Development of an Energy-Based Experimental Method for Estimation of Fatigue Crack Evolution in Titanium Alloys

This paper presents an experimental study of energy dissipation caused by fatigue crack growth in Grade 2 titanium and titanium alloys Ti-1.1Al-0.9Mn and Ti-4.6Al-1.77V using the original heat flux method. It is shown that significant structural changes occur in the material under plastic deformation, leading to internal energy evolution. As is known, a large part of the deformation energy is dissipated as heat. The developed method allows high-accuracy measurements of the heat flux caused by plastic zone development at the crack tip directly in the fatigue experiment. Simultaneous measurements of the crack length and displacements in the stress concentration zone allow estimating the energy balance of the tested specimens. Analysis of the obtained data confirms that the stored strain energy reflecting the structural state of the material can be used as a fracture criterion. Based on the heat flux data, a kinetic equation is derived for predicting the rate of fatigue crack growth under Paris’s law by the energy dissipation rate.