PSI - Issue 31

Alok Gupta et al. / Procedia Structural Integrity 31 (2021) 15–21 Alok Gupta et al. / Structural Integrity Procedia 00 (2019) 000–000

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the test set-up and the mating faces of the interfacing parts were defined using the linear bonded contacts. The material density for the aluminium block was adjusted to consider the missing mass of the bolts, nuts and washers which were not explicitly included in the FE model. The material properties assigned in the FE model are shown in Table 1. The predicted fundamental mode of the assembly was found to be at 85.6 Hz which was an axial bending mode of the bracket (Fig. 3).

Table 1. Material properties for FE modal analysis.

Part (Material)

Young’s modulus E (GPa)

Poisson’s ratio 

Density  (Kg/m 3 )

Bracket (Ti-6Al-4V) [ MMPDS‐15 (2020a) ] Fixture (Aluminium) [ MMPDS‐15 (2020b) ] Block (Aluminium) [ MMPDS‐15 (2020b) ]

110 72.4 72.4

0.31 0.33 0.33

4429 2760

3316*

* Density adjusted for missing mass of bolts, nuts and washers

Holes to Mount Sensor

Holes to Fix Bracket

100 mm

192 mm

Build Direction

Fig. 2. Shaker table test – SLM bracket assembly parts 94 mm

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

2.2. Material and specimen manufacturing Ti-6Al-4V (Grade 23) Extra Low Interstitials (ELI) plasma atomised powder, supplied by LPW Technology, was used. The analysis of the powder showed the mean chemical composition as Ti Bal, Al 6.4, V 4.0, FE 0.19, O 0.12, N 0.02, H 0.002, C 0.02 (wt. %), which is in line with the ASTM-B348 (2019). The powder size was distributed between 15 – 45  m with mean of the distribution centered at 30  m. The SLM bracket was made using an EOSINT M280 SLM machine. The machine used a laser power of 170 W, operated in argon atmosphere and had a substrate of Grade 5 Ti-6Al-4V material which was preheated to 35  C. The layer deposition speed was kept at 150 mm/s, laser scan speed was 1250 mm/s and layer thickness used was 30  m. The specimens were removed from the substrate plate using the Wire-EDM cutting process post build. Subsequently, the build supports were removed and aqua blasting was carried out to remove the loosely sintered powder particles and improve the surface finish. The build orientation of the bracket is shown in Fig. 1. The bracket was stress relieved at 650  C for 3 hours in an argon atmosphere and was subsequently furnace cooled to room temperature. 2.3. Testing details The vibration tests were conducted on the Derritron electromagnetic shaker (model VP1500N), shown in Fig. 4, with a maximum force (sinusoidal) capacity of 75 KN and a maximum acceleration of 100 g in the 20 – 200 Hz frequency range. A 16 channel ‘Vibrunner’ controller was used to control the shaker and to collect the dynamic response data from the shaker. Endevco accelerometers were used to control the shaker and to measure the input and output responses. The accelerometers were bonded using ‘pc24’ glue and lightweight tufnol cubes were used as the mounting blocks. The input excitation to the shaker table was in the vertical direction, which is the axial direction of the bracket. Three lightweight accelerometers (in the axial, radial and tangential directions, each weighing 3 grams,