The present study consists of a theoretical and experimental investigation of the effect of axial mean stresses on the high cycle fatigue behaviour of DIN 34CrNiMo6 high strength steel in quenched and tempered conditions. The axial S-N curves under 4 different stresses ratios were obtained. Experimental results show that increasing the value of the tension mean stresses gradually reduces the axial stress amplitude the material can withstand without failure. Moreover, the compressive mean stresses show a beneficial effect in terms of the axial fatigue strength, resulting in a non-symmetrical Haigh diagram. A historic review of the axial mean stress effect is presented, showing the shape of the Haigh diagrams for ductile metals and presenting the most-known empirical and physical theories. The results for this steel are compared with the physical theories of Findley based on the critical plane; the Froustey’s and Marin’s methods, based on energetic theories; and the Crossland invariants method based on the Gough’s theory of fatigue damage. Taking into account the experimental results, a physical fatigue function based on energetic considerations is proposed. Its application to the fatigue case with mean stresses can be interpreted in terms of a balance of elastic energies of distortion and volume change. Macro-analyses of specimen fracture appearance were conducted in order to obtain the fracture characteristics for different mean stress values.

The mean stress effect remains a critical aspect in multiaxial fatigue analysis. This work presents a new criterion that, based on the classical Findley criterion, applies a material-dependent exponent to the mean normal stress term and includes the ultimate tensile stress as a fitting parameter. This way of considering the non-linear effect of the mean stress, with a material-dependent rather than a fixed exponent, is totally innovative among the multiaxial fatigue criteria found in the literature. In order to verify its accuracy, the new criterion has been checked against an extended version of the Papuga database of multiaxial experimental tests with 485 results, and compared with the criteria by Findley, Robert, and Papuga. The new criterion provides outstanding results for pure uniaxial cases, with multiaxial performance similar to the Robert criterion with a smaller range of error and a conservative trend, even surpassing the popular Papuga method in several relevant loading scenarios. These features enhance the applicability and versatility of the criterion for its use in the fatigue design of structural components.

Mean stress effect remains as a critical aspect in multiaxial fatigue analysis. This work presents a new criterion which, based on classical Findley criterion, applies a material-dependent exponent to the mean normal stress term and includes the ultimate tensile stress as a fitting parameter. The criterion has been checked against an extended version of the Papuga database of multiaxial experimental tests with 485 results, and compared with the criteria by Findley, Robert and Papuga. The new criterion provides outstanding results for pure uniaxial cases, with multiaxial performance similar to Robert criterion with a smaller range of error and a conservative trend. These features enhance the applicability and versatility of the criterion for its use in fatigue design of structural components.

La mayoría de los componentes de máquina están sometidos a fatiga, siendo el caso general el de fatiga multiaxial. Actualmente no existe ningún método que prevalezca claramente sobre los demás, así es que existen numerosos métodos y cada año surgen nuevos, que ajustan mejor o peor según el material o caso de carga estudiado. En este sentido, recientemente se ha publicado el método de plano crítico de Abasolo, una evolución del reconocido método de Findley que considera el efecto no lineal de la tensión normal media elevando dicho termino a un exponente dependiente del material. En un trabajo previo se llevó a cabo una comparación de los métodos de Abasolo, Findley, Robert y Papuga frente a una extensa database experimental. En esa comparativa el método de Abasolo daba buenos resultados generales, destacando especialmente en los casos uniaxial y de torsión puros, dos casos particulares de fatiga multiaxial que sin embargo están ampliamente presentes en los componentes y sistemas estructurales mecánicos. Sin embargo, dada la gran cantidad de métodos que existen en la actualidad, resulta de interés aumentar el número de métodos empleados en la comparativa. Así pues, en este trabajo se realiza una versión extendida de dicha comparativa incluyendo varios métodos de plano crítico y de enfoque global, contrastando sus resultados para diferentes materiales y casos de carga recogidos en una base de datos compuesta por 486 casos recopilados de la literatura.