Interrupted tests

A series of experiments were carried out in the stick slip boundary for various contact pressure for a range of loading cycles.

The tests were terminated after a predetermined number of cycles to observe the type of damage observable after sectioning the fretted specimen. The tests were carried out in the range of contact pressure from 70 MPa to 260 MPa and the number of cycles ranged from 600,000 cycles to 5,000,000 cycles.

Table 4.6 - Interrupted test series

Test No Nominal pressure

(MPa)

Number of cycles Slip amplitude

(Hin)

Test 1 1 100 600,000 21

Test I 2 140 ' 600,000 24

Test I 3 180 600,000 32

Test I 4 160 1,600,000 30

Test I 5 120 2,000,000 28

Test 16 70 2,000,000 18

Test 17 110 2,800,000 22

Test 18 90 2,800,000 20

Test 19 145 4,100,000 30

Test 1 10 80 3,000,000 18

Test 1 11 80 5,000,000 17

Test 1 12 260 2,000,000 36

Figure 4.52 - Damage observed in left and right corner for Test 1 1; Nominal contact pressure -1 0 0 MPa, Stroke - 21 [Am, No of cycles 600,000.

Test II was carried out at 100 MPa nominal contact pressure for 600,000 cycles. The measured slip amplitude was 21 /mi. No cracks could be observed on the damage surface for this test. The surface damage observed in Test II is shown in Figure 4.51.

(a) (b)

Figure 4.53- Damage observed in left and right corner for Test I 2; Nominal contact pressure -1 4 0 MPa, Stroke - 24 fim , No of cycles 600,000.

The surface damage observed in Test I 2 is shown in Figure 4.52. Test I 2 was carried out at 140 MPa nominal contact pressure for 600,000 cycles. The measured slip amplitude was 24 fim. No cracks could be observed on the damage surface for

Trend of the crack p a th \

Actual crack oath

Figure 4.54- Damage observed in left and right corner for Test I 3; Nominal contact pressure -1 8 0 MPa, Stroke - 32 /xm, No of cycles 600,000.

Test I 3 was carried out at 180 MPa nominal contact pressure for 600,000 cycles.

The measured slip amplitude was 32 fim. The surface damage observed in Test 13 is shown in Figure 4.54. Two cracks were observed on the damage surface for this test.

Furthermore, the crack path observed is similar to the crack initiation angle and the crack path observed in the preliminary test series for tests PI, P2 and p4.

Trend of the crack path \

Actual crack path

(a) (b)

Figure 4.55- Damage observed in left and right corner for Test I 4; Nominal contact pressure -1 6 0 MPa, Stroke - 30 fim , No of cycles 1,600,000.

Test I 4 was carried out at 160 MPa nominal contact pressure for 1,600,000 cycles.

The measured slip amplitude is 30 /mi. The surface damage observed in Test I 4 is shown in Figure 4.55. Two cracks could be observed on the damage surface for this test. Further more, the crack path observed in test 14 is similar to the crack initiation angle and the crack path observed in the preliminary test series for test PI, test P2 and test p4.

(a) (b)

Figure 4.56- Damage observed in left and right corner for Test I 5; Nominal contact pressure -1 2 0 MPa, Stroke - 28 fim , No of cycles 2,000,000.

The test I 5 was carried out at 120 MPa nominal contact pressure for 2,000,000 cycles. The measured slip amplitude was 28 fim. No cracks could be observed on the damage surface for this test. The surface damage observed in the Test I 5 is shown in Figure 4.56.

(a) (b)

Figure 4.57- Damage observed in left and right corner for Test I 6; Nominal contact pressure - 70 MPa, Stroke -1 8 f im, No of cycles 2,000,000.

The test 16 was carried out at 70 MPa nominal contact pressure for 2,000,000 cycles.

The measured slip amplitude was 18 /mi. No cracks could be observed on the damage surface for this test. The surface damage observed in the Test 16 is shown in Figure 4.57.

(a) (b)

Figure 4.58- Damage observed in left and right corner for Test I 7; Nominal contact pressure -1 1 0 MPa, Stroke - 22 /am , No of cycles 2,800,000.

The test I 7 was carried out at 110 MPa nominal contact pressure for 2,800,000 cycles. The measured slip amplitude was 28 /un. The surface damage observed in the Test 17 is shown in Figure 4.58. No cracks could be observed on the damage surface for this test.

20 pm

(a) (b)

Figure 4.59- Damage observed in left and right corner for Test I 8; Nominal contact pressure - 90 MPa, Stroke - 20 /xm, No of cycles 2,800,000.

The test I 8 was carried out at 90 MPa nominal contact pressure for 2,800,000 cycles.

The measured slip amplitude was 20 fim. No cracks could be observed on the damage surface for this test. The surface damage observed in the Test I 8 is shown in Figure 4.59.

Trend of the

Actual crack path

(a) (b)

Figure 4.60- Damage observed in left and right corner for Test I 9; Nominal contact pressure -1 4 5 MPa, Stroke - 30 f im, No of cycles 4,100,000.

The test I 9 was carried out at 145 MPa nominal contact pressure for 4,100,000 cycles. The measured slip amplitude as 30 fim. The surface damage observed in the Test I 9 is shown in Figure 4.60. A crack was visible on the right hand side of the contact surface for this test. Further, the crack path observed in the test I 9 is similar to the crack initiation angle and the crack path observed in the preliminary test series for test P 1, test P2 and test p4.

(a) (b)

Figure 4.61 - Damage observed in left and right corner for Test 1 10; Nominal contact pressure - 80 MPa, Stroke -1 8 f im, No of cycles 3,000,000.

The test I 10 was carried out at 80 MPa nominal contact pressure for 3,000,000 cycles. The measured slip amplitude was 18 fim. No cracks could be observed on the damage surface for this test. The surface damage observed in the Test 110 is shown in Figure 4.61.

(a) (b)

Figure 4.62- Damage observed in left and right corner for Test 1 11; Nominal contact pressure - 80 MPa, Stroke -1 7 (Jbm, No of cycles 5,000,000.

The test 111 was carried out at 80 MPa nominal contact pressure for 5,000,000 cycles. The measured slip amplitude was 17 /mi. The surface damage observed in the Test I I 1 is shown in Figure 4.62.No cracks could be observed on the damage surface for this test.

(a) (b)

Figure 4.63- Damage observed in left and right corner for Test 1 12; Nominal contact pressure - 260 MPa, Stroke - 36 jam , No of cycles 2,000,000.

The test I 12 was carried out at 260 MPa nominal contact pressure for 2,000,000 cycles. The measured slip amplitude as 36 /m i.. The surface damage observed in the Test I 12 is shown in Figure 4.63. Two cracks could be observed on the damage surface for this test. Further, the crack path observed in the test I 4 is well in agreement with the crack initiation angle and the crack path observed in the preliminary test series for test PI, test P2 and test p4. The surface damages observed in the P series and the I series have been discussed in Chapter 6, Section 6.5.