Łukasz Pejkowski

Steel X2CrNiMo17-12-2 Testing for Uniaxial, Proportional and Non-Proportional Loads as Delivered and in the Annealed Condition

The article presents the results of fatigue life and fractographic testing of steel X2CrNiMo17-12-2 exposed to proportional and non-proportional fatigue loads. The following load types were applied: tension-compressive strength, torsion, proportional combined/complex loads produced by tension-compressive strength and torsion as well as non-proportional combined load – by tension-compressive strength and torsion by the phase shift angle φ=90°. The paper analyses the effect of the load method on the fatigue life and fractography of fatigue fractures recorded, and especially the effect of non-proportional load.

Criteria Evaluation for Fatigue Life Estimation under Proportional and Non-Proportional Loadings

The paper presents the fatigue criteria, representing the integral criteria, most frequently reported in literature. They were verified for uniaxial loadings and for combined: tension-compression with torsion both proportional and non-proportional. The verification involved a comparison of the fatigue life reported based on the criterion with the experimental fatigue life.

Plastic strain energy of CuZn37 brass in low-cycle multiaxial fatigue regime

This paper presents the results of a plastic strain energy calculations for the CuZn37 brass under multiaxial fatigue loading. Fatigue tests were performed on the hollow specimens subjected to fully reversed tension-compression, torsion, proportional loading, 90° out-of-phase non-proportional loading and two another non-proportional loadings with frequency differences. All test were strain-controlled. Calculations of a strain energy were based on midlife strain hysteresis loops data and Ramberg-Osgood equation constants. Some tests are observed by thermographic camera. The plastic strain energy was also determined on the base of the specimen surface temperature. All results were compared and discussed.

Steady-state temperature determination on the base of hysteresis loop energy for CuZn37 brass

This paper presents the verification of the relationship between the temperature and the hysteresis loop energy for the CuZn37 brass under multiaxial fatigue loading. Fatigue tests were performed on the hollow specimens subjected to fully reversed tension-compression, torsion, proportional loading, 90° out-of-phase non-proportional loading and two another non-proportional loadings with frequency differences. All test were strain-controlled. Calculations of a plastic strain energy were based on midlife strain hysteresis loops data. The calculated specimen temperatures were compared with temperatures observed by thermographic camera.

Multiaxial Fatigue Life Assessment Method Based on the Mean Value of Modified Second Invariant of the Deviatoric Stress

Stress invariants approach to the multiaxial fatigue life estimation is generally based on the root mean square value of second invariant of the deviatoric stress amplitude and the value of hydrostatic stress. Such an approach omits a significant part of the information about multiaxial load history. It is particularly noticeable in case of non-proportional loadings, which lead to a reduction of fatigue life (i.e. [1–3]). In this work a new method based on the mean value of modified second invariant of the deviatoric stress has been presented.

Modification of Zenner and Liu Criterion due to Non-Proportionality of Fatigue Load by Means of MCE Approach

The results of experimental verification of Zenner and Lius criterion confirm its efficiency in the case of estimation of fatigue life for proportional loading. Due to application of general damage parameter, the criterion is useful in case of various types of proportional loading and for multiple materials. However, for non-proportional loadings, of high non-proportionality level, the error of estimation of fatigue lives often exceeds scatter band 3. The hereby work presents a proposal for Zenner and Lius criterion modification based upon introduction of loading non-proportionality measure with minimum circumscribed ellipse method (MCE).