Study on Damage Accumulation and Life Prediction with Loads below Fatigue Limit Based on a Modified Nonlinear Model

Area of Science:

• Materials Science
• Mechanical Engineering
• Solid Mechanics

Background:

• Traditional fatigue theories often ignore the impact of sub-fatigue limit loads on damage accumulation.
• This oversight leads to significant discrepancies between predicted and actual fatigue life, particularly under variable amplitude loading.

Purpose of the Study:

• To develop a novel fatigue damage model that incorporates the effects of loads below the fatigue limit.
• To enhance the accuracy of fatigue life predictions by considering both strengthening effects and cumulative damage from these low loads.

Main Methods:

• A new damage model was formulated, integrating an exponential function for strengthening effects and a fuzzy logic approach with membership functions (MFs) for cumulative damage.
• The model's efficacy was validated using experimental data from variable amplitude loading tests.

Main Results:

• The proposed model, utilizing Cauchy membership functions, achieved a significantly lower prediction error (8.38%) compared to the linear model (35.18%) and the original Chaboche model (16.09%).
• Implementation for a compressor blade under a realistic loading spectrum demonstrated the model's practical applicability.

Conclusions:

• The novel fatigue damage model effectively accounts for sub-fatigue limit loads, leading to more accurate fatigue life assessments.
• This enhanced model offers a substantial improvement for predicting the service life of components subjected to complex loading conditions.