Contents lists available at ScienceDirect Journal of Materials Processing Tech. journal homepage: www.elsevier.com/locate/jmatprotec Efect of a moving automated shot peening and peening parameters on surface integrity of Low carbon steel AL-Mokhtar O. Mohamed ⁎ , Zoheir Farhat, Andrew Warkentin, James Gillis Dalhousie University, Canada ARTICLEINFO Associate Editor: Z Cui Keywords: Shot peening Peening saturation Peening coverage Peening parameters Peening efect Almen strip ABSTRACT Shot peening is a widely utilized process in industry. It helps to increase fatigue and stress corrosion resistance by creating benefcial compressive residual surface stresses of materials. Whilst very good results are achieved with this process, there is always an increasing demand by industry and material researchers for improved material surface quality, system reliability, and consistency controls of the process. First main objective of this workwastostudytheefectofanautomatedmovingshotpeeningprocessonthesurfaceintegrityoflowcarbon steelmaterial.Secondobjectivewastodiscussandpresentpeeningsaturationandintensityresultsandmodelin anewapproachintermsofpeeningspeedsalongsidethetraditionalprocedurewhichshowspeeningsaturation andintensityresultsintermsofpeeningtimes.Thirdobjectiveofthisstudywastoexaminetheefectsof:process air pressure, nozzle stand-of distance, nozzle speed, and peening angle on coverage, saturation, and surface quality utilizing the moving shot peening. This study showed that 276kPa air pressure, 203mm stand-of dis- tance, and 5.3mm/sec nozzle speed are the optimum conditions for the shot peening process parameters ex- amined on standard Almen strips samples which resulted in minimize surface irregularities, maximize com- pressed layer thickness and uniformity, and minimize process time. 1. Introduction The shot peening process is a widely used as a mechanical surface treatment in the aerospace and automotive industries. The process is benefcial forincreasingresistancetofatigue,stresscorrosioncracking, hydrogen-assisted cracking, and wear, as well as for mitigating pro- blems associated with surface and near surface porosity as reported in the work of, among others, Mahagaonkar et al. (2008), Kim et al. (2014),and Vielmaetal.(2014).Shotpeeninginvolvesbombardingthe surface of a component with a stream of small particles with high hardness, called shots. The process induces work-hardened and results in a compressed surface layer (Kirk and Fall, 2007; Zhan et al., 2013; Vielmaetal.,2014).Theintensityofpeeningisdefnedbytheamount of energy (in the form of compressive residual stress) induced into the part and is measured according to an industry standard known as the Almen test. The test uses standardized steel test strips – Almen strips (KirkandFall,2007).TheAlmenstripsareexposedtoashotstreamfor varying amounts of time. Shot peening induces compressive stress on onesideoftheAlmenstripthatcausesthestriptobendintoanarc.The height of the arc is measured and is referred to as the intensity. In- tensity,asafunctionofpeeningexposuretime,isplottedandisreferred to as the saturation curve. Saturation is said to have occurred when doubling the exposure time results in no more than a 10% increase in intensity. Often the desire to guarantee 100% part coverage results in over-peening of the component leading to a reduction of peening ben- efts (Bagherifard et al., 2012; Sakamoto et al., 2015). Over-peening maygiverisetosurfacedamageandadropinfatiguelife,inspiteofan increase in surface hardening and deeper compressive residual stress felds (Vielma et al., 2014). Furthermore, the compressive stress pro- duced during shot peening at the surface induces tensile stresses in the coreofthepart(Koeneckeetal.,1982).Thecombinedefectsoftensile stresses and embrittlement provide the right conditions for crack nu- cleation and propagation in the surface, which ultimately can result in delamination (Kim et al., 2014). Over-peening transfers fatigue crack nucleation from the surface to the subsurface and with a signifcant increase in Almen intensity, more fatigue cracks may form (Cecchin et al., 2014; Liu et al., 2009). Over-peening may also induce excessive surface damage, such as burrs, micro-cracks, micro-laps, and micro- folds.Thesesurfacedefectscreatestressconcentrationsthatmayreduce fatigue performance. Many researchers have performed optimization studies on the shot peening process. For instance, Wang et al. (2008) developed an opti- mization model that provided preliminary peening parameters for a given shape. The optimization methodology was based on fnding https://doi.org/10.1016/j.jmatprotec.2019.116399 Received 26 July 2018; Received in revised form 9 September 2019; Accepted 16 September 2019 ⁎ Corresponding author. E-mail address: mokhtar.o.m@dal.ca (A.-M.O. Mohamed). Journal of Materials Processing Tech. 277 (2020) 116399 Available online 17 September 2019 0924-0136/ Crown Copyright © 2019 Published by Elsevier B.V. All rights reserved. T