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.

Analysis of Branched Interface Cracks

1990 ◽  
Vol 57 (4) ◽  
pp. 887-893 ◽  
Author(s):  
D. J. Mukai ◽  
R. Ballarini ◽  
G. R. Miller
Keyword(s):  
Energy Release Rate ◽  
Energy Release ◽  
Interface Crack ◽  
Finite Length ◽  
Release Rate ◽  
Rate Ratio ◽  
Maximum Energy ◽  
Crack Branching ◽  
Maximum Energy Release ◽  
Branch Crack

A solution is presented for the problem of a finite length crack branching off the interface between two bonded dissimilar isotropic materials. Results are presented in terms of the ratio of the energy release rate of a branched interface crack to the energy release rate of a straight interface crack with the same total length. It is found that this ratio reaches a maximum when the interface crack branches into the softer material. Longer branches tend to have smaller maximum energy release rate ratio angles indicating that all else being equal, a branch crack will tend to turn back parallel to the interface as it grows.

Crack Tunneling in Cement Sheath of Hydrocarbon Well

2015 ◽  
Vol 83 (1) ◽  
Author(s):  
Zhengjin Wang ◽  
Yucun Lou ◽  
Zhigang Suo
Keyword(s):  
Energy Release Rate ◽  
Energy Release ◽  
Release Rate ◽  
Maximum Energy ◽  
Large Area ◽  
Annular Gap ◽  
Small Cracks ◽  
Cement Sheath ◽  
Well Cement ◽  
Maximum Energy Release

In a hydrocarbon well, cement fills the annular gap between two steel casings or between a steel casing and rock formation, forming a sheath that isolates fluids in different zones of the well. For a well as long as several kilometers, the cement sheath covers a large area and inevitably contains small cracks. The cement sheath fails when a small crack grows and tunnels through the length of the well. We calculate the energy release rate at a steady-state tunneling front as a function of the width of the tunnel. So long as the maximum energy release rate is below the fracture energy of the cement, tunnels of any width will not form. This failsafe condition requires no measurement of small cracks, but depends on material properties and loading conditions. We further show that the critical load for tunneling reduces significantly if the cement/casing and cement/formation interfaces slide.

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