scholarly journals Polytope Sector-Based Synthesis and Analysis of Microstructural Architectures With Tunable Thermal Conductivity and Expansion

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Jonathan B. Hopkins ◽  
Yuanping Song ◽  
Howon Lee ◽  
Nicholas X. Fang ◽  
Christopher M. Spadaccini
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Material Property ◽  
Analytical Methods ◽  
Positive Zero ◽  
Bulk Property ◽  
Element Analysis ◽  
Thermal Expansion Coefficients ◽  
Projection Microstereolithography ◽  
2D And 3D

The aim of this paper is to (1) introduce an approach, called polytope sector-based synthesis (PSS), for synthesizing 2D or 3D microstructural architectures that exhibit a desired bulk-property directionality (e.g., isotropic, cubic, orthotropic, etc.), and (2) provide general analytical methods that can be used to rapidly optimize the geometric parameters of these architectures such that they achieve a desired combination of bulk thermal conductivity and thermal expansion properties. Although the methods introduced can be applied to general beam-based microstructural architectures, we demonstrate their utility in the context of an architecture that can be tuned to achieve a large range of extreme thermal expansion coefficients—positive, zero, and negative. The material-property-combination region that can be achieved by this architecture is determined within an Ashby-material-property plot of thermal expansion versus thermal conductivity using the analytical methods introduced. These methods are verified using finite-element analysis (FEA) and both 2D and 3D versions of the design have been fabricated using projection microstereolithography.

scholarly journals Polytope Sector-Based Synthesis and Analysis of Microarchitectured Materials With Tunable Thermal Conductivity and Expansion

2015 ◽  
Author(s):  
Jonathan B. Hopkins ◽  
Howon Lee ◽  
Nicholas X. Fang ◽  
Christopher M. Spadaccini
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Material Property ◽  
Analytical Methods ◽  
Positive Zero ◽  
Bulk Property ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Projection Microstereolithography ◽  
2D And 3D

The aim of this paper is to (1) introduce an approach, called Polytope Sector-based Synthesis, for synthesizing 2D or 3D microstructural architectures that exhibit a desired bulk-property directionality (e.g., isotropic, cubic, orthotropic, etc.), and (2) provide general analytical methods that can be used to rapidly optimize the geometric parameters of these architectures such that they achieve a desired combination of bulk thermal conductivity and thermal expansion properties. Although the methods introduced can be applied to general beam-based microstructural architectures, we demonstrate their utility in the context of an architecture that can be tuned to achieve a large range of extreme thermal expansion coefficients — positive, zero, and negative. The material-property-combination region that can be achieved by this architecture is determined within an Ashby-material-property plot of thermal expansion vs. thermal conductivity using the analytical methods introduced. Both 2D and 3D versions of the design have been fabricated using projection microstereolithography.

Finite element analysis of WC–Al2O3 composites

2014 ◽  
Vol 03 (01) ◽  
pp. 1450002
Author(s):  
Satyanarayan Patel ◽  
Rahul Vaish
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Thermal Expansion ◽  
Analytical Methods ◽  
Object Oriented ◽  
Stress And Strain ◽  
Thermal And Mechanical Properties ◽  
Element Analysis

Object oriented finite element analysis (OOF2) is used to estimate the thermal and mechanical properties of WC– Al 2 O 3 composites. In the present work, five compositions of 10%, 20%, 30%, 40% and 50% Al 2 O 3 (by volume) are studied. Young's modulus, thermal conductivity and thermal expansion coefficient are estimated using OOF2 and compared with other known analytical methods. Stress and strain contours are plotted to study the thermal and mechanical behavior of composites. It is found that the stresses are largely concentrated at the interfaces of the WC– Al 2 O 3 phases.

scholarly journals Organizing Cells Within Non-Periodic Microarchitectured Materials That Achieve Graded Thermal Expansions

2015 ◽  
Author(s):  
Jonathan B. Hopkins ◽  
Lucas A. Shaw ◽  
Todd H. Weisgraber ◽  
George R. Farquar ◽  
Christopher D. Harvey ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Thermal Expansion ◽  
Young’S Modulus ◽  
Young's Modulus ◽  
Element Analysis ◽  
Thermal Expansion Coefficients ◽  
Large Lattice ◽  
Unit Cells ◽  
Expansion Coefficients ◽  
Bulk Behavior

The aim of this paper is to introduce an approach for optimally organizing a variety of different unit cell designs within a large lattice such that the bulk behavior of the lattice exhibits a desired Young’s modulus with a graded change in thermal expansion over its geometry. This lattice, called a graded microarchitectured material, can be sandwiched between two other materials with different thermal expansion coefficients to accommodate their different expansions or contractions caused by changing temperature while achieving a desired uniform stiffness. First, this paper provides the theory necessary to calculate the thermal expansion and Young’s modulus of large multi-material lattices that consist of periodic (i.e., repeating) unit cells of the same design. Then it introduces the theory for calculating the graded thermal expansions of a large multimaterial lattice that consists of non-periodic unit cells of different designs. An approach is then provided for optimally designing and organizing different unit cells within a lattice such that both of its ends achieve the same thermal expansion as the two materials between which the lattice is sandwiched. A MATLAB tool is used to generate images of the undeformed and deformed lattices to verify their behavior and various examples are provided as case studies. The theory provided is also verified and validated using finite element analysis and experimentation.

Variation of the Expansion Coefficient of Nanofluids With Temperature: A Correction for Conductivity Data

2012 ◽  
Vol 3 (4) ◽  
Author(s):  
Efstathios E. Michaelides
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Conductivity Data ◽  
Volumetric Fraction ◽  
Solid Materials ◽  
Strong Function ◽  
Temperature Changes ◽  
Thermal Expansion Coefficients ◽  
High Thermal Expansion ◽  
Expansion Coefficients

The two constituent phases of the nanofluids have thermal expansion coefficients that are significantly different. Moreover, the variability of the thermal expansion coefficients of fluids with temperature is significantly higher than that of solid materials. The mismatch of the thermal expansion coefficients creates changes of the volumetric fraction of solids with temperature changes. The changes can be significant with fluids that have high thermal expansion coefficients, such as refrigerants and fluids that operate close to their critical points. Since the thermal conductivity of nanofluids is a very strong function of the volumetric fraction of the nanoparticles, these changes of the volumetric fraction may cause significant effects on the thermal conductivity of the nanofluids, which must be accounted for in any design process.

Design of Nonperiodic Microarchitectured Materials That Achieve Graded Thermal Expansions

2016 ◽  
Vol 8 (5) ◽  
Author(s):  
Jonathan B. Hopkins ◽  
Lucas A. Shaw ◽  
Todd H. Weisgraber ◽  
George R. Farquar ◽  
Chris D. Harvey ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Compliant Mechanism ◽  
System Level ◽  
Element Analysis ◽  
Ambient Temperatures ◽  
Thermal Expansion Coefficients ◽  
Layered Coatings ◽  
Unit Cells ◽  
Expansion Coefficients

The aim of this paper is to introduce an approach for optimally organizing a variety of nonrepeating compliant-mechanism-like unit cells within a large deformable lattice such that the bulk behavior of the lattice exhibits a desired graded change in thermal expansion while achieving a desired uniform stiffness over its geometry. Such lattices with nonrepeating unit cells, called nonperiodic microarchitectured materials, could be sandwiched between two materials with different thermal expansion coefficients to accommodate their different expansions and/or contractions induced by changing ambient temperatures. This capability would reduce system-level failures within robots, mechanisms, electronic modules, or other layered coatings or structures made of different materials with mismatched thermal expansion coefficients. The closed-form analytical equations are provided, which are necessary to rapidly calculate the bulk thermal expansion coefficient and Young's modulus of general multimaterial lattices that consist first of repeating unit cells of the same design (i.e., periodic microarchitectured materials). Then, these equations are utilized in an iterative way to generate different rows of repeating unit cells of the same design that are layered together to achieve nonperiodic microarchitectured material lattices such that their top and bottom rows achieve the same desired thermal expansion coefficients as the two materials between which the lattice is sandwiched. A matlab tool is used to generate images of the undeformed and deformed lattices to verify their behavior and an example is provided as a case study. The theory provided is also verified and validated using finite-element analysis (FEA) and experimentation.

Designing Microstructural Architectures With Thermally Actuated Properties Using Freedom, Actuation, and Constraint Topologies

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Jonathan B. Hopkins ◽  
Kyle J. Lange ◽  
Christopher M. Spadaccini
Keyword(s):  
Thermal Expansion ◽  
Bulk Material ◽  
Negative Thermal Expansion ◽  
Element Analysis ◽  
Thermal Expansion Coefficients ◽  
Design Requirements ◽  
Expansion Coefficients ◽  
Thermally Actuated ◽  
Constraint Topologies

In this paper, we demonstrate how the principles of the freedom, actuation, and constraint topologies (FACT) approach may be applied to the synthesis, analysis, and optimization of microstructural architectures that possess extreme or unusual thermal expansion properties (e.g., zero or large negative-thermal expansion coefficients). FACT provides designers with a comprehensive library of geometric shapes, which may be used to visualize the regions wherein various microstructural elements can be placed for achieving desired bulk material properties. In this way, designers can rapidly consider and compare a multiplicity of microstructural concepts that satisfy the desired design requirements before selecting the final concept. A complementary analytical tool is also provided to help designers rapidly calculate and optimize the desired thermal properties of the microstructural concepts that are generated using FACT. As a case study, this tool is used to calculate the negative-thermal expansion coefficient of a microstructural architecture synthesized using FACT. The result of this calculation is verified using a finite element analysis (FEA) package called ale3d.

Measurements of Thermal Properties of Gaskets for the Design of Bolted Flange Joints Under Thermal Conduction Conditions

2006 ◽  
Author(s):  
Takahiro Ohmura ◽  
Kanji Hanashima ◽  
Junichi Nyumura ◽  
Toshiyuki Sawa
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Effective Thermal Conductivity ◽  
Linear Thermal Expansion ◽  
Absolute Temperature ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Bolted Flange ◽  
The Relationship

In this study, the thermal properties of the gaskets, which were used for designing the bolted flange joints, such as effective thermal conductivity, specific heat, linear thermal expansion coefficient and so on were measured. Especially, the effective thermal conductivities were measured by using the heat flow method. The relationship between the gasket structure and the thickness was shown by using an equivalent thermal resistance, and an empirical equation of effective thermal conductivity, which was related to the bulk density and absolute temperature, was proposed by deriving the heat conduction in solid, radiation and gas. Also, in the measurement of the linear thermal expansion coefficients of the gaskets, the measured values were shown to change substantially below 150 °C, and to depend on the heating rate and the load applied on the gasket sample.

Thermophysical Properties of Gd2O3 Doped SrHfO3 Ceramic

2015 ◽  
Vol 816 ◽  
pp. 237-241 ◽  
Author(s):  
Wen Ma ◽  
Yi Ren ◽  
Xi Long Jin ◽  
Ya Hong Liang ◽  
Bao Dong Chen ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Phase Transitions ◽  
High Temperature ◽  
Solid State ◽  
Solid State Reaction Method ◽  
Reaction Method ◽  
Long Period ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients

Gd2O3 (10mol%) doped SrHfO3 (Sr (Hf0.9Gd0.1)O2.95) was synthesized by solid state reaction method. The phase stability of the synthesized Sr (Hf0.9Gd0.1)O2.95 powder at high temperature of 1450 oC for a long period and in a temperature range of RT-1400 oC was characterized by XRD and DSC, respectively. The thermal expansion coefficients (TECs) of bulk Sr (Hf0.9Gd0.1)O2.95 were recorded by a high-temperature dilatometer, indicating that the phase transitions of SrHfO3 are suppressed remarkably by doping Gd2O3. The thermal conductivity of bulk Sr (Hf0.9Gd0.1)O2.95 at 1000 oC is ~1.95 W/m·K, which is ~11% lower than that of bulk 8YSZ.

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