Brittle fracture of solids caused by intense electron beams

In the mid 1960s, powerful pulse electron beam accelerators having a voltage of some millions of volts were invented and later used to fracture various materials. Experimental data analysis allowed discovery of a new mode of fracture in several ductile crystals caused by a specific energy supply to the crack tip. The mode differs from well known thermomechanical modes of fracture caused by the “ heat-thermostress-crack ” mechanism. This new mode is called the electron fracture mode (EFM). It is characterized by the following three special features, (i) Initial macrocracks in a specimen do not affect the threshold of fracture; that is, the value of the beam intensity at which the specimen breaks, (ii) The fracture of different materials, which can be very ductile at usual mechanical loads, occurs in a brittle manner; that is, the specimen usually splits by a crack without any residual deformation, (iii) The splitting cracks propagate with supersonic velocities. These data are controversial from the point of view of common fracture mechanics and, hence, they cannot be understood or explained from the traditional position.The purpose of the present study is to create a simple practical model of the EFM. The basic viewpoint can be briefly summarized as follows: during irradiation of a solid by a high intensity electron beam, some solid plasma clots are formed and act as “ blades ” or “ wedges,” cutting the crystalline specimen.In the Introduction, experimental data on the EFM are analyzed and discussed, while the peculiarities of the EFM are specified. As a result, it is concluded that the processes caused by the EFM are unusual for the common concepts of fracture mechanics. In Section 2 the invariant Γ-integrals of an electromagnetic deformable medium are modified for supersonic singularities. The basic model and some problems serving to explain and describe the EFM are formulated. In Section 3, the relativistic electron interactions in beams are considered. Using Γ-integrals, we derive the law of the interaction of two moving relativistic charges; that is, the generalized Coulomb's law for relativistic charges. In particular, when two relativistic electrons, e, move with the same velocity, v, one behind the other along a rectilinear trajectory, the force, F, acting upon the rear electron is equal to: where R is the distance between the electrons, c is the speed of light in the vacuum, and a is the phase-speed of light in a medium having electromagnetic constants, μ, , and '. It appears that two electrons moving faster than the phase-speed of light attract one to the other, as distinct from the common Coulomb law. Hence, the beams of such relativistic electrons tend to self-pack and self-compress. The latter problem is studied using a periodic chain model of the electron beam. In Section 4, the dynamic elastic problem of supersonic cutting by a thin wedge is formulated and solved, and the drag force is calculated. In Section 5, the problem of deceleration of the moving wedge is solved in quasi-steady approximation. The length of a resulting cut, that is, the final crack, is determined. Some applications of the analytical solutions are given. In Section 6, the theoretical results are analyzed and compared with experimental results. The role of relativistic electrons is estimated and some parameters of solid-state electron plasma clots are defined. In the Conclusion, the necessity of further study of this mysterious phenomenon is emphasized.     

Transparent conducting indium oxide thin films grown by low-temperature metal organic chemical vapor deposition

We have grown indium oxide thin films on silicon substrates at low temperature by metal organic chemical vapor deposition. Polycrystalline film growth could only be obtained at temperatures below 400 °C. Above 400 °C, metallic indium deposition dominated. We have investigated the effect of substrate temperature and reactor pressure on the film growth and structural properties in the range of 250-350 °C and 5 ^? 10³-4 ^? 10⁴ Pa. The film grown at 300 °C exhibited a resistivity of about 3.6 × 10^− 3 Ω cm and a maximal optical transmittance of more than 95% in the visible range. The film showed an optical band gap of about 3.6 eV.     

Fracture Waves Revisited

Self-sustaining fracture waves hypothesized by Galin and Cherepanov (1966) have been observed in shock-compressed glasses and in Prince Rupert’s drops, but their speed did not correspond to the predicted value. This controversy is addressed in the present note. We now assume that this speed is equal to the local velocity of sound in the particulate material just behind the wave front, and show that, then, it is in a reasonable agreement with test data. The specific heat spent on the self-sustaining fracture wave in soda lime glass is estimated to be 1 to 20 J/g for moderately high pressures.     

Rayleighons

In the present paper, the idea is advanced that super-deep penetration of some microparticles into various metal targets observed by hypervelocity impact represents the self-propagation of a specific internal solitary wave forming a cavity with the projectile moving inside without drag. This solitary wave is named the rayleighon because it propagates with the Rayleigh speed. The cavity of a rayleighon is shown to be free of tractions. Rayleighon energy is proven to be conserved because there is no absorbtion or emission of energy (as distinct from cracks and dislocations absorbing or emanating energy). A family of rayleighons that have been computed are provided in this paper.     

Rose Petal Tea as an Antioxidant-rich Beverage: Cultivar Effects

ABSTRACT Twelve rose cultivars were selected by field tasting as potential sources of edible flowers. Hot water infusions (teas) of air‐dried petals of these cultivars were assayed for antioxidant activity, total phenols, and total anthocyanins contents. Their composition was analyzed by high‐performance liquid chromatography (HPLC). Green tea was tested in parallel as a reference antioxidant‐rich beverage. Rose petal teas from different cultivars exhibited scavenging capacity toward 2,2′‐azino‐bis‐(3‐ethylbenzothiazoline)‐6‐sulfonate cation radical (ABTS+) ranging between 712.7 and 1770.7 μM Trolox equivalents (TE) per gram of dry petals, as compared with 1227.6 μM TE/g dry weight in the green tea. The range of total phenols content in rose teas was 50.7 to 119.5 mg gallic acid equivalents (GAE) per gram of dry matter, as compared with 62.1 mg GAE/g dry weight in the green tea. The rose teas were rich in free gallic acid. The highest values of antioxidant activity, total phenols, and gallic acid contents were found in the cultivars San Francisco, Katharina Zeimet, and Mercedes and in the essential‐oil‐bearing rose Rosa damascena. The correlation coefficients between antioxidant activity, on the 1 hand, and the contents of total phenols and of gallic acid in various rose cultivars, on the other hand, were 0.79 and 0.81, respectively. No clear relationship between anthocyanin level and radical‐scavenging activity was revealed. Teas from different rose cultivars significantly differed in their sensory properties. It was concluded that dried rose petals may be used for preparing antioxidant‐rich caffeine‐free beverages, either separately or in combination with other herbal materials.     

Fractal fracture mechanics—A review

The revolution in geometry, which has recently created the notion of the fractional dimension of real world bodies and has formed fractal geometry, has substantially influenced fracture science. An experimentally measured crack in real materials has appeared to be substantially a fractal, that is, a geometrical object of fractional dimension. In the present paper, an attempt has been undertaken to provide an account of some achievements in this area, herein called “Fractal Fracture Mechanics”.