Micro-scale energy dissipation mechanisms during dynamic fracture in natural polyphase ceramic blocks

The dynamic fracture of natural polyphase ceramic (granite) blocks by high-speed impact at 207 m/s, 420 m/s and 537 m/s has been investigated. An electromagnetic railgun was used as the launch system. Results reveal that the number of fragments increases substantially, and the dominant length scale in their probability distributions decreases, as the impact energy is increased. Micro-scale studies of the fracture surfaces reveals evidence of localized temperatures in excess of 2000 K brought on by frictional melting via fracturing and slip along grain boundaries in orthoclase and plagioclase, and via transgranular fracture (micro-cracking) in quartz. The formation of SiO₂- and TiO₂-rich spheroids on fracture surfaces indicates that temperatures in excess of 3500 K are reached during fracture.     

An acoustic-emission characterization of the failure modes in polymer-composite materials

A new methodology for the analysis of failure modes in composite materials by means of acoustic emission techniques has been developed. A single-carbon-fiber composite based on a polyester matrix, has been used as a simple model. The occurrence of fiber-breakage during tensile loading tests has been observed by a polarized light microscope and concurrently detected by a resonant acoustic probe. The resonant probe has been used as a trigger for the reading of fiber failure events. Single acoustic emission events from a wide-band probe has been recorded for FFT Analysis. The single-fiber specimen, having a unique failure mode, has advantages for the standardization of AE techniques for the quantitative analysis of failures in polymer-composite materials.

The same procedure can be exploited to investigate other failure modes namely, fiber matrix solidus debonding and matrix cracking.     

冲击载荷作用下岩石破碎数值模拟及试验研究

运用数值模拟方法研究了冲击载荷作用下的岩石微观结构特性变化,通过对岩石内部应力分布及裂纹分布图可以得出冲击载荷破岩时岩石内部在垂直方向产生一个拉应力区和一个压应力区,刀具下方的拉应力最大;中间裂纹扩展速度比径向和侧向裂纹都要快,裂纹面呈三角形状。在多功能试验装置上对花岗岩进行冲击载荷破岩试验,试验结果表明:单纯提高冲击载荷对破岩效果不会有很大的提高,存在一个最佳破岩冲击能(63J)。     

"Leo Rangell and I: Where do we differ?" Response to Dr. Wallerstein: Part I.

Responds to a commentary by R. Wallerstein (see record 2007-10890-011) on the present author's original article (see record 2006-05420-002) regarding the evolution of psychoanalytic theory. I do not believe that misunderstanding or misrepresentation has played a part in these differences. What I think has been at play for almost 20 years has been a difference in outlook on scientific and social issues, and in our interpretations of the historical course of events affecting psychoanalytic theory. These are reversing in recent years, which I welcome. No objective events have taken place to account for these changes, only subjective developments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An efficient fluid-solid coupled finite element scheme for weapon fragmentation simulations

An efficient finite element (FE) scheme to deal with a class of coupled fluid-solid problems is presented. The main ingredients of such methodology are: an accurate Q1/P0 solid element (trilinear in velocities and constant piecewise-discontinuous pressures); a large deformation plasticity model; an algorithm to deal with material failure, cracking propagation and fragment formation; and a fragment rigidization methodology to avoid the possible numerical instabilities that may produce pieces of material flying away from the main solid body. All the mentioned schemes have been fully parallelized and coupled using a loose-embedded procedure with a well-established and validated computational fluid dynamics (CFD) code (FEFLO). A CSD and a CFD/CSD coupled case are presented and analyzed.     

Tools for implementing network protocols

This paper describes two software tools—a message manager and a map manager—used to implement network protocols. The tools are provided as part of the x-kernel, an operating system kernel designed to support the construction and composition of protocols. For each tool, we briefly motivate the network task that needs to be done, give a high-level specification of the tool, outline the algorithms and data structures used to implement the tool and give concrete examples of how the tool is used to implement real protocols. We also demonstrate how the tools, even though they are designed for general use, perform efficiently.     

Patterns of species richness and introduced species in native freshwater fish faunas of a Mediterranean‐type basin: the Guadiana River (southwest Iberian Peninsula)

In this study, we analysed the factors affecting species richness and introduced species component patterns in native fish faunas of 30 streams of the Middle Basin of the Guadiana River. From a principal component analysis and a stepwise multiple regression analysis performed on a data matrix composed of ten hydrological and biotic variables, we showed that: (1) fish species richness increased with stream length and watershed area, (2) the number of native species in a stream declined as channelizations and river regulation (constructions of dams) are higher, whereas introduced species increased in the same way, (3) the two main negative factors affecting native ichthyofaunas affected dissimilar ecological areas: channelizations, which depend on land‐use intensity of floodplain, mainly occurred in lower reaches of streams, but construction of dams mainly took place in upper sections of rivers, (4) the length of the remaining well‐preserved reaches in a stream appeared to be the only factor accurately predicting native fish species richness, and (5) native fish faunas of small isolated streams are more vulnerable to habitat alteration than those of large streams. Both isolation and fragmentation of populations were recorded, so the conservation status of native and highly endemic fish fauna of the study area is extreme. Protection of the few still extant, well‐preserved small streams and upper reaches, habitat restoration of channeled areas, and inclusion of the need for native fish fauna conservation in long‐term public planning of water use become a priority. Fish communities appear to be a sensitive indicator of biological monitoring to assess environmental degradation. Copyright © 2001 John Wiley & Sons, Ltd.     

Model for the Atmospheric Fragmentation and Scattering of a Small Celestial Body

This paper considers the interaction of a small celestial body with a planetary atmosphere, which is treated as a two-stage process: the first stage is the fragmentation of the parental body (a model for this stage was developed by the authors) and the second stage involves breakup and scattering of the fragments. A model for the second stage is proposed in which the breakup is treated as a two-phase process of macrodisplacement of the fragments resulting from the fracture of the parental body. In the first phase there is accelerated rotation of the fragments around their centers of mass with preservation of contact between them. By the moment the contact ceases, they acquire a transverse velocity and there comes the second phase — the dispersion of the fragments, which ends with their scattering on the ground. A feature of this model is that the breakup occurs by an aerodynamic mechanism. In an analysis of the first phase of breakup, a system of differential equations for the kinetostatics of the fragments is formulated. Calculations are performed using as an example the atmospheric breakup of the Sikhote Alin meteoroid and the scattering of its fragments on the ground. It is shown that along with the numerical method for solving the system, an approximate analytical method is also possible. Calculation results for both methods are close and are in good agreement with observations of the indicated phenomenon.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 3, pp. 121–132, May–June, 2005.     

Instability and fragmentation of expanding liquid systems

This analysis pursues the underlying physics governing the expansion, dispersal and breakup of a thin walled steel right circular cylinder filled with liquid after being impacted by a high velocity aluminum sphere. The impact generates a radially expanding coherent thin shell of liquid which stays together to at least a diameter 8 times that of the original cylinder. An instability criterion is proposed and developed based on the opposing forces of stabilizing inertial pressures and destabilizing viscous resistance. This criterion is compared to test data where possible in order to ascertain its ability to predict liquid breakup of the shell. The breakup theory developed here predicts the extensive expansion of the unthickened liquid prior to fragmentation as observed in the experiments. This result lends some credence to the underlying physics pursued here and its ability to predict the onset of liquid fragmentation.