Abstract. Deep Cold Rolling (DCR) process is used in various industries to improve the fatigue life of metallic parts by introducing work hardening, deep layer of compressive residual stresses and polished surface finish. In this paper, the influences of the angled design for a hydrostatic tool and its indentation depth to impart compressive residual stresses are studied and compared to its straight tool counterpart for treatment of IN718 material. Residual stress depth profile measurements, using the XRD technique, were employed to determine differences caused by using the angled and straight tool design. Higher rolling forces are measured in an angled tool design with a high indentation depth as compared to a straight tool design caused by the slip stick effect on the internal parts of the tool. This leads to high plastic deformation in the test material significantly affecting the compressive residual stress depth profile depending on its exisiting state. IntroductionAero engine metallic parts experience high levels of mechanical and thermal loading, high and low cycle fatigue and foreign object damage (FOD) [1] in service that can lead to early retirement. Suitable mechanical surface treatments applied onto aero engine metallic parts can prolong fatigue life, improve wear resistance and avoid stress corrosion by introducing work hardening, deep compressive residual stresses and polished surface finish [1,2].Commonly used mechanical surface treatments in the aero engine manufacturing industry are shot peening (SP) and laser shock peening (LSP). Deep cold rolling (DCR), another mechanical surface treatment, uses a rolling ball element that is pressed at high pressure against a metallic part to impart a deep layer of compressive residual stress. Its process parameters that significantly affect the mechanical properties are hydrostatic pressure, rolling tool, contact angle of the tool, stepover, feed rate, yield strength and geometry of the material [6,7]. DCR is a cost effective localised treatment process that can be easily integrated to a robot arm or CNC platform. SP and DCR, are capable of generating high dislocation densities in the near surface regions that inhibit crack initiation although the residual stresses tend to relax faster when the part experiences high temperatures [1,3,4,5]. Deep compressive residual stresses are achieved through LSP and DCR, which help to arrest the crack during the crack propagation stage after FOD impacts and corrosion damages [1,2]. The ability of DCR to generate high cold work at the near surface as well deep compressive residual stresses makes it a good choice for mechanical surface treatment. DCR creates a nanocrystalline surface layer in the range of 3µm [4]. The nanocrystalline structure acts as a good resistance to fatigue crack initiation up to a moderate temperature but deteriorates the creep resistance at elevated temperature [4].The magnitude of the rolling force applied on to the part is a combined effect of the hydrostatic pressure, ball diameter and contact an...
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