CC BY
27HiLASE-I-20
Mechanisms of residual stress generation using Laser Shock Peening
N. Smyth1, M. Leering1, M. Fitzpatrick1
1Coventry University, Faculty of Engineering- Environment & Computing, Coventry, United Kingdom
Laser Shock Peening (LSP) is an advanced surface treatment used to introduce beneficial compressive residual stress in metallic structures. These residual stresses can significantly enhance fatigue performance thus extend the service life and increase the damage tolerance of safety critical components and structures. Therefore, LSP can provide major cost and safety benefits when applied correctly. However, this complex process can have the opposite effect when poor process parameters are selected or if tensile balancing stresses are not considered.
Laser peening requires preselection of a number of processing parameters each having an influence on the induced residual stress field. With the advancements in laser technology, the 'Bivoj' laser system at HiLASE is one of the most versatile and customisable systems available to carry out LSP activities. We conducted an experimental investigation in which the most significant processing parameters, namely laser energy, pulse duration and spot size, were independently varied to characterise their effect on the formation of residual stresses in aerospace aluminium. The resultant residual stress fields were measured using incremental hole drilling method.
Using the unique capabilities of the Bivoj system, we have been able to purely study the effects of the laser pulse temporal profile on the formation of residual stresses. In the past, similar studies would have to be carried out over many laser systems. By using a single system experimental error and laser variation between sources have been reduced. The distribution of laser intensity and the manner in which energy is supplied to the target surface has been seen to greatly affect the outcome of the processing. The temporal profile was varied from classical LSP shapes such as a Gaussian and flat top to double peaked profiles. The constructive interference of the propagating stress waves created by the two pulse peaks can lead to high magnitude and deeper introduced residual stresses. The peak intensity and full width half maximum have been kept constant across all profiles, as shown in the normalised intensity plots in figure 1. In parallel with experimental programme is a series of mechanistic finite element simulations of the pulse and material interaction.
Time [ns] Time [ns]
Fig. 1. Normalised Laser Shock Peening temporal profile.
