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Spallation of thin films driven by pockets of energy concentration

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journal contribution
posted on 03.05.2017, 08:51 authored by Christopher HarveyChristopher Harvey, Bin Wang, Simon WangSimon Wang
A hypothesis is made that delamination can be driven by pockets of energy concentration (PECs) in the form of pockets of tensile stress and shear stress on and around the interface between a thin film and a thick substrate, where PECs can be caused by thermal, chemical or other processes. Based on this hypothesis, three analytical mechanical models are developed to predict several aspects of the spallation failure of elastic brittle thin films including nucleation, stable and unstable growth, size of spallation and final kinking off. Both straight-edged and circular-edged spallations are considered. The three mechanical models are established using partition theories for mixed-mode fracture based on classical plate theory, first-order shear-deformable plate theory and full 2D elasticity. Experimental results show that all three of the models predict the initiation of unstable growth and the size of spallation very well; however, only the 2D elasticity-based model predicts final kinking off well. The energy for the nucleation and stable growth of a separation bubble comes solely from the PEC energy on and around the interface, which is ‘consumed’ by the bubble as it nucleates and grows. Unstable growth, however, is driven both by PEC energy and by buckling of the separation bubble. Final kinking off is controlled by the fracture toughness of the interface and the film and the maximum energy stored in the separation bubble. This work will be particularly useful for the study of spallation failure in thermal barrier coating material systems

History

School

  • Aeronautical, Automotive, Chemical and Materials Engineering

Department

  • Aeronautical and Automotive Engineering

Published in

Theoretical and Applied Fracture Mechanics

Volume

92

Pages

1 - 12

Citation

HARVEY, C.M., WANG, B. and WANG, S., 2017. Spallation of thin films driven by pockets of energy concentration. Theoretical and Applied Fracture Mechanics, 92, pp. 1-92.

Publisher

© Elsevier Ltd

Version

AM (Accepted Manuscript)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

Acceptance date

20/04/2017

Publication date

2017-04-21

Notes

This article was published in the journal Theoretical and Applied Fracture Mechanics [© Elsevier] and the definitive version is available at: https://doi.org/10.1016/j.tafmec.2017.04.011

ISSN

1872-7638

Language

en