Singular Integral Equations. By N.I. Muskhelishvili. Translated fromthe 2nd Russian edition by J.R.M. Radok. Pp. 447. F1. 28.50. 1953. (Noordhoff, Groningen)

The activity of non-basal slip systems and dynamic recovery at room temperature in fine-grained AZ31B magnesium alloys

Compression properties of a refractory multi-component alloy, Ta20Nb20Hf20Zr20Ti20, were determined in the temperature range of 296–1473 K and strain rate range of 10−1–10−5 s−1. The properties were correlated with the microstructure developed during compression testing. The alloy was produced by vacuum arc melting, and it was hot isostatically pressed (HIPd) and homogenized at 1473 K for 24 h prior to testing. It had a single-phase body-centered cubic structure with the lattice parameter a = 340.4 pm. The grain size was in the range of 100–200 μm. During compression at a strain rate of έ = 10−3 s−1, the alloy had the yield strength of 929 MPa at 296 K, 790 MPa at 673 K, 675 MPa at 873 K, 535 MPa at 1073 K, 295 MPa at 1273 K and 92 MPa at 1473 K. Continuous strain hardening and good ductility (e ≥ 50%) were observed in the temperature range from 296 to 873 K. Deformation at T = 1073 K and έ ≥ 10−3 s−1 was accompanied by intergranular cracking and cavitation, which was explained by insufficient dislocation and diffusion mobility to accommodate grain boundary sliding activated at this temperature. The intergranular cracking and cavitation disappeared with an increase in the deformation temperature to 1273 and 1473 K or a decrease in the strain rate to ~10−5 s−1. At these high temperatures and/or low-strain rates the alloy deformed homogeneously and showed steady-state flow at a nearly constant flow stress. Partial dynamic recrystallization, leading to formation of fine equiaxed grains near grain boundaries, was observed in the specimens deformed at 1073 and 1273 K and completed dynamic recrystallization was observed at 1473 K.

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Microstructure and Elevated Temperature Properties of a Refractory TaNbHfZrTi Alloy

Crack tip and associated domain integrals from momentum and energy balance

Cleavage, dislocation emission, and shielding for cracks under general loading

Cottrell's theory of stable growth of cleavage microcracks is critically assessed for mild steels below the embrittlement transition temperature. The theory is shown to correspond to experiments if one abandons the assumption that the number of crack dislocations is equal to the number of piled-up dislocations at the stress considered. Reasons are presented why the equation for dislocation pile-ups should not be applied to the growth of microcracks. We replace it by the experimental fact that the unstable crack length amounts to a few grain diameters. Then the idea of stable microcrack growth proves consistent with experimental results.

Critical assessment of the theory of brittle fracture

Two mechanisms for cavity nucleation are described below, namely, first the rupturing of atomic bonds by high local stresses, especially across grain boundaries or other interfaces, and second the condensation of atomic vacancies.

Nucleation of Creep Cavities/Basic Theories

Creep Crack Initiation and Growth

As was pointed out in Section 5.7, cavities usually nucleate continuously over substantial fractions of the creep rupture life of metals and engineering alloys. Attempts to calculate the rupture lifetime must take this fact into account.

The Cavity Size Distribution Function for Continuous Cavity Nucleation. Rupture Lifetimes and Density Changes

Rupture lifetimes of engineering alloys are generally much greater than one would expect from the rate of diffusive cavity growth. Motivated by this general observation, Dyson (1976, 1979) proposed his constrained cavity growth model, which is explained next.

Hermann Riedel

Papers

Critical assessment of the theory of brittle fracture

Nucleation of Creep Cavities/Basic Theories

Creep Crack Initiation and Growth

The Cavity Size Distribution Function for Continuous Cavity Nucleation. Rupture Lifetimes and Density Changes

Constrained Diffusive Cavitation of Grain Boundaries