Crack resistance of structural steels under static and cyclic loading

The article deals with the investigation of static and fatigue crack resistance of normalized steels 40Kh and 30KhGSA, and also of steel 40Kh after hardening and tempering at 500°C with the object of working out recommendations for the use of normalized steel 40Kh for making axles of tractor trailers produced at the Chelyabinsk Engineering Works. The article presents the results of static tests of cylindrical specimens with annular cracks under conditions of axial tension which showed that the crack resistance K_1C of heat-treated steel 40Kh is up to 20% higher than after normalization. The crack resistance K_1C of normalized steel 30KhGSA has intermediate values. We carried out fatigue tests of the above-mentioned steels by concentrated bending, and from the results we plotted kinetic diagrams of fatigue failure and determined the threshold values of the characteristics of fatigue crack resistance K_th and K_fc which confirmed the data of the static tests. It was established that normalized steel 40Kh can be recommended as material of axles for tractor trailers with a load capacity of up to 10 tons for which the safety factor K_s is at least 2–2.5.Translated from Problemy Prochnosti, No. 7, pp. 28–31, July, 1990.     

Crack resistance of steels within the microsecond loading range

Dynamical strength and crack resistance experimental results have been analyzed. Space-time fracture model and criterion have been proposed, which describe the space-time fracture pattern.     

Fatigue strength of steels under multicycle impact loading

The functional dependence of the fatigue limit under impact loading on the fatigue limit in harmonic loading was derived for structural steels, together with the dependence of the coefficient of the effect of impact on impact toughness. The impact toughness values at which multicycle impact loading is detrimental are determined.Translated from Problemy Prochnosti, No. 3, pp. 87–93, March, 1994.     

Cold resistance of steels in static loading in conditions with high plastic strains

The authors propose and construct dependences of the cracking resistance characteristics (K_c ^*/_B)² and (K_c ^*/S_K)² on test temperature which can be used to determine critical temperatures in conditions with high plastic strains. Equations are derived for calculating the cold resistance of both laboratory specimens and components without time-consuming tests.Translated from Problemy Prochnosti, No. 1, pp. 21–25, January, 1990.     

Influence of electrolytic hydrogenation on cyclic crack resistance of chromium-nickel steels

Within the framework of linear fracture mechanics, we estimate the resistance of chromium-nickel 06Kh17N13M3, 07Kh16N6, and 10Kh26N5M steels to hydrogen embrittlement after various thermal treatments. We established that electrolytic hydrogenation leads to a considerable increase in the growth rate of fatigue cracks in steels with maximum in a low-amplitude range (by approximately a factor of 5–25 as compared with tests in air). The optimal mode of thermal treatment of 10Kh26N5M steel corresponds to quenching at 1293 K and annealing at 623 K. This mode ensures high plastic characteristics and maximum resistance to fatigue fracture in air in the course of electrolytic saturation with hydrogen, and long-term holding in a chloride-containing environment. We recommend this steel for the manufacture of critical parts of oil separators of marine ships. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 4, pp. 63–67, July–August, 1999.     

Cyclic strength of pearlitic steels under conditions of elastoplastic loading

We study the elastoplastic flow of pearlitic steels extensively used for technological purposes under the conditions of low-cycle loading at elevated temperatures and propose an equation of state for the evaluation of the accumulated level of strains as a function of the number of cycles, properties of the material, and parameters of loading. Deceased. Slavyansk State Pedagogical Institute, Slavyansk, Ukraine. Translated from Problemy Prochnosti, No. 3, pp. 133–137, May–June, 2000.     

Crack initiation and growth path under multiaxial fatigue loading in structural steels

In real engineering components and structures many accidental failures occur due to unexpected or additional loadings, such as additional bending or torsion. There are many factors influencing the fatigue crack paths, such as the material type (microstructure), structural geometry and loading path. It is widely believed that fatigue crack nucleation and early crack growth are caused by cyclic plasticity. This paper studies the effects of multiaxial loading paths on the cyclic deformation behaviour, crack initiation and crack path. Three types of structural steels are studied: Ck45, medium carbon steel, 42CrMo4, low alloy steel and the AISI 303 stainless steel. Four biaxial loading paths were applied in the tests to observe the effects of multiaxial loading paths on the additional hardening, fatigue crack initiation and crack propagation orientation. Fractographic analyses of the plane orientations of crack initiation and propagation were carried out by optical microscope and SEM approaches. It is shown that these materials have different crack orientations under the same loading path, due to their different cyclic plasticity behaviour and different sensitivity to non-proportional loading. Theoretical predictions of the damage plane were conducted using the critical plane approaches, either based on stress analysis or strain analysis (Findley, Smith–Watson–Topper, Fatemi–Socie, Wang–Brown–Miller, etc). Comparisons of the predicted crack orientation based on the critical plane approaches with the experimental observations for the wide range of loading paths and the three structural materials are shown and discussed. Results show the applicability of the critical plane approaches to predict the fatigue life and crack initial orientation in structural steels.     

Crack tip heating in short-fibre composites under fatigue loading conditions

Crack tip heating in cyclically loaded short-fibre polymer matrix composites occurs by a combination of hysteretic heating and frictional heating. While the former mechanism is caused by plastic and viscoelastic deformations within the polymeric matrix, the latter is due to interfacial friction between matrix and fibres, and crack surface interference associated with crack closure. The relative contribution of these two principal mechanisms depends upon a number of variables including the viscoelastic and plastic characteristics and frictional properties of the matrix polymer, the degree of interfacial adhesion, the fibre content and fibre orientation distribution and the loading conditions. The results confirm that even in a tension/tension loading mode, frictional heating may play a dominant role, at least in some systems.     

Crack patterns in thin layers under temperature loading Part II: Cyclic loading

The paper presents an analysis of cracking and delamination of an elastic plate bonded to a rigid substrate. The plate is subjected to a cyclic temperature loading. The bond between the plate and the substrate is simulated using rigid-frictional and rigid-cohesive-frictional interface models. The states of adaptation or incremental failure are distinguished in the case of the softening interfacial law. The proposed modelling is validated to predict fragmentation of a concrete pavement subjected to temperature loading. The obtained results can serve as reference solutions for numerical calculations of more complex cases.     

The kinetics of damage accumulation in heat-resistant steels under different loading conditions

The investigation results are presented for the kinetics of damage accumulation and the process of deformation in a heat-resistant steel 10GN2MFA for different loading conditions under complex stress state.