Analysis of the uniaxial fatigue behaviour of 42CrMo4 Q&T steel specimens extracted from the big end of a marine engine connecting rod using the heat dissipation approach

Among the energy-based approaches to estimate the fatigue life of steel specimens, the experimental method based on the heat dissipation (or intrinsic dissipation) per cycle, Q, proved effective for correlating the effects of geometrical stress concentrations, uniaxial and multiaxial loadings, and mean stress. The mean stress effect requires a properly defined temperature-corrected parameter Q. The parameter Q is readily evaluable using temperature measurements and in this investigation it has been employed for fatigue strength assessment of plain specimens, extracted from a 42CrMo4 Q&T connecting rod big end of a marine engine. Completely reversed, strain-controlled, constant amplitude fatigue tests were carried out and the Q parameter evolution was monitored during each test by suddenly stopping the fatigue test several times and measuring the cooling gradient of material temperature. As result, besides the traditional strain-life (εa-2Nf) curve, the Q-Nf curve was also obtained, which is expected to be applicable for correlating notch and mean stress effects in future investigations.