THE PROBLEM OF SCATTER OF FRACTURE TOUGHNESS DATA

The authors studied the influence of the conditions for growing an initial fatigue crack on the scatter of fracture toughness data determined under static loading. It was found that the values of static fracture toughness for cyclically softening steels at temperatures below the brittle-to-ductile transition are essentially dependent on the degree of the material fatigue damage in the vicinity of the crack tip during the final stage of crack initiation. A method is proposed for evaluating the fracture toughness under static loading which makes it possible to take into account the material damage in the vicinity of the crack tip.     

Damage accumulation in light alloys on programmed loading. Part 2. Effects of fretting corrosion

A study has been made on how fretting corrosion affects damage accumulation in programmed loading with two-step blocks for D16AT, VT14, and AMg6 alloys. The accumulation is dependent on the relation between the stresses in the steps and the yield point for the surface layer of material. The hardening in the high step is due to the residual compressive stresses, which cause plastic strain with loading beyond the yield point of the surface layer but elastic strain in the internal layers.Translated from Problemy Prochnosti, No. 12, pp. 31–37, December, 1992.     

Fatigue strength and cyclic crack resistance of titanium alloy VT3-1 in different structural states. Communication 1. Study procedure and experimental results

Procedures are described for studying the fatigue strength and cyclic crack resistance characteristics of alloy VT3-1 in different structural states achieved by varying thermomechanical treatment (TMT) parameters. TMT schedules, alloy structure and texture characteristics, and also the size of structural elements typical for an alloy structural state are given. Results are given for static tensile, fatigue, and crack resistance tests on alloy VT32-1 in different structural and textural states, and they are analyzed.Translated from Problemy Prochnosti, Nos. 5–6, pp. 3–11, May–June, 1995.     

Fatigue strength and cyclic crack resistance of titanium alloy VT3-1 in different structural states. Communication 2. Procedure for considering the effect of structure on fatigue limit

On the basis of experimental results presented in communication 1 for a study of the fatigue strength of two-phase titanium alloy VT3-1 in different structural states it is shown that the fatigue limit for the alloy increases with a reduction in the average size of a structural element critical for cyclic strength. A numerical model is developed by means of linear fracture mechanics approaches which makes it possible from available data about the size of structural parameters for the alloy to predict the fatigue limit of smooth specimens.Translated from Problemy Prochnosti, Nos. 5–6, pp. 12–17, May–June, 1995.     

Prediction of crack resistance for heat-resistant steels taking into account the specimen size effect. Communication 1. Results of experimental investigations

We present a large volume of unique experimental data on local fracture parameters and crack resistance characteristics of different structural alloys, including steels 15Kh2MFA and 15Kh2NMFA and their welded joints, subjected to different heat treatments, simulating exposure to different doses of radiation bombardment and used in manufacturing VVéR-440 and VVéR-1000 atomic reactor pressure vessels. These experimental results allow us to generalize the scientific conclusions concerning the scale effect in fracture mechanics, since they were obtained by investigating many materials (σ_0.2 = 270–1500MPA) over a broad range of variation in specimen thickness (t=12.5–150 mm) and experimental temperature (T=77–573 K). The data on the fracture toughness characteristics of a broad class of structural alloys suggest that the scale effect is complex and contradictory, depending first of all on the range of variation in the specimen thickness and the physicomechanical properties of the material, including those determined by the effect of production and service factors. On the whole, the experimental data support the possibility noted in various literature sources that there are three different types of dependences of the fracture toughness on the specimen size (the fracture toughness can increase, decrease, or stay the same as the specimen size increases). It does not seem possible to predict and explain these dependences within approaches proposed earlier. Translated from Problemy Prochnosti, No. 1, pp. 5–25, January–February, 1997.