Optimised laser peening strategies for damage tolerant aircraft structures

Simulation models were constructed to explore the influence of compressive residual stress on fatigue crack growth rates in aluminium sheet. Balanced residual stress fields resulting from imposition of compressive stresses in laser peen patches were calculated. Growth rates of cracks approaching, traversing and propagating away from peen patches were calculated using modified superposition models. Effects of patch dimensions and position on residual stress fields, growth rates and life were investigated. Overall life varied widely depending on the balance between retardation and acceleration; many peen arrangements had little or no life benefit. Implications of the results for damage tolerant design are discussed.