Investigation of Changes in Fatigue Damage Caused by Mean Load under Block Loading Conditions

Area of Science:

• Materials Science
• Mechanical Engineering
• Fatigue Analysis

Background:

• Material fatigue properties can vary with the number of load cycles.
• Existing fatigue life calculation algorithms may not fully account for these variations.
• Mean strain significantly influences material behavior under cyclic loading.

Purpose of the Study:

• To develop and validate a novel calculation model for estimating fatigue life under block loading with non-zero mean strain.
• To investigate the impact of mean strain on stress-strain curve parameters (K' and n').
• To quantify the differences in fatigue damage calculations when mean strain effects are considered versus neglected.

Main Methods:

• Development of a novel calculation model incorporating mean strain effects on stress-strain curve parameters.
• Simulation of material fatigue under block loading with varying mean strain values using triangular strain waveforms.
• Comparison of fatigue damage calculations using standard stress-strain parameters versus those adjusted for mean strain.

Main Results:

• Neglecting mean strain effects leads to significant variations in total fatigue damage, ranging from 10% (at 0.2% mean strain) to 3.5% (at 0.6% mean strain).
• The most substantial discrepancies in partial fatigue damage calculations were observed for a mean strain of 0.4%.
• Simulation results confirm that elevated mean strains alter material properties, necessitating their inclusion in fatigue life assessments.

Conclusions:

• Mean strain significantly affects material fatigue properties and must be considered in fatigue life calculations.
• The proposed model provides a more accurate estimation of fatigue life under complex block loading conditions.
• Accurate material response modeling under block loads requires accounting for the influence of mean strain on cyclic deformation parameters.