PSI - Issue 13

Robert Kruzel et al. / Procedia Structural Integrity 13 (2018) 1626–1631 Kruzel and Ulewicz / Structural Integrity Procedia 00 (2018) 000 – 000

1630

5

Table 3. Fatigue testing parameters for cords A , B and C

Cord

Cord construction

Number of cycles

Length of sample, mm

Load, kN

675

800 800 800 800 800 800 800 800 800 800 800 800

0.40 0.40 0.40 0.40 0.30 0.30 0.30 0.30 0.20 0.20 0.20 0.20

1350 2700 5400 1350 2700 5400 675 1350 2700 5400 675

A

3 + 6

B

2+2 x 0.25

C

2x0.30

Table 4. Results of measurements of tensile strength, R m , with indicated number of fatigue cycles, N of steel used for cords D-G . Cord Number of cycles, N 0* 675 1350 2700 5400 A 1665.1 1661.4 1655.8 1632.1 1571.9 B 938.9 936.8 928.1 902.1 870.7 C 443.1 442.1 432.5 402.8 385.7 The fatigue strength of steel wire depends largely on the metallurgical purity of the material, and especially on its contents of non-metallic inclusions (silicon, sulphur and nitrogen), because it is around those impurities that high stress concentrations form, which result in wire cracking. Therefore, in the subsequent part of the investigation, the strength parameters were determined for cords made of different steel grades (cords D - G ) of construction 2 x 0.30, while considering the fact that for this type of construction (cord C ), the greatest difference in strength decrease after the bending process was observed. Subjected to testing was wire of a diameter of  1.60 mm, from which, after the drawing process,  0.30 mm - diameter wires were used for splicing the cord under consideration are obtained. The mechanical properties of the wire are given in Table 5. The bidirectional bending test was performed in accordance with the standard PN-ISO 7801: 1996 applicable to determining the resistance of wire to plastic deformation; whereas, the fatigue properties of cords made from the above wires are shown in Table 6.

Table 5. The mechanical properties of respective  1.60 mm-diameter wires after heat treatment

Strength [MPa]

Number of twists [100×d]

Number of bends 5 [mm]

Cord

R m -average

Min.-Max. 1300-1340 1280-1300 1240-1260 1150-1190

Average

Min.-Max.

Average

Min.-Max.

D E F G

1335 1285 1255 1175

33 30 40 31

26-39 24-36 32-44 28-36

10 10 10 10

8-12 8-12 9-11 9-11

Table 6. The mechanical and fatigue properties of finished 2 x 0.30 construction cords

Breaking force, [N]

Load, F [kN]

Time [min.]

Number of cycles

Length of sample, [mm]

Cord

Average

Min.-Max.

D E F G

410 400 410 390

405-415 395-405 400-420 385-400

290 280 270 250

13824 13200 12076 11904

1270 1300 1320 1330

0.20 0.20 0.20 0.20

As demonstrated by the data in Table 7, cords D-G of construction 2 x 0.30 with the use of load of a magnitude of 0.20 kN showed a gradual decrease in strength after subjecting them to a specified fatigue. After 675 fatigue cycles, a slight (< 0.3%) decrease in breaking force was observed for all of the examined cords ( D-G ). By contrast, after 5400 fatigue cycles, the highest percentage drop (12.73 %) in tensile strength was observed for cord D , and the lowest (5.43