摘要:

AbstractThe time‐domain boundary element method is applied to study the propagation of discrete cracks under dynamic loadings. The principles of linear elastic fracture mechanics are employed to accurately represent the stress singularity in front of the crack tip. A fracture criterion suitable for brittle materials is employed to determine the time and direction of the propagating crack. Discrete crack closure under dynamic loadings is modelled and the response of a 2‐D cracked body is obtained by direct integration of the equations of motion. Results are presented for three test problems wherein the accuracy and usefulness of the proposed formulation is established through comparisons with available data. 'It is expected that this formulation can be used to study the seismic cracking of mass concrete structures such as gravity d

ISSN:0029-5981    

DOI:10.1002/nme.1620350802

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractAn algorithm for integrating the constitutive equations for an elasto‐viscoplastic cubic crystal is presented which is shown to be easily employed in a polycrystalliné analysis. Anisotropic elastic behaviour is incorporated into the standard constitutive equations for ductile single crystals. The algorithm is shown to be efficient, robust and general. The primary advantage of this algorithm is that is provides an implicit integration of the plastic deformation gradient while including the elastic response. This permits taking large time steps while maintaining accuracy and stability. Several polycrystalline examples are presented to demonstrate the effect of the time step on the solution. Examples also are presented which compare the algorithm described herein to an algorithm which neglects the elastic part of the deformation. In addition, the effect of the anisotropic component of the elasticity is investigated by comparing the results with those obtained assuming isotropic elastici

ISSN:0029-5981    

DOI:10.1002/nme.1620350803

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractIt has been shown2that a four‐noded membrane element of trapezoidal shape must either lock or fail constant strain patch tests. That result is generalized here to establish similar limitations for all finite elements. A modal analysis is used to show that essential coupling exists between low modes whose displacement states can be exactly represented by an element's basis functions and higher modes whose displacement states cannot be so represented. Such coupling can be avoided only when an element has particular shapes. In all other cases the element designer is faced with the choice of patch test failure in a low mode or locking in a higher mode. Several examples are describe

ISSN:0029-5981    

DOI:10.1002/nme.1620350804

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractIn this paper the formulation of a new triangular element based on the Reissner/Mindlin plate theory is presented. The element has three nodes and three d.o.f. per node only. It is based on constant bending modes plus incompatible energy orthogonal higher order bending modes. The transverse shear effects are represented using the moment equilibrium and the constitutive equations. Discrete (collocation) shear constraints are considered on each side to relate the kinematical and the independent shear strains. The element has a proper rank, is completely locking free, passes all constant patch‐tests exactly. The detailed numerical evaluation shows that the element, called DST‐BK, is a robust and high‐performance element for thick and thin p

ISSN:0029-5981    

DOI:10.1002/nme.1620350805

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractLinear equality multipoint constraint conditions define a vector space which is used to construct an orthogonal projection operator. Another orthogonal projection operator follows from the complement to the constrained vector space. A procedure is developed in which these operators are used in a systematic fashion to solve a set of algebraic equations subject to a set of multipoint constraints. In addition to elementary examples to illustrate the procedure, a problem associated with an incompressible, isotropic, elastic material is solved using four‐node quadrilateral finite elements. The method of orthogonal projections provides the insight to show that, with the application of the incompressibility constraint, convergence is obtained for any arbitrary value of Poisson's ratio chosen sufficiently far from the value of one‐half, which is the value normally associated with incompressibility. The bending performance of the incompressible four‐node quadrilateral can be adjusted with artificial values of Poisson's ratio. The result is that calculations are performed with full numerical quadrature of the element, and mesh locking, hourglass instabilities and subsequent modifications to the element stiffness matrix are av

ISSN:0029-5981    

DOI:10.1002/nme.1620350806

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA multigrid method is described that can solve the generalized eigenvalue problem encountered in structural dynamics. The algorithm combines relaxation on a fine mesh with the solution of a singular equation on a coarse mesh. A sequence of coarser meshes may be used to quickly solve this singular equation using another multigrid method. The hierarchy of increasingly finer meshes can be further exploited using a nested iteration scheme, whereby initial approximations to the fine mesh eigenvectors are computed using interpolated coarse mesh eigenvectors. The solution of some simple plate problems on a Convex C240 demonstrates the efficiency of a vectorized version of the multigrid algorithm.

ISSN:0029-5981    

DOI:10.1002/nme.1620350807

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe behaviour of the multigrid method is studied by solving some simple test problems. Optimum choices for some of the parameters are discussed, together with effective techniques for solving the coarse mesh correction equation. The effects of ill‐conditioning on the performance of the algorithm are examined. In particular, thin shells and non‐uniform meshes are observed to slow convergence. The solution of practical, large scale problems demonstrates the utility and speed of the proposed multigrid method. For example, the first 10 eigensolutions of a stiffened plate problem with 193 536 degrees‐of‐freedom were computed in 1.6 CPU hours using 42 Mbytes of memory on a Conv

ISSN:0029-5981    

DOI:10.1002/nme.1620350808

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe scope of the present paper is the study of cracks having a given geometry by taking into account unilateral contact and friction phenomena between the two sides of the crack. The arising problem is highly non‐classical because of the inequality relations describing the unilateral contact and friction interface conditions. The indirect BIEM is extended appropriately in order to treat this problem. Numerical examples concerning the calculation of stress intensity factors under the unilateral contact and friction interface conditions illustrate the developed metho

ISSN:0029-5981    

DOI:10.1002/nme.1620350809

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractIn this paper a finite element technique for the discretization of kinetic energy of bodies subjected to large rigid motion and small deformation (which we refer to as quasi‐rigid motion) is presented. First, on the basis of a separation between the rigid displacement and the deformation, the relevant kinematic relationships are derived. A standard assumed‐mode approach is used to describe the deformation displacement field by a linear combination of known functions. Then, the computation of the kinetic energy leads to the definition of a set of tensors, which are configuration‐independent (like the mass matrix in a linear setting) and fully characterize the body non‐linear dynamic behaviour introduced by large rotation. A computer code has been developed, in order to extend an existing FE package, for the computation of these tensors. Details of the technique, including storage requirements and suggestions for model reduction, are given. Finally, two examples are presented: (i) the result of the computation of one of the introduced tensors; (ii) the development of the non‐linear model of a rota

ISSN:0029-5981    

DOI:10.1002/nme.1620350810

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0029-5981    

DOI:10.1002/nme.1620350811

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY