Mechanical size effects of amorphous polymer-derived ceramics at the nanoscale: experiments and ReaxFF simulations

Nanoscale ◽  
2019 ◽  
Vol 11 (15) ◽  
pp. 7447-7456 ◽  
Author(s):  
Aniruddh Vashisth ◽  
Sumit Khatri ◽  
Seung Ho Hahn ◽  
Weiwei Zhang ◽  
Adri C. T. van Duin ◽  
...  
Keyword(s):  
Size Effect ◽  
Size Effects ◽  
Amorphous Polymer ◽  
Polymer Derived Ceramics ◽  
Polymer Derived Ceramic

Here we report an unprecedented mechanical size effect at the nanoscale in polymer-derived ceramic (PDC) nanofibers.

Particle size effects in the selective hydrogenation of cinnamaldehyde over supported palladium catalysts

RSC Advances ◽  
2016 ◽  
Vol 6 (79) ◽  
pp. 75541-75551 ◽  
Author(s):  
Feng Jiang ◽  
Jian Cai ◽  
Bing Liu ◽  
Yuebing Xu ◽  
Xiaohao Liu
Keyword(s):  
Particle Size ◽  
Size Effect ◽  
Selective Hydrogenation ◽  
Size Effects ◽  
Palladium Catalysts ◽  
Particle Size Effect ◽  
Particle Size Effects ◽  
Supported Palladium Catalysts ◽  
Supported Palladium ◽  
Palladium Particles

Palladium particles of different sizes obtained directly and indirectly by various methods were studied to clarify the particle size effect in the selective hydrogenation of cinnamaldehyde (CAL).

Modeling of Size Effects on the Flow Stress of Type 304 Stainless Steel and Application in Coining Process

2007 ◽  
Author(s):  
Gap-Yong Kim ◽  
Muammer Koc ◽  
Jun Ni
Keyword(s):  
Grain Size ◽  
Stainless Steel ◽  
Flow Stress ◽  
Size Effect ◽  
Size Effects ◽  
Specimen Size ◽  
304 Stainless Steel ◽  
Length Scales ◽  
Type 304 ◽  
Type 304 Stainless Steel

Application of microforming in various research areas has received much attention due to the increased demand for miniature metallic parts that require mass production. For the accurate analysis and design of microforming process, proper modeling of material behavior at the micro/meso-scale is necessary by considering the size effects. Two size effects are known to exist in metallic materials. One is the “grain size” effect, and the other is the “feature/specimen size” effect. This study investigated the “feature/specimen size” effect and introduced a scaling model which combined both feature/specimen and grain size effects. Predicted size effects were compared with experiments obtained from previous research and showed a very good agreement. The model was also applied to forming of micro-features by coining. A flow stress model for Type 304 stainless steel taking into consideration the effect of the grain and feature size was developed and implemented into a finite element simulation tool for an accurate numerical analysis. The scaling model offered a simple way to model the size effect down to length scales of a couple of grains and extended the use of continuum plasticity theories to micro/meso-length scales.

Study of the Size Effects and Friction Conditions in Microextrusion—Part II: Size Effect in Dynamic Friction for Brass-Steel Pairs

2007 ◽  
Vol 129 (4) ◽  
pp. 677-689 ◽  
Author(s):  
Lapo F. Mori ◽  
Neil Krishnan ◽  
Jian Cao ◽  
Horacio D. Espinosa
Keyword(s):  
Grain Size ◽  
Friction Coefficient ◽  
Size Effect ◽  
Contact Pressure ◽  
Size Effects ◽  
Numerical Models ◽  
Kolsky Bar ◽  
Experimental Results ◽  
Material Response ◽  
Dynamic Coefficients

In this paper, the results of experiments conducted to investigate the friction coefficient existing at a brass-steel interface are presented. The research discussed here is the second of a two-part study on the size effects in friction conditions that exist during microextrusion. In the regime of dimensions of the order of a few hundred microns, these size effects tend to play a significant role in affecting the characteristics of microforming processes. Experimental results presented in the previous companion paper have already shown that the friction conditions obtained from comparisons of experimental results and numerical models show a size effect related to the overall dimensions of the extruded part, assuming material response is homogeneous. Another interesting observation was made when extrusion experiments were performed to produce submillimeter sized pins. It was noted that pins fabricated from large grain-size material (211μm) showed a tendency to curve, whereas those fabricated from billets having a small grain size (32μm), did not show this tendency. In order to further investigate these phenomena, it was necessary to segregate the individual influences of material response and interfacial behavior on the microextrusion process, and therefore, a series of frictional experiments was conducted using a stored-energy Kolsky bar. The advantage of the Kolsky bar method is that it provides a direct measurement of the existing interfacial conditions and does not depend on material deformation behavior like other methods to measure friction. The method also provides both static and dynamic coefficients of friction, and these values could prove relevant for microextrusion tests performed at high strain rates. Tests were conducted using brass samples of a small grain size (32μm) and a large grain size (211μm) at low contact pressure (22MPa) and high contact pressure (250MPa) to see whether there was any change in the friction conditions due to these parameters. Another parameter that was varied was the area of contact. Static and dynamic coefficients of friction are reported for all the cases. The main conclusion of these experiments was that the friction coefficient did not show any significant dependence on the material grain size, interface pressure, or area of contact.

scholarly journals Size Effect in Fracture of Sandwich Structure Components: Foam and Laminate

2001 ◽  
Author(s):  
Zdeněk P. Bažant ◽  
Yong Zhou ◽  
Drahomír Novák ◽  
Isaac M. Daniel
Keyword(s):  
Size Effect ◽  
Size Effects ◽  
Sandwich Structure ◽  
Maximum Load ◽  
Material Strength ◽  
Large Structures ◽  
Nominal Strength ◽  
Sandwich Plates And Shells ◽  
Extensive Test ◽  
Plates And Shells

Abstract In the design of sandwich plates and shells for very large structures, such as ships in the range of 100 m length, it is very important to take the size effect on the nominal strength into account, and do so in a realistic, physically justified, manner. Before the size effect is addressed for a sandwich structure, it must be understood for its components — the foam core and the laminate skins. In the current practice, the size effects are automatically attributed to the randomness of material strength, as described by the Weibull theory. The purpose of this paper is to show that in both the foam and the laminate there are deterministic size effects, which are generally more pronounced. They are caused by stress redistribution and energy release due to the growth of large fractures or large cracking zones prior to attaining the maximum load. This deterministic size effect is verified and calibrated by new tests of notched specimens of rigid close-cell vinyl foam. A combined deterministic-probabilistic theory of size effect of the laminates is proposed and verified by extensive test data.

scholarly journals Size Effects in Ruthenium-Based Thick-Film Resistors: Rutile vs. Pyrochlore-Based Resistors

1991 ◽  
Vol 14 (3) ◽  
pp. 163-173 ◽  
Author(s):  
M. Prudenziati ◽  
F. Sirotti ◽  
M. Sacchi ◽  
B. Morten ◽  
A. Tombesi ◽  
...  
Keyword(s):  
Size Effect ◽  
Thick Film ◽  
Sheet Resistance ◽  
Firing Temperature ◽  
Size Effects ◽  
Conductive Phase ◽  
Lower Sheet ◽  
Lower Sheet Resistance

The size effect, namely the change of sheet resistance, Rsas a function of resistor length, has been investigated in layers whose conductive phase evolves from Pb-rich (Ru-deficient pyrochlores) to Pb2Ru2O6.5and finally to RuO2by increasing the firing temperature. It is found that Bi diffusion from the terminations is responsible for lower sheet resistance values in shorter resistors whatever the conductive phase is. On the contrary, Ag diffusion is responsible for lower sheet resistance values in shorter resistors only in the case of ruthenate conductive grains while the reverse is observed in RuO2-based layers. Size effect can be suppressed with Pt/Au-based terminations provided that no Bi is contained and with Au-metallorganic-based contact provided that the peak firing temperature is not too high.

Review of Research Progress on Size Effect in Micro-Forming

2016 ◽  
Vol 717 ◽  
pp. 118-121 ◽  
Author(s):  
T.T. Qiu ◽  
Ying Ke Hou ◽  
H.L. Cao
Keyword(s):  
Size Effect ◽  
Size Effects ◽  
Test Methods ◽  
Research Progress ◽  
Test Apparatus ◽  
Micro Forming ◽  
High Productivity ◽  
Material Usage ◽  
Deformation Behaviors ◽  
Micro Level

Microforming process is a promising approach to manufacture microparts for its high productivity, high material usage and good part properties. However, when the part size is scaled down from macro to micro level, the deformation behaviors of materials change and the size effects occur. This makes it difficult to use microforming process in industry. In the last decade, many studies have been conducted with different test methods and materials. In this paper, the main test apparatus and the methods used to study the size effect and the significant results are reported.

Experimental Investigation of Size Effects of FCC Polycrystal by Shear Banding

1999 ◽  
Vol 121 (2) ◽  
pp. 156-161
Author(s):  
Osamu Watanabe ◽  
Takayuki Kurata
Keyword(s):  
Size Effect ◽  
Cross Section ◽  
Size Effects ◽  
Rectangular Cross Section ◽  
Pure Aluminum ◽  
Shear Banding ◽  
Compressive Loading ◽  
Thickness Effect ◽  
Internal Mechanism ◽  
Meso Scale

Several plasticity phenomena display a size effect where the smaller the size is the stronger its response. This effect relates to the plastic gradients, appearing in plastically inhomogeneous material. The present paper describes results of an experimental meso-scale study using the specimens having rectangular cross section made of FCC polycrystal of pure Aluminum and OFHC Copper under the tensile or compressive loading. Experimental measurements are carried out to investigate thickness effect and grain size effect in connection with size effect, and the internal mechanism of plastic flow in the specimens is also discussed.

scholarly journals Size Effects in Small Radial Turbines

1984 ◽  
Author(s):  
K. H. Scrimshaw ◽  
T. J. Williams
Keyword(s):  
Size Effect ◽  
Internal Pressure ◽  
Steady Flow ◽  
Fatigue Failure ◽  
Significant Influence ◽  
Size Effects ◽  
Radial Flow ◽  
Flow Conditions ◽  
Peak Efficiency ◽  
Radial Turbines

The existence of size effects in small radial flow turbines, such as those used in automotive turbocharger units, has been investigated under steady flow conditions. Three geometrically similar turbines (rotor diameters 101.6, 67.73 and 50.8 mm respectively) have been tested and a ‘size’ effect was observed with the dimensionless mass flow and peak efficiency diminishing with a decrease in rotor diameter. Internal pressure variations were observed in all three turbines which could have a significant influence in relation to blade fatigue failure.

scholarly journals Modeling of the Size Effects on the Behavior of Metals in Microscale Deformation Processes

2006 ◽  
Vol 129 (3) ◽  
pp. 470-476 ◽  
Author(s):  
Gap-Yong Kim ◽  
Jun Ni ◽  
Muammer Koç
Keyword(s):  
Grain Size ◽  
Size Effect ◽  
Size Effects ◽  
Specimen Size ◽  
Material Behavior ◽  
Accurate Analysis ◽  
Analysis And Design ◽  
Scaling Model ◽  
Simple Tension ◽  
Two Parameters

For the accurate analysis and design of microforming process, proper modeling of material behavior at the micro/mesoscale is necessary by considering the size effects. Two size effects are known to exist in metallic materials. One is the “grain size” effect, and the other is the “feature/specimen size” effect. This study investigated the feature/specimen size effect and introduced a scaling model which combined both feature/specimen and grain size effects. Predicted size effects were compared with three separate experiments obtained from previous research: a simple compression with a round specimen, a simple tension with a round specimen, and a simple tension in sheet metal. The predicted results had a very good agreement with the experiments. Quantification of the miniaturization effect has been achieved by introducing two parameters, α and β, which can be determined by the scaling parameter n, to the Hall–Petch equation. The scaling model offers a simple way to model the size effect down to length scales of a couple of grains and to extend the use of continuum plasticity theories to micro/mesolength scales.

Size effect on the mechanical properties of microfabricated polysilicon thin films

2001 ◽  
Vol 16 (8) ◽  
pp. 2223-2228 ◽  
Author(s):  
J. N. Ding ◽  
Y. G. Meng ◽  
S. Z. Wen
Keyword(s):  
Thin Films ◽  
Mechanical Properties ◽  
Size Effect ◽  
Surface Area ◽  
Fracture Strength ◽  
Size Effects ◽  
Microelectromechanical Systems ◽  
Governing Parameter ◽  
Average Value ◽  
Microtensile Test

A new microtensile test device using a magnetic-solenoid force actuator was developed to evaluate the mechanical properties of microfabricated polysilicon thin films that were 100–660 mm long, 20–200 μm wide, and 2.4-μm thick. It was found that the measured average value of Young's modulus, 164 GPa ± 1.2 GPa, falls within the theoretical bounds. The average fracture strength is 1.36 GPa with a standard deviation of 0.14 GPa, and the Weibull modulus is 10.4–11.7. Statistical analysis of the specimen size effects on the tensile strength predicated the size effects on the length, the surface area, and the volume of the specimens. The fracture strength increases with an increase of the ratio of surface area to volume. In such cases, the size effect can be corrected to the ratio of the surface area to volume as the governing parameter. The test data accounts for the uncertainties in mechanical properties and may be used to enhance the reliability and design of polysilicon microelectromechanical systems devices.

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