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.

scholarly journals Thermal Expansion Behavior in the A2M3O12 Family of Materials

Solids ◽  
2021 ◽  
Vol 2 (1) ◽  
pp. 87-107
Author(s):  
Hongfei Liu ◽  
Weikang Sun ◽  
Zhiping Zhang ◽  
La’Nese Lovings ◽  
Cora Lind
Keyword(s):  
Thermal Expansion ◽  
Physical Properties ◽  
Coefficient Of Thermal Expansion ◽  
Negative Thermal Expansion ◽  
Future Studies ◽  
The Past ◽  
Expansion Behavior ◽  
Wide Range ◽  
Anomalous Thermal Expansion ◽  
Published Research

Over the past several decades, research on anomalous thermal expansion materials has been rapidly growing, and increasing numbers of compounds exhibiting negative thermal expansion (NTE) have been reported. In particular, compounds with formula A2M3O12 have attracted considerable attention. A2M3O12 family materials offer a wide range of possible compositions due to the chemical flexibility of the A and M sites. According to published research, more than half of them possess NTE properties. This paper reviews the range of physical properties displayed by materials in the A2M3O12 family. Research on improving material imperfections and controlling the coefficient of thermal expansion in the A2M3O12 family are systematically summarized. Finally, challenges and questions about the developments of these A2M3O12 NTE compounds in future studies are also discussed.

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.

Hygrothermal Behavior of Advanced Polymers Above Water Boiling Temperatures

2014 ◽  
Vol 136 (1) ◽  
Author(s):  
Changsoo Jang ◽  
Bongtae Han
Keyword(s):  
Thermal Expansion ◽  
Moisture Content ◽  
Coefficient Of Thermal Expansion ◽  
Measurement Data ◽  
Hybrid Procedure ◽  
Boiling Temperature ◽  
Hygrothermal Behavior ◽  
Expansion Behavior ◽  
Wide Range ◽  
Moisture Conditions

Hygroscopic and thermal expansion behavior of advanced polymers is investigated when subjected to combined high temperature and moisture conditions. An enhanced experimental–numerical hybrid procedure is proposed to overcome the limitations of the existing methods when used at temperatures above the water boiling temperature. The proposed procedure is implemented to measure the hygrothermal strains of three epoxy molding compounds and a no-filler underfill over a wide range of temperatures including temperatures beyond the water boiling temperature. The effects of moisture content on the glass transition temperature (Tg) and coefficient of thermal expansion (CTE) are evaluated from the measurement data. A formulation to predict the Tg change as a function of moisture content is also presented.

scholarly journals A Proposal for a Composite with Temperature-Independent Thermophysical Properties: HfV2–HfV2O7

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 5021
Author(s):  
Philipp Keuter ◽  
Anna L. Ravensburg ◽  
Marcus Hans ◽  
Soheil Karimi Aghda ◽  
Damian M. Holzapfel ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Temperature Coefficient ◽  
Thermophysical Properties ◽  
Coefficient Of Thermal Expansion ◽  
Negative Thermal Expansion ◽  
Phase Fraction ◽  
Formation Temperature ◽  
Oxygen Mobility ◽  
Zero Temperature ◽  
Coefficient Of Elasticity

The HfV2–HfV2O7 composite is proposed as a material with potentially temperature-independent thermophysical properties due to the combination of anomalously increasing thermoelastic constants of HfV2 with the negative thermal expansion of HfV2O7. Based on literature data, the coexistence of both a near-zero temperature coefficient of elasticity and a coefficient of thermal expansion is suggested for a composite with a phase fraction of approximately 30 vol.% HfV2 and 70 vol.% HfV2O7. To produce HfV2–HfV2O7 composites, two synthesis pathways were investigated: (1) annealing of sputtered HfV2 films in air to form HfV2O7 oxide on the surface and (2) sputtering of HfV2O7/HfV2 bilayers. The high oxygen mobility in HfV2 is suggested to inhibit the formation of crystalline HfV2–HfV2O7 composites by annealing HfV2 in air due to oxygen-incorporation-induced amorphization of HfV2. Reducing the formation temperature of crystalline HfV2O7 from 550 °C, as obtained upon annealing, to 300 °C using reactive sputtering enables the synthesis of crystalline bilayered HfV2–HfV2O7.

Investigation of fatigue behavior of centrifuged series 3000 Al with addition of 26 wt% Cu

2020 ◽  
Vol 234 (10) ◽  
pp. 1375-1385
Author(s):  
Aref Mehditabar ◽  
Seyed E Vahdat ◽  
Gholam-Hossein Rahimi
Keyword(s):  
Electron Microscopy ◽  
Thermal Expansion ◽  
High Performance ◽  
Volume Fraction ◽  
Coefficient Of Thermal Expansion ◽  
Fatigue Behavior ◽  
Centrifugal Casting ◽  
Image Analyzer ◽  
Casting Technique ◽  
Wide Range

More than 70% of mechanical parts in a wide range of engineering fields fail by fatigue. In addition, centrifugal casting is identified as the most effective casting technique for production of high performance cylindrical parts. In this regard, the present work aims to investigate the fatigue behavior of series 3000 Al with addition of 26 wt% Cu produced through horizontal centrifugal casting method. Microstructure characterizations are precisely studied using scanning transmission electron microscopy and field emission scanning electron microscopy in conjunction with image analyzer software. Also, compressive behavior, hardness, coefficient of thermal expansion, and wear rate ( Wr) are measured applying Zwick Z100, Vickers hardness, DIL 805A/D, and pin-on-disc machines, respectively. The results indicate that the main intermetallic compound is Al2Cu-based particle, and a volume fraction of 31 vol.% is obtained. Besides, the compressive strength of 460 MPa, elastic modulus of 10.986 GPa, hardness of 152 HV, coefficient of thermal expansion of 1.7 × 10−5 1/°C, and wear resistance of 3.3 × 10−6 g/mm2 are measured. Finally, the four-point bending fatigue test is performed and the fatigue ratio of 0.109 at about 106 cycles to failure is obtained.

scholarly journals Оптоакустический генератор ультразвука на основе структуры с таммовским плазмоном и органическим активным слоем

2021 ◽  
Vol 47 (7) ◽  
pp. 17
Author(s):  
Е.И. Гиршова ◽  
Е.П. Микитчук ◽  
А.В. Белоновский ◽  
К.М. Морозов ◽  
К.А. Иванов
Keyword(s):  
Thermal Expansion ◽  
Laser Radiation ◽  
Active Medium ◽  
Organic Material ◽  
Coefficient Of Thermal Expansion ◽  
Organic Layer ◽  
Mechanical Vibrations ◽  
High Coefficient ◽  
New Class ◽  
Additional Layer

Currently, a new class of ultrasound generators is being actively developed, based on the conversion of optical energy of laser radiation into ultrasonic mechanical vibrations. It was shown theoretically that an efficient optoacoustic generator can be realized using a structure with a Tamm plasmon as an active medium. This article discusses the improvement of such an optoacoustic generator by adding a layer of organic material (polydimethylsiloxane), which has an extremely high coefficient of thermal expansion. Modeling of the properties of the structure was carried out, which showed that the use of polydimethylsiloxane as an additional layer of the structure of an optoacoustic transducer is expedient at frequencies up to 50 MHz. It was also shown that the addition of an organic layer leads to an increase in the efficiency of optoacoustic conversion by 4 orders of magnitude.

High Temperature Stability of Zirconium Tungstate

2020 ◽  
Vol 993 ◽  
pp. 771-775
Author(s):  
Ping Zhai ◽  
Xiao Feng Duan ◽  
Da Qian Chen
Keyword(s):  
Thermal Expansion ◽  
High Temperature ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Solid Phase ◽  
Coefficient Of Thermal Expansion ◽  
Negative Thermal Expansion ◽  
Tungstic Acid ◽  
High Temperature Stability ◽  
Zirconium Tungstate

In this paper, zirconium tungstate ceramic with negative thermal expansion coefficients was prepared from zirconium oxide and tungstic acid by solid phase synthesis and high temperature quenching technique with a sintering temperature of 1200 °C. The phase structure of the material was determined by X ray and the thermal expansion coefficient was measured by dilatometer, while the TG-DTA analysis of the prepared material was also carried out. The results showed that zirconium tungstate with high purity could be obtained by rapid chilled while fired at 1200 °C. The coefficient of thermal expansion at 300 °C was minus 8.5413 × 10-6K-1, which is identical with the theoretical value. The thermal expansion coefficient of the material was negative fired lower than 750 °C, while it was positive fired higher than 750 °C, and this indicates that the decomposition temperature of zirconium tungstate is about 750 °C.

New Technique for AB Initio Atomistic Potentials and Application to Thermal Expansion of Ni/Cr Alloys

1992 ◽  
Vol 291 ◽  
Author(s):  
J. Mei ◽  
B.R. Cooper ◽  
Y.G. Hao ◽  
S.P. Lim ◽  
F.L. VanScoy
Keyword(s):  
Thermal Expansion ◽  
Ab Initio ◽  
Density Functional ◽  
Interatomic Potential ◽  
Coefficient Of Thermal Expansion ◽  
Many Body ◽  
Functional Theory ◽  
Transition Metal Alloys ◽  
Wide Range ◽  
Dynamics Simulations

ABSTRACTA scheme of developing ab initio many body potentials based on total energy calculations within density functional theory (DFT) is presented and demonstrated for transition metal alloys. An ab initio interatomic potential for Ni/Cr alloys is constructed with no input from experimental data. Molecular dynamics simulations have been performed to study thermal expansions. The coefficient of thermal expansion (CTE) has been calculated over a wide range of temperature, and good agreement is obtained between theory and experiment.

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