Description of a curved boundary shape without first derivative discontinuities

For the two‐dimensional isoparametric 8‐node element an additive condition is formulated, so that the function describing the domain boundary is continually differentiable at the common nodes on the boundary. This condition will be satisfied by moving the mid‐side nodes into a special position. The advantage in using this modified element will be shown by an example of the elasto‐plastic calculation of a double‐edge notched specimen.