Cyclic AE count rate and crack growth rate under low cycle fatigue fracture loading

In the low cycle fatigue fracture testing with KS (or JIS) SS41 steel, crack growth rate, AE count rate and J-integral range are measured to get empirical relationships between crack growth rate and J-integral range, AE count rate and J-integral range as well as AE count rate and crack growth rate. All the relationships are shown to be linear on the log—log graphs. It is also shown that the linear relationships can be formulated by using Dunegan's assumption and elastic-plastic fracture mechanics along with the well-known relationships of crack growth rate and J-integral range. It is concluded that the differences between experimental and theoretical values are due to the problem of Dunegan's assumption.     

Effect of loading rate on crack velocities in HSC

This paper presents the recent results of an experimental program aimed at disclosing the loading rate (loading-point-displacement rate) effect on the crack velocity in high-strength concrete (HSC). Eighteen three-point-bend tests were conducted using either a servo-hydraulic machine or a self-designed drop-weight impact device. Four strain gauges mounted along the ligament of the specimen were used to measure the crack velocity. Six different loading rates were applied, from 10⁻⁴ mm/s to 10³ mm/s (average strain rate from 10⁻⁶ to 10⁻¹ s⁻¹), i.e., a low loading-rate range (5.50 × 10⁻⁴ mm/s, 0.55 mm/s and 17.4 mm/s) and a high loading-rate range (8.81 × 10² mm/s, 1.76 × 10³ mm/s and 2.64 × 10³ mm/s). At low loading rates, the crack propagates with increasing velocity. Under high loading rates, the crack propagates with slightly decreasing velocity, though the maximum crack speed reached up to 20.6% of the Rayleigh wave speed of the tested HSC. In addition, the loading-rate effect on crack velocities is pronounced within the low loading-rate regime, whereas it is minor under the high loading-rate range.     

Predicting the rate of fatigue crack growth in biaxial low-cycle loading

The authors propose a new criterion of predicting the rate of crack growth in biaxial loading based on analysis of the local stress-strain state of the crack tip, the size of the plastic zone, and the plasticity margin of cyclic failure. The derived calculation dependences are compared with the experimental data obtained by the authors and other investigators. The results are in satisfactory agreement as a result of taking into account the effect of the load level, the properties of the material, and the biaxial loading.Translated from Problemy Prochnosti, No. 5, pp. 18–23, May, 1991.     

Effect of an asymmetrical load cycle on the fatigue limit of materials

Moscow. Translated from Problemy Prochnosti, No. 7, pp. 36–41, July, 1989.     

Effect of loading rate on microstructural features of steel failure in crack propagation

A quantitative and qualitative fracture analysis has been carried out on 40Kh and St.3 steel specimens. The existence of a certain loading rate threshold has been established whose exceeding changes the regularities of the effect of the loading rate on the shape and parameters of the fracture microrelief. This corresponds to the speed dependence of dynamic crack resistance of steel.Translated from Problemy Prochnosti, No. 2, pp. 20–24, February, 1991.     

Influence of the loading path on fatigue crack growth under mixed-mode loading

Fatigue crack growth tests were performed under various mixed-mode loading paths, on maraging steel. The effective loading paths were computed by finite element simulations, in which asperity-induced crack closure and friction were modelled. Application of fatigue criteria for tension or shear-dominated failure after elastic–plastic computations of stresses and strains, ahead of the crack tip, yielded predictions of the crack paths, assuming that the crack would propagate in the direction which maximises its growth rate. This approach appears successful in most cases considered herein.     

Threshold stress intensity factor and crack growth rate prediction under mixed-mode loading

A new mixed-mode threshold stress intensity factor is developed using a critical plane-based multiaxial fatigue theory and the Kitagawa diagram. The proposed method is a nominal approach since the fatigue damage is evaluated using remote stresses acting on a cracked component rather than stresses near the crack tip. An equivalent stress intensity factor defined on the critical plane is proposed to predict the fatigue crack growth rate under mixed-mode loading. A major advantage is the applicability of the proposed model to many different materials, which experience either shear or tensile dominated crack growth. The proposed model is also capable to nonproportional fatigue loading since the critical plane explicitly considers the influence of the load path. The predictions of the proposed fatigue crack growth model under constant amplitude loading are compared with a wide range of fatigue results in the literature. Excellent agreements between experimental data and model predictions are observed.     

Effect of plastic anisotropy on crack growth resistance under mode 1 loading

Crack growth in a solid with plastic anisotropy is modeled by representing the fracture process in terms of a traction-separation law specified on the crack plane, and crack growth resistance curves are calculated numerically. A phenomenological elastic-viscoplastic material model is applied, using one of two different anisotropic yield criteria to account for the plastic anisotropy. The analyses are carried out for conditions of small scale yielding, with mode I loading conditions far from the crack-tip. Different initial orientations of the principal axes relative to the crack plane are considered and it is found that the steady-state fracture toughness is quite sensitive to the type of anisotropy and to the angle of inclination of the principal axes relative to the crack plane.     

Creep crack growth under history-dependent loading

We discuss the influence of loading history on creep crack growth. Our attention is mainly focused on the following three aspects of this problem: (i) principal laws of history-dependent creep strain of materials; (ii) creep behavior of cracks, including the choice of suitable fracture parameters that may help to predict cracking; (iii) the importance of taking the history-dependent response of the material into account. We performed numerical calculations based on the use of an appropriate constitutive model and fracture theory for (1) and (2), respectively, to analyze results of tests for (3).Battelle, Columbus, Ohio. UES Incorporated, Dayton, Ohio. Published in Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 4, pp. 37–45, July – Augus, 1994.