EFFECT OF STRAIN HARDENING CAPACITY ON FATIGUE LIFE OF STRUCTURAL STEEL

A single edge cracked panel subjected to monotonic and cyclic loading has been
analyzed using two-dimensional elastic-plastic finite element program. The effect of
strain hardening exponent on the stress-strain and the deformation behavior at the crack
tip ws studied at different maximum applied stress ranges. The analysis was performed
for the plane stress state at constant amplitude loading of zero stress ratio. Relevant
kinematic parameters corresponding to loading and unloading phases of a cycle were
computed and correlated. Parameters controlling the fatigue life of the structural
elements, i.e. plastically deformed zone and crack tip opening displacement were
estimated and correlated.
The results indicated that with increasing the strain hardening exponent, the normal
tensile stress decreases within the crack tip plastic zone while the normal tensile strain
showed ah opposite trend. Also the normal tensile stress tends to be constant inside the
monotonic plastic zone at the higher values of the strain hardening exponent irrespective
of the value of the applied stress range. The results also show that the crack tip opening
displacement increases with increasing the strain hardening exponent, whilst the plastic
zone showed an opposite trend. Those behaviors were analyzed for their correlation. A
previously developed crack tip deformation parameter to correlate fatigue crack growth
was modified to include the effect of strain hardening capacity of the material,