Abstract: The new structure composition theory of variable topology mechanisms, including metamorphic mechanisms, is studied and found. The new concepts such as the invariant element, the invariant subchain, the variable element, the variable subchain and the cell-variator etc. of variable topology mechanisms are put forward and defined. Four new theorems on structure composition of variable topology mechanisms are given and proved. They are the theorem of relation between topological structure of a variable topology mechanism and its topological configurations in every phase, the invariant subchain theorem of a variable topology mechanism, the variable subchain theorem of a variable topology mechanism and the composition theorem of a variable topology mechanism. One new theorem on the equivalent transformation of the incidence relation cell-variator is found out and their validity is strictly proved. The classifications of the cell-variators and the diagram representations of three kinds of cell-variators are studied. The structure composition theory of variable topology mechanisms provides new fundament for the topological structural analysis and synthesis of variable topology mechanisms.

Key words: Cell-variator, Composition, Mechanism, Metamorphic, Structure, Variable topology, Ultrasonic welding Magnesium alloys Titanium alloys Welding parameter Tensile strength Fatigue property