Application of the eigenstrain approach to predict the residual stress distribution in laser shock peened AA7050-T7451 samples

Abstract

Laser Shock Peening allows the introduction of deep compressive residual stresses into metallic components. It is applicable to most metal alloys used for aerospace applications. The method is relatively expensive in application, and therefore development studies often rely heavily on Finite Element Modelling to simulate the entire process, with a high computational cost. A different approach has been used recently, the so-called eigenstrain approach. The present study looks at the feasibility of applying the eigenstrain method for prediction of the residual stress in a sample that contains curved surface features. The eigenstrain is determined from a simple geometry sample, and applied to the more complex geometry to predict the residual stress after Laser Shock Peening. In particular the prediction of residual stress at a curved edge, and for different values of material thickness, have been studied. The research has demonstrated that the eigenstrain approach gives promising results in predicting residual stresses when both the thickness and the geometry of the peened surface is altered.

Low cycle fatigue life prediction in shot‐peened components of different geometries—part I: residual stress relaxation

“…It is noteworthy that relatively simple geometries (such as plates and blocks), where there is no significant change between the samples studied, were used in . Coratella et al further validated this transferability from a flat, planar surface to curved surfaces. However, in more complex geometries (such as the notched geometry with high stress concentration studied here), this may be less reasonable because the eigenstrain distribution introduced by the peening process is likely to be affected by changes in the component geometry.…”

A benchmark fracture mechanics solution for a two-dimensional eigenstrain problem considering residual stress, the stress intensity factor, and superposition

“…In that work, a simplified eigenstrain field was determined from limited residual stress measurement data, and finite element models where used to determine the full residual stress field from the eigenstrain. Coratella et al [9] provide a recent validation of that earlier work in aerospace aluminum alloy (7050-T7451) samples with residual stresses from laser shock peening (LSP). Luckhood, Jun, and Korsunsky [10] have used the eigenstrain method to analyze residual stresses measured in friction stir welds.…”

“…Figure 11 shows the yy component of stress separated using Eq. (9). The stress from eigenstrain σ* is zero outside the central square area, and constant inside it, due to the discontinuous behavior of the eigenstrain.…”

“…It is important to recognize that the stress field shown in Figure 5 is the total residual stress (σ TOT ), which can be considered as a superposition of the stress due to the eigenstrain only (σ*), and the residual stress arising to satisfy equilibrium (σ EQ ) [7]. This relationship can be expressed as (9) The stress σ* can be calculated using the stress-strain relationship . Figure 11 shows the yy component of stress separated using Eq.…”

Development and Application of the Contour Method to Determine the Residual Stresses in Thin Laser-Peened Aluminium Alloy Plates

“…One of the limitations of the method is that a full 2D stress map can be obtained for one stress direction only. However, by employing additional approaches such as application of the eigenstrain theory [7][8][9], multiple cuts, [10,11] and/or the superposition principle [12,13], multiple stress components can be obtained. Another limitation of the method is that near-surface residual stresses are challenging to obtain owing to cutting and measurement artefacts [14].…”