Issue 50

K. Meftah et alii, Frattura ed Integrità Strutturale, 50 (2019) 276-285; DOI: 10.3221/IGF-ESIS.50.23 282 0 0 i i i i i i i i i N N w N N                                                                  (31) It is now necessary to express the rotations given here in the element of reference according to rotations in the local coordinate system:   xk k k yk k J                    (32) where J k is the inverse Jacobian matrix components. N UMERICAL EXAMPLES he resulting mathematical model of the proposed Q4  element and the classical associative plasticity model are implemented into a FORTRAN calculation code to account for small strain elasto-plastic problems. A nonlinear elasto-plastic behavior of bending plates under mechanical loading with different boundary conditions and different aspect ratios were studied. Both problems involve square plates subjected to a uniformly distributed load of magnitude 1 KN / m ². The material is considered as elasto-plastic (where the material is considered elastic perfectly plastic and the von Mises model is adopted) with: L = 1.0 ; h = 0.5 and 0.01 ; E = 10.92 GPa;  = 0.3 and Yield stress Y  = 1600 MPa. Because of the symmetry, only a quarter of the plate is modeled using 4×4 mesh as shown in Fig. 3. X Y  L L Sym .  Sym .  Figure 3 : Square plate, its finite element models. Simply supported square plate In the first elasto-plastic example, a simply supported square plate subjected to uniformly distributed load is considered. The results are presented in Figs. 4 and 5 and shows the load-deflection curves with respect to the maximum deflection when nondimensional incremental load intensity is 0 . ² q L M ( M 0 fully plastic moment 0 . . ² 4 Y M L h   ). This figure also shows a comparison among the Hétérosis finite element solution obtained by Owen and Hinton [1]. The central displacements, for comparison of plates with different thicknesses ( h = 0.01 and 0.5), have been normalized as: 0 . . ² W D M L where     3 2 . 12(1 ) D E h    is the flexural rigidity of the plate. The results obtained from the present 4- node element Q4  agree well with those obtained from the 9-node Hétérosis element reported in Reference [1]. From the observation of the figures, it is possible to conclude that the accuracies of the present 4-node new element globally close T