Abstract：Element NQ6 drops its anti-distortion performance for additional linear items introduced into Q6’s non-conforming internal shape functions when forcing strong patch test. In order to resume and even improve the anti-distortion performance it is proposed to carry out reverse treatment on these linear modifications. The adjustment process is simple: taking the linear correction term as one-dimensional direction which influences element performance, doing reverse search to determine favorable step size. Some typical examples are tested, the results show that reverse adjustment is effective, with adjustment factor set to mirror value -1, and further extended to -2, the resulting elements are less sensitive to distortion than the original Q6 and NQ6, especially the value near -2 is efficacious for elimination of shear locking in MacNeal slender beam. Because of reverse treatment, new elements pass strong patch test only for parallelogram mesh, in general pass weak patch test. Except this, the overall performance and accuracy is close to the best of various 4-node quadrilateral elements. The proposed method, which obtains items to effect anti-distortion performance by strong patch test and then adjusts them reversely, suggests a new way to improve other Q6-type non-conforming element’s anti-distortion performance.
2015, Vol. 36 
