Abstract: Based on the variational principle of combinative stability,combined hybrid methods posed by Zhou Tianxiao are absolutely convergent and stabilized. Zhou has advocated a systematic approach to enhanced stress/strain schemes and has designed a family of lower-order elements which are affine-equivalent to n-cube (n=2,3).The energy orthogonal relation between the conforming part and the non-conforming part of displacements interpolation functions in triangular element is given,in which the stress is interpolated by linear polynomials on each element,but the displacements are interpolated by the sum of conforming linear and nonconforming quadratic polynomials.Furthermore,this element is equivalent to the conforming triangular linear element,that is,the non-conforming parts have no contribution to enhanced strains.

Key words: combinative stability, energy orthogonality, enhanced strain