Pressure and friction dependent mechanical strength – cracks and plastic flow

The mechanical properties of a polymer composite plastic bonded explosive, EDC37, have been investigated as a function of hydrostatic confining pressure between 0.1 and 138 MPa. The results indicate different failure processes in two pressure ranges, a low pressure range between about 0.1 and 7 MPa and a higher pressure range between about 7 and 138 MPa. In the low pressure range slow crack processes are important in failure while in the higher pressure range plastic flow dominates. The pressure dependence of the compressive strength in the low pressure range is attributed to coulomb friction between surfaces of closed shear cracks and from the observed linear increase of the strength with pressure and the angle of the fracture plane a friction coefficient is obtained. Friction coefficients can also be obtained from the ratio of the compressive to tensile strength and directly from the above angle. The friction coefficients obtained from these separate observations are in agreement and this is taken as strong evidence for the importance of this friction in determining strength and mechanical failure. These results clearly establish experimentally the role of friction in determining strength with or without applied pressure. An empirical relationship between strength, pressure and strain rate is also obtained for this pressure range and the failure strength of EDC37 is more sensitive to pressure than strain rate.     

Sino-German Workshop on Chemical and Physical Interactions between Particles and Fluids

Hosted by the Institute of Process Engineering, CAS, China, and the Technical University Hamburg-Harburg, Germany, and supported by the Sino-German Science Center in Beijing, the Sino-German Workshop on Chemical and Physical Interactions between Particles and Fluids was held in Beijing, on October 24-31,2004.     

Applied Mathematics and Mechanics

This journal is on applied mathematics and mechanics published in the People's Republic of China. Our editorial committee,headed by Professor Chien Wei-zang,Academician of Chinese Academy of Sciences,President of Shanghai University,and Professor Zhou Zhe-wei,consists of scientists in the fields of applied mathematics and mechanics all over China.     

Applied Mathematics and Mechanics

“Applied Mathematics and Mechanics”is a nation-wide academic periodical wichis jointly edited by90 odd scholars in the fields of mechanics and mathematics inthe People’s Republic of China.prof.chien Wei-zang,president of shanghai Uni-versity of Technology,is the Editor-in-chief.Prof.Yeh Kai-yuan of Lanzhou Uni-versity is the Vice Editor-in-chief.It is sponsored by Chongqing Jiaotong Insti-     

erimental and statistical anal

f tone pattern showed the steady and variable parts in each tone of Changsha(长沙) dialect Moreover, the on-going variations of tone were found from gro     

Intrinsic Geometry and Analysis of Diffusion Processes and L ∞-Variational Problems

The aim of this paper is twofold. First, we obtain a better understanding of the intrinsic distance of diffusion processes. Precisely, (a) for all n ≧ 1, the diffusion matrix A is weak upper semicontinuous on Ω if and only if the intrinsic differential and the local intrinsic distance structures coincide; (b) if n = 1, or if n ≧ 2 and A is weak upper semicontinuous on Ω, the intrinsic distance and differential structures always coincide; (c) if n ≧ 2 and A fails to be weak upper semicontinuous on Ω, the (non-)coincidence of the intrinsic distance and differential structures depend on the geometry of the non-weak-upper-semicontinuity set of A. Second, for an arbitrary diffusion matrix A, we show that the intrinsic distance completely determines the absolute minimizer of the corresponding L ^∞-variational problem, and then obtain the existence and uniqueness for given boundary data. We also give an example of a diffusion matrix A for which there is an absolute minimizer that is not of class C ¹. When A is continuous, we also obtain the linear approximation property of the absolute minimizer.     

The moiré method and the evaluation of principal-moment and stress directions

This paper discusses, in relation to the moiré method as used for the solution of plate bending and two-dimensional stress problems, two graphical techniques for the determination of the directions of principal moments and stresses.The so-called isoclinic method and the point method are described.The application of these new techniques on three different models—a circular disk under diametrically opposite loads and two different circular plates subjected to a lateral load—are fully discussed.The graphically determined principal-stress and moment directions show excellent agreement with analytically determined comparable values.Paper was presented at 1963 SESA Annual Meeting held in Boston, Mass., on November 6–8.     

Poynting and axial force–twist effects in nonlinear elastic mono- and bi-layered cylinders: Torsion,axial and combined loadings

The Poynting effect, in which a cylinder elongates or contracts axially under torsion, is an important nonlinear phenomenon in soft materials. In this paper, analytical solutions are obtained for homogeneous and bi-layered cylinders under torsion, axial and combined loadings, employing second-order elasticity and Lagrangian equilibrium equations. Explicit parameters for judging the sign of the Poynting effect are given. It is found that the effect in a soft composite may be significantly amplified over that in homogeneous materials and that it is strongly influenced by the interface position and by the material configuration in the composite. A coupled axial force–twist effect under combined loading, i.e., the twist of a torsionally loaded cylinder can be affected by the axial loading, is also found. Comparison of the predictions with the torque-tension-twist data for cardiac papillary muscles shows reasonable agreement. The solutions also provide the basis for a mechanistic method of determining third-order elastic constants.     

Shock-Wave–Vortex Interactions: Shock and Vortex Deformations, and Sound Production

In this paper we study the interaction of a shock wave with a cylindrical vortex. The objective of the study is to characterize the shock and vortex deformations and the mechanism of sound generation. The approach relies on the solution of the two-dimensional Euler equations by means of a high order finite volume weighted-ENO scheme. In order to provide some guidance into the analysis we have also developed an acoustic analogy of the problem by formulating a wave equation for the pressure disturbance that is solved analytically by means of Green's functions. A systematic study has been conducted by investigating the effects of vortex intensity and shock strength. Specifically, we have determined the dependence of shock distortion and vortex compression, and its subsequent nutation upon shock and vortex strengths. The acoustic field generated through shock--vortex interactions has been found to evolve in three stages and to exhibit a three sound quadrupolar directivity. In the early stages of the interaction the sound generated due to shock distortion shows a dipolar character, which then changes to a quadrupolar one due to a restoring mechanism that acts during the interaction of the shock with the rear part of the vortex. In the third stage secondary sounds are formed, which also show a quadrupolar directivity. The acoustic analogy applied to weak shock--vortex interactions also confirms the numerically predicted sound generation mechanism. Received 12 July 1999 and accepted 18 November 1999     

Dynamic stiffness characteristics of aero-engine elastic support structure and its effects on rotor systems: mechanism and numerical and experimental studies

The support structure of a rotor system is subject to vibration excitation,which results in the stiffness of the support structure varying with the excitation frequency(i.e., the dynamic stiffness). However, the dynamic stiffness and its effect mechanism have been rarely incorporated in open studies of the rotor system. Therefore, this study theoretically reveals the effect mechanism of dynamic stiffness on the rotor system. Then,the numerical study and experimental verification are conducted on...     

Magnetic nanoparticles and concentrated magnetic nanofluids： Synthesis, properties and some applications

This paper reviews some recent results concerning chemical synthesis of magnetic nanoparticles and preparation of various types of magnetic nanofluids. Structural properties and behaviour in external magnetic field of magnetic nanofluids will be emphasized with relation to their use in leakage-free rotating seals and in biomedical applications.     

The Symplectic Evans Matrix,¶and the Instability of Solitary Waves and Fronts

Hamiltonian evolution equations which are equivariant with respect to the action of a Lie group are models for physical phenomena such as oceanographic flows, optical fibres and atmospheric flows, and such systems often have a wide variety of solitary-wave or front solutions. In this paper, we present a new symplectic framework for analysing the spectral problem associated with the linearization about such solitary waves and fronts. At the heart of the analysis is a multi-symplectic formulation of Hamiltonian partial differential equations where a distinct symplectic structure is assigned for the time and space directions, with a third symplectic structure – with two-form denoted by Ω– associated with a coordinate frame moving at the speed of the wave. This leads to a geometric decomposition and symplectification of the Evans function formulation for the linearization about solitary waves and fronts. We introduce the concept of the symplectic Evans matrix, a matrix consisting of restricted Ω-symplectic forms. By applying Hodge duality to the exterior algebra formulation of the Evans function, we find that the zeros of the Evans function correspond to zeros of the determinant of the symplectic Evans matrix. Based on this formulation, we prove several new properties of the Evans function. Restricting the spectral parameter λ to the real axis, we obtain rigorous results on the derivatives of the Evans function near the origin, based solely on the abstract geometry of the equations, and results for the large |λ| behaviour which use primarily the symplectic structure, but also extend to the non-symplectic case. The Lie group symmetry affects the Evans function by generating zero eigenvalues of large multiplicity in the so-called systems at infinity. We present a new geometric theory which describes precisely how these zero eigenvalues behave under perturbation. By combining all these results, a new rigorous sufficient condition for instability of solitary waves and fronts is obtained. The theory applies to a large class of solitary waves and fronts including waves which are bi-asymptotic to a nonconstant manifold of states as $|x|$ tends to infinity. To illustrate the theory, it is applied to three examples: a Boussinesq model from oceanography, a class of nonlinear Schr?dinger equations from optics and a nonlinear Klein-Gordon equation from atmospheric dynamics. Accepted August 7, 2000 ?Published online January 22, 2001     

Void nucleation and growth in mineral-filled PVC – An experimental and numerical study

The nucleation and growth of voids in mineral-filled PVC have been investigated through experimental and numerical studies. Uniaxial tensile specimens were deformed in tension to different elongation levels and then unloaded. The macroscopic strain fields were recorded by use of digital image correlation. After the test, the microstructure of the deformed specimens was investigated in a scanning electron microscope. It was found that the observed volume strain on the macroscale is related to void growth on the microscale. In addition, finite element simulations were performed on unit cell models representing the microstructure of the material in a simplified manner. The numerical simulations demonstrate macroscopic dilation as a result of void growth. Moreover, the numerical simulations indicate that the experimentally observed stress-softening response of the PVC composite material may result from matrix-particle debonding.     

Synthesis and surface modification of magnetic particles for application in biotechnology and biomedicine

Magnetic particles have numerous applications in biotechnology and biomedicine. In this paper we reviewed the synthesis, surface modification and some applications of magnetic particles with focus on their synthesis and surface modification. Various methods have been developed for the production of magnetic particles （magnetic nanoparticles and magnetic composite particles）. For future application magnetic particles must be modified to obtain stability and surface functional groups. Finally, the application of magnetic particles in magnetic separation, drug delivery, hyperthermia, and magnetic resonance imaging are discussed.     

Energy Dissipation and Regularity for a Coupled Navier–Stokes and Q-Tensor System

We study a complex non-Newtonian fluid that models the flowof nematic liquid crystals. The fluid is described by a system that couples a forced Navier–Stokes system with a parabolic-type system. We prove the existence of global weak solutions in dimensions two and three.We show the existence of a Lyapunov functional for the smooth solutions of the coupled system and use cancellations that allow its existence to prove higher global regularity in dimension two. We also show the weak–strong uniqueness in dimension two.     

Book Review：Bifurcation and Chaos in Engineering by Yushu Chen and Andrew Leung

I was wery impressed by the high mathematical level of this text and reference book.