PSI - Issue 46

Alok Gupta et al. / Procedia Structural Integrity 46 (2023) 35–41 Alok Gupta et al. / Structural Integrity Procedia 00 (2021) 000–000

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1. Introduction The Selective Laser Melting (SLM) process, which is a type of Additive Manufacturing (AM), is a significantly and rapidly progressing field to achieve improvements in design methods, design parts in complex shapes in different materials, avoid tooling cost, and provide high material usage efficiency [Gupta et al. (2021a)]. Ti-6Al-4V is a widely used material in the aerospace industry due to its high strength to weight ratio and good corrosion resistance properties [Baragetti et al. (2019)]. In the aerospace industry, fatigue is a major cause of component failure [Gorelik (2017)]. As per the current practice, carefully designed aerospace components are analysed in detail, making sure that the component has adequate static and fatigue strength and demonstrates compliance against the strict certification rules defined by the European Aviation Safety Agency [European Union Aviation Safety Agency (2018)]. On an aero-engine, the brackets are used as structural components to support the accessories (sensors, pipes and electrical harnesses etc.). These brackets are designed to withstand engine-driven vibrations (CS-E 650) and it also needs to be demonstrated that no complete detachment of the bracket, leading to a hazardous situation, will occur in an extreme event such as a Fan Blade Off (FBO) event (CS-E 810) [European Union Aviation Safety Agency (2018)]. Additionally, the brackets also typically experience complex thermo-mechanical loading during engine operation, which if not considered in the design analysis, could cause low cycle fatigue failure of the bracket. Brusa et al. (2017) and Leuders et al. (2017) have studied the fatigue performance of AM parts but with limited relevance to the end applications in terms of loading and lifing of AM parts. Seabra et al. (2016) designed and made a topologically optimised aerospace SLM bracket, but they could only show a satisfactory comparison between the Finite Element (FE) predictions and the static testing results. Furthermore, Gupta et al. (2021b), in their previous study, have studied the modal and High Cycle Fatigue (HCF) performances of an aerospace bracket through shaker table testing, and based on the testing results, the minimum HCF ‘g’ load capability was evaluated. Although all these published studies do not cover the full range of loading scenario experienced by the aerospace components, they provide good encouragement to use AM parts in safety critical applications [Gupta et al. (2021b)]. In this work, the Low Cycle Fatigue (LCF) performance of a weight optimized SLM Ti-6Al-4V bracket has been characterised. Displacement-controlled LCF testing was carried out at 200  C and the bracket performance was evaluated against the number of cycles expected for the defined loading conditions. In addition, the fracture behavior

of the bracket is discussed. 2. Experimental Campaign 2.1. Experimental set-up and test conditions

The SLM bracket in a ‘struts & connectors’ shape and optimized for its weight is shown in Fig. 1. The main struts, running in the longitudinal direction, are designed to carry the load whereas the transverse running members, termed as ‘connectors’, provide lateral stiffness to the load carrying main struts. The bracket weighs 106 grams which was significantly less than the mass of an equivalent sheet metal Ti-6Al-4V bracket (200 grams).

Main Struts

Connectors

Fig. 1. SLM Ti-6Al-4V ‘strut & connector’ bracket geometry (dims in mm) (not to the scale)