scholarly journals Control of Thermophysical Properties of Langasite-Type La3Ta0.5Ga5.5O14 Crystals for Pressure Sensors

Crystals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 936
Author(s):  
Haruki Usui ◽  
Makoto Tokuda ◽  
Kazumasa Sugiyama ◽  
Takuya Hoshina ◽  
Takaaki Tsurumi ◽  
...  
Keyword(s):  
Thermal Stress ◽  
High Temperatures ◽  
Thermal Stresses ◽  
Pressure Sensors ◽  
Czochralski Method ◽  
Order Type ◽  
Cation Site ◽  
Young’S Moduli ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients

We present a possible method to reduce the anisotropy of the thermal stress generated on langasite-type La3Ta0.5Ga5.5O14 (LTG) piezoelectric crystals arising from the mismatch of the thermal expansion coefficients and Young’s moduli of the crystals and metals at high temperatures. To formulate this method, the thermal stresses of order-type langasite crystals, in which each cation site is occupied by one element only, were calculated and compared to each other. Our results suggest that the largest cation site affects the thermal stress. We attempted to replace La3+ in LTG by a larger ion and considered Sr2+. Single crystals of strontium-substituted LTG (Sr-LTG) were grown using the Czochralski method. The thermal stress along the crystallographic c-axis decreased but that perpendicular to the c-axis increased by strontium substitution into the LTG crystal. The anisotropic thermal stress was reduced effectively. The Sr-LTG single crystal is a superior candidate material for pressure sensors usable at high temperatures.

Thermal Expansion Coefficients and Thermal Stresses in an Aligned Short Fiber Composite With Application to a Short Carbon Fiber/Aluminum

1985 ◽  
Vol 52 (4) ◽  
pp. 806-810 ◽  
Author(s):  
Y. Takao ◽  
M. Taya
Keyword(s):  
Thermal Expansion ◽  
Thermal Stress ◽  
Carbon Fiber ◽  
Thermal Stresses ◽  
Short Fiber ◽  
Short Carbon Fiber ◽  
Thermal Expansion Coefficients ◽  
Equivalent Inclusion Method ◽  
Expansion Coefficients ◽  
Short Carbon

A formulation to compute the effective thermal expansion coefficients (αc) of an anisotropic short fiber-reinforced composite and the thermal stress (σ) induced in and around the fiber is developed. The formulation is based on the Eshelby’s equivalent inclusion method. Main emphasis is placed on short Carbon fiber/Aluminum. The thermal stress due to a uniform temperature rise ΔT is computed at points just outside the fiber. The effects of various parameters on αc and σ are also investigated.

Thermal Stress in a Coated Short Fiber Composite

1987 ◽  
Vol 109 (1) ◽  
pp. 59-63 ◽  
Author(s):  
Hiroshi Hatta ◽  
Minoru Taya
Keyword(s):  
Thermal Expansion ◽  
Thermal Stress ◽  
Stress Field ◽  
Thermal Stresses ◽  
Fiber Composite ◽  
Short Fiber ◽  
Critical Parameters ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Short Fiber Composite

When a coated short fiber composite is subject to temperature change, thermal stresses in and around the coated fibers are induced due to the mismatch of thermal expansion coefficients of the constituents. The problem of the above thermal stresses in a coated short fiber composite is solved by using the Eshelby’s equivalent inclusion method under the assumption of thin coating. A parametric study is then conducted to examine the effect of thermo-mechanical properties of the coating on the stress field in an and around a coated short fiber. It is found in this study that critical parameters influencing the thermal stress field are the thermal expansion coefficients of the fiber and coating.

Thermal Stress Analysis of a Bi-Material Layered Structure

2010 ◽  
Vol 450 ◽  
pp. 161-164 ◽  
Author(s):  
Shiuh Chuan Her ◽  
Chin Hsien Lin ◽  
Shun Wen Yeh
Keyword(s):  
Thermal Expansion ◽  
Thermal Stress ◽  
Thermal Stresses ◽  
Dissimilar Materials ◽  
Beam Theory ◽  
Layered Systems ◽  
Thermal Expansion Coefficients ◽  
Parametric Studies ◽  
Expansion Coefficients ◽  
Good Agreement

Thermal stress induced by the mismatch of the thermal expansion coefficients between dissimilar materials becomes an important issue in many bi-layered systems, such as composites and micro-electronic devices. It is useful to provide a simple and efficient analytical model, so that the stress level in the layers can be accurately estimated. Basing on the Bernoulli beam theory, a simple but accurate analytical formulation is proposed to evaluate the thermal stresses in a bi-material beam. The analytical results are compared with finite element results. Good agreement demonstrates that the proposed approach is able to provide an efficient way for the calculation of the thermal stresses. It is shown that thermal stresses are linear proportion to the ratio of thermal expansion coefficients between the two materials. Parametric studies reveal that thermal stresses in each layer are decreasing with the increase of thickness, and are increasing with the increase of Young’s modulus ratio between the two materials.

Modelling of III-Nitride Epitaxial Layers Grown on Silicon Substrates with Low Dislocation-Densities

MRS Advances ◽  
2019 ◽  
Vol 4 (13) ◽  
pp. 755-760 ◽  
Author(s):  
Khaled H. Khafagy ◽  
Tarek M. Hatem ◽  
Salah M. Bedair
Keyword(s):  
Thermal Stresses ◽  
Life Time ◽  
Epitaxial Layers ◽  
Silicon Substrates ◽  
Thermal Expansion Coefficients ◽  
Dislocation Densities ◽  
Large Lattice ◽  
Expansion Coefficients ◽  
And Performance ◽  
Mesh Convergence

ABSTRACTLarge lattice and thermal expansion coefficients mismatches between III-Nitride (III N) epitaxial layers and their substrates inevitably generate defects on the interfaces. Such defects as dislocations affect the reliability, life time, and performance of photovoltaic (PV) devices. High dislocation densities in epitaxial layer generate higher v-shaped pits densities on the layer top surface that also directly affect the device performance. Therefore, using an approach such as the embedded void approach (EVA) for defects reduction in the epitaxial layers is essential. EVA relies on the generation of high densities of embedded microvoids (∼108/cm2), with ellipsoidal shapes. These tremendous number of microvoids are etched near the interface between the III N thin-film and its substrate where the dislocation densities present with higher values.This article used a 3-D constitutive model that accounts the crystal plasticity formulas and specialized finite element (FE) formulas to model the EVA in multi-junction PV and therefore to study the effect of the embedded void approach on the defects reduction. Mesh convergence and 2-D analytical solution validation is conducted with accounting thermal stresses. Several aspect and volume ratios of the embedded microvoids are used to optimize the microvoid dimensions.

Thermal Stress Analysis for Air Inlet Part of Ramjet

2005 ◽  
Vol 297-300 ◽  
pp. 2253-2260 ◽  
Author(s):  
Song Heo Koo ◽  
Young Shin Lee ◽  
Jae Hoon Kim ◽  
S.J. Kim ◽  
Young Jin Choi
Keyword(s):  
Thermal Stress ◽  
Structural Design ◽  
Transient Temperature ◽  
Preliminary Design ◽  
Thermal Coefficient ◽  
The Finite Element Method ◽  
Thermal Boundary Conditions ◽  
Thermal Expansion Coefficients ◽  
Air Inlet ◽  
Expansion Coefficients

The purpose of this study is to estimate structural characteristic for air inlet part of ramjet in condition of flight at 12-15km height. Because air inlet part of ramjet is heated up to 700oK, high temperature properties such as Young’s modulus, thermal expansion coefficients and thermal conductivity coefficients are applied to the analysis. The analysis of transient temperature and thermal stress was performed by the finite element method with nonlinear code ABAQUS. The analysis was performed using several thermal coefficient and material properties to select preliminary design model for flight condition. Thermal boundary conditions were applied at ramjet inlet part until 0.01sec. The results of the analysis recommend tendency of thermal stress and temperature distribution. These are useful to select the structural material and to determine shape of air inlet part which satisfy the structural design safety.

Growth and Thermal Characterization of Yb:Y0.923Lu0.071VO4

2013 ◽  
Vol 709 ◽  
pp. 192-196
Author(s):  
Shi Ming Zhang ◽  
Bing Teng ◽  
De Gao Zhong ◽  
Bing Tao Zhang ◽  
Shu Jie Zhuang ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Diffusion Coefficients ◽  
Laser Crystal ◽  
Thermal Characterization ◽  
Czochralski Method ◽  
X Ray ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Structure Density

A new mixed laser crystal, Yb0.006Y0.923Lu0.071VO4, has been successfully grown using the Czochralski method. X-ray powder diffraction analysis shows that the crystal has ZrSiO4 structure. Density, thermal expansion coefficients, specific heat and thermal diffusion coefficients were measured, and the thermal conductivity coefficients were determined.

Thermal Stresses Under Engine Heat Flux—Part 1: Ceramic Coating on Metal Substrate

1992 ◽  
Vol 114 (4) ◽  
pp. 291-297 ◽  
Author(s):  
B. E. Sheets ◽  
K. Kokini
Keyword(s):  
Heat Flux ◽  
Thermal Expansion ◽  
Bond Coat ◽  
Thermal Stresses ◽  
Ceramic Coating ◽  
Metal Substrate ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Edge Delamination ◽  
Moduli Of Elasticity

The thermal stresses in a ceramic coating bonded to a metal substrate generated by heat flux conditions in an engine were studied. Edge delamination of the coating was related to the displacements of an interface crack between the ceramic and the metal. The effects of varying the thermal expansion coefficients of the ceramic, the bond coat and the metal, thin moduli of elasticity, their thicknesses and the initial stress-free temperature were determined.

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