Plastic collapse of pipe bends under combined internal pressure and in-plane bending

Plastic collapse of pipe bends with attached straight pipes under combined internal pressure and in-plane closing moment is investigated by elastic–plastic finite element analysis. Three load histories are investigated, proportional loading, sequential pressure–moment loading and sequential moment–pressure loading. Three categories of ductile failure load are defined: limit load, plastic load (with associated criteria of collapse) and instability loads. The results show that theoretical limit analysis is not conservative for all the load combinations considered. The calculated plastic load is dependent on the plastic collapse criteria used. The plastic instability load gives an objective measure of failure and accounts for the effects of large deformations. The proportional and pressure–moment load cases exhibit significant geometric strengthening, whereas the moment–pressure load case exhibits significant geometric weakening

Parametric finite-element studies on the effect of tool shape in friction stir welding

The success of the Friction Stir Welding (FSW) process, and the weld quality produced, depends significantly on the design of the welding tool. In this paper the effect of variation in various tool geometry parameters on FSW process outcomes, during the plunge stage, were investigated. Specifically the tool shoulder surface angle and the ratio of the shoulder radius to pin radius on tool reaction force, tool torque, heat generation, temperature distribution and size of the weld zone were investigated. The studies were carried out numerically using the finite element method. The welding process used AA2024 aluminium alloy plates with a thickness of 3 mm. It was found that, in plunge stage, the larger the pin radius the higher force and torque the tool experiences and the greater heat generated. It is also found that the shoulder angle has very little effect on energy dissipation as well as little effect on temperature distribution

Effect of spin relaxations on the spin mixing conductances for a bilayer structure

The spin current can result in a spin-transfer torque in the normal-metal(NM)|ferromagnetic-insulator(FMI) or normal-metal(NM)|ferromagnetic-metal(FMM) bilayer. In the earlier study on this issue, the spin relaxations were ignored or introduced phenomenologically. In this paper, considering the FMM or FMI with spin relaxations described by a non-Hermitian Hamiltonian, we derive an effective spin-transfer torque and an effective spin mixing conductance in the non-Hermitian bilayer. The dependence of the effective spin mixing conductance on the system parameters (such as insulating gap, \textit{s-d} coupling, and layer thickness) as well as the relations between the real part and the imaginary part of the effective spin mixing conductance are given and discussed. We find that the effective spin mixing conductance can be enhanced in the non-Hermitian system. This provides us with the possibility to enhance the spin mixing conductance

Correlated Spectral and Temporal Variability in the High-Energy Emission from Blazars

Blazar flare data show energy-dependent lags and correlated variability between optical/X-ray and GeV-TeV energies, and follow characteristic trajectories when plotted in the spectral-index/flux plane. This behavior is qualitatively explained if nonthermal electrons are injected over a finite time interval in the comoving plasma frame and cool by radiative processes. Numerical results are presented which show the importance of the effects of synchrotron self-Compton cooling and plasmoid deceleration. The use of INTEGRAL to advance our understanding of these systems is discussed.Comment: 8 pages, 5 figures, uses epsf.sty, rotate.sty Invited paper in "The Extreme Universe," 3rd INTEGRAL Workshop, 14-18 September 1998, Taorimina, Ital

When Both Transmitting and Receiving Energies Matter: An Application of Network Coding in Wireless Body Area Networks

A network coding scheme for practical implementations of wireless body area networks is presented, with the objective of providing reliability under low-energy constraints. We propose a simple network layer protocol for star networks, adapting redundancy based on both transmission and reception energies for data and control packets, as well as channel conditions. Our numerical results show that even for small networks, the amount of energy reduction achievable can range from 29% to 87%, as the receiving energy per control packet increases from equal to much larger than the transmitting energy per data packet. The achievable gains increase as a) more nodes are added to the network, and/or b) the channels seen by different sensor nodes become more asymmetric.Comment: 10 pages, 7 figures, submitted to the NC-Pro Workshop at IFIP Networking Conference 2011, and to appear in the conference proceedings, published by Springer-Verlag, in the Lecture Notes in Computer Science (LNCS) serie