1988 Fiscal Year Final Research Report Summary
Development of Environment Adjusting Device for Fatigue Testing Apparatus Installed to Field Emission Type Scanning Electron Microscope and Study on Crack Closure Mechanism
| Project/Area Number |
62850019
|
|---|
| Research Category |
Grant-in-Aid for Developmental Scientific Research
|
| Allocation Type | Single-year Grants |
|---|
| Research Field |
機械材料工学
|
|---|
| Research Institution | Osaka University |
|---|
Principal Investigator |
JONO Masahiro Faculty of Engineering, Osaka University, Professor, 工学部, 教授 (20029094)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
YASUI Kazuo Faculty of Engineering, Osaka University, Research Assistant, 工学部, 助手 (50029047)
SUGETA Atsushi Faculty of Engineering, Osaka University, Research Assistant, 工学部, 助手 (60162913)
|
|---|
| Project Period (FY) |
1987 – 1988
|
| Keywords | Field Emission Type Scanning Electron Microscope / Direct Observation / Fatigue Crack / Environment Adjusting Device / Crack Closure / Vacuum Environment / Unloading Elastic Compliance Method / コンピュータ制御 |
|---|
| Research Abstract |
Since the fatigue phenomenon is considered to be intrinsically localized in a very small portion of material,microscopic study becomes useful to identify the detailed mechanism of it, and attempts such as direct observations of grow-ing fatigue crack have been made by using a specially designed fatigue testing apparatus which can operate in the specimen chamber of the scanning electron microscope(SEM). however, it is feared that the vacuum environment of specimen chamber of the SEM can affect the observed fatigue crack growth and closure behaviors. From this point of view, in this study, an environment adjusting device which can supply desirable gases to the near portion of fatigue crack tip in the specimen chamber has been developed, and direct observations of fatigue crack both in air and vacuum environments were made with the aid of micro-com-puter control.
Fatigue crack opening point was found higher in vacuum than in air for Mode I crack of grain oriented silicon iron, suggesting t
… More
hat the rewelding of crack tip in vacuum is related to crack closure and oxide induced crack closure is not dominant for Mode I crack. Through the test on randomly oriented silicon iron,it was found that grain orientation and grain boundary strongly affect fatigue crack growth direction and crack closure in the relatively low growth rate regime. However, the effect of grain orientation seemed to disappear in the high growth rate region.
In addition, the effects of air and vacuum environments and microstructure of the materials on fatigue crack closure behaviors were investigated on four kinds of P/M aluminum alloys and Ni-Cr steel based on the fracture mechanics and fractographical studies. Crack opening points in air were found to depend on the roughness of fracture surfaces, indicating the importance of roughness induced crack closure at the low groth rate regime in air. On the other hand, those in vacuum were found almost constant irrespective of surface roughness. Cyclic softening characteristics of the material was found to affect crack closure. Less
|
