PSI - Issue 38

Alok Gupta et al. / Procedia Structural Integrity 38 (2022) 40–49 Author name / Structural Integrity Procedia 00 (2021) 000 – 000

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5. Future Work Recommended Predictive fracture mechanics-based approaches for small and long crack growth are required to be developed for life predictions of SLM parts with intrinsic anomalies (defects) [Gupta et al. (2020)]. Jones et al. (2020) and Gupta et al. (2020) have proposed some effective analytical models to predict the crack growth life of small cracks in AM Ti 6Al-4V alloy, which requires extending to SLM parts. The bracket fatigue strengths (LCF and HCF) at elevated temperature should also be explored as part of the future research to assess fatigue strength of the bracket in its true operating environment. 6. Conclusions • Tensile and LCF coupon tests were performed to study the mechanical and fatigue properties of the SLM Ti-6Al-4V material. This data was then used to set the test parameters for the LCF tests on the bracket. • The mechanical strength (0.2% PS and UTS) of the SLM Ti-6AL-4V was found to be higher than the conventionally made annealed Ti-6Al-4V bar, but the overall ductility values were lower. The higher mechanical strength was due to the needle shape martensitic α ’ HCP grains. There was a slight improvement in strength and ductility values with increase in the test strain rate. • Cyclic softening was observed in the LCF coupon tests performed at strain levels higher than the material elastic limit. The cyclic softening was attributed to an increase in the dislocation density and formation of martensitic α ’ sun -grains in the material. • Bracket LCF responses exhibit an excellent flexibility of the structure, under relatively large displacement loads, with insignificant overall plasticity deformation. Local fracture is believed to be related to the stress concentration and possibly the SLM defects. • The bracket met the LCF design targets as demonstrated by the cyclic testing. The carefully designed weight optimized bracket has shown good fatigue performance, which is very much needed to build the confidence of practicing engineers for successful deployment of the SLM technology. Acknowledgements The authors would like to thank Rolls-Royce plc and the EPSRC for the support under the Prosperity Partnership Grant \ Cornerstone: Mechanical Engineering Science to Enable Aero Propulsion Futures, Grant Ref: EP/R004951/1. Also, our sincere thanks to Mr. Daniel Cousins (Rolls-Royce Plc.) for his contribution on the development of bracket design, and to Mr Shane Maskill (Nottingham University) for conducting the laboratory tests. References Gupta, A., Bennett, C. J., & Sun, W., 2021a. The role of defects and characterisation of tensile behaviour of EBM additive manufactured Ti-6Al 4V : An experimental study at elevated temperature. Engineering Failure Analysis 120. https://doi.org/10.1016/j.engfailanal.2020.105115 Baragetti, S., Borzini, E., Božić, Z., & Arcieri, E. V., 2019. Fracture surfaces of Ti-6Al-4V specimens under quasi-static loading in inert and aggressive environments. Engineering Failure Analysis 103, 132 – 143. https://doi.org/10.1016/j.engfailanal.2019.04.072. Gorelik, M., 2017. Additive manufacturing in the context of structural integrity. International Journal of Fatigue 94, 168 – 177. https://doi.org/10.1016/j.ijfatigue.2016.07.005. Gupta, A., Bennett, C. J., & Sun, W, 2021b. Fatigue response of selective laser melted Ti-6Al-4V bracket: an experimental study, Structural Integrity Procedia, 31, 15-21. European Union Aviation Safety Agency: Certification specifications and acceptable means of compliance for engines CS-E, Amendment 5, 2018. Brusa, E., Sesana, R., & Ossola, E., 2017. Numerical modeling and testing of mechanical behavior of AM titanium alloy bracket for aerospace applications. Procedia Structural Integrity 5, 753 – 760. https://doi.org/10.1016/j.prostr.2017.07.166. Leuders, S., Meiners, S., Wu, L., Taube, A., Tröster, T., & Niendorf, T., 2017. Structural components manufactured by selective laser melting and investment casting - Impact of the process route on the damage mechanism under cyclic loading. Journal of Materials Processing Technology 248(May), 130 – 142. https://doi.org/10.1016/j.jmatprotec.2017.04.026.