1,721,247 research outputs found
Telithromycin and quinupristin-dalfopristin resistance in clinical isolates of Streptococcus pyogenes: SMART Program 2001 data
No full textNumerical analysis of three-dimensional extrusion of arbitrarily shaped sections by the method of weighted residuals
No full textFinite element analysis of steady-state three-dimensional extrusion of sections through curved dies
No full textA finite element analysis is made for steady-state three-dimensional extrusion of non-circular sections such as elliptic and clover-leaf sections through curved dies. In treating the incompressibility, the penalty constraint method, based on the rigid-plastic material model, is used. The initial guess for the initial velocity field is based on that of general upper-bound solutions for extrusion of arbitrarily shaped sections from round billets. Finite element computations are carried out for extrusion of elliptic and clover-leaf sections, but the present analysis can be further applied to general non-circular sections. The work-hardening effect is considered by integrating the effective strain rate along each stream line through interpolation by the least squares method. Experiments are carried out at room temperature and the experimental results are compared with numerical results in flow pattern and strain distribution. It is thus shown that the proposed numerical method is effective for detailed and reliable analysis of steady-state three-dimensional extrusion. © 1989
An upper-bound solution for axisymmetric extrusion of composite rods through curved dies
No full textThe study is concerned with an analysis of forward extrusion of composite rods through curved dies. A kinematically admissible velocity field is derived by assuming proper streamlines and applying the flow function concept to each material region of plastic deformation. Two kinds of flow functions are chosen in order to compare the effect of the choice of the flow functions. The effect of work-hardening is incorporated approximately by calculating the strains at the exit of both materials. The upper-bound method is then employed to determine the extrusion pressure for various process variables. The experiments are carried out with commercially pure aluminum and copper billets for various reductions of area and cone angles at room temperature. The experimental results are then compared with the theoretical calculations. The comparison shows that the second-order flow function is in better agreement with the experimental observation both in extrusion loads and in deforming regions
ANALYSIS OF CENTER-SHIFTED BACKWARD EXTRUSION OF ECCENTRIC TUBES USING ROUND PUNCHES
No full textAn analytical method is proposed for analyzing center-shifted backward extrusion (or piercing) of eccentric tubes from circular billets. A kinematically admissible velocity field is derived to formulate an upper-bound solution using the velocity-transformed central-flow model. The configuration of the deforming boundary surfaces is determined by minimizing the extrusion power with respect to some chosen parameters. Two kinds of functions describing the deformation boundary are compared and discussed. Aluminum is used as the working material in the experiments and the work-hardening effect is taken into consideration. The computed results are compared with the experimental results for different center-shift values (eccentricity) of the punch. It is shown that the theoretical predictions for extrusion load give good upper-bounds when compared with the experimental results
Numerical analysis of three-dimensional extrusion of elliptic sections by the method of weighted residuals
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