The combined hybrid finite element method is of an intrinsic mechanism of enhancing coarse_mesh_accuracy of lower order displacement schemes.It was confirmed that the combined hybrid scheme without energy error leads to enhancement of accuracy at coarse meshes,and that the combination parameter plays an important role in the enhancement.As an improvement of conforming bilinear Q 4_plane element,the combined hybrid method adopted the most convenient quadrilateral displacements_stress mode,i.e.,the mode of compatible isoparametric bilinear displacements and pure constant stresses.By adjusting the combined parameter,the optimized version of the combined hybrid element was obtained and numerical tests indicated that this parameter_adjusted version behaves much better than Q 4_element and is of high accuracy at coarse meshes.Due to elimination of stress parameters at the elemental level,this combined hybrid version is of the same computational cost as that of Q 4_element.
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