A statistical strength criterion for low temperature brittle fracture of metals

A statistical approach is presented to strength analysis of metals under conditions of low-temperature embrittlement. The approach involves two categories of defects leading to fracture: primary defects, present in the original structure in the form of microvoids, microcracks, inclusions etc., and secondary defects, formed under load through the action of the dislocational mechanisms involved in initiation of crack nuclei.An arbitrary pattern of primary and secondary defects is considered, on the assumption of approximate stochastic independence. This permits determination of the probability of brittle fracture under any mode of stressing. Development of a major crack is treated as a multistage process, whereby fracture may be considered either as a sequence of violated limit equilibria, or as a discontinuous Markov process. The role of thermal fluctuations in the latter case is demonstrated. As an example, limiting fracture-stress curves are determined for a plane model based on Stroh's mechanism. Results show that the temperature dependence of the fracture stress is governed by the mode of stressing and by the structure of the material.     

Calculating the time-to-rupture of brittle solids in surface-active media

A method of computing the time dependence of strength of brittle solids in surface-active media which do not change the principal mechanism of fracture but only accelerate crack growth is presented. The method is based on applying the Fick law to the surface diffusion of the medium on the free surface of a crack growing in a specimen. Approximate calculation of the time-to-rupture of inorganic glass in air is carried out producing results in good agreement with experimental data.     

The effect of high hydrostatic pressures on the cohesive strength of brittle materials

Experiments have been conducted to determine the fracture threshold for cast iron and steel when subjected to hydrostatic pressures up to 11300 kg/cm². General agreement with a maximum elastic strain theory of failure is found.

---

Zusammenfassung Es wurden Versuche durchgefuehrt zur Bestimmung der Bruchschwelle von Gusseisen and Stahl unter hydrostatischen Drucken his zu 11300 kg/cm²: Allgemeine Uebereinstimmung mit einer Bruchtheorie maximaler elastischer Dehnung wurde gefunden.

---

Résumé Des expériences ont été effectuées pour déterminer le seuil de rupture des fontes et des aciers soumis à des pressions hydrostatiques jusqu' à 11300 kg/cm². Une concordance générale avec la théorie de la tension elastique maximum de rupture a été trouvée.

     

Temperature dependence of the effect of liquid metals on the long-time strength of solid metals

This article describes long-time strength tests carried out at various temperatures on copper in liquid bismuth, a nickel alloy in sodium, and armco iron in zinc. It is shown that experimental data is in good agreement with theoretical concepts about the effect of adsorption, corrosion and diffusion of liquid metals on the properties of solids.     

Rate effect of concrete strength under initial static loading

The dynamic strength enhancement of concrete under different initial static loadings is investigated in this paper. The mechanism of the influence of the inertia effect on the dynamic strength of concrete is discussed first by analyzing a single dimension of freedom system, which shows that the inertia effect only influences the dynamic loading part. The dynamic strength of concrete at initial static loading is calculated assuming a single crack model with consideration of free water viscosity using dynamic fracture mechanics. The dynamic stress intensity factor of the crack under linearly increasing loading on the basis of an initial static loading is achieved. The relationship between the dynamic strength increase factor and the static stress level is obtained. The comparison between the results by the model proposed in this paper and those by experiments in some available references indicates a good agreement.