Fatigue crack growth in bending: Successful correlation of mean stress (stress ratio) effects using the change in net‐section strain energy

Abstract

A physically based correlation of mean stress (or stress ratio) effects, during fatigue crack growth in bending, is demonstrated using the concept of the change in net‐section cyclic strain energy. This study extends the net‐section approach, which was successfully demonstrated previously for middle‐cracked tension specimens, here to bending. A straightforward analytical derivation of the change in net‐section cyclic strain energy is shown using the mechanics of beam bending. Using experimental data, it is shown that the change in net‐section cyclic strain energy successfully correlates the effect of mean stress on fatigue crack growth rates for a steel, an aluminium alloy, a titanium alloy, and a WC‐Co cermet. It is also shown that the net‐section‐based stress intensity factor, morphed from the change in net‐section strain energy, agrees excellently with the fracture mechanics‐based stress intensity factor. This is to show that the proposed net‐section‐centric fracture mechanics approach for fatigue is physical and that the origin of fracture mechanics stress intensity factor appears to be actually rooted in the change in the net‐section strain energy. Hence, the net‐section‐centric approach appears to be superior to the crack‐centric conventional fracture mechanics approach, and a physical treatment of the fatigue crack growth behaviour appears to be possible.