Fatigue and Fracture Mechanics XXV

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Authors: Sebastian Kamiński, Marcel Szymaniec, Tadeusz Łagoda
Abstract: In this work an investigation of internal structure influence on mechanical and fatigue properties of ferritic-pearlitic steels is shown. Ferrite grain size and phase volume fraction of three grades of structural steel with similar chemical composition, but different mechanical properties, were examined. Afterwards, samples of the materials were subjected to cyclic bending tests. The results and conclusions are presented in this paper
Authors: Krzysztof Gołoś
Abstract: In the paper monotonic, cyclic and fatigue data for En295 steel were presented. Subsequently, the experimental results for two-step loading sequence (low-to-high (L—H) loading, and high-to-low (H—L) and three-step loading sequence (L-H-L and H-L-L) were presented. The analysis showed that all loading sequences affects the cumulative damage in En295 steel. In the analysis an energy based cumulative damage hypothesis presented by Golos and Ellyin was applied. The predictions based on the analyzed Golos-Ellyin cumulative damage hypothesis are compared with the obtained data for En295 steel and is found to be in fairly good agreement.
Authors: Łukasz Pejkowski, Dariusz Skibicki
Abstract: 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.
Authors: Dorota Kocańda, Andrzej Górka, Krzysztof Grzelak, Janusz Torzewski, Ellina Łunarska, Hryhoriy Nykyforchyn, Volodymyr Kyryliv
Abstract: In the paper low (LCF) and high cycle fatigue (HCF) behavior of the S355J2 low alloyed steel after surface frictional-mechanical treatment in a corrosive environment (3.5 % NaCl ) has been presented. The treatment was used in order to improve mechanical and fatigue properties of the steel. Obtained experimental results indicate an insignificant improvement of mechanical and fatigue properties of the strengthened steel under the conditions of corrosion at constant amplitude cyclic loading. It is particularly noticeable in the range of low-cycle fatigue.
Authors: Dariusz Boroński, Robert Sołtysiak, Zbigniew Lutowski
Abstract: Joining aluminium alloys with the use of welding techniques often impairs their strength properties and in some cases it is very difficult or even impossible. An alternative method for joining this type of material is friction welding including FSW welding. The airplane aluminium alloy 2024-T3 is an example of material that can be welded using this method. Heat emitted during the process, which contributes to the material plasticisation in the zones of welding, causes significant changes in the material structure, thus affecting the joint properties. Fatigue life calculations of this type of joint can be performed according to different approaches. One of them is a local approach which requires knowledge of local strains or stresses within the notch zone. This paper is a presentation of exemplary results of experimental and numerical tests of strain in the zone of notch that occur in a joint under time variable loading.
Authors: Ewa Marcisz, Dariusz Rozumek, Zbigniew Marciniak
Abstract: The work presents fatigue characteristics of C45 steel that have been obtained at controlled energy parameter and nominal stress. The tested material has been subjected to fully reversed bending on MZGS-100Ph fatigue test stand.
Authors: Ewelina Böhm, Marta Kurek, Tadeusz Łagoda
Abstract: The paper proposes a new model of fatigue damage accumulation based on the memory of the material and developed on the basis of memorizing of the meaningless material. The comparison of damage accumulation between the classical and proposed models for chosen materials are in favor of the authors model.
Authors: Grzegorz Szala
Abstract: According to the performed analysis of fatigue phenomena occurring in metals, the effects of fatigue appear in the form of lines and slip bands under loading conditions producing variable stresses with values below the fatigue limit of these metals. It is commonly accepted that variable stresses with constant amplitude of values below 0.4 of the fatigue limit do not cause plastic strain in grains (lines and slip bands), thus they do not affect the fatigue life. This study is an attempt of quantitative assessment of the influence of stresses with values below the fatigue limit on fatigue life by using tests with programed two-step loading (variable-amplitude). Tests were performed with the use of C45 steel specimens.
Authors: Bogdan Ligaj
Abstract: The article presents the results of low and high cycle fatigue tests of C45 steel for constant and variable amplitude loading in the stress and energy based approach. Values of the cumulated energy of plastic strain ΣΔWpl for programmed loading (at selected levels of stress amplitude Sa) were found to meet reliability criteria for results obtained in the condition of constant amplitude loading. (R= -1). It was also found that the results obtained in the energy based approach are characterised by a smaller range of relative difference changes (δ(N) = 0,77 to 1,17) than the results obtained in the stress based approach (δ(N) = 0,15 to 1,94). At stress level Sa = 428 MPa, (corresponding to yield point of C45 steel) value δ(N) is similar for the stress based approach and energy based approach.

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