Influence of Pre-Strain on Static and Fatigue Properties of S420M Steel

Abstract

This paper reports the results of static tensile and low-cycle fatigue tests on S420M steel specimens. As-received (unstrained) and pre-strained specimens were used during the tests. Based on the static tensile tests carried out, no effect of pre-strain on the basic strength parameters of the S420M steel was found. Low-cycle fatigue tests showed that the pre-strain of the specimens causes a change in the cyclic properties of the steel and a slight increase in fatigue life compared to that of the as-received specimens. The greatest increase in durability was observed at the lowest strain levels.

Effect of Testing Conditions on Low-Cycle Fatigue Durability of Pre-Strained S420M Steel Specimens

“…No such phenomenon was found when testing as-received samples (the value of σ m was often close to the force measurement error). A detailed analysis of stress asymmetry in the conditions of controlled deformation is included in [10]. The analysis of Figures 5 and 6 shows that during cyclic loads, the plastic strain of as-received specimens is significantly different from the corresponding plastic strain of pre-deformed specimens.…”

“…With the increase in strain amplitude, the diversity of the obtained durability decreases. Detailed information on the impact of initial strains on the durability of S420M steel specimens under controlled strain conditions is described in [10] and will not be repeated here. In the case of tests carried out under conditions of controlled stress = const., the durability of pre-deformed specimens is significantly lower than that of as-received specimens (Figure 9).…”

“…In papers [7][8][9], a beneficial effect of the initial deformation on the strength characteristics obtained as a result of carrying out static tensile tests was demonstrated for precipitation-strengthened stainless steel SUH660 [7], complex phase steel CP800 [8], and austenitic stainless steel AISI 304L [9]. However, such an improvement in basic strength parameters due to initial deformation was not observed for S420M steel [10].…”

“…A slight dependence of fatigue life on the initial deformation temperature was found. Mrozi ński et al in [10] considered the straincontrolled fatigue tests of S420M steel specimens after initial deformation and observed a slight increase in the fatigue life of pre-strained specimens. The largest increase in fatigue life was detected at the lowest strain levels.…”

“…Due to frequent cases of overloads of these types of objects, tests are necessary to investigate how such events influence the durability of S420M steel elements. The experiments determining the basic strength parameters of both as-received and pre-strained S420M steel specimens in a static tensile test were already performed and described in [10]. It was shown that a pre-strain of S420M steel specimens of as much as 33% of the total elongation (A 5 ) does not reduce the basic strength parameters determined in the static tensile test.…”