A thermomechanical study of the mode II impact response of fatigue cracks and sharp notches

This paper presents a detailed thermomechanical comparison between fatigue pre-cracked and sharp-notched Ti-6Al-4 V specimens under dynamic mode II loading. Using a single-point impact experiment, the response of these specimens was investigated through synchronized high-speed thermal and visual imaging. Frictional heating was isolated by comparing the thermal energy in fatigue pre-cracked specimens, which exhibited crack flank friction, to that of notched specimens with negligible friction. The fatigue pre-cracked specimens displayed non-uniform temperature distributions, with localized “hot spots” along the crack flanks, indicating significant frictional heating. These thermal patterns bear a strong resemblance to those previously reported in shear bands, though they arise from different physical mechanisms. Friction accounted for over 75 % of the thermal energy in the fatigue pre-cracked specimens, while plastic deformation is suggested as the primary source of heat generation in the notched specimens. Additionally, temperatures in the fatigue specimens were up to three times higher than in notched specimens. These findings highlight the critical role of friction in thermal dissipation during mode II loading.