scholarly journals Analysis of Antichiral Thermomechanical Metamaterials with Continuous Negative Thermal Expansion Properties

Materials ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2139 ◽  
Author(s):  
Debajyoti Saha ◽  
Paul Glanville ◽  
Eduard G. Karpov
Keyword(s):  
Thermal Expansion ◽  
Negative Thermal Expansion ◽  
Thermal Expansivity ◽  
Design Parameters ◽  
Model Parameters ◽  
Theoretical Predictions ◽  
Thermal Expansion Effect ◽  
Generic Theory ◽  
Expansion Effect ◽  
Node Size

Negative thermal expansion is an interesting and appealing phenomenon for various scientific and engineering applications, while rarely occurring in natural materials. Here, using a universal antichiral metamaterial model with bimetal beams or strips, a generic theory has been developed to predict magnitude of the negative thermal expansion effect from model parameters. Thermal expansivity of the metamaterial is written as an explicit function of temperature and only three design parameters: relative node size, chirality angle, and a bimetal constant. Experimental measurements follow theoretical predictions well, where thermal expansivity in the range of negative 0.0006–0.0041 °C−1 has been seen.

Raman Band Redshifting of α-Cu2(OH)3Cl with Decreasing the Temperature

2012 ◽  
Vol 430-432 ◽  
pp. 391-394
Author(s):  
Xiao Dong Liu ◽  
Xing Liang Xu ◽  
Dong Dong Meng ◽  
Masayoshi Fujihala ◽  
Xu Guang Zheng ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Laser Heating ◽  
Raman Band ◽  
Negative Thermal Expansion ◽  
Polycrystalline Sample ◽  
Heating Effect ◽  
Lattice Thermal Expansion ◽  
Geometric Frustration ◽  
Thermal Expansion Effect ◽  
Expansion Effect

Raman spectra of the magnetic geometric frustration material – the botallackite-structure α-Cu2(OH)3Cl polycrystalline sample were measured down to liquid N2 temperature. It is found that the hydroxyl stretching bands shift abnormally according to the lattice thermal expansion effect of normal materials, i.e., they redshift with decreasing the sample temperature (negative thermal expansion) using liquid N2 cooling while other bands blueshift. This abnormality was also confirmed by observing the band-shifting caused by local laser heating effect using different laser powers, and can be qualitatively explained by checking the local hydroxyl environment with a trimeric hydrogen bond.

Monitoring and Control of Thermal Expansion Effect on Machining Process of Aluminum Alloy Parts

2015 ◽  
Vol 809-810 ◽  
pp. 33-38 ◽  
Author(s):  
Ştefan Adrian Moldovan ◽  
Vasile Năsui
Keyword(s):  
Thermal Expansion ◽  
Aluminum Alloy ◽  
Milling Process ◽  
Machining Process ◽  
Machining Accuracy ◽  
Technological Problem ◽  
Monitoring And Control ◽  
Machining Processes ◽  
Thermal Expansion Effect ◽  
Expansion Effect

In this paper we present a technological problem encountered in the machining accuracy of the parts for aerospace made of aluminum alloy extruded profile with length up to 10 meters. Those parts have very tight tolerances and on milling process appear several factors that influence the repeatability of machining processes, the main one being the thermal expansion effect.

scholarly journals Micro-structured medium with large isotropic negative thermal expansion

2019 ◽  
Vol 475 (2232) ◽  
pp. 20190468 ◽  
Author(s):  
Luigi Cabras ◽  
Michele Brun ◽  
Diego Misseroni
Keyword(s):  
Thermal Expansion ◽  
Coefficient Of Thermal Expansion ◽  
Negative Thermal Expansion ◽  
Simple Relation ◽  
Space Structures ◽  
New Class ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Innovative Materials ◽  
New Generation

A challenge in nano- and micro-mechanics is the realization of innovative materials exploiting auxetic behaviour to tailor thermal expansion properties. For this purpose, a new class of micro-structured media possessing an extremely wide range of tunable (positive, negative or even zero) thermal expansion is proposed and analytically and experimentally assessed. For this class of isotropic Mechanical-Auxetic Thermal-Shrinking media, the effective coefficient of thermal expansion is explicitly linked to two microstructural variables via a simple relation, allowing the design with desired values. The theoretical predictions for the negative thermal properties are fully validated by the experimental and numerical outcomes. The simplicity of the proposed structure makes the design useful for the production of a new generation of advanced media, with applications ranging from micromechanical devices to large civil and space structures.

Direct and indirect thermal expansion effects in turbulent premixed flames

2011 ◽  
Vol 689 ◽  
pp. 149-182 ◽  
Author(s):  
Vincent Robin ◽  
Arnaud Mura ◽  
Michel Champion
Keyword(s):  
Thermal Expansion ◽  
Velocity Field ◽  
Large Scale ◽  
Turbulent Transport ◽  
Premixed Flames ◽  
Small Scale ◽  
Flame Surface ◽  
Thermal Expansion Effect ◽  
Expansion Effect ◽  
Turbulent Premixed

AbstractThe thermal expansion induced by the exothermic chemical reactions taking place in a turbulent reactive flow affects the velocity field so strongly that the large-scale velocity fluctuations as well as the small-scale velocity gradients can be governed by chemistry rather than by turbulence. Moreover, thermal expansion is well known to be responsible for counter-gradient turbulent diffusion and flame-generated turbulence phenomena. In the present study, by making use of an original splitting procedure applied to the velocity field, we establish the occurrence of two distinct thermal expansion effects in the flamelet regime of turbulent premixed combustion. The first is referred to as the direct thermal expansion effect. It is associated with a local flamelet crossing contribution as previously considered in early analyses of turbulent transport in premixed flames. The second, denoted herein as the indirect thermal expansion effect, is an outcome of the turbulent wrinkling processes that increases the flame surface area. Based on a splitting procedure applied to the velocity field, the respective influences of the two effects are identified and analysed. Furthermore, the theoretical analysis shows that the thermal expansion induced through the local flames can be treated separately in the usual continuity and momentum equations. This description of the turbulent reactive velocity field, leads also to relate all of the usual turbulent quantities to the reactive scalar field. Finally, algebraic closures for the turbulent transport terms of mass and momentum are proposed and successfully validated through comparison with direct numerical simulation data.

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