scholarly journals Lower and Upper Bound Shakedown Analysis of Structures With Temperature-Dependent Yield Stress

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
Haofeng Chen
Keyword(s):  
Lower Bound ◽  
Yield Stress ◽  
Upper Bound ◽  
Solid Mechanics ◽  
Yield Condition ◽  
Static Field ◽  
Upper And Lower Bounds ◽  
Residual Stress Field ◽  
Temperature Dependent ◽  
Shakedown Analysis

Based upon the kinematic theorem of Koiter (1960, “General Theorems for Elastic Plastic Solids,” in Progress in Solid Mechanics 1, J. N. Sneddon and R. Hill, eds., North-Holland, Amsterdam, pp. 167–221) the linear matching method (LMM) procedure has been proved to produce very accurate upper bound shakedown limits. This paper presents a recently developed LMM lower bound procedure for shakedown analysis of structures with temperature-dependent yield stress, which is implemented into ABAQUS using the same procedure as for upper bounds. According to the Melan’s theorem (1936, “Theorie statisch unbestimmter Systeme aus ideal-plastichem Baustoff,” Sitzungsber. Akad. Wiss. Wien, Math.-Naturwiss. Kl., Abt. 2A, 145, pp. 195–210), a direct algorithm has been carried out to determine the lower bound of shakedown limit using the best residual stress field calculated during the LMM upper bound procedure with displacement-based finite elements. By checking the yield condition at every integration point, the lower bound is calculated by the obtained static field at each iteration, with the upper bound given by the obtained kinematic field. A number of numerical examples confirm the applicability of this procedure and ensure that the upper and lower bounds are expected to converge to the theoretical solution after a number of iterations.

scholarly journals Lower and Upper Bound Shakedown Analysis of Structures With Temperature-Dependent Yield Stress

2009 ◽  
Author(s):  
Haofeng Chen
Keyword(s):  
Lower Bound ◽  
Yield Stress ◽  
Upper Bound ◽  
Yield Condition ◽  
Static Field ◽  
Upper And Lower Bounds ◽  
Residual Stress Field ◽  
Temperature Dependent ◽  
Shakedown Analysis ◽  
Shakedown Limit

Based upon the kinematic theorem of Koiter, the Linear Matching Method (LMM) procedure has been proved to produce very accurate upper bound shakedown limits. This paper presents a recently developed LMM lower bound procedure for shakedown analysis of structures with temperature-dependent yield stress, which is implemented into ABAQUS using the same procedure as for upper bounds. According to the Melan’s theorem, a direct algorithm has been carried out to determine the lower bound of shakedown limit using the best residual stress field calculated during the LMM upper bound procedure with displacement-based finite elements. By checking the yield condition at every integration point, the lower bound is calculated by the obtained static field at each iteration, with the upper bound given by the obtained kinematic field. A number of numerical examples confirm the applicability of this procedure and ensure that the upper and lower bounds are expected to converge to the theoretical solution after a number of iterations.

scholarly journals On the Rank of $p$-Schemes

10.37236/3097 ◽  
2013 ◽  
Vol 20 (2) ◽  
Author(s):  
Fateme Raei Barandagh ◽  
Amir Rahnamai Barghi
Keyword(s):  
Lower Bound ◽  
Prime Number ◽  
Lower Bounds ◽  
Upper Bound ◽  
Upper And Lower Bounds ◽  
Minimum Rank

Let $n>1$ be an integer and $p$ be a prime number. Denote by $\mathfrak{C}_{p^n}$ the class of non-thin association $p$-schemes of degree $p^n$. A sharp upper and lower bounds on the rank of schemes in $\mathfrak{C}_{p^n}$ with a certain order of thin radical are obtained. Moreover, all schemes in this class whose rank are equal to the lower bound are characterized and some schemes in this class whose rank are equal to the upper bound are constructed. Finally, it is shown that the scheme with minimum rank in $\mathfrak{C}_{p^n}$ is unique up to isomorphism, and it is a fusion of any association $p$-schemes with degree $p^n$.

scholarly journals When is non-trivial estimation possible for graphons and stochastic block models?‡

2017 ◽  
Vol 7 (2) ◽  
pp. 169-181
Author(s):  
Audra McMillan ◽  
Adam Smith
Keyword(s):  
Lower Bound ◽  
Lower Bounds ◽  
Upper Bound ◽  
Upper And Lower Bounds ◽  
Random Networks ◽  
Block Models

Abstract Block graphons (also called stochastic block models) are an important and widely studied class of models for random networks. We provide a lower bound on the accuracy of estimators for block graphons with a large number of blocks. We show that, given only the number $k$ of blocks and an upper bound $\rho$ on the values (connection probabilities) of the graphon, every estimator incurs error ${\it{\Omega}}\left(\min\left(\rho, \sqrt{\frac{\rho k^2}{n^2}}\right)\right)$ in the $\delta_2$ metric with constant probability for at least some graphons. In particular, our bound rules out any non-trivial estimation (that is, with $\delta_2$ error substantially less than $\rho$) when $k\geq n\sqrt{\rho}$. Combined with previous upper and lower bounds, our results characterize, up to logarithmic terms, the accuracy of graphon estimation in the $\delta_2$ metric. A similar lower bound to ours was obtained independently by Klopp et al.

scholarly journals BÜCHI COMPLEMENTATION MADE TIGHTER

2006 ◽  
Vol 17 (04) ◽  
pp. 851-867 ◽  
Author(s):  
EHUD FRIEDGUT ◽  
ORNA KUPFERMAN ◽  
MOSHE Y. VARDI
Keyword(s):  
Lower Bound ◽  
Upper Bound ◽  
Blow Up ◽  
Careful Analysis ◽  
Point Of View ◽  
Upper And Lower Bounds ◽  
Theoretical Point ◽  
Infinite Words ◽  
Büchi Automata ◽  
Buchi Automata

The complementation problem for nondeterministic word automata has numerous applications in formal verification. In particular, the language-containment problem, to which many verification problems is reduced, involves complementation. For automata on finite words, which correspond to safety properties, complementation involves determinization. The 2n blow-up that is caused by the subset construction is justified by a tight lower bound. For Büchi automata on infinite words, which are required for the modeling of liveness properties, optimal complementation constructions are quite complicated, as the subset construction is not sufficient. From a theoretical point of view, the problem is considered solved since 1988, when Safra came up with a determinization construction for Büchi automata, leading to a 2O(n log n) complementation construction, and Michel came up with a matching lower bound. A careful analysis, however, of the exact blow-up in Safra's and Michel's bounds reveals an exponential gap in the constants hiding in the O( ) notations: while the upper bound on the number of states in Safra's complementary automaton is n2n, Michel's lower bound involves only an n! blow up, which is roughly (n/e)n. The exponential gap exists also in more recent complementation constructions. In particular, the upper bound on the number of states in the complementation construction of Kupferman and Vardi, which avoids determinization, is (6n)n. This is in contrast with the case of automata on finite words, where the upper and lower bounds coincides. In this work we describe an improved complementation construction for nondeterministic Büchi automata and analyze its complexity. We show that the new construction results in an automaton with at most (0.96n)n states. While this leaves the problem about the exact blow up open, the gap is now exponentially smaller. From a practical point of view, our solution enjoys the simplicity of the construction of Kupferman and Vardi, and results in much smaller automata.

A Multi-Surface Plasticity Method for Lower Bound Shakedown Load

2019 ◽  
Vol 795 ◽  
pp. 458-465
Author(s):  
Alan Jappy ◽  
Donald Mackenzie ◽  
Hao Feng Chen
Keyword(s):  
Finite Element ◽  
Lower Bound ◽  
Finite Number ◽  
Upper Bound ◽  
Direct Method ◽  
Extreme Points ◽  
Residual Stress Field ◽  
Periodic Load ◽  
Surface Plasticity ◽  
Elastic Shakedown

A new direct method for calculation of lower bound shakedown limits based on Melan’s theorem and a novel, non-smooth multi-surface plasticity model is proposed and implemented in a Finite Element environment. The load history is defined by a finite number of extreme points defining the load-envelope of a periodic load set. The shakedown problem is stated as a plasticity problem in terms of a finite number of independent yield conditions, solved for a residual stress field that satisfies a piecewise, non-smooth yield surface defined by the intersection of multiple yield surfaces. The implemented Finite Element procedure is applied to two shakedown problems and the results compared with lower and upper bound elastic shakedown solutions given by the Linear Matching Method, LMM. The example analyses show that the proposed Elastic-Shakedown Multi Surface Plasticity (EMSP) method defines robust lower bound shakedown limits between the LMM lower and upper bound limits, close to the LMM upper bound.

Limit Analysis of Flow Through Inclined Converging Planes

1980 ◽  
Vol 102 (2) ◽  
pp. 109-117 ◽  
Author(s):  
M. Kiuchi ◽  
B. Avitzur
Keyword(s):  
Lower Bound ◽  
Plane Strain ◽  
Upper Bound ◽  
Limit Analysis ◽  
Velocity Fields ◽  
The Body ◽  
Design Flow ◽  
Upper And Lower Bounds ◽  
Lower Upper ◽  
Flow Through

A variety of mathematical models may be used to analyze plastic deformation during a metal-forming process. One of these methods—limit analysis—places the estimate of required power between an upper bound and a lower bound. The upper- and lower-bound analysis are designed so that the actual power or forming stress requirement is less than that predicted by the upper bound and greater than that predicted by the lower bound. Finding a lower upper-bound and a higher lower-bound reduces the uncertainty of the actual power requirement. Upper and lower bounds will permit the determination of such quantities as required forces, limitations on the process, optimal die design, flow patterns, and prediction and prevention of defects. Fundamental to the development of both upper-bound and lower-bound solutions is the division of the body into zones. For each of the zones there is written either a velocity field (upper bound) or a stress field (lower bound). A better choice of zones and fields brings the calculated values closer to actual values. In the present work, both upper- and lower-bound solutions are presented for plane-strain flow through inclined converging dies. For the upper bound, trapezoidal velocity fields, uni-triangular velocity fields, and multi-triangular velocity fields have been dealt with and the solutions compared to previously published work on cylindrical velocity fields. It was found that in different domains of the various combinations of the process parameters, different patterns of flow (cylindrical, triangular, etc.) provide lower upper-bound solutions. The lower-bound solution for plane-strain flow through inclined converging planes is newly developed.

scholarly journals ON THE POSSIBLE RANKS AMONG MATRICES WITH A GIVEN PATTERN

2010 ◽  
Vol 02 (03) ◽  
pp. 363-377 ◽  
Author(s):  
CHARLES R. JOHNSON ◽  
YULIN ZHANG
Keyword(s):  
Lower Bound ◽  
Lower Bounds ◽  
Upper Bound ◽  
Null Space ◽  
Upper And Lower Bounds ◽  
Minimum Rank

Given are tight upper and lower bounds for the minimum rank among all matrices with a prescribed zero–nonzero pattern. The upper bound is based upon solving for a matrix with a given null space and, with optimal choices, produces the correct minimum rank. It leads to simple, but often accurate, bounds based upon overt statistics of the pattern. The lower bound is also conceptually simple. Often, the lower and an upper bound coincide, but examples are given in which they do not.

Thermal Stress in a Viscoelastic-Plastic Plate With Temperature-Dependent Yield Stress

1960 ◽  
Vol 27 (2) ◽  
pp. 297-302 ◽  
Author(s):  
H. G. Landau ◽  
J. H. Weiner ◽  
E. E. Zwicky
Keyword(s):  
Residual Stress ◽  
Stress Distribution ◽  
Yield Stress ◽  
Plastic Material ◽  
Numerical Procedure ◽  
Yield Condition ◽  
Residual Stress Distribution ◽  
Transient Temperature ◽  
Temperature Dependent ◽  
Perfectly Plastic

Equations are given for the determination of transient and residual stresses in plates subject to transient temperature distributions, based on the assumption of a viscoelastic, perfectly plastic material obeying a von Mises temperature-dependent yield condition. A numerical procedure for integrating the equations is developed and applied to the case of a symmetrically cooled plate. It is found that, for steel, viscoelasticity has little effect on the residual stress distribution, but the temperature dependence of yield stress is important. The types of residual stress distribution after cooling are similar to those for an elastic-plastic material with constant yield stress, and for this case the residual stress is given approximately by formulas developed earlier for a slowly varying heat input.

BOUNDS ON THE PRICE OF STABILITY OF UNDIRECTED NETWORK DESIGN GAMES WITH THREE PLAYERS

2011 ◽  
Vol 12 (01n02) ◽  
pp. 1-17 ◽  
Author(s):  
VITTORIO BILÒ ◽  
ROBERTA BOVE
Keyword(s):  
Lower Bound ◽  
Network Design ◽  
Lower Bounds ◽  
Upper Bound ◽  
Cost Allocation ◽  
Upper And Lower Bounds ◽  
Price Of Stability ◽  
Undirected Network ◽  
Basic Case

After almost seven years from its definition,2 the price of stability of undirected network design games with fair cost allocation remains to be elusive. Its exact characterization has been achieved only for the basic case of two players2,7 and, as soon as the number of players increases, the gap between the known upper and lower bounds becomes super-constant, even in the special variants of multicast and broadcast games. Motivated by the intrinsic difficulties that seem to characterize this problem, we analyze the already challenging case of three players and provide either new or improved bounds. For broadcast games, we prove an upper bound of 1.485 which exactly matches a lower bound given in Ref. 4; for multicast games, we show new upper and lower bounds which confine the price of stability in the interval [1.524; 1.532]; while, for the general case, we give an improved upper bound of 1.634. The techniques exploited in this paper are a refinement of those used in Ref. 7 and can be easily adapted to deal with all the cases involving a small number of players.

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