Influence Of Scale Effect Research Articles

Influence of scale effect on surface morphology in laser powder bed fusion technology

ABSTRACT Laser powder bed fusion (LPBF) of multi-scaled structures is a prominent direction pursued by innovative designs and engineering applications. However, understanding the impact of scale effect on the effectiveness of actual structures is a pressing challenge. This work investigates the influence of structure scale on surface morphology and mechanical property by fabricating tensile samples with gauge diameters ranging from 0.2 mm to 5.0 mm. For the hatching scanning strategy, the surface roughness drastically reduces by ∼51% as the diameter increases. This appears to be the coupling results of heat accumulation, molten pool morphology at the end of single-track, overlap between multi-tracks within a layer, and successive rotational buildup between layers. Moreover, decreasing the diameter substantially reduces the tensile strength. Fortunately, a hatching-contour scanning strategy is proposed to eliminate the scale effect of surface morphology and strength. These efforts provide essential guidance for the broader application of multi-scaled structures.

Modal displacement analyses of Lamb waves in micro/nano-plates based on the consistent couple stress theory

In micro-scale structures, the influence of scale effects on the mechanical properties cannot be ignored, and the continuum mechanics theory cannot effectively describe guided wave propagation. This paper studies modal displacements in an isotropic micro/nano-scale plate — an essential factor for the mode selection of Lamb waves in non-destructive testing technology. To achieve this, the consistent couple stress theory, which additionally accounts for the impact of scale effects on wave propagation, has to be employed. A mathematical derivation method with singular value decomposition is proposed, and the excitation amplitude is computed by applying a normal stress source to evaluate the in-plane and out-of-plane displacements. The results indicate that the in-plane displacement vanishes on the plate surface for anti-symmetric modes when the phase velocity equals the velocity of shear waves. Moreover, the intersections of symmetric and anti-symmetric dispersion curves identify specific frequencies at which the out-of-plane displacement vanishes on the free surface. These findings highlight the difference in modal displacement characteristics between micro-scale and macro-scale structures. The results from this study may furnish theoretical guidance for ultrasonic non-destructive testing of microstructures.

Investigations into size dependence on the behavior of rocks with a “V” notch and hole under uniaxial compression

This study employed a combination of experimental analysis and numerical simulations using the Particle Flow Code (PFC2D) to investigate the impact of interaction between porosity and V-shaped notch on the breakage behavior of gypsum-based rock-like samples. Also, the influence of scale effect on the notch-hole interaction has been investigated while the “<” notches were positioned at three different orientations (0°, 45°, and 90°) relative to the X-axis. Parallel to the experimental phase, nine samples with analogous “<” shape notches, as well as nine additional models featuring different “>” shape notches, were generated and assessed through numerical simulations. The findings indicate that crack propagation was primarily governed by the notch shape, asymmetric line angle, and model dimensions. Notably, the rock bridge located between the “<” shape notch and the hole exhibited significantly greater breakage compared to other notch configurations (i.e., “>” shape notch). Moreover, the volume of damage increased with the inclination of the asymmetric line and the model's dimensions. Both the angle of the asymmetric line and the model's size contributed to enhanced sample strength. Elevating the asymmetric line angle, simulation size, and V-shaped notch led to the creation of more fractures, consequently resulting in a heightened occurrence of failure events in rock-like materials. Delay failure occurred in models containing “>” shaped notch while abrupt failure occurred in models containing “<” shaped notch. The experimental results affirm that PFC2D faithfully replicated the sample's failure pattern and strength. This study is useful for rock engineering design when delay failure and or abrupt failure threaten the stability of rock engineering structures.

Influence of scale effect on flow field offset for ships in confined waters

To investigate the flow field characteristics of full-scale ships advancing through confined waters, the international standard container ship (KRISO Container Ship) was considered as a research object in this study. Using the RANS equation, the volume of fluid method and the body force method were selected to investigate the hydrodynamic characteristics of a model-scale ship (the model-scale ratio λ=31.6) and a full-scale ship advancing through confined waters at low speed. A virtual disk was used in the full-scale model to determine the influence of the propeller on the ship’s flow field. First, the feasibility of the numerical calculations was verified. This proves the feasibility of the numerical and grid division methods. The self-propulsion point of the full-scale ship at Fr=0.108 is determined. The calculation cases of model-scale and full-scale ships (with or without virtual disks) at different water depths and distances between the ship and the shore were calculated, and the changes in the hull surface pressure, the flow field around the ship, and the wake fraction near the ship propeller disk in different calculation cases were determined and compared. The variations in the surge force, sway force, and yaw moment between the model- scale and full-scale ships were generally consistent. In very shallow water (H/T=1.3), the non-dimensional force and moment coefficients for model-scale ships increase more rapidly with decreasing distance from shore, suggesting that using model-scale ships to investigate the wall effect in very shallow water will result in predictions that are biased towards safety. By comparing full-scale ships with and without propellers, it was discovered that the surge force, sway force, and yaw moment were marginally greater in the propeller-equipped ship due to the suction effect, and the accompanying flow before and after the propeller was slightly smaller, with less asymmetry.

A Review of the Complex Flow and Heat Transfer Characteristics in Microchannels.

Continuously improving heat transfer efficiency is one of the important goals in the field of energy. Compact heat exchangers characterized by microscale flow and heat transfer have successfully provided solutions for this purpose. However, as the characteristic scale of the channels decreases, the flow and heat transfer characteristics may differ from those at the conventional scale. When considering the influence of scale effects and changes in special fluid properties, the flow and heat transfer process becomes more complex. The conclusions of the relevant studies have not been unified, and there are even disagreements on some aspects. Therefore, further research is needed to obtain a sufficient understanding of flow structure and heat transfer mechanisms in microchannels. This article systematically reviews the research about microscale flow and heat transfer, focusing on the flow and heat transfer mechanisms in microchannels, which is elaborated in the following two perspectives: one is the microscale single-phase flow and heat transfer that only considers the influence of scale effects, the other is the special heat transfer phenomena brought about by the coupling of microscale flow with special fluids (fluid with phase change (pseudophase change)). The microscale flow and heat transfer mechanisms under the influence of multiple factors, including scale effects (such as rarefaction, surface roughness, axial heat conduction, and compressibility) and special fluids, are investigated, which can meet the specific needs for the design of various microscale heat exchangers.

Influence of Scale Effect on Strength and Deformation Characteristics of Rockfill Materials.

The hybrid method was adopted to model the original gradation of rockfill materials. According to the specification requirements, three simulated gradations of rockfill materials have been obtained. By the same token, the corresponding maximum particle sizes are 20 mm, 40 mm and 60 mm, respectively. With samples prepared under the same criterion of relative density, the scale effect on strength and deformation characteristics of the rockfill materials were studied by large-scale and consolidated-drained triaxial compression tests. The results show that when the confining pressure is higher, the peak deviator stress decreases with the increase of the maximum particle size. With the increase of the maximum particle size, the cohesion of rockfill materials gradually increases and the internal friction angle gradually decreases. Under the condition of the same maximum particle size, with the increase of confining pressure, the volume strain at the phase transition increases gradually, while the stress ratio at the phase transition decreases. Under the same confining pressure, the larger the particle size is, the smaller the volume strain becomes and the lower the stress ratio at the phase transition is. Therefore, the research results can provide a theoretical basis for establishing the constitutive model of rockfill materials considering the scale effect.

Influence of Scale Effect of Photodetector on Visibility Measurement Uncertainty

Influence of Scale Effect of Photodetector on Visibility Measurement Uncertainty

Influence of scale effect and injection speed on morphology and structure of the microinjection molded isotactic polypropylene parts

AbstractThe morphology and microstructure as well as their forming mechanism of the parts in microinjection molding process are critical. In this work, the coupling effect of scale factor and injection speed on the morphology of the microparts was systematically investigated. Neat isotactic polypropylene parts with thicknesses of 1 mm, 200 μm, and 100 μm were molded at different injection speeds. Polarized light microscope and wide‐angle X‐ray diffraction were used to inspect the microstructures along the sample thickness. In this way, three kinds of typical morphology were observed in the parts, including typical skin‐core structure for the parts with the thickness of 1 mm, noncore shear layer structure for the parts with the thickness of 200 μm, and special skin‐core structure with large fraction of columnar crystal for the parts with the thickness of 100 μm. Most interestingly, it was intuitively and straightforward found that the wall slip occurs when the injection speed exceeds a certain value. Specifically, opposite morphological change trend can be obtained when the parts were molded at different levels of injection speeds. Based on these experimental observations, the formation mechanism was proposed to interpret the morphological evolution. Our work provides a new insight for better understanding the morphology evolution mechanism for microinjection molding parts.

Определение структур в микросхемах, чувствительных к воздействию космических частиц

The article considers the influence of scaling effects on the stability of integrated circuits (IC) under the influence of cosmic particles. There are two directions of scaling: reduction of topological dimensions of IC elements and optimization of energy consumption due to design and technological solutions. The paper analyzes the main effects (SEU, SEL, SEHE, SEGR and MBU) on the sensitivity of the IC to single events (SE)

Numerical study of scale effect on the wake dynamics of a propeller

In this study, the effects of the scale on the evolution of propeller wake is simulated and analyzed under open water conditions. The simulation is conducted using numerical techniques based on the detached eddy simulation method. The open water performance such as thrust and torque are analyzed for validation, and the instantaneous flow field, vortical structure and the kinetic energy spectra are investigated for the scale effect on the wake dynamics of a propeller. The results indicated that the influence of scale effect on load and wake dynamics of a propeller can differ significantly under different conditions. Under lighter loading condition, the average spanwise circulation at full-scale are considerably larger than those at model-scale at the range of inner radius, and the full-scale propeller exhibits a stronger blade shed vortex. Analysis of vortical structure shows that the transition-to-instability position of vortices vary under different conditions. Power spectral density analysis of the kinetic energy demonstrates that the kinetic energy of full-scale propellers is generally proportionally larger than that of model-scale propellers.

An empirical statistical constitutive relationship for rock joint shearing considering scale effect

The scale effect of rock joint shearing is of great significance in rock engineering. Most existing shear constitutive models could describe the pre- and post-peak deformation of rock joints, but only in one particular scale, that is, those existing models will fail to depict the rock joint shearing in different length scales. Therefore, this study aims to establish a constitutive relationship for rock joints with considering the scale effect. Based on the assumption of a random statistical distribution of rock material strength and statistical mesoscopic damage theory, damage variables are defined as the ratio of the number of damaged elements to the total number in the shear process. Together with the nonlinear relationship between the microelement failure and the joint scale, an empirical statistical constitutive relationship for joint is established. And then, the determination method of constitutive relationship parameters and the variation laws with the scale are discussed. Results show that the predicted results of the proposed empirical relationship not only agree well with the experimental results but also fully describe nonlinear deformation, pre-peak softening, post-peak softening, residual stage, and other mechanical properties of the shear deformation of joint with different dimensions, thereby demonstrating the rationality of the constitutive relationship. The physical meaning of the constitutive relationship parameters is clear, and the expressions of the constitutive relationship parameters can be deduced from the experimental results. In addition, the influence of scale effect on the shear deformation of rock joints can be quantified using parameters, which help accurately describe the action form of scale effect.

Optimal design and numerical analysis of the rapid precooler

Under the background of highly compact heat exchanger design core for the hypersonic aerospace precooled engine, a rapid precooler is designed and its performance is simulated under the high-altitude background. To this end, firstly, according to the known parameter range, a plate tube-fin rapid precooler unit with the optimal parameters is designed by using the genetic algorithm to find the minimum of the objective function-entransy dissipation number. Then introducing the roughness viscosity coefficient into the improved finite volume method, the effect of rapid heat transfer enhancement is obvious. The fin design can improve the heat transfer efficiency of the heat exchanger unit by 46.5%. Finally, the rapid precooler is designed based on the unit. The performance simulation results indicate that the average temperature has decreased by 735 K for less than 1.5 ms hot air flowing through the rapid precooler at a high speed. The purpose of rapid heat transfer enhancement is achieved. Also we explore the influence of different hot air velocity and coolant velocity on rapid precooler and investigate the influence of scale effect on heat transfer performance.

Micromechanical study on the influence of scale effect in the first stage of damage in composites

The variation in the apparent strength of a lamina in a laminate depending on the stacking sequence and thicknesses of the laminas of the laminate has been a matter of interest since the initiation of the extension of the applicability of composites. This fact led to the concept of in-situ strength, the problem itself being covered as a scale effect. In this paper this question is revisited moving towards the level where the damage appears, that is the micromechanical level. As the origin of the effect under consideration, the variation of thickness, takes place at a different level (mesomechanical), a multi-scale model is developed. It is possible in this model to vary the thickness of the lamina under consideration and to observe its effect on the damage. In this paper, only the first stage of damage, which appears in form of debondings between fibres and matrix, is taken into consideration. The analysis carried out shows that there is no scale effect at this first stage of the damage, which is corroborated by experimental evidences.

The Study of Regional R&amp;D Innovation Efficiency Based on Improved Two-Stage DEA Model: Evidence from 30 Provinces of China

The improved two-stage DEA model removed constrains that efficiency values of decision making units are not greater than one by means of the handling method in super-BCC model. In this way, those efficient DMUs were separated from the efficient frontier and therefore the problem that they were unable to sort in the traditional two-stage DEA model. In the meantime, this improved model gave full consideration to the dual role of intermediate outputs and the influence of scale effect， which gave the evaluation results larger reference value. Lastly, the case study of 30 provinces demonstrated the feasibility and rationality of the improved model. It is found that the level of research and innovation efficiency in east China is the highest; the comprehensive efficiency and stage efficiency of mid-south and north China are high; the comprehensive efficiency level in southwest and northwest China is high while the efficiency of scientific research and development is low; the efficiency of research and innovation in northeast China is lowest.

On correct nonlocal generalized theories of elasticity

The paper discusses nonlocal elasticity theories among which are models of media with defect fields, gradient elasticity theories, and hybrid nonlocal elasticity theories. Gradient theories are analyzed, and their correctness properties are examined. Applied theories that satisfy the correctness conditions are developed, and known applied gradient theories are verified for the correctness properties. A new nonlocal generalized theory has been developed for which the operator of balance equations is represented as the product of the equilibrium operator of classical elasticity theory and the Helmholtz operator. It is shown that this theory is one-parameter and is the only representative of hybrid models constructed by a complete system of equations for forces and moments. Unlike classical elasticity that is free from scale parameters characterizing the internal material structure, nonlocal elasticity theories naturally incorporate these parameters. That is why they are suitable for the modeling of scale effects and find application in the solution of numerous applied problems for heterogeneous structures with developed phase interfaces where the degree of influence of scale effects depends on the density of phase boundaries. Nonlocal continuum models are especially attractive for modeling the properties of various micro/nanostructures, elastic properties of composites and structured materials with submicron- and nanosized internal structures in which effective properties are to a great extent defined by the scale effects (short-range interaction effects of cohesion and adhesion). Generalized elasticity theories even for isotropic materials contain many additional physical constants that are difficult or impossible to determine experimentally. Applied models with a small number of additional physical parameters are therefore of great interest. However, the reduction of nonlocal theories aimed at reducing the number of additional parameters is a nontrivial task and may lead to incorrect theories. The goal of this paper is to study the symmetry properties in gradient theories, to analyze the correctness of gradient theories, and to develop applied one-parameter elasticity theories.

Factor Decomposition of Regional Carbon Emissions from Energy Consumption for China

This paper calculates the carbon emissions from energy consumption of 30 provinces in China through 2000-2010, and research correlation of factors such as regional economic gap and regional characteristics of carbon emissions in the process of regional economic coordinated development. The LMDI decomposition model is used to decompose the growth rate of China’s carbon emissions into 4 types of driving factors, i.e. GDP, industrial pollutants emission intensity, industrial structure and imbalance of regional economic development, to analyze influence of scale effect, technical effect, industrial structure effect and regional spatial structure effect on carbon emissions in the process of China's regional economic development. The results show that: The scale effect is determinants of carbon emissions increasing. The technical effect is the most important force to inhibit the increment of carbon emissions. Industrial structure effect and regional spatial structure effect on carbon emissions are not yet stable, but have a certain pull impact on increasing carbon emissions.

Influence of Scale Effect on Filling Behavior of Injection Molding by Visualization Method

Abstract For better understanding of thin-wall injection molding processes, a visualization injection mold and high speed camera were used to observe the dynamic filling behavior of melt in cavities with different thicknesses during the injection molding process. The impact of the scale effect on the melt-filling rate and filling imbalance in the multi-cavity were also studied. Results indicated that the filling behavior of the melt during the multi-cavity molding process was related to the cavity thickness. The experiment results can be used to describe the filling imbalance phenomenon during the injection molding process and to provide experimental evidence for precise injection molding technology at the micro scale.

On the microeconomics of diversification under learning

This paper investigates the microeconomics of diversification, based on a two-period model of an owner-managed firm facing uncertainty. The analysis focuses on the role of learning. Economies of diversification are defined based on a certainty equivalent and its decomposition into three components: expected profit (capturing scope effects), the risk premium (measuring the cost of risk aversion), and the value of information associated with learning. For each component, the influence of scale effects, trans-ray concavity effects, and income effects on economies of diversification are examined. By integrating risk, scope and the role of information, the analysis provides new insights into the microeconomics of diversification. While scope economies and risk aversion can provide general incentives for diversification, we argue that information and learning can give incentives to specialize. Implications for economic analysis are discussed.

Systemic Corruption, Scale Effects and Forest Harvesting

This paper explores the influence of scale effects and corruption on forest harvesting. Policy-maker and bureaucratic corruption are considered sequentially. Overall, the corrupt policy maker chooses a less stringent forest policy. Moreover, this permissive forest policy partly enhances bureaucratic corruption. This paper therefore partially supports the idea of systemic corruption. Finally, it appears that a larger number of lobbying firms tends to increase this effect.

Influence of scaling effects on designing for power efficiency of a micropreconcentrator

Rapid and reliable assessment of volatile and semivolatile organic compounds in the environment using gas chromatography (GC) is often limited by cost of analysis, and time delays between sampling and analysis. Many environmental monitors incorporating GC systems are too large for portability, and lack sufficient sensitivity and/or selectivity to serve as practical environmental monitors. Frequently, a complete system redesign, due to nonlinear power scaling relative to component size, is required to reduce the mass and volume of power supplies, especially for the micro-systems of present interest. Here, we examined four strategies in reducing power demand by the largest consumer of power in a model micro GC, the preconcentrator. Our simulations included alterations in heater pad placement/size, reduction of thermal mass in the device, vacuum sealing, and incorporation of a gas dwell time during preconcentrator heating. Our numerical results were in general agreement with experimental findings in simpler systems, in terms of the benefits of vacuum sealing. The greatest reductions in power demand were achieved with vacuum sealing (51%) and reductions in thermal mass (15%). Future work will address structural and materials issues involved in reduction of thermal mass, and also optimization of power supplies required to meet the multilevel power demands of these complex microelectromechanical systems.