The nature of specimen-size-effect on fatigue crack growth and net-section fracture mechanics approach to extract the size-independent behavior

Abstract A specimen-size-effect is found in the experimental fatigue crack growth behavior of single-edge-cracked fracture specimens, where the specimen length-to-width ratio was varied by about a factor of four. This effect appears from certain geometric correction factors (GCFS) used for the calcuation of the stress intensity range in fracture mechanics. It is shown that the net-section-based fracture mechanics approach provides a unique correlation of the fatigue crack growth data, for all specimen sizes, when the change in the net-section strain energy is used as the crack driving force parameter. The fatigue crack growth data could be correlated extremely well, when an effective specimen length, including the elastic strain energy of the specimen portion within the grips, is included in the driving force calculations. This effective length is determined by shear-lag analysis. It is also demonstrated that a true size-independent fatigue crack growth behavior can be obtained through the net-section based approach, using the concept of the change in net-section strain energy.