Laser Peening without Coating as a Surface Enhancement Technology

Abstract

Employing optical phase-contrast microscopy we study the morphology of ultrashort pulsed laser-induced modifications in bulk fused silica and in other optical transparent materials for different conditions of irradiation. The influence of the input pulse energy, focusing depth, and number of pulses per site is investigated in order to establish optimal irradiation conditions for direct writing of waveguiding elements. The results obtained suggest that an increase of the refractive index is systematically accompanied by a region of lower index of refraction along the optical axis, presumably due to micro-explosion in the high energy-exposed regions, and the locations of this region is material dependent. Nevertheless, the creation of an hypothetical void in the interaction zone does not allow a complete explanation of the modifications observed and other mechanisms have to be invoked to explain the presence of regions with higher index of refraction. Different interaction regimes with respect to the input energy and to the number of shots per site can be established from these observations, emphasizing the role of nonlinear pulse propagation and plasma generation. To complement the experimental observations we simulate the propagation of an ultrashort laser pulse in bulk silica using the non-linear Schrödinger equation and determine the distribution of energy along the propagation axis. The results are in good agreement with the experimental observations and provides insights into the mechanisms controlling the interaction between ultrashort laser pulses and transparent materials.

Random-type scanning patterns in laser shock peening without absorbing coating in 2024-T351 Al alloy: A solution to reduce residual stress anisotropy

“…Differences between the magnitude of the residual stress after LSP in the x-direction (s x ) and in the y-direction (s y ) in the surface region are found in multitude of Refs. [12][13][14][15], but until now the explanation for this residual stress anisotropy has been an open question [8]. Trdan et al [16] (in which residual stress evaluation also confirmed beneficial compressive residual stresses after LSPwC, with higher compressive residual stress in the advancing LSPwC) studied the LSPwC effects on the dislocation generation, dislocation transition and grain refinement through-depth distribution, which could be related to the residual stress anisotropy.…”

“…1) [8][9][10][11]. However, zigzag-type scanning patterns induce residual stress anisotropy as collateral effect.…”

Impact of plasticity generated by Rayleigh waves on the residual stress behavior of structural components subjected to laser peening

“…They found that the size and number of corrosion pits can be decreased by half as a result of laser peening process. Although conventional laser peening process takes advantage of the sacrificial overlay, laser peening without coating has been employed for the underwater maintenance of nuclear power plants in Japan (Sano et al, 2006). This process results in surface roughness and may have thermal effects due to direct ablation, but can increase in the fatigue life of the component.…”

Thin-sheet-metal bending by laser peen forming with femtosecond laser

“…The process using this effect has been called laser peening. Sano et al (2006) have reported that laser peening is useful in preventing stress corrosion cracks in nuclear power reactors. And Sano et al (2007) have applied laser peening to rotorcraft components.…”