Itzhak Kalev - Academia.edu (original) (raw)

Papers by Itzhak Kalev

International Journal for Numerical Methods in Engineering, 1977

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A procedure for the local stiffness modifications of large structures is described. It enables st... more A procedure for the local stiffness modifications of large structures is described. It enables structural modifications without an a priori definition of the changes in the original structure and without loss of efficiency due to multiple loading conditions. The solution procedure, implemented in NASTRAN, involved the decomposed stiffness matrix and the displacement vectors of the original structure. It solves the modified structure exactly, irrespective of the magnitude of the stiffness changes. In order to investigate the efficiency of the present procedure and to test its applicability within a design environment, several real and large structures were solved. The results of the efficiency studies indicate that the break-even point of the procedure varies between 8% and 60% stiffness modifications, depending upon the structure's characteristics and the options employed.

A computerized tool for the analysis of time independent cyclic plasticity structural response, l... more A computerized tool for the analysis of time independent cyclic plasticity structural response, life to crack initiation prediction, and crack growth rate prediction for metallic materials is described. Three analytical items are combined: the finite element method with its associated numerical techniques for idealization of the structural component, cyclic plasticity models for idealization of the material behavior, and damage accumulation criteria for the fatigue failure.

Journal of Aircraft, 1977

Journal of Aircraft, 1981

An analytical approach for low-cycle fatigue prediction is presented. The approach combines a cyc... more An analytical approach for low-cycle fatigue prediction is presented. The approach combines a cyclic plasticity model with the finite element method and a damage accumulation criterion for ductile metals. The cyclic plasticity model is based on the concept of the combination of several yield surfaces. The surfaces are related to the material uniaxial stress-strain curve idealized by piecewise linear segments. The damage criterion is based on the Coffin-Manson formulae modified for the mean stress variation effect. It is extended to the multiaxial varying stress-strain field and applied for both the crack initiation and the crack growth processes. The stable slow crack growth rate is approximated by the damage accumulation gradient computed from the cracked finite element models. This procedure requires fatigue testing data of only smooth specimens under constant strain amplitudes. The present approach is illustrated by numerical examples of an aircraft wing stiffened panel subjected to compression, which causes material yielding and residual tension.

International Journal for Numerical Methods in Engineering, 1977

An elasto-plastic finite element small displacement procedure to predict the behaviour of structu... more An elasto-plastic finite element small displacement procedure to predict the behaviour of structures under cyclic loads is presented. The solution combines incremental procedure with correction for equilibrium and iterative scheme. Applications are made for a rectangular strip and a notched bar under cyclic axial loads. Flow theory pf plasticity with either isotropic hardening or kinematic linear hardening is used.

Computers & Structures, 1972

Abstract A computer method for three dimensional analysis of multistory structures is presented. ... more Abstract A computer method for three dimensional analysis of multistory structures is presented. There are no restrictions referring to types of stiffening elements, their layout and changes in floor plane and variations in cross-sectional properties with height of the structure. The number of stiffening elements which may be included in analysis is practically unlimited. The loads may be vertical and lateral at arbitrary locations. Elastic warping of thin-walled members is included in analysis. The macro-flow-chart of the computer program and results of a numerical example is given.

Computers & Structures, 1981

Abstract An analytical procedure for prediction of the cyclic plasticity effects on both the stru... more Abstract An analytical procedure for prediction of the cyclic plasticity effects on both the structural fatigue life to crack initiation and the rate of crack growth is presented. The crack initiation criterion is based on the Coffin-Manson formulae extended for multiaxial stress state and for inclusion of the mean stress effect. This criterion is also applied for the accumulated damage ahead of the existing crack tip which is assumed to be related to the crack growth rate. Three cyclic plasticity models, based on the concept of combination of several yield surfaces, are employed for computing the crack growth rate of a cracked plane stress panel under several cyclic loading conditions.

Computer Methods in Applied Mechanics and Engineering, 1977

A finite element approach for cyclic elastic-plastic dynamic analysis is presented. A hardening m... more A finite element approach for cyclic elastic-plastic dynamic analysis is presented. A hardening model suited for cyclic plasticity behavior is incorporated. It is composed of several yield surfaces, and nonlinear stress-strain curves can be included. The central difference timewise operator is employed to solve the equations of motion. Comparison is made with the Newmark operator. Numerical examples illustrate the effect of cyclic plastic deformations on the dynamic response of simple problems. Comparison is presented for the structural behavior as predicted by the present hardening model and by the isotropic hardening model.

A hardening model for representing the cyclic plasticity behavior is described. The concept of se... more A hardening model for representing the cyclic plasticity behavior is described. The concept of several yield is described. The concept of several linear hardening rule is surfaces, each of which obeys Prager's linear hardening rule is employed. The nonlinear stress-strain curve is idealized by piecewise segments. A finite element solution is combined with the present hardening model. The solution combines linear iterations with incremental procedure and equilibrium corrections. Numerical results are presented for a rectangular strip with cyclic dependent hardening properties. The influence of the number of iterations on the solution accuracy is checked and compared with alternative approach. Experimental results of a notched bar subjected to three cyclic loading conditions are compared with those predicted from a plane stress finite element model.

International Journal for Numerical Methods in Engineering, 1977

[

A procedure for the local stiffness modifications of large structures is described. It enables st... more A procedure for the local stiffness modifications of large structures is described. It enables structural modifications without an a priori definition of the changes in the original structure and without loss of efficiency due to multiple loading conditions. The solution procedure, implemented in NASTRAN, involved the decomposed stiffness matrix and the displacement vectors of the original structure. It solves the modified structure exactly, irrespective of the magnitude of the stiffness changes. In order to investigate the efficiency of the present procedure and to test its applicability within a design environment, several real and large structures were solved. The results of the efficiency studies indicate that the break-even point of the procedure varies between 8% and 60% stiffness modifications, depending upon the structure's characteristics and the options employed.

A computerized tool for the analysis of time independent cyclic plasticity structural response, l... more A computerized tool for the analysis of time independent cyclic plasticity structural response, life to crack initiation prediction, and crack growth rate prediction for metallic materials is described. Three analytical items are combined: the finite element method with its associated numerical techniques for idealization of the structural component, cyclic plasticity models for idealization of the material behavior, and damage accumulation criteria for the fatigue failure.

Journal of Aircraft, 1977

Journal of Aircraft, 1981

An analytical approach for low-cycle fatigue prediction is presented. The approach combines a cyc... more An analytical approach for low-cycle fatigue prediction is presented. The approach combines a cyclic plasticity model with the finite element method and a damage accumulation criterion for ductile metals. The cyclic plasticity model is based on the concept of the combination of several yield surfaces. The surfaces are related to the material uniaxial stress-strain curve idealized by piecewise linear segments. The damage criterion is based on the Coffin-Manson formulae modified for the mean stress variation effect. It is extended to the multiaxial varying stress-strain field and applied for both the crack initiation and the crack growth processes. The stable slow crack growth rate is approximated by the damage accumulation gradient computed from the cracked finite element models. This procedure requires fatigue testing data of only smooth specimens under constant strain amplitudes. The present approach is illustrated by numerical examples of an aircraft wing stiffened panel subjected to compression, which causes material yielding and residual tension.

International Journal for Numerical Methods in Engineering, 1977

An elasto-plastic finite element small displacement procedure to predict the behaviour of structu... more An elasto-plastic finite element small displacement procedure to predict the behaviour of structures under cyclic loads is presented. The solution combines incremental procedure with correction for equilibrium and iterative scheme. Applications are made for a rectangular strip and a notched bar under cyclic axial loads. Flow theory pf plasticity with either isotropic hardening or kinematic linear hardening is used.

Computers & Structures, 1972

Abstract A computer method for three dimensional analysis of multistory structures is presented. ... more Abstract A computer method for three dimensional analysis of multistory structures is presented. There are no restrictions referring to types of stiffening elements, their layout and changes in floor plane and variations in cross-sectional properties with height of the structure. The number of stiffening elements which may be included in analysis is practically unlimited. The loads may be vertical and lateral at arbitrary locations. Elastic warping of thin-walled members is included in analysis. The macro-flow-chart of the computer program and results of a numerical example is given.

Computers & Structures, 1981

Abstract An analytical procedure for prediction of the cyclic plasticity effects on both the stru... more Abstract An analytical procedure for prediction of the cyclic plasticity effects on both the structural fatigue life to crack initiation and the rate of crack growth is presented. The crack initiation criterion is based on the Coffin-Manson formulae extended for multiaxial stress state and for inclusion of the mean stress effect. This criterion is also applied for the accumulated damage ahead of the existing crack tip which is assumed to be related to the crack growth rate. Three cyclic plasticity models, based on the concept of combination of several yield surfaces, are employed for computing the crack growth rate of a cracked plane stress panel under several cyclic loading conditions.

Computer Methods in Applied Mechanics and Engineering, 1977

A finite element approach for cyclic elastic-plastic dynamic analysis is presented. A hardening m... more A finite element approach for cyclic elastic-plastic dynamic analysis is presented. A hardening model suited for cyclic plasticity behavior is incorporated. It is composed of several yield surfaces, and nonlinear stress-strain curves can be included. The central difference timewise operator is employed to solve the equations of motion. Comparison is made with the Newmark operator. Numerical examples illustrate the effect of cyclic plastic deformations on the dynamic response of simple problems. Comparison is presented for the structural behavior as predicted by the present hardening model and by the isotropic hardening model.

A hardening model for representing the cyclic plasticity behavior is described. The concept of se... more A hardening model for representing the cyclic plasticity behavior is described. The concept of several yield is described. The concept of several linear hardening rule is surfaces, each of which obeys Prager's linear hardening rule is employed. The nonlinear stress-strain curve is idealized by piecewise segments. A finite element solution is combined with the present hardening model. The solution combines linear iterations with incremental procedure and equilibrium corrections. Numerical results are presented for a rectangular strip with cyclic dependent hardening properties. The influence of the number of iterations on the solution accuracy is checked and compared with alternative approach. Experimental results of a notched bar subjected to three cyclic loading conditions are compared with those predicted from a plane stress finite element model.