angle and surface-volume ratio of the liquid bulge held by the supported liquid/vapour interface.

Effect of Topographical Feature Size on the Trend of Cell Behaviors

Since the adaptation of surface topography in the biomedical engineering field, its promising ability in the modulation of cell behaviors and functions has been highlighted by comparing the cell behaviors on patterned and nonpatterned substrates. However, growing evidence indicates that not only the topography itself but also its size can significantly affect the cell behaviors and functions. In this review, the effect of topographical feature size on the biointerface-mediated control of cell behavior is overviewed. The cell behaviors such as migration, differentiation, cell reprogramming, cell phenotype, and transfection, in general, showed two representative trends: biphasic and monotonic as the feature size changed. Based on the observations, we suggest that the sophisticated design of geometrical feature size might be a key regulator on the control of cell behaviors and functions.

Topology optimization of a flexible multibody system with variable-length bodies described by ALE–ANCF

Recent years have witnessed the application of topology optimization to flexible multibody systems (FMBS) so as to enhance their dynamic performances. In this study, an explicit topology optimization approach is proposed for an FMBS with variable-length bodies via the moving morphable components (MMC). Using the arbitrary Lagrangian–Eulerian (ALE) formulation, the thin plate elements of the absolute nodal coordinate formulation (ANCF) are used to describe the platelike bodies with variable length. For the thin plate element of ALE–ANCF, the elastic force and additional inertial force, as well as their Jacobians, are analytically deduced. In order to account for the variable design domain, the sets of equivalent static loads are reanalyzed by introducing the actual and virtual design domains so as to transform the topology optimization problem of dynamic response into a static one. Finally, the novel MMC-based topology optimization method is employed to solve the corresponding static topology optimization problem by explicitly evolving the shapes and orientations of a set of structural components. The effect of the minimum feature size on the optimization of an FMBS is studied. Three numerical examples are presented to validate the accuracy of the thin plate element of ALE–ANCF and the efficiency of the proposed topology optimization approach, respectively.

Nonlinear bending of functionally graded porous micro/nano-beams reinforced with graphene platelets based upon nonlocal strain gradient theory

Fast improvements in technology causes to provide the ability to manipulate porous graded materials for using in directed design of micro/nano-structures. The prime objective of the current study is to anticipate the size-dependent nonlinear bending of functionally graded porous micro/nano-beams reinforced with graphene platelets, and subjected to the uniform distributed load together with an axial compressive load. Via the nonlocal strain gradient theory of elasticity, two entirely different features of size effects are incorporated in the third-order shear deformable beam model. In addition to the uniform distribution of porosity, three different functionally graded porosity distributions along the thickness of micro/nano-beams are supposed in such a way that the relationship between coefficients related to the relative density and porosity is considered for an open-cell metal foam. On the basis of Hamilton's principle, the non-classical governing differential equations of motion are established. After that, the Galerkin method in conjunction with an improved perturbation technique is utilized to attain explicit analytical expressions for nonlocal strain gradient load-deflection paths of the functionally graded porous micro/nano-beams reinforced with the graphene nanofillers. It is observed that the type of porosity dispersion pattern has no considerable influence on the significance of size effects. However, by approaching the axial compressive load to the critical buckling value, the significance of the both nonlocality and strain gradient size dependencies on the nonlinear bending behavior of functionally graded porous micro/nano-beams increases, and this increment in the nonlocal small scale effect is more considerable than in the strain gradient one.

Feature Size Effect on Formability of Multilayer Metal Composite Sheets under Microscale Laser Flexible Forming

Multilayer metal composite sheets possess superior properties to monolithic metal sheets, and formability is different from monolithic metal sheets. In this research, the feature size effect on formability of multilayer metal composite sheets under microscale laser flexible forming was studied by experiment. Two-layer copper/nickel composite sheets were selected as experimental materials. Five types of micro molds with different diameters were utilized. The formability of materials was evaluated by forming depth, thickness thinning, surface quality, and micro-hardness distribution. The research results showed that the formability of two-layer copper/nickel composite sheets was strongly influenced by feature size. With feature size increasing, the effect of layer stacking sequence on forming depth, thickness thinning ratio, and surface roughness became increasingly larger. However, the normalized forming depth, thickness thinning ratio, surface roughness, and micro-hardness of the formed components under the same layer stacking sequence first increased and then decreased with increasing feature size. The deformation behavior of copper/nickel composite sheets was determined by the external layer. The deformation extent was larger when the copper layer was set as the external layer.

Effect of electrode sub-micron surface feature size on current generation of Shewanella oneidensis in microbial fuel cells

Abstract Microbial fuel cells (MFCs) are envisioned to serve as compact and sustainable sources of energy; however, low current and power density have hindered their widespread use. Introduction of 3D micro/nanostructures on the MFC anode is known to improve its performance by increasing the surface area available for bacteria attachment; however, the role of the feature size remains poorly understood. To delineate the role of feature size from the ensuing surface area increase, nanostructures with feature heights of 115 nm and 300 nm, both at a height to width aspect ratio of 0.3, are fabricated in a grid pattern on glassy carbon electrodes (GCEs). Areal current densities and bacteria attachment densities of the patterned and unpatterned GCEs are compared using Shewanella oneidensis Δ bfe in a three-electrode bioreactor. The 115 nm features elicit a remarkable 40% increase in current density and a 78% increase in bacterial attachment density, whereas the GCE with 300 nm pattern does not exhibit significant change in current density or bacterial attachment density. The current density dependency on feature size is maintained over the entire 160 h experiment. Thus, optimally sized surface features have a substantial effect on current production that is independent of their effect on surface area.

On the Scale Dependence of Micro Hydromechanical Deep Drawing

Tooling feature size to minimum thickness becomes small in micro scale products and its ratio affects the deformation behavior in micro sheet forming significantly. In this study, the effect of this relative tooling feature size on drawing characteristics and effects to improve the drawability, such as friction holding effect, hydrodynamic lubrication effect and compression effect by blank edge radial pressure, in micro hydromechanical deep drawing (MHDD) are investigated using plasticity theory and numerical simulation. The results show that the micro drawing characteristics in MHDD can be improved by applying counter pressure. However, the required fluid pressures for friction holding and hydrodynamic lubrication effects increase as the relative punch diameter and/or die shoulder radius to thickness decrease, although the compression effect by radial pressure on the blank edge is independent of the relative tooling feature size.

Size Effects on Formability of Copper Foil in Flexible Micro-Bending Process

The occurrence of size effects in the microforming leads to the uncertainties in process determination and quality control. In this research, a series of experiments were conducted in UTM4104 testing machine to investigate the grain size effect and feature size effect in micro-bending. Different grain size (d), thickness to grain size ratio () and micro-mold feature size (W) were prepared to explore size effects on formability of copper foil. The formability characterized by forming depth, deformation uniformity and surface integrity was discussed. It was found that the normalized forming depth presented a gradually rise and then declined markedly when N value further decreased to 0.79. The ductile fracture mode was observed for all grain-sized workpiece and the corresponding limit forming depth decreased with increasing grain size. Besides, the thickness thinning distribution and microhardness distribution showed the similar variation tendency like M. Both the standard deviation of thickness reduction and the roughed degree of surface topography indicated the worsening deformation uniformity of the foils with a larger grain size. The inhomogeneous plastic flow of material may be the reason to explain the depression near fracture location which is only observed in coarse-grained workpiece. Overall, it is concluded that the fine-grained copper exhibited better formability as the coarse-grained workpiece experienced severe strain incompatibility.

Influence of stacking fault energy on friction of nanotwinned metals

The unique dislocation–twin boundary (TB) interactions that govern the extraordinary mechanical properties of nanotwinned (NT) metals have the strong intrinsic effect of material energy and the extrinsic effect of feature size. In this work, we perform molecular dynamics (MD) simulations to elucidate fundamental deformation mechanisms of two NT face-centered cubic (FCC) metals (Cu and Pd) under probe-based friction, with an emphasis on evaluating the influence of both material’s intrinsic energy barrier and extrinsic grain size on the microscopic deformation behavior and correlated macroscopic frictional results of the materials. Simulation results reveal that individual deformation modes of dislocation mechanisms, dislocation–TB interactions, TB-associated mechanisms, deformation twinning and grain boundary (GB) accommodation work in parallel in the plastic deformation of the materials, and their competition is strongly influenced by both the intrinsic energy barriers for the nucleation of stacking faults and twin faults, and the extrinsic grain size. Consequently, both the frictional response and worn surface morphology present strong anisotropic characteristics. It is also found that the deformation behavior of NT Pd under a localized multi-axis stress state is significantly different from that which occurs under a uniaxial stress state. These findings will advance the rational design and synthesis of nanostructured materials with advanced frictional properties.

Nanotopography promoted neuronal differentiation of human induced pluripotent stem cells

Inefficient neural differentiation of human induced pluripotent stem cells (hiPSCs) motivates recent investigation of the influence of biophysical characteristics of cellular microenvironment, in particular nanotopography, on hiPSC fate decision. However, the roles of geometry and dimensions of nanotopography in neural lineage commitment of hiPSCs have not been well understood. The objective of this study is to delineate the effects of geometry, feature size and height of nanotopography on neuronal differentiation of hiPSCs. HiPSCs were seeded on equally spaced nanogratings (500 and 1000nm in linewidth) and hexagonally arranged nanopillars (500nm in diameter), each having a height of 150 or 560nm, and induced for neuronal differentiation in concert with dual Smad inhibitors. The gratings of 560nm height reduced cell proliferation, enhanced cytoplasmic localization of Yes-associated protein, and promoted neuronal differentiation (up to 60% βIII-tubulin+ cells) compared with the flat control. Nanograting-induced cell polarity and cytoplasmic YAP localization were shown to be critical to the induced neural differentiation of hiPSCs. The derived neuronal cells express MAP2, Tau, glutamate, GABA and Islet-1, indicating the existence of multiple neuronal subtypes. This study contributes to the delineation of cell-nanotopography interactions and provides the insights into the design of nanotopography configuration for pluripotent stem cell neural lineage commitment.

The size effect on deformation behavior in microscale laser shock flexible drawing

Abstract A microscale laser shock flexible drawing (µLSFD) is a novel ultrahigh strain rate manufacturing technology that provides an effective means for fabricating complicated microparts shapes in foil. However, the size effect phenomenon in ultrahigh strain rate microforming is still largely unknown. In this work, the micro-mold and process parameters were designed to investigate the size effects based on the similarity theory. The parts were formed using annealed copper foils with four different grain sizes to study the grain size effect. The parts were fabricated by use of different micro-molds and copper foils with varying thicknesses but with the same annealing temperature to investigate the effect of feature size. The experimental results indicated that the depth of the formed parts increased with an increase in the grain size; the forming depth decreased significantly when the feature dimension was smaller than a critical value. The surface roughness and the thickness thinning ratio of the formed parts increased when the grain size and feature dimension increased. The maximum thinning ratio appeared at the bottom of the formed parts. The regression analysis revealed that the material deformation was more homogeneous with a decrease in the grain size and an increase in the feature dimensions when the µLSFD process was employed. This study provides a theoretical basis for the investigation of size effects in laser shock flexible forming.

A Chemical Mechanical Planarization Model Including Global Pressure Distribution and Feature Size Effects

In this paper, we propose a chip-scale Chemical mechanical polishing (CMP) model based on the Greenwood–Williamson theory combining the effects of both the pad bulk deformation and the feature size, which are mainly responsible for global pressure distribution and feature-scale removal rate variation, respectively. A reference camber is first constructed to simulate the pad bulk deformation, which can be directly introduced into the global pressure distribution computation for incorporating the long-range characteristics of chip profiles. Then, both the effective curvature and the modified distribution function of pad asperity height are involved in the material removal rate. The model is first verified through some experimental data from CMP test structures and found to be in good agreement with the test data. For further validating the rationality and accuracy of the present model, some simulations are compared with our experimental data and discussed in detail.

Electron delocalization in heterogeneous AunHm systems

We studied the size effects in homogeneous Aun nanoclusters (n = 11–21, 31–37) and a heterogeneous “planar” AunHm nanocluster (n = 13, 31, m = 1–12, 1–6) by computer simulation in the electron density functional approximation. The correlation between the features of size effects on the physicochemical properties of heterogeneous AunHm nanoclusters and a sequence of electronic magic numbers demonstrates a delocalized nature of occupied electronic states with near-Fermi energy.

Size effects on tensile strength of aluminum–bronze alloy at room temperature

Variations in tensile yield strength of annealed CuAl7 copper alloy were investigated. Both grain and feature size effects could be observed. Statistical analysis revealed that the grain size effect was greater than the feature size effect. The grain size effect on the tensile yield strength of the alloy was very significant. The feature size effect was very significant or significant when the specimen thickness was no more than 0.50 mm, while the effect was insignificant or completely absent when the specimen thickness was greater than 0.50 mm. In addition to grain size d and specimen thickness t, the t/d ratio of the specimen can also affect the tensile yield strength. The tensile yield strength of the alloy was almost a constant when the t/d ratio was greater than a critical value (approximately 21). Otherwise, the strength tended to increase with an increasing value of t/d, except for the specimen with a thickness of 0.25 mm. The size effects on the tensile strength of the CuAl7 copper alloy were compared with the effects on the compression strength. It was found that the size effect intensity on the compression yield strength was greater than that on the tensile yield strength.

Nanostructure-Preserved Hematite Thin Film for Efficient Solar Water Splitting.

High-temperature annealing above 700 °C improves the activity of photoelectrochemical water oxidation by hematite photoanodes by increasing its crystallinity. Yet, it brings severe agglomeration of nanostructured hematite thin films and deteriorates electrical conductivity of the transparent conducting oxide (TCO) substrate. We report here that the nanostructure of the hematite and the conductivity of TCO could be preserved, while the high crystallinity is attained, by hybrid microwave annealing (HMA) utilizing a graphite susceptor for efficient microwave absorption. Thus, the hematite thin-film photoanodes treated by HMA record 2 times higher water oxidation photocurrents compared to a conventional thermal-annealed photoanode. The enhanced performance can be attributed to the synergistic effect of a smaller feature size of nanostructure-preserved hematite and a good electrical conductivity of TCO. The method could be generally applied to the fabrication of efficient photoelectrodes with small feature sizes and high crystallinity, which have been mutually conflicting requirements with conventional thermal annealing processes.

Lubrication characterisation analysis of stainless steel foil during micro rolling

Physical parameters, such as microscopic and roughness, play important roles in microforming process due to an increasing ratio of surface to volume of the deformed material. The study on lubrication characterisation in microforming is getting more attractive to researchers because traditional models are not reliable in this scaled down process. In this study, the micro rolling deformation characterisation has been investigated on SUS 304 stainless steel considering lubricant effect and feature size effect. The foil thickness plays an important role in the tribological features of micro rolling. The evolutions of both oil film thickness and foil surface are analysed accordingly. All the results have been verified experimentally via the new developed 2-Hi desktop micro rolling mills.

Block Co-Polymers for Nanolithography: Rapid Microwave Annealing for Pattern Formation on Substrates

The integration of block copolymer (BCP) self-assembled nanopattern formation as an alternative lithographic tool for nanoelectronic device fabrication faces a number of challenges such as defect densities, feature size, pattern transfer, etc. Key barriers are the nanopattern process times and pattern formation on current substrate stack layers such as hard masks (e.g., silicon nitride, Si3N4). We report a rapid microwave assisted solvothermal (in toluene environments) self-assembly and directed self-assembly of a polystyrene-block-polydimethylsiloxane (PS-b-PDMS) BCP thin films on planar and topographically patterned Si3N4 substrates. Hexagonally arranged, cylindrical structures were obtained and good pattern ordering was achieved. Factors affecting BCP self-assembly, notably anneal time and temperature, were studied and seen to have significant effects. Graphoepitaxy within the topographical structures provided long range, translational alignment of the patterns. The effect of surface topography feature size and spacing was investigated. The solvothermal microwave based technique used to provide periodic order in the BCP patterns showed significant promise and ordering was achieved in much shorter periods than more conventional thermal and solvent annealing methods. The implications of the work in terms of manufacturing technologies are discussed.

Nanoporous gold as a neural interface coating: effects of topography, surface chemistry, and feature size.

Designing neural interfaces that maintain close physical coupling of neurons to an electrode surface remains a major challenge for both implantable and in vitro neural recording electrode arrays. Typically, low-impedance nanostructured electrode coatings rely on chemical cues from pharmaceuticals or surface-immobilized peptides to suppress glial scar tissue formation over the electrode surface (astrogliosis), which is an obstacle to reliable neuron-electrode coupling. Nanoporous gold (np-Au), produced by an alloy corrosion process, is a promising candidate to reduce astrogliosis solely through topography by taking advantage of its tunable length scale. In the present in vitro study on np-Au's interaction with cortical neuron-glia co-cultures, we demonstrate that the nanostructure of np-Au achieves close physical coupling of neurons by maintaining a high neuron-to-astrocyte surface coverage ratio. Atomic layer deposition-based surface modification was employed to decouple the effect of morphology from surface chemistry. Additionally, length scale effects were systematically studied by controlling the characteristic feature size of np-Au through variations in the dealloying conditions. Our results show that np-Au nanotopography, not surface chemistry, reduces astrocyte surface coverage while maintaining high neuronal coverage and may enhance neuron-electrode coupling through nanostructure-mediated suppression of scar tissue formation.

Analysis of Micro/Mesoscale Sheet Forming Process by Strain Gradient Plasticity and Its Characterization of Tool Feature Size Effects

Conventional material models cannot describe material behaviors precisely in micro/mesoscale due to the size/scale effects. In micro/mesoscale forming process, the reaction force, localized stress concentration, and formability are not only dependent on the strain distribution and strain path but also on the strain gradient and strain gradient path caused by decreased scale. This study presented an analytical model based on the conventional mechanism of strain gradient (CMSG) plasticity. Finite element (FE) simulations were performed to study the effects of the width of microchannel features. Die sets were fabricated and micro/mesoscale sheet forming experiments were conducted. The results indicated that the CMSG plastic theory achieves better agreements compared to the conventional plastic theory. It was also found that the influence of strain gradient on the forming process increases with the decrease of the geometrical parameters of tools. Furthermore, the feature size effects in the forming process were evaluated and quantitated by the similarity difference and the similarity accuracy. Various tool geometrical parameters were designed based on the Taguchi method to explore the influence of the strain gradient caused by the decrease of tool dimension. According to the scale law, the difference and accuracy of similarity were calculated. Greater equivalent strain gradient was revealed with the decrease of tool dimension, which led to the greater maximum reaction force error due to the increasing size effects. The main effect plots for equivalent strain gradient and reaction force indicated that the influence of tools clearance is greater than those of punch radius, die radius, and die width.