scholarly journals Microcrack propagation induced by dynamic infiltration of calcium-magnesium-alumino-silicate in columnar structures for thermal barrier coatings

2020 ◽  
Author(s):  
Shaochen Tseng ◽  
Chingkong Chao ◽  
Weixu Zhang ◽  
X.L. Fan
Keyword(s):  
Energy Release Rate ◽  
Energy Release ◽  
Release Rate ◽  
Thermal Barrier ◽  
High Porosity ◽  
Columnar Microstructure ◽  
Premature Failure ◽  
Barrier Coating ◽  
Microcrack Propagation ◽  
Calcium Magnesium

Abstract Columnar-structured thermal barrier coating systems (TBCs) possess a strain tolerant columnar microstructure wherein the gaps between the columns are filled with high-porosity oxides. At high temperatures, columnar-structured TBCs may be eroded via contact with a significant amount of calcium-magnesium-alumina-silicate (CMAS). A numerical model is proposed to estimate the temperature and stress fields of the microcracks induced by the CMAS infiltration. The energy release rate is evaluated to understand the influence of CMAS on the microcracks in the columnar microstructure. The effects of CMAS on the microcrack propagation are discussed in detail by using the extended finite element method. The results demonstrate that both the stress and energy release rate near the microcrack were found to dramatically increase when the CMAS reached the microcrack. Moreover, increasing the time of CMAS infiltration could destroy the thermal insulation provided by the top coat and considerably increase the energy release rate. The present analysis reveals that the vertical cracks are easily to initiate from the microstructure column and coalesce with adjacent horizontal and vertical pores, thereby resulting in premature failure of TBCs via delamination.

scholarly journals The Influence of Transient Thermal Gradients and Substrate Constraint on Delamination of Thermal Barrier Coatings

2012 ◽  
Vol 80 (1) ◽  
Author(s):  
S. Sundaram ◽  
D. M. Lipkin ◽  
C. A. Johnson ◽  
J. W. Hutchinson
Keyword(s):  
Energy Release Rate ◽  
Energy Release ◽  
Release Rate ◽  
Early Stage ◽  
Maximum Energy ◽  
Thermal Barrier ◽  
Substrate Thickness ◽  
Thermal Gradients ◽  
Surface Cooling ◽  
Transient Thermal

A systematic study of factors affecting the delamination energy release rate and mode mix of a thermal barrier coating attached to a substrate is presented accounting for the influence of thermal gradients combined with rapid hot surface cooling. Transient thermal gradients induce stress gradients through the coating and substrate, which produce overall bending if the substrate is not very thick and if it is not constrained. Due to their influences on the coating stresses, substrate thickness and constraint are important aspects of the mechanics of delamination of coating-substrate systems, which must be considered when laboratory tests are designed and for lifetime assessment under in-service conditions. Temperature gradients in the hot state combined with rapid cooling give rise to a maximum energy release rate for delamination that occurs in the early stage of cooling and that can be considerably larger than the driving force for delamination in the cold state. The rates of cooling that give rise to a large early stage energy release rate are identified.

Delamination Susceptibility of Coatings Under High Thermal Flux

2009 ◽  
Vol 76 (4) ◽  
Author(s):  
Z. Xue ◽  
A. G. Evans ◽  
J. W. Hutchinson
Keyword(s):  
Energy Release Rate ◽  
Energy Release ◽  
Release Rate ◽  
Thermal Flux ◽  
High Heat ◽  
High Heat Flux ◽  
Energy Release Rates ◽  
Calcium Magnesium ◽  
Detailed Assessment ◽  
Alumino Silicate

Delamination of coatings initiated by small cracks paralleling the free surface is investigated under conditions of high thermal flux associated with a through-thickness temperature gradient. A crack disrupts the heat flow thereby inducing crack tip stress intensities that can become critical. A complete parametric dependence of the energy release rate and mode mix is presented in terms of the ratio of the crack length to its depth below the surface and coefficients characterizing heat transfer across the crack and across the gaseous boundary layer between the surface and the hot gas. Proximity to the surface elevates the local temperature, which in turn, may significantly increase the crack driving force. A detailed assessment reveals that the energy release rates induced by high heat flux are capable of extending subsurface delaminations in thermal barrier coatings, but only when the modulus has been elevated by either calcium-magnesium-alumino-silicate (CMAS) penetration or sintering. Otherwise, the energy release rate remains well below the toughness.

Stress Intensity Factors for Interfacial Cracks in Thick Thermal Barrier Coatings

1998 ◽  
Author(s):  
C. Bjerken ◽  
C. Persson
Keyword(s):  
Energy Release Rate ◽  
Energy Release ◽  
Release Rate ◽  
Thermal Barrier ◽  
Intensity Factors ◽  
Mode Mixity ◽  
Release Rates ◽  
Edge Angle ◽  
Interfacial Cracks ◽  
Energy Release Rates

Abstract A straight-forward method for calculating the stress intensity factors (or the energy release rate and mode mixity) for interfacial cracks in bi-materials has been developed. An existing method for homogeneous materials, based on the computation of the energy release rate from the nodal forces and displacements given by a finite element analysis, was modified to include the mismatch in material properties. Thick thermal barrier coatings usually fail as a result of cracking near the interface. The influence of the thickness and the edge angle of the coating on the energy release rate and mode mixity for a small edge crack at the interface of a TBC system subjected to thermal loading was investigated. It was established that the high energy release rates obtained for thick coatings can be reduced by decreasing the edge angle of the coating. Additionally a comparison with energy release rates given by J-integral computations has been done.

Calculating Energy Release Rate as a Function of Crack Length Using a Multiple-Step Crack Closure Technique in Tire Finite Element Models

2018 ◽  
Vol 46 (3) ◽  
pp. 130-152
Author(s):  
Dennis S. Kelliher
Keyword(s):  
Finite Element ◽  
Energy Release Rate ◽  
Crack Length ◽  
Energy Release ◽  
Crack Closure ◽  
Release Rate ◽  
Fatigue Behavior ◽  
Three Dimensions ◽  
Quantitative Prediction ◽  
Closure Technique

ABSTRACT When performing predictive durability analyses on tires using finite element methods, it is generally recognized that energy release rate (ERR) is the best measure by which to characterize the fatigue behavior of rubber. By addressing actual cracks in a simulation geometry, ERR provides a more appropriate durability criterion than the strain energy density (SED) of geometries without cracks. If determined as a function of crack length and loading history, and augmented with material crack growth properties, ERR allows for a quantitative prediction of fatigue life. Complications arise, however, from extra steps required to implement the calculation of ERR within the analysis process. This article presents an overview and some details of a method to perform such analyses. The method involves a preprocessing step that automates the creation of a ribbon crack within an axisymmetric-geometry finite element model at a predetermined location. After inflating and expanding to three dimensions to fully load the tire against a surface, full ribbon sections of the crack are then incrementally closed through multiple solution steps, finally achieving complete closure. A postprocessing step is developed to determine ERR as a function of crack length from this enforced crack closure technique. This includes an innovative approach to calculating ERR as the crack length approaches zero.

scholarly journals Effect of the Characteristic Size and Content of Graphene on the Crack Propagation Path of Alumina/Graphene Composite Ceramics

Materials ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 611
Author(s):  
Benshuai Chen ◽  
Guangchun Xiao ◽  
Mingdong Yi ◽  
Jingjie Zhang ◽  
Tingting Zhou ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Energy Release Rate ◽  
Energy Release ◽  
Release Rate ◽  
Volume Content ◽  
Phase Interface ◽  
Average Energy ◽  
Characteristic Size ◽  
Composite Ceramics ◽  
Graphene Composite

In this paper, the Voronoimosaic model and the cohesive element method were used to simulate crack propagation in the microstructure of alumina/graphene composite ceramic tool materials. The effects of graphene characteristic size and volume content on the crack propagation behavior of microstructure model of alumina/graphene composite ceramics under different interfacial bonding strength were studied. When the phase interface is weak, the average energy release rate is the highest as the short diameter of graphene is 10–50 nm and the long diameter is 1600–2000 nm. When the phase interface is strong, the average energy release rate is the highest as the short diameter of graphene is 50–100 nm and the long diameter is 800–1200 nm. When the volume content of graphene is 0.50 vol.%, the average energy release rate reaches the maximum. When the velocity load is 0.005 m s−1, the simulation result is convergent. It is proven that the simulation results are in good agreement with the experimental phenomena.

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