PSI - Issue 14

G Vamsi Krishna et al. / Procedia Structural Integrity 14 (2019) 820–829 G. Vamsi Krishna / Structural Integrity Procedia 00 (2018) 000–000

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4.3. Experimental result

Random vibration responses of all three axes for both the plate configurations are tabulated in Table 3. Spectral plots of responses are shown in Fig.12 (a), Fig. 12 (b) and Fig. 12 (c) for long, pitch and yaw axes respectively. Over plotting of spectral responses are shown both for Aluminium and honeycomb mounting brackets for better comparison in Fig. 12 (a), Fig. 12 (b) and Fig. 12 (c).

Table 3. Vibration Test Results in all three axes in g rms

Vibration response in g rms for 0.020 g

2 /Hz (5.35 g

rms ) input

Longitudinal axis

Pitch axis

Yaw axis

Aluminum bracket

Honeycomb bracket

Aluminum bracket

Honey comb bracket

Aluminum bracket

Honeycomb bracket

Sl.No

Response Location

R1

Between RINS & MINGS

15.91

5.57

7.45

8.34

9.48

12.38

R1:On RINS lug near plate beam

10 1

R1:Between RINS & MINGS

R1:On RINS lug near plate beam

10 1

10 2

Rms = 12.376(Aluminum plate) Rms = 9.4774(Honey comb plate)

Rms = 15.9128(Aluminum plate) Rms = 5.5709(Honey comb plate)

(122.0703,2.9014)

Rms = 8.3372@Honey comb plate Rms = 7.4538@Aluminum plate

(141.6016,16.4953)

10 1

(126.9531,1.5271)

10 0

(156.25,1.534)

10 0

(151.3672,0.6292)

(512.6953,0.4229)

10 0

(351.5625,0.8599)

(385.7422,0.1901)

(136.7188,0.3453)

10 -1

10 -1

10 -1

(361.3281,0.0411)

g 2 /Hz

g 2 /Hz

g 2 /Hz

10 -2

10 -2

10 -2

10 -3

(39.0625,0.4151)

10 -3

(97.6563,0.3501)

10 -3

10 -4

10 -5

10 -4

10 -4

200 400 600 800 1000 1200 1400 1600 1800 2000

200 400 600 800 1000 1200 1400 1600 1800 2000

200 400 600 800 1000 1200 1400 1600 1800 2000

Frequency (Hz)----->

Frequency (Hz)----->

Frequency (Hz)----->

Fig. 12. (a): Overplot on responses of Honeycomb bracket and aluminium alloy bracket in (a) long axis; (b) pitch axis; (c) yaw axis

The comparative overall vibration response levels, measured in g rms at the critical location identified on bracket is tabulated in Table 3. The overall response level of both the brackets are comparable for vibration input along pitch and yaw axes. For vibration input along longitudinal axis, the response levels of honeycomb bracket are around 3 times lower than the response level of aluminum bracket. But the overall response of both the brackets is well within the package acceptance test limits of 25 grms, along all the 3 directions. 5. Conclusions Honeycomb mounting brackets are very good alternative for conventional all metallic aluminium alloy brackets. Honeycomb brackets can be very easily configured by varying face sheet and honeycomb core thicknesses to meet all the functional requirements of mounting brackets viz. sufficient static margin of safety against high deceleration flight loads and limiting the vibration response on packages mounted over it, within specified limits for the input vibration experienced during flight. In the comparative study carried out for mounting of two subsystems weighing around 13 kg, tremendous weight saving on mounting brackets - 1.7 kg honeycomb bracket weight vs 10.5 kg aluminium alloy bracket - could be achieved without compromising in factor of safety and amplification of vibration responses. The random vibration response for both brackets is comparable and within acceptable limits in pitch and yaw axes. The comparative response is substantially less in longitudinal axis for honeycomb bracket. Further, a method using aluminium sleeves is proposed for honeycomb brackets to eliminate the problem of localised buckling due to bolt torquing. Further study can be carried out to improve the fundamental natural frequency of honeycomb bracket assembly for mounting of navigation sensor packages with low frequency of operation.