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

Creep Crack Growth

The extension of a macroscopic crack is analysed based on the crack-tip stress field in a creeping body and on models for micro-void growth. The growth rate of the macro-crack depends on the applied load, which is expressed through the path-independent integral C*. At low levels of C*, i.e., small crack growth rates, the void growth mechanism by diffusion prevails, whereas at high C*-values the voids grow mainly by creep.

The Extension of a Macroscopic Crack at Elevated Temperature by the Growth and Coalescence of Microvoids

Life prediction methods for constrained grain boundary cavitation

Two different constitutive models are employed to describe creep crack growth under small-scale creep conditions theoretically. The first model combines elastic/nonlinear viscous deformation fields \(\mathop \varepsilon \limits^ \cdot = \mathop \sigma \limits^ \cdot /E + A{\sigma ^n}\) with a critical-strain criterion, e = e c to be satisfied at a structural distance x c , ahead of the crack. The deformation fields are characterized by three singular fields — the remote elastic field, the HRR field in the creep zone, if one exists, and the Hui-Riedel (HR) field near the growing crack tip. At small stress intensity factors, crack growth is found to become irregular and to tend to instabilities. This is a consequence of the properties of the HR field.

Creep crack growth under small-scale creep conditions

The time-dependent deformation and cracking behavior of the quenched and tempered steel 15 NiCuMoNb 5 was investigated in the temperature range 20°C to 400°C. Fracture mechanics tests were carried out under various loading conditions including load-hold times of up to three weeks. The time-dependent crack growth can be described by the crack resistance (JR-) curve. Only above 300°C, the JR-curves obtained from constant-load tests start to deviate substantially from constant-displacement-rate tests. In this temperature range, the Ct-parameter, which has been developed for creep crack growth testing, can be used to describe crack growth rates. For practical purposes, it is important to note that hold-time effects reduce the load-bearing capacity of cracked specimens by less than 10 percent for the present material and testing conditions.

Hermann Riedel

Papers

Creep Crack Growth

The Extension of a Macroscopic Crack at Elevated Temperature by the Growth and Coalescence of Microvoids

Life prediction methods for constrained grain boundary cavitation

Creep crack growth under small-scale creep conditions

Time-dependent deformation and fracture of steel between 20°C and 400°C