An equivalent ellipse method to analyse the fatigue behaviour following ‘multi-surface initiations’

This paper discusses the mechanisms of fatigue when cracks synergetically initiate in multiple sites at the surfaces of specimen. Metal–matrix composites such as aluminium matrix composites reinforced by silicon carbide particles are good candidates to accelerate fatigue failures following multi-surface initiations (MSIs). Closure effects of MSIs on the variation of fatigue behaviour were explored for various applied stress in two states of composite used: pre-treated state and non-pre-treated state. Using an equivalent ellipse method (EEM), it is found that the quality of surface finish of the specimen is of great role in crack initiation and growth. It is revealed that total lifetime of specimen is sensitive to heat treatment. Considering no transition from small to long crack, predictive formula used leads to identification of the Paris law exponent. It is found that this exponent is sensitive to both the applied load and the value of crack growth rate below threshold.