Semifinished product made from a shape memory alloy having a two-way effect and method for manufacturing the same

Abstract

The present invention relates to a semifinished product made from a shape memory alloy having a two-way effect, and to a method for manufacturing the same. An objective in this case is to produce a two-way effect in the shape memory alloy in simple fashion and using only few process steps, so that the semifinished product made of the shape memory alloy at the austenite/martensite phase transition, is able to pass through a large number of deformation cycles, and it exhibits high effect amounts, without requiring a protracted training of the shape memory alloy or externally acting forces. In one single deformation step, a linear, superelastic phase is additionally produced in the shape memory alloy, thereby introducing a restoring force to the shape memory alloy, so that, under the action of this restoring force, the shape memory alloy passes repeatedly through the deformation cycle during the austenite/martensite phase transition.

What is claimed is:  
     
         1 . A semifinished product comprising: 
 a shape memory alloy, the shape memory alloy including an active martensitic/austenitic phase and a linear, superelastic phase forming a restoring force in the shape memory alloy, the shape memory alloy capable of running through a deformation cycle several times during an austenite/martensite phase transition under action of the restoring force.    
     
     
         2 . The semifinished product as recited in  claim 1 , wherein the alloy has an outer cross-sectional side and a mid-cross-sectional area, the linear, superelastic phase being situated at the outer cross-sectional side and the active martensitic/austenitic phase being situated in the mid-cross-sectional area; in response to heating, the martensitic phase entering into the austenitic phase, under deformation of the shape memory alloy, and, in response to cooling, returning to the martensitic phase, the shape memory alloy returning to a shape before deformation, through the action of the restoring force.  
     
     
         3 . The semifinished product as recited in  claim 1 , wherein the shape memory alloy has stress distributions, so that tensile and compressive forces are produced which lead to a curvature of the semifinished product.  
     
     
         4 . The semifinished product as recited in  claim 3 , wherein the tensile forces run on an outer curvature side and the compressive forces on an inner curvature side of the semifinished product.  
     
     
         5 . The semifinished product as recited in  claim 1 , wherein the shape memory alloy is an alloy capable of exhibiting a two-way effect.  
     
     
         6 . The semifinished product as recited in  claim 1 , wherein the shape memory alloy is composed of 55 wt % nickel and of 45 wt % titanium.  
     
     
         7 . The semifinished product as recited in  claim 1 , wherein, in a cold, martensitic state, the shape memory alloy has a nearly closed, annular shape and, in response to heating, enters into a high-temperature austenite phase, the shape memory alloy being shortened, so that the semifinished product opens; and, at a transition to the low-temperature martensite phase, expands under the action of the restoring force and returns to the nearly closed, annular shape.  
     
     
         8 . The semifinished product as recited in  claim 7 , wherein, in the cold, martensitic state, the product has a smaller radius of curvature than in the warm, austenitic state.  
     
     
         9 . A method for manufacturing a semifinished product from a shape memory alloy having a two-way effect comprising the steps of: 
 carrying in out a deformation step in the low-temperature martensite phase of an active martensitic/austenitic phase, and    producing a linear, superelastic phase in the shape memory alloy so as to introduce a restoring force to the alloy, so that, under the action of the restoring force, a deformation cycle of the shape memory alloy is passed through several times during an austenite/martensite phase transition.    
     
     
         10 . The method as recited in  claim 9 , wherein the shape memory alloy is deformed such that the linear, superelastic phase is produced at an outer cross-sectional side of the semifinished product, and, in the cold state, the martensitic phase is in a mid-cross-sectional area of the semifinished product; in response to heating, the martensitic phase entering into an austenitic phase, under deformation of the shape memory alloy, and, in response to cooling of the martensitic phase, the shape memory alloy returning to the shape before deformation under the action of the restoring force.  
     
     
         11 . The method as recited in  claim 9 , wherein, as the result of deformation, stress distributions are introduced to the shape memory alloy, so that tensile and compressive forces are produced, which lead to a curvature of the semifinished product.  
     
     
         12 . The method as recited in  claim 9 , wherein the shape memory alloy is in a bar-, band- or wire shape and further comprising drawing the shape memory alloy in a cold martensitic state over a mandrel.  
     
     
         13 . The method as recited in  claim 12 , further comprising cutting the shape memory alloy into individual, curved sections, without the stress distributions introduced to the shape memory alloy being thereby influenced; and securing the curved sections to a substrate.  
     
     
         14 . The method as recited in  claim 9 , wherein the alloy is in a wire shape and further comprising weaving the alloy into fabric structures, the wire-shaped shape memory alloy being drawn over lancets.  
     
     
         15 . A curved semifinished product made of a shape memory alloy comprising: 
 an outer surface including an active martensitic/austenitic phase; and    a section interior to the outer surface including a linear, superelastic phase forming a restoring force in the shape memory alloy, the curved product having an opening capable of widening and narrowing under action of the restoring force.