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The reliable calculation of the fatigue life of high‐strength steels and components requires the systematic investigation of the cyclic deformation behaviour and the comprehensive evaluation of proceeding fatigue damage. Besides mechanical stress‐strain hysteresis measurements, temperature and electrical resistance measurements were used for the detailed characterisation of the fatigue behaviour of the steel SAE 4140 in one quenched and tempered, one normalised, one bainitic and one martensitic condition. To guarantee optimal operation conditions the new fatigue life calculation method “PHYBAL” on the basis of generalised Morrow and Basquin equations was developed. It is a short‐time procedure which requires the data of only three fatigue tests for a rapid and nevertheless precise determination of S‐N (Woehler) curves. Consequently, “PHYBAL” provides the opportunity to reduce significantly experimental time and costs compared to conventional test methods.

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A B S T R A C T In this paper, mechanical stress-strain-hysteresis, temperature and electrical resistance measurements are performed for the detailed characterization of the fatigue behaviour of quenched and tempered SAE 4140 steel used for many applications in the automotive industry. Stress-controlled load increase and constant amplitude tests (CATs) were carried out at ambient temperature on servo-hydraulic testing systems. The applied measurement methods depend on deformation-induced changes of the microstructure in the bulk material and represent the actual fatigue state. The plastic strain amplitude, the change in temperature and the change in electrical resistance can be equally used for an assessment of baseline fatigue properties in generalized cyclic deformation curves as well as in generalized Morrow and Coffin-Manson curves. On the basis of comprehensive experimental fatigue data, the physically based fatigue life calculation method 'PHYBAL' based on the generalized Basquin equation was developed. S-N (Woehler) curves calculated with 'PHYBAL' using data from only three fatigue tests agree very well with the conventionally determined ones.Keywords fatigue assessment; fatigue life calculation; quenched and tempered SAE 4140 steel; stress-strain hysteresis measurements; temperature measurements; electrical resistance measurements. N O M E N C L A T U R E b = fatigue strength exponent b M = fatigue strength exponent of generalized Basquin equation c = fatigue ductility exponent c M = fatigue ductility exponent of generalized Coffin-Manson equation K = cyclic hardening coefficient K M = cyclic hardening coefficient of generalized Morrow equation M = measured values ε a,p , T or R n = cyclic hardening exponent n M = cyclic hardening exponent of generalized Morrow equation N = number of cycles N f = number of cycles to failure Q = quotient of measured values determined in a load increase test and two constant amplitude tests T A = austenitizing temperature T 1 , T 2 , T 3 = local temperatures R = change in electrical resistance