J. Appl. Cryst.の発刊に際して

https://material.karlov.mff.cuni.cz/people/janecek/studenti/FyzMetNano/Estrin_AM61_2013_782.pdf

Extreme grain refinement by severe plastic deformation: A wealth of challenging science

The purpose of this review is to discuss the development and the state of the art in dynamic testing techniques and dynamic mechanical behaviour of rock materials. The review begins by briefly introducing the history of rock dynamics and explaining the significance of studying these issues. Loading techniques commonly used for both intermediate and high strain rate tests and measurement techniques for dynamic stress and deformation are critically assessed in Sects. 2 and 3. In Sect. 4, methods of dynamic testing and estimation to obtain stress–strain curves at high strain rate are summarized, followed by an in-depth description of various dynamic mechanical properties (e.g. uniaxial and triaxial compressive strength, tensile strength, shear strength and fracture toughness) and corresponding fracture behaviour. Some influencing rock structural features (i.e. microstructure, size and shape) and testing conditions (i.e. confining pressure, temperature and water saturation) are considered, ending with some popular semi-empirical rate-dependent equations for the enhancement of dynamic mechanical properties. Section 5 discusses physical mechanisms of strain rate effects. Section 6 describes phenomenological and mechanically based rate-dependent constitutive models established from the knowledge of the stress–strain behaviour and physical mechanisms. Section 7 presents dynamic fracture criteria for quasi-brittle materials. Finally, a brief summary and some aspects of prospective research are presented.

/pdf/a-review-of-dynamic-experimental-techniques-and-mechanical-2kstp2wfg4.pdf

A Review of Dynamic Experimental Techniques and Mechanical Behaviour of Rock Materials

Review of experimental techniques for high rate deformation and shock studies

Failure of metals I : brittle and ductile fracture

The high strain rate dependence of the flow stress of metals and alloys is described from a dislocation mechanics viewpoint over a range beginning from conventional tension/compression testing through split Hopkinson pressure bar (SHPB) measurements to Charpy pendulum and Taylor solid cylinder impact tests and shock loading or isentropic compression experiment (ICE) results. Single crystal and polycrystal measurements are referenced in relation to influences of the crystal lattice structures and nanopolycrystal material behaviours. For body centred cubic (bcc) metals, the strain rate sensitivity (SRS) is in the yield stress dependence as compared with the face centred cubic (fcc) case of being in the strain hardening property. An important consequence is that an opposite ductility influence occurs for the tensile maximum load point strain that decreases with strain rate for the bcc case and increases with strain rate for the fcc case. Different hexagonal close packed (hcp) metals are shown to foll...

/pdf/high-strain-rate-properties-of-metals-and-alloys-1vmx3spvaq.pdf

High strain rate properties of metals and alloys

This paper describes the response of explosives to stress and impact and in particular the mechanisms of ‘ hot-spot production. Samples in the form of single crystals, powder layers, pressed pellets, gels, polymer bonded explosives (PBXS) and propellants have been studied. Techniques used include a drop-weight facility with transparent anvils which allows photography at microsecond framing intervals, an instrumented drop-weight machine, a miniaturized Hopkinson bar system for high strain rate property measurement, laser speckle for studying the deformation and fracture of PBXS, an automated system for analysing speckle patterns and heat sensitive film for recording the positions and temperatures of hot spots. Polishing and staining methods have been developed to observe the microstructure of PBXS and failure during quasi-static loading. Ignition, when it occurred, took place at local hot-spot sites. Evidence is discussed for a variety of ignition mechanisms including adiabatic shear of the explosive, adiabatic heating of trapped gases during cavity collapse, viscous flow, friction, fracture and shear of added particles and triboluminescent discharge.

Hot-spot ignition mechanisms for explosives and propellants

The high strain rate compressive behaviour of polycarbonate and polyvinylidene difluoride

Polymers are increasingly being used in applications where they are rapidly deformed. However, compared with metals, relatively few studies of their mechanical properties at high rates of strain have been published. This paper describes an investigation of the rapid deformation behaviour in compression of a number of widely used polymeric materials. The necessity of properly characterizing polymers is discussed, as the variation of commercial grades bearing the same name is considerable, and furthermore these materials are much more susceptible to change during storage than say metals. The importance of thermal properties to rapid, and hence adiabatic, deformation is pointed out, and tables of such properties are presented. Extensive use was made of high-speed photography (interframe time 7 $\mu $s) to study qualitatively the behaviour of solid discs of polymers at strain rates of 2.5 $\times $ 10$^{3}$ s$^{-1}$. The framing speed was sufficiently fast to capture fracture initiation and subsequent failure of all the polymers studied, including polycarbonate (PC), which fails in an almost explosive manner. The darkening of heat-sensitive film in contact with deforming discs was also investigated. Quantitatively, this technique was used to check the applicability of Avitzur's analysis (Avitzur (Israel J. Technol. 2, 295-304 (1964)) of a deforming annulus to polymers. Agreement was found to be good and hence friction could be measured during deformation at high rates of strain for the first time. Studies were also carried out to determine the best lubricant for rapid compressive testing. Petroleum jelly was found to reduce the friction closest to zero. An optically identical system was set up in an Instron mechanical testing machine both to perform friction studies and to explore deviation from incompressible behaviour. Agreement with Avitzur's analysis was found to be poorer, and no lubricant was found to reduce friction below about 3-4%. PC, with a very high value of frictional stress, showed evidence of a change in volume. Allowances were made for the elastic indentation of the anvils. Higher strain rates were achieved by using an instrumented drop-weight machine and a direct impact Kolsky bar, both developed in this laboratory. Care was taken to eliminate sources of error, including friction and calibration errors. The strain rate sensitivity of the polymers ranged from 5-15 MPa per decade of strain rate. However, most showed some softening as the strain rate was raised from 10$^{3}$ to 10$^{4}$ s$^{-1}$, the exceptions being polybutylene teraphthalate (PBT) and polyvinylidene difluoride (PVDF).

Stephen M. Walley

Papers

Review of experimental techniques for high rate deformation and shock studies

High strain rate properties of metals and alloys

Hot-spot ignition mechanisms for explosives and propellants

The high strain rate compressive behaviour of polycarbonate and polyvinylidene difluoride

A study of the rapid deformation behaviour of a range of polymers