FEM results reveal that angular displacement by power function can be used to describe friction constraint on side faces, and zone of no ideal HPT tend to stable when exponent is not less than 8.

• 有限元分析结果表明，可用幂函数形式的角位移约束来简化侧面摩擦，当幂指数不小于8时，试样上非HPT变形区域大小趋于稳定；