Fatigue assessment and fatigue life calculation of quenched and tempered SAE 4140 steel based on stress–strain hysteresis, temperature and electrical resistance measurements

Abstract

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

Experimental Energy Balance During the First Cycles of Cyclically Loaded Specimens Under the Conventional Yield Stress

“…Thus, different authors developed some rapid experimental methods to determine the fatigue limit using variations of the mean temperature [6][7][8][9][10][11], the first and second temperature harmonics [12], or the dissipated energy [13,14] as a function of the applied stress. Unfortunately, fatigue limit resulting from these approaches are often questionable for the physical reasons leading to these estimations are not yet well understood.…”

“PHYBAL” a Short‐Time Procedure for a Reliable Fatigue Life Calculation

“…It can be done in exactly the same manner by using the plastic strain amplitude or the change in temperature, cf. [11][12] . In Figure 8(a) the cyclic stress-resistance (s a -DR) curve for the load levels of the load increase test (Figure 7 As can be seen in Figure 8(b), the experimentally determined lifetimes N f, exp.…”

“…For electrical resistance measurements a DC-power supply was fixed at both shafts and DR was measured with two wires spot welded at the transition of the gauge length and the shafts (Figure 3), cf. [11][12][13][14] .…”

Cyclic deformation behaviour, microstructural evolution and fatigue life of duplex steel AISI 329 LN

“…LITs have proven to allow for a fast first assessment of the endurance limit using just one single specimen [18,19]. It must be noted that this statement only holds true, if the term endurance limit relates to a commonly used ultimate number of cycles in the HCF regime, e.g., N max = 2 Á 10 6 cycles.…”

“…The change in the slope at a stress amplitude r RW,LIT is caused by increasing plastic deformations and can be used for the assessment of the endurance limit [3,18,19]. The stress amplitude Additional LITs were performed at a frequency of 130 Hz to underline the adaptability of the ''PHYBAL LIT ''-concept to high frequency conditions.…”