Fatigue Strength of Heat‐treatable Steel Under Static Multiaxial Compression Stresses

Abstract

ty compared to pearlitic cast iron (EN-GJS-600±3). The cyclic deformation curves of ADI show in contrast to the behaviour of heat-treatable steels no cyclic strain softening. The fatigue crack growth behaviour of ADI is different in the threshold region and the Paris region compared to the pearlitic cast iron. The threshold value is lower, caused by the higher strength, but the fatigue crack growth resistance in the Paris region is higher. The fatigue behaviour of ADI is thus useful for safety-relevant components.Technical parts are multiaxially loaded mainly by a combination of constant and alternating stress components. Specially negative constant stress components which are often implemented as multiaxial internal stresses will have a great influence on the dynamic strength.Loading of the material due to exclusively constant or alternating multiaxial stresses can be attributed to that of a state of uniaxial stress using a theory of failure. The fracture behaviour of the material is of greatest importance to the selection of the theory of failure. With ductile behaviour the material will fail by the nucleation and growth of shear microcracks, whereas with brittle behaviour the failure is governed by the nucleation and growth of mode I tensile cracks. In the first case the strength behaviour is very realistically described by the distortion energy hypothesis, in the second case by the normal stress hypothesis. This corresponds with the statement that the ratio of the equivalent yield point R p0,2 to the shear yield point s F as well as the ratio of the fatigue limit under fully reserved stresses r W to the fatigue limit under fully reserved shear stresses s W with ductile material behaviour is nearly Ö3 and with brittle behaviour nearly 1. However, the structure-dependent types of transition from plastic fracture to brittle fracture are characteristic of technical materials so that the necessity was seen to develop a theory of failure which is adaptable to the failure behaviour of the material.The evaluation of multiaxial stresses with constant and also alternating stress components has shown to be more complex than the evaluation of the mentioned special cases. A great number of theories of failure were suggested, among them the so-called quadratic criterion of failure, [1] the shearing stress intensity hypothesis [2] and the Dang Van criterion. [3] On evaluation of multiaxial loads with tensile prestresses, especially the shearing stress intensity hypothesis shows a good correspondence with experimental results. However, the known theories do not show a sufficient adaptation to the changed strength properties when compressive loads are applied. COMMUNICATIONS 544Table 5. Constants of the ESACRACK-model for ADI and EN-GJS-600±3. DK 0 [MPaÖm] K C [MPaÖm] C 2 [mm/cycle/ (MPaÖm) n ] n p q C th+ EN-GJS-1000±5 5.0 46 5.0´10 ±8 2.7 0.25 0.25 1.0 EN-GJS-600±3 7.8 38 1.2´10 ±9 4.1 0.25 0.25 1.9Note: DK 0 is the threshold value DK th for R = 0, a = 0.3 and S max /r 0 =2.5 ±[*] Prof.

Influence of mean shear stress on the torsional fatigue behaviour of 34CrNiMo6 steel

“…The application of Eq. (16) to the uniaxial case results in a symmetrical Haigh diagram σ m -σ a , which contradicts the experimental results for most ductile steels [57,66]. Moreover, Crossland [35] demonstrated that mean compressive hydrostatic stresses benefited the torsional fatigue limit, and he proposed a linear function to model their effect.…”

Differences in the response to in-phase and out-of-phase multiaxial high-cycle fatigue loading

“…Inner pressurizing of tube specimens intrinsically causes non-zero mean stresses. There are several cases where outer pressure is also applied [25], [26], but the pressure is not alternating. There is at least one case of another potentially interesting load combination using cruciform specimens [27], but the numbers of specimens used for each fatigue curve are not big enough.…”

Mean Stress Effect on the Axial Fatigue Strength of DIN 34CrNiMo6 Quenched and Tempered Steel

“…In general, these formulas come from empirical approaches to correlate groups of tests on particular materials. In the literature it is widely documented that there is no general empirical law to relate the effect of mean stress on the fatigue limit [3][4][5].…”