PSI - Issue 24

Giovanni Zonfrillo et al. / Procedia Structural Integrity 24 (2019) 296–309 G. Zonfrillo et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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• tightening of the spring pack to the nominal stress level for the test with re-tightening to the same value after 1500 seconds; • tightening of the spring pack to a slightly lower stress level with respect to the nominal one for the test with re-tightening to the nominal value after 60 seconds.

Temperature remains constant throughout the tests.

Results. Table 1 shows the results of test campaign broken down by stress level, springs configuration and clamping method. Data refer to average values of several repetitions of the same test. An illustrative trend of the clamping force is shown in figure 12, which shows the measurements of the tests carried out for conditions 1 and 5.

Table 1. Decay of the clamping force: results of the test campaign

Time = 480 (s)

Time = 3000 (s)

Test end

Load (σ) (MPa)

Springs Disassembly/Configuration

Average deformation at test start ( με ) Test duration (s)

Average deformation loss (με)

Average stress loss (MPa)

Average deformation/load loss (%)

Average deformation loss (με)

Average stress loss (MPa)

Average deformation/load loss (%)

Average deformation loss (με)

Average stress loss (MPa)

Average deformation/load loss (%)

- Disassembly of springs - Springs mounted in parallel/series - No disassembly of springs - Springs mounted in parallel/series - No disassembly of springs - Springs mounted in series - No disassembly of springs - Springs mounted in parallel/series

495 MPa (time = 0 s) 495 MPa (time = 0 s) 495 MPa (time = 0 s) 447 MPa (time = 0 s) 495 MPa (time 120 s) 495 MPa (time = 0 s) 495 MPa (time 1500 s) 495 MPa (time = 0 s) 495 MPa (time 1500 s) 396 MPa (time = 0 s) 396 MPa (time = 0 s) 594 MPa (time = 0 s) 594 MPa (time = 0 s) 594 MPa (time = 0 s)

2500

3000

21 4.2 0.84 30 5.9 1.20

30

5.9

1.20

1

2

2500

3000

8

1.6 0.32 13 2.6 0.52

13

2.6

0.52

3

2470

3600

10 2.0 0.41

-

-

-

14

2.8

0.58

2250 (time = 0 s) 2500 (time = 120 s) 2500 (time = 0 s) 2500 (time = 1500 s) 25 0 (time = s) 2500 (time = 1500 s) 2000 (time = 0 s) 20 (time = 0 s) 3000 (time = 0 (s)) 3000 (time = 0 s) 3000 (time = 0 s)

2500

-

-

-

-

-

-

3

0.6

0.12

4

5000

-

-

-

8

1.6 0.32

10

2.0

0.40

5

5000

-

-

-

-

-

-

10

2.0

0.40

6

- Disassembly of springs - Springs mounted in parallel/series

Test mode

3000

19 3.8 0.95 22 4.4 1.10

22

4.4

1.10

7

3000

8

1.6 0.40 10 2.0 0.50

10

2.0

0.50

8

5000

17 3.4 0.57 34 6.7 1.13 44.4

8.8

1.48

9

- No disassembly of springs - Springs mounted in parallel/series

20000

-

-

-

-

-

-

50.5 10.0 1.68

10

230000

-

-

-

-

-

-

65.0 12.9 2.17

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The results show that the spring assembly procedure influences the decay of the clamping force. With regard to configuration with 4 springs in series and 8 in parallel and spring set disassembled and reassembled before the start of each test, the decay percentage is about 2.5 times greater than that relative to the case in which the spring system is simply unloaded. Another significant element is the amount of load applied: as the load increases, also the percentage