The Mechanics of Indentation Induced Lateral Cracking

The mechanics governing the lateral cracks that form when a hard object plastically penetrates a ceramic is presented. The roles of indentation load, penetration depth, and work of indentation are all highlighted, as are the influences of the mechanical properties of the material. A closed form solution for cracking induced by expansion of a two-dimensional cavity is used to bring out essential features related to parametric dependence and scaling. The three-dimensional axisymmetric problem for an annular crack driven by a rigid spherical or conical indenter is solved using numerical methods. The region of highest tensile stress is identified corresponding to the location where a crack is most likely to nucleate. This location coincides with the depth below the surface where the crack will expand parallel to the surface under mode I conditions. The solutions have been substantiated by comparison with measurements of the cracks that form upon Vickers indentation. The basic formula for the crack radius has been used to predict trends in cracking upon static penetration and impact by a projectile. In both cases, the extent of the cracking is substantially diminished by increasing the toughness of the material. The yield strength has a much smaller effect. The cracks caused by penetration and the volume removed per impact both decrease marginally at higher yield strength.     

Gas leakage rate through reinforced concrete shear walls: Numerical study

Unlined reinforced concrete shear walls are often used as ‘tertiary boundaries’ in the United States Department of Energy (DOE) to house dangerous gases. An unanticipated event, such as an earthquake, may cause gases stored inside the walls to disperse into the environment resulting in excess pollution. To address this concern, in this paper, a methodology to numerically predict the gas leakage rate through these shear walls under lateral loading conditions is proposed. This methodology involves finite element and flow rate analysis. Strain distributions are obtained from the finite element analysis, and then used to simulate the crack characteristics on the concrete specimen. The flow rate through the damaged concrete specimen is then estimated using flow rate formulas available from the literature. Results from an experimental specimen are used to evaluate the methodology, and particularly its robustness in the flow rate estimation.     

Annoucement of a Round Robin on the Analysis of the Peel Test

There is some controversy over the analysis of the peel test when there is significant plastic deformation. To resolve this controversy a round robin on its analysis is announced contributions to which are invited. Details are given of test cases to be analysed.     

Parameter Estimation in Finite Element Simulations of Rayleigh Waves

Spectral analysis of surface waves measurements are used to develop subsurface soil profiles or as a tool to delineate abandoned crown pillar structures. Finite element modeling of Rayleigh waves has practical application in simulating SASW measurements. Developing a reliable and accurate finite element model to simulate Rayleigh waves requires the proper mesh dimensions and attenuation parameters. This research proposes a new simplified methodology for quantifying mesh dispersion effects. In addition, methods of verifying damping ratios for numerical simulations are presented. The evaluation of an array of nodal displacements in the frequency–wave-number domain effectively illustrates mesh dispersion effects and the presence of parasitic modes of vibration. Calculations of damping ratio show that mass and stiffness damping parameters are valid within a specified frequency bandwidth. The new techniques are tested for a half-space model; however, they can be used for the analysis of layered media. In addition, equations are given for the calculation of linear Rayleigh damping. These equations satisfy the conditions of an average damping with minimum variance within the frequency bandwidth of interest.     

The x-kernel: a platform for accessing internet resources

x-kernel is an experimental operating system for personal workstations that allows uniform access to resources throughout a nationwide internet: an interconnection of networks similar to the TCP/IP internet. This network is also called the National Research and Education Network (NREN). The x-kernel supports a library of protocols, and it accesses different resources with different protocol combinations. In addition, two user-level systems that give users an integrated and uniform interface to resources have been built on top of the x-kernel. These two systems-a file system and a command interpreter-hide differences among the underlying protocols     

Free Radical Chemistry. Part 9.1 Approaches to Fluorinated Polyethers—Model Compound Studies

Using peroxide, γ-, and UV-irradiation, free radical addition reactions of hexafluoropropene to diethers and to 18-crown-6 have been investigated and mono-, di-, and poly-adducts have been obtained. Factors influencing these additions, especially polar characteristics of intermediate radicals, have been elucidated. Adducts of 18-crown-6 retain a capacity to complex to alkali-metal ions.     

The three-dimensional locomotor dynamics of African (Loxodonta africana) and Asian (Elephas maximus) elephants reveal a smooth gait transition at moderate speed

We examined whether elephants shift to using bouncing (i.e. running) mechanics at any speed. To do this, we measured the three-dimensional centre of mass (CM) motions and torso rotations of African and Asian elephants using a novel multisensor method. Hundreds of continuous stride cycles were recorded in the field. African and Asian elephants moved very similarly. Near the mechanically and metabolically optimal speed (a Froude number (Fr) of 0.09), an inverted pendulum mechanism predominated. With increasing speed, the locomotor dynamics quickly but continuously became less like vaulting and more like bouncing. Our mechanical energy analysis of the CM suggests that at a surprisingly slow speed (approx. 2.2 m s(-1), Fr 0.25), the hindlimbs exhibited bouncing, not vaulting, mechanics during weight support. We infer that a gait transition happens at this relatively slow speed: elephants begin using their compliant hindlimbs like pogo sticks to some extent to drive the body, bouncing over their relatively stiff, vaulting forelimbs. Hence, they are not as rigid limbed as typically characterized for graviportal animals, and use regular walking as well as at least one form of running gait.     

What Makes a Good City in Pre-schoolers' Eyes? Findings from Participatory Planning Projects in Australia and New Zealand

Pre-schooler's voices are absent in urban planning and design. With the possible exception of playgrounds, there is limited knowledge about their experiences in and expectations for urban environments. This paper discusses pre-schoolers' aspirations and desires for aesthetic and accessible green spaces as well as social and physical connectedness. Although this age range has so far been limited in its ability to inform policy and decision-makers, it is argued that pre-schoolers have the capacity and capability of making valuable contributions to design. In the eyes of pre-schoolers, creating a good city means to live in a safe place full of diverse destinations in which they can become streetwise and socialize as part of society.