2003 Fiscal Year Final Research Report Summary
Investigation On Near-Threshold Fatigue Crack Growth Behavior by Using Nano-and Mesoscale Simulation and Observation
| Project/Area Number |
13450048
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Materials/Mechanics of materials
|
|---|
| Research Institution | Osaka University |
|---|
Principal Investigator |
KUBO Shiro Osaka University, Graduate School of Engineering, Professor, 大学院・工学研究科, 教授 (20107139)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
TSUJI Masahiro Osaka University, Graduate School of Engineering, Research Associate, 大学院・工学研究科, 助手 (10132630)
SAKAGAMI Takahide Osaka University, Graduate School of Engineering, Associate Professor, 大学院・工学研究科, 助教授 (50192589)
|
|---|
| Project Period (FY) |
2001 – 2003
|
| Keywords | High Temperature Fatigue / Fatigue Crack Growth / Threshold / Molecular Dynamics / Fracture Mechanics / Simulation |
|---|
| Research Abstract |
In the present research, nanoscale molecular dynamics, macroscale experiment, and mesoscale observations were applied to the near-threshold fatigue crack growth behavior. The results obtained are summarized as follows.
1.High temperature fatigue crack propagation experiments were conducted for SUS 304 stainless steel, in air and in vacuum. It was found that the fatigue crack growth resistance was higher in a vacuum than in air. The threshold value of fatigue crack growth attained maximum around 550℃ in a vacuum and in air. After the threshold behavior was observed in the K decreasing tests, the crack was found to grow again when the maximum K value was increased in air and in a vacuum. By repeating this process a so-called true threshold was attained. The effect of temperature on relationship between crack growth rate da/dN and Δ K was small.
Fatigue crack growth experiments were made also for Ni base super alloy and aged material.
Mesoscale observations were made to find relationship between slip, plastic deformation and crack growth.
2.Nanoscale simulation of the near-threshold fatigue crack propagation in iron were made by using the molecular dynamics. Crack growth was observed under mode II loading as well as mode I loading. Crack growth direction under mixed mode loading agreed well with that predicted by the maximum circumferential stress criterion.
Effect of tilt grain boundary and twist grain boundary on the near-threshold fatigue crack growth was examined using the molecular dynamics. While cracks sometimes grew across Σ73 and Σ99 small angle grain boundaries, the barrier was higher for, Σ9 and Σ11 largel angle grain boundaries. For the twist grain boundary perpendicular to crack plane, the grain boundary was found to impede the fatigue crack growth.
|
