Bethlehem Hot-Rolled XF Sheet Steels

Fatigue Properties
A structural member subject to cyclic stress can fail at a load whose maximum amplitude is considerably smaller than the load required to produce static failure. It is this property of structural materials that is so troublesome to designers of structures and components (e.g., wheels) which are subject to cyclic loads and vibrations.

To provide the designer with necessary design data, cyclic strain-life curves (Figure 9) and cyclic stress�strain curves (Figure 10) are illustrated for B50XF and B80XF. To further assist designers, the table below summarizes the monotonic and cyclic parameters for these two grades. The tests to develop these data were conducted according to ASTM E 606�80. The cyclic strain-life and stress-strain parameters can be used to estimate fatigue performance for various notched conditions using the local-strain or Neuber life assessment model.

Typical Parameters for Fatigue Design

Grades	B50XF	B80XF
Thickness, inch (mm)	0.107 (272)	0.082 (2.08)
Monotonic
Yield strength, Sy, ksi, (MPa)1	58.1 (401)	82.6 (570)
Tensile strength, Su, ksi (MPa)1	70.5	93.5 (645)
Cyclic
Yield strength, Sy1, ksi, (MPa)1	49.9 (344)	75.7 (522)
Strain-hardening exponent, n'	0.113	0.0817
Strength coefficient, k', ksi (MPa)	101.0 (697)	126.0 (869)
Fatigue strength coefficient, o'f, ksi (MPa)	163.0 (1124)	222.0 (1531)
Fatigue strength exponent, b	-0.113	-0.110
Fatigue ductility coefficient, e'f	1.38	3.14
Fatigue ductility exponent, c	-0.682	-0.852

1. 0.2% offset yield strength