Experimental investigation of Mode I fatigue crack growth behavior of titanium foils

A low-cost experimental apparatus has been developed to investigate the Mode I fatigue crack growth behavior of thin metallic foils and sheets. The apparatus utilizes magnetic coupling between a ceramic magnet and a rotating steel disk to induce cyclic tensile loads in notched rectangular test specimens.To illustrate the testing apparatus, Mode I fatigue crack growth in 30 Dm thick high purity titanium foils was studied. Experiments were performed at ambient temperature using a loading frequency of 2 Hz and a nominal stress ratio of 0.1. The cyclic crack growth data could be fit to a Paris relationship between crack growth rate and stress-intensity range. The stress intensity factor exponent, m, in the Paris relationship was between 4 and 5, which is comparable to the relatively high values found in the literature for the tension-tension fatigue of other metallic bulk materials. Self-similarity analysis was used to explain the observed higher m values for thin metallic foils.