1995 Fiscal Year Final Research Report Summary
A Study on Method for Evaluating Fracture Strength of Brittle Thin Films Using a Small Spherical Indentation
| Project/Area Number |
05452123
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Materials/Mechanics of materials
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| Research Institution | The University of Electro-Communications |
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Principal Investigator |
TAKAMATSU Tohru The University of Electro-Communications Lecturer, 電気通信学部, 講師 (00106890)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUMURA Takashi The University of Electro-Communications Department of Mechanical and Control En, 電気通信学部, 助手 (00251710)
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| Project Period (FY) |
1993 – 1995
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| Keywords | Thin Film / Small Spherical Indenter / Indentation / Fracture Strength |
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| Research Abstract |
The aim of this research is to study the method for evaluating fracture Stregth of brittle thin films using a small spherical indentation. The principal results of the research are summarized as follows.
1. An attempt was made to evaluate Young's E and fracture strength sigma_f of a thin film of permaloy and SiO_2 with a thickness of 2mum using cross-shaped micro-specimens. It was found that E and sigma_f could be evaluated nearly using the proposed method.
2. The microfracture strength of TiN film or Al_2O_3 film with a thickness of 2mum coated on a WC substrate was evaluated by indenting a spherical indenter. It was found that as spherical indenter was smaller, the ring crack initiation strength was large. An attempt was made to estimate the bending fracture strength of the bulk materials from the ring crack initiation strength using the concept of effective area. A reasonable value was obtained for the bending fracture strength.
3. Before evaluation of fracture strength of a thin film
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coated on a substrate by indenting a spherical indenter, indentation tests on Si_3N_4 bulk plates using a Si_3N_4 spherical indenter were carried out. The relationship between the ring crack initiation strength evaluated from indentation tests and bending fracture strength was examined using the concept of effective area. It was found that the ring crack initiation strength was larger than the bending fracture strength and as spherical indenter was smaller, the ring crack initiation strength was larger. It was found that ring crack initiation strength could not be related to conventional bending fracture strength, using the concept of effective area.
4. To find the cause that the ring crack initiation strength of Si_3N_4 bulk plates evaluated by the sphere indentation method could not be related to conventional bending fracture strength, using the concept of effective area, a ring crack initiation model of a surface microcrack was applied. It was confirmed that the difference between the ring crack initiation strength and bending fracture strength could be interpreted qualitatively. Less
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