Thermal Stresses Under Engine Heat Flux—Part 2: Thin Metallic Films on Ceramic Coatings

1992 ◽  
Vol 114 (4) ◽  
pp. 298-308 ◽  
Author(s):  
K. Kokini ◽  
B. E. Sheets
Keyword(s):  
Heat Flux ◽  
Thermal Stresses ◽  
Ceramic Coatings ◽  
Plastic Behavior ◽  
Film Material ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Edge Delamination ◽  
Moduli Of Elasticity ◽  
Interface Edge

The thermal stresses in a metallic thin film bonded to a ceramic coating on a metal substrate, generated by heat flux conditions in an engine, were studied. The film yields as a result of differential contraction and its thermo-plastic behavior is determined. Edge delamination of the film is related to the displacements of an interface edge crack between the film and ceramic. The effects of varying the surface roughness of the interface, the thickness of the film, the film material, the thermal expansion coefficients and the moduli of elasticity of the ceramic and metal on the stresses in the film and the crack are studied.

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.

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.

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.

Parametric study on the influence of material properties and geometry on the thermally induced bistability of composite laminates

2021 ◽  
pp. 095440622110456
Author(s):  
Samir A Emam ◽  
Tarun Pherwani ◽  
Aravindh Anil ◽  
Aeman Muhammed
Keyword(s):  
Thermal Expansion ◽  
Aspect Ratio ◽  
Material Properties ◽  
Parametric Study ◽  
Composite Laminates ◽  
Thickness Ratio ◽  
Thermally Induced ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Moduli Of Elasticity

This paper presents a parametric study on the key parameters that control the thermally induced bistability of cross-ply laminates. The influence of the material properties including the moduli of elasticity and the thermal expansion coefficients and the laminate’s geometry including the aspect ratio (AR) and the width-to-thickness ratio are investigated. The unsymmetric [Formula: see text] and the antisymmetric [Formula: see text] cross-ply laminates are investigated. Five key parameters are varied: the number of plies, the width-to-thickness ratio, the laminate’s aspect ratio, the ratio of the moduli of elasticity, and the ratio of the thermal expansion coefficients of the lamina. The laminate is assumed flat at the cured temperature and a uniform temperature gradient is applied until it is reduced to the room temperature. For each set of parameters, the stable equilibrium shapes of the laminate are obtained using a Ritz model. The ABAQUS finite element package is used to validate the model and an excellent agreement is obtained. Results that show the variation of the curvatures with the width-to-thickness ratio and the onset of the bistability for a variety of parameters are presented. The ratio of the moduli of elasticity and the thermal expansion coefficients significantly affect the critical width-to-thickness ratio at which the laminates become bistable. The unsymmetric laminates show bistability at a lower width-to-thickness ratio compared with the antisymmetric laminates. The results also show that the higher the aspect ratio, the lower the critical width-to-thickness ratio for stability for both laminates.

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.

Thermal Stress in a Coated Short Fibre Composite

1986 ◽  
Vol 53 (3) ◽  
pp. 681-689 ◽  
Author(s):  
Yozo Mikata ◽  
Minoru Taya
Keyword(s):  
Stress Field ◽  
Thermal Stresses ◽  
Fibre Composite ◽  
Extreme Case ◽  
Short Fibre ◽  
Thermal Expansion Coefficients ◽  
Stress Functions ◽  
Expansion Coefficients ◽  
Short Fibre Composite ◽  
Good Agreement

When a coated short fibre composite is subjected to temperature change, thermal stresses in and around the coated fibres are induced due to the mismatch of thermal expansion coefficients of the constituents, resulting in a possibility of cracking in the coating. The problem of the above thermal stresses in a coated short fibre composite is solved by using the Boussinesq-Sadowsky stress functions. The present results are compared with Eshelby’s solutions for an extreme case and good agreement between the two methods is obtained. A parametric study is then conducted to examine the effect of the geometry and thermo-mechanical properties of the coating on the stress field in and around a coated short fibre. It is found in this study that the stress field in the coating is sensitive to the properties and geometry of the coating.

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