Papers by Keyword: Upper Bound

Abstract: A metal extrusion was process that extrusion puncture perforate surface of material to throw and flow across outlet of die. This operation was a complex process in extrusion while penetration occurred at same time. This process can be seen in many production operations, like in forming of making portion of metal strip, and forming of extruded portion in a complex fineblanking with extrusion operation. Also exhibit the operation properties and give the method of numerical solution. So increasing load to 610KN with increased friction factor to 0.7 and increased with increasing the reduction ratio and stroke of operation. For the results and mesh distortion, with allocations of strains may be predicted. Analyzing results was submitted of metal extruded may be classified into two zones for the different lineaments deformation. moreover, energy in the zones of deformation may be classified into two parts for their different lineaments of internal zone and contact zone with the die . Fracture location has been found from simulations. Keyword Load, Extrusion, upper bound, numerical solution

Abstract: The kinematic (upper bound) method of limit analysis is a powerful technique for evaluating rigorous bounds on limit loads that are often very close to the true limit load. While generalized computational techniques for two-dimensional (e.g., plane strain) problems are well established, methods applicable to three-dimensional problems are relatively underdeveloped and underutilized, due in large part to the cumbersome nature of the calculations for analytical solutions and the large computation times required for numerical approaches. This paper proposes a simple formulation for three-dimensional limit analysis that considers material obeying the Mohr-Coulomb yield condition and collapse mechanisms consisting of sliding rigid blocks separated by planar velocity discontinuities. A key advantage of the approach is its reliance on a minimal number of unknowns, can dramatically reduce processing time. The paper focuses specifically on tetrahedral blocks, although extension to alternative geometries is straightforward. For an arbitrary but fixed arrangement of blocks, the procedure for computing the unknown block velocities that yield the least upper bound is expressed as a second-order cone programming problem that can be easily solved using widely available optimization codes. The paper concludes with a simple example and remarks regarding extensions of the work.

Abstract: There is a one-to-one relationship between nonnegative matrix pairs and two-colored digraph. With the knowledge of graph theory, by studying the associated directed digraph of a class of special nonnegative matrix pairs, that is a class of two-colored digraphs whose uncolored digraph have 3n-1 vertices and consists of one (3n-1)-cycle and one n-cycle are considered. The exponent and characteristic of extreme two-colored digraphs are given.

Abstract: With the explosive growth of wireless applications, the subscribers’ requirements of QoS (Quality of Service) are increasing as well. In this paper, the upper bound of the tolerant delay of services in wireless access network is investigated, by mapping core network onto a cost-variable directed graph, where the cost is construed as the average service delay of the flows traveling in core network that depends on the current load. A multicommodity minimal cost flow mathematics problem is then derived and solved by Price-directive Decomposition and Lagrangian Relaxation. Simulations are carried out in two typical core networks and some valuable conclusions are gained.

Abstract: In this paper, the process of bi-metallic tube backward extrusion through a conical punch, by means of upper bound method and finite element method is investigated. A cylindrical admissible velocity field is developed and by calculating the internal, shear and frictional powers, the extrusion force is estimated. The extrusion process is also simulated by using the finite element code, ABAQUS. Analysis and simulations are done for two types of bi-metallic tubes: aluminum as core, copper as sleeve (Al-Cu) and copper as core, aluminum as sleeve (Cu-Al). The extrusion force from the upper bound method is compared with the Finite Element results. This comparison shows that the upper bound predictions are in good agreement with the Finite Element results. The results also show that, the extrusion force in the case of Al-Cu tube is smaller than Cu-Al tube and in both types of bi-metallic tubes, the aluminum leaves the deformation zone sooner than the copper. Finally the effects of various extrusion parameters, such as the friction factor, reduction in area and semi-punch angle upon the extrusion force are investigated and the optimum semi-punch angle is determined.

Abstract: By exploring the nature of the analogy between optimum trusses and optimum layouts of discontinuities, a novel numerical analysis method for rock/soil masses is proposed in this paper. The procedure is used to determine the critical layout of discontinuities and associated upper bound limit analysis for stability problems. The alternative approximation procedure to the traditional finite element method might involve discretization of a given body using a suitably large number of nodes laid out on a grid, with the failure mechanism comprising the most critical subset of potential discontinuities interconnecting these nodes. Potential discontinuities which interlink nodes laid out across the problem domain are permitted to crossover one another, giving a much wider search space than when such discontinuities are located only at the edges of finite elements of fixed topology. Highly efficient SOCP (second-order cone programming) solvers can be employed when certain popular failure criteria are specified (e.g. Hoek-Brown and Mohr-Coulomb). Stress/velocity singularities are automatically identified and visual interpretation of the output is straightforward. Several numerical examples including rock slope are studied by the new method, and the results are very close to those calculated by using analytical method and FEM.

Abstract: Historical masonry buildings located in the Southern Italy are usually built with irregular stones joined with mortar with poor mechanical properties. Therefore, piers and spandrels ultimate resistance is not always well predicted by simplified formulas suggested by codes of practice, which typically are tailored to regular patterns. In this framework, we present a two-step numerical model –within the equivalent frame approach assumption– for the pushover analysis of in-plane loaded historical masonry walls constituted by an irregular assemblage of stones. In Step I, ultimate bending moment-shear force strength domains of piers and spandrels are derived by means of a heterogeneous upper bound FE limit analysis and the results are stored in a database. Assessing the capacity of both piers and spandrels is crucial for correctly predicting the ultimate resistance of masonry walls acted upon by in-plane loads. Heterogeneous limit analysis is particularly suitable for computing failure loads, since it permits a distinct modeling of stones and mortar joints. Appropriate static and kinematic boundary conditions are set to account for the complex interaction of internal forces and deformed shapes of single elements. At Step II, a frame model of the masonry wall is assembled, where piers and spandrels are modeled as elastic Timoshenko beams. At each analysis step it is checked that the internal forces in each structural element are smaller than the failure loads stored in the database created at Step I. If the capacity is exceeded, suitable flexural hinges are introduced at the end of the structural elements. The resistance of the element is then set to zero when a limit chord rotation is exceeded. With the numerical tool developed, a real scale old masonry oil-mill located in the Southern Italy is analyzed in the inelastic range under increasing static loads.

Abstract: Plastic deformation process resulting in ultra fine grained materials which are rapidly grasping applications due to their superior mechanical properties remain an area of continued research interest. Generally, the influence of die land length and web to flange ratio in grain refinement subsequent to plastic deformation process have not being adequately exploited especially in complex die opening geometries. In the present study, the effect of these parameters on extrusion pressure and morphological change in I-shaped die opening geometry is investigated and reported. A forward extrusion rig is designed and manufactured for the purpose of experimental investigation. The upper bound analysis shows that increasing die land length leads to increasing relative extrusion pressure. Optimum web to flange ratio of 0.45 is numerically simulated and recommended to extrude I-shaped lead alloy with minimum load requirement. The experimental results reveal that increasing area ratio leads to quasi-sinusoidal pattern in surface hardness of I-shaped section irrespective of strain rate value. Increasing web to flange ratio, therefore, leads to increasing anisotropy of the I-shaped lead alloy. The extruded sections were examined with optical metallurgical microscope, and it is observed that increasing strain rate results in profound refinement of grain and inclusions in lead alloy even at room temperature.

Abstract: Extrusion through mathematically contoured die plays a critical role in improvement of surface integrity of extruded product. There is gradual deformation which results in the uniform microstructure. In the present investigation non-dimensional extrusion pressure and optimum die length for cosine die profile has been obtained by three dimensional upper bound method using dual stream function method for different reductions. The theoretical modeling has been validated with experiments. The experimental results are found to be compatible with the theory.

Abstract: In this paper, an upper bound approach of rotating compression forming of ring is established. Using the upper bound approach, the effects of friction factor, reduction, aspect ratio etc upon compression force, radius of neutral surface, internal radius, spiral lead etc are investigated systematically. The experiment of rotating compression forming of ring made of aluminum alloy A6061 was carried out. Comparisons between the analytical results and the experiment are used to verify the validity of present upper bound approach. The analytical results are in good agreement with the experiment.