ABSTRACT
Fatigue failure has been one of great concern in engineering. Fatigue cumulative
damage theory is to study accumulation of fatigue damage and fatigue failure criteria
under fatigue loads. It is an important tool for accurate and reasonable prediction of
the fatigue life for engineering structures and components. When engineering
structures and components are in service, most of loads are low amplitude loads
under the fatigue limit. However, researchers are not sure the role of these loads in
the fatigue damage accumulation. This paper studies the fatigue cumulative damage
theory at the support of Shanghai International Cooperation project and Shanghai
Natural Science Foundation.
The contents are as follows:
1, Analyzing the existing fatigue damage accumulation model, these models mainly
focus on load damaging and rarely consider low amplitude loads under the fatigue
limit. It often leads to the predicted results much lower than the results of the fatigue
test whose load spectrums contain a large number of low amplitude loads under the
fatigue limit.
2, Study on the low-loading strengthening features with different samples as the
experiment object. The results indicate that the practical parts have more highlighted
low-loading strengthening characteristics than the standard samples, which has a clear
region for strengthening cycles and strengthening loads.
3, On the basis of the L. M. Kachanov damage variable, a effective stress function is
presented which is invoke in the processing formula for cumulative damage. Then the
fatigue accumulating formula, along with the life predicting formula are obtained.
4, Using the domestic 40Cr samples as the torsion fatigue object, experiments are
accomplished on situations where low amplitude loads under the fatigue limit are
applied. The results meet industrial requirements completely.
The research is an improvement for fatigue cumulating damage. It extended the
load strengthening and damage to the load under the fatigue limit. The research
provides theoretical support and reference for improving the fatigue design of
mechanical structures and components and the lightweight design based on the
strengthening characteristics.
Key Words:Fatigue Cumulating Damage, load Strengthening, Load
Damaging, Coefficient of Effective Area