si material , which has been considered to be very brittle , and hard to bend , is heated to at least its brittle - ductile transition temperature . a bending moment is applied to a heated portion of the si material so that a slip deformation is generated . whereby it is possible to perform bending , and to greatly improve a degree of freedom for machining the si material . the si material has a brittle - ductile transition temperature which transfers from a brittle to a ductile state at its brittle - ductile transition temperature . at the transition temperature or more , the si material is in a state that a slip can to be generated between its crystals in response to a bending torque applied thereto . thus , when a bending moment is applied to the heated portion of the si material which is heated to the transition temperature or more , a slip is generated between lattices or between crystal grains in the heated portion , so that the si material is deformed .