TABLE 1 CHEMICAL COMPOSITION (wt %) OF THE STEELS C Mn Si P S Cr V A l 0.80 0.69 0.23 0.012 0.009 0.265 0.060 0.004 TABLE 2 NOMENCLATURE, DIAMETER AND MECHANICAL PROPERTIES OF THE STEELS Steel A4 l45 A6 8.15 0.68 196.7 1.239 1 S21 2.50 8.69 7.50 0.62 202.4 1.27 1 1 S26 2.74 7.98 7 .OO 0.58 198.8 l S06 1.762 2.34 1 1.49 E: Young's modulus, oy: yield strength, 0,: ultimate tensile stress (UTS) P, n: Ramberg-Osgood parameters: E = o/E +(o/P)" Fracture Tests Cylindrical samples of 30 cm were used by cutting the steel wires. Samples were subjected to axial fatigue to produce a precrack before the fracture test. The precracking programme was designed so that the maximum stress intensity factor at the final stage (just before the fracture test) never exceeded 60% of the critical stress intensity factor reached at final failure. This condition was checked after the fracture tests to reject those specimens precracked at higher loads. Fig. l shows the specimens used in the fracture tests. Figure 1: Cracked bars used in the experimental programme.
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