Abstract
We study the detailed mechanism of formation and propagation of spiral cracks upon spherical indentation on a thick diamond-like carbon (DLC) film deposited on a ductile steel substrate. Unlike the conventional ring cracks appeared just outside the impression, the non-axisymmetric spiral cracks are formed within the crater. Integrated acoustic emission (AE) and corrosion potential fluctuation (CPF) techniques are applied to monitor the crack process in situ. It is found that spiral cracking is possible only within a relatively narrow range of maximum indentation force, below which there is no fracture and above which the ring cracks are formed. Detailed stress analyses show that the spiral cracks are nucleated below the indenter when the equivalent stress is above a critical level, which then extends during unloading. The proposed theory agrees well with experimental observations and it is expected such mechanism can be extended to similar brittle film/ductile substrate systems. © 2008 Elsevier B.V. All rights reserved.
| Original language | English |
|---|---|
| Pages (from-to) | 67-76 |
| Number of pages | 9 |
| Journal | Materials Science and Engineering: A |
| Volume | 496 |
| Issue number | 44958 |
| DOIs | |
| Publication status | Published - 2008 |
| Externally published | Yes |
Funding
The work of A.Y. is supported in part of Grant-in-Aid for Young Scientist of (B) (No. 19760075) of the Ministry of Education, Culture, Sports, Science and Technology, Japan, and Research Grant (General research for Electricity & Energy) of TEPCO research foundation. The work of L.L. and X.C. is supported in part by National Science Foundation CMMI-0407743 and CMMI-CAREER-0643726.
Keywords
- Diamond-like carbon film
- Spherical indentation
- Spiral crack