Literature Review III

As an active member in the surface modification field, LSPT routinely reviews technical papers published on surface modification technologies.  To share some of the information that is currently available in the community with our customers, we are continuing a website feature where we review a published article from the array of journals available and note a few key items.
The paper up for review this week is titled “Studies on fatigue life enhancement of pre-fatigued spring steel specimens using laser shock peening.”  by P. Ganesh et al.  The article is available for purchase at http://www.sciencedirect.com/science/article/pii/S0261306913008480.  Several images, the article highlights, and the abstract can also be reviewed at this site.
Within the laser peening industry there continues to be significant growth of the technology in the area of recovering fatigue damage on samples. This paper is another excellent example of how laser peening offers an opportunity to recover damage on parts in service and extend them well beyond the initial lifec estimate. The authors observed life extension greater than 15x that of unpeened springs. Additional information in the article relates to the recovery of compressive residual stresses on bare processed surfaces. As we have mentioned a few times on this site before, the article data reinforces that bare surface laser peening should be used only if conventional laser peening with an opaque overlay is not feasible. The authors used both paint and black tape in their studies and achieved similar results between the two methods of opaque overlays. Both of these opaque overlay methods require manual labor and stand to benefit by replacement with LSP Technologies RapidCoater technology.
The work in this paper was performed using an Nd:YAG laser with pulse energies and widths that require small spot impressions. While the parts experienced significant benefits from laser peening, additional gain can be obtained with higher energies and larger spots. Larger processing spot diameters allow the shockwave to reach greater depths before attenuating below the HEL.
In summary, if you are interested in researching the benefits of laser peening on steel structures or structures that have been pre-fatigued prior to laser peening, this is a great article to get started with.