PSI - Issue 71

Oleg Plekhov et al. / Procedia Structural Integrity 71 (2025) 10–17

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̇ intensity of the plastic deformation rate ̇ , 0 reference rate of the intensity of plastic deformation Temperature 0 reference temperature melting temperature , acoustic impedances of water and the coating material (absorbing layer) model parameter ( ≈0.2 ) laser energy density P Pressure V free surface velocity c velocity of the longitudinal acoustic wave ρ specimen density 1. Introduction

Laser shock peening (LSP) (Wu et al., 2018 – 2020; Tang et al., 2018) generates subsurface compressive residual stresses (CRS) via high-energy laser-induced shockwaves, achieving depths up to 2 mm without material heating due to nanosecond pulses. Unlike conventional methods (shot blasting, ultrasonic riveting, etc.) (Abdulstaar et al., 2014; Xie et al., 2016), LSP’s rapid pulses enable complex part processing and deeper CRS fields. CRS counteracts tensile stresses, inhibiting fatigue crack initiation (Guo et al., 2018; Zhelnin et al., 2023). Optimal CRS distribution requires precise laser parameter selection. While experimental testing (Vshivkov et al., 2024) is limited by time and measurement challenges, numerical approaches like finite element modeling (Warren et al., 2008) and eigenstrain-based methods (Coratella et al., 2015) efficiently analyze LSP effects, including spot geometry and pulse impacts (Kostina et al., 2024; Sakhvadze et al., 2020). Simplified eigenstrain models are favored for rapid simulation of multiple laser impacts. The verification of numerical models LSP faces challenges due to experimental difficulties in measuring the depth distribution of compressive residual stresses (CRS) and the dependence on pressure impulse parameters generated by laser-induced shock waves. In this study, an experimental setup was developed, combining the hole-drilling method (ASTM E837-13a) for conventional residual stress assessment and photon Doppler velocimetry (PDV) for direct measurement of shock impulse parameters. PDV enabled the correlation between laser energy input and mechanical impulse amplitude, enhancing the accuracy of the LSP numerical model by incorporating real impulse data. The model, validated using copper (a single-phase material with well-known properties) and Ti-6Al-4V, demonstrated strong agreement between simulated and experimental CRS profiles, enabling the selection of optimal LSP parameters. The method’s effectiveness was confirmed by fatigue tests on titanium specimens with stress concentrators, where LSP significantly extended their fatigue life. 1. Materials under investigation In order to investigate the peculiarities of pressure impulse generation, two types of materials were studied. One of them was copper Cu-M1 (Cu-ETP, Europe; C1100, USA). It was chosen as simple single-phase metal material. The second material is Ti-6Al-4V, an alloy that has high practical importance and is widely used in the aviation industry. The geometry of the samples utilized for pressure impulse measurement is shown in Fig. 1a. To investigate the dynamics of elastic precursor a range of specimen thicknesses was employed in the experiments, including 0.5, 0.7, and 1.0 mm for copper and 0.8, 1.0, and 1.4 mm for Ti-6Al-4V.

a

b

Fig. 1: (a) Specimen geometry for studying velocity of free surface of target during impact (b) geometry of Ti specimens for fatigue experiments.