Fatigue-resistance sheet slitting method and resulting sheet

Abstract

A sheet of material ( 111 ) having a plurality of bend-inducing structures ( 113 ) configured and positioned to produce bending along a bend line ( 115 ). The bend-inducing structures ( 113 ) have arcuate return portions ( 122 ) extending from opposite ends ( 121 ) back along the bend-inducing structures ( 113 ) toward the other return portion ( 122 ) and each return portion ( 122 ) has a length dimension and a radius of curvature reducing stress concentrations. Preferably, the length dimension of the arcuate return portion ( 122 ) is in excess of twice the thickness. The lateral distance, LD, to which the bend-inducing structures ( 113 ) is formed in the sheet away from the bend line ( 115 ) is preferably minimized by small radius arcs ( 125 ) which connect the return portions ( 122 ) to the remainder of the bend-inducing structures ( 113 ). A method of forming a structure ( 131 ) from a sheet of material ( 111 ) to resist cyclical loading is also disclosed, as is a method to increase the fatigue resistance of a structure ( 131 ) formed by bending a sheet of material ( 111 ) along a bend line ( 115 ) having a plurality of bend-inducing structures ( 113 ).

1 . A sheet of material formed for bending along a bend line comprising: 
 a sheet of material having a plurality of bend-inducing structures configured and positioned to produce bending along the bend line, at least one bend-inducing structure having arcuate return portions extending from opposite ends of the bend-inducing structure and returning along the bend-inducing structure toward the other return portion, the return portions each being configured to significantly reduce stress concentrations resulting from loads oriented in a direction transverse to the bend line.    
   
   
       2 . The sheet of material as defined in  claim 1  wherein, 
 the bend-inducing structures are one of slits, grooves and steps.    
   
   
       3 . The sheet of material as defined in  claim 2  wherein, 
 the arcuate return portions curve away from the bend line proximate the opposite ends and curve back toward the bend line at distal ends of the return portions.    
   
   
       4 . The sheet of material as defined in  claim 3  wherein, 
 the arcuate return portions have a length dimension along the bend line equal to at least about 2 times the thickness dimension of the sheet of material.    
   
   
       5 . The sheet of material as defined in  claim 3  wherein, 
 the arcuate return portions each have a length dimension along the bend line equal to at least about 20 percent of the overall length of the bend-inducing structure along the bend line.    
   
   
       6 . The sheet of material as defined in  claim 4  wherein, 
 the arcuate return portions have a radius of curvature section over a majority of their length of at least 2 times the thickness dimension of the sheet of material.    
   
   
       7 . The sheet of material as defined in  claim 4  wherein, 
 the arcuate return portions have a radius of curvature section over a majority of their length of at least 3 times the thickness dimension of the sheet of material.    
   
   
       8 . The sheet of material as defined in  claim 2  wherein, 
 the bend-inducing structure is an arc having a convex side facing and extending along the bend line, and    the opposite ends of the arc transition to the return portions along arcs having a radius of curvature of between about 0.1 to about 1.0 times the thickness dimension of the sheet of material.    
   
   
       9 . The sheet of material as defined in  claim 2  wherein, 
 the transverse dimension of the bend-inducing structure from the bend line is less than about 20 percent of the overall length dimension of the bend-inducing structure.    
   
   
       10 . The sheet of material as defined in  claim 2  wherein, 
 the bend-inducing structures are formed by a plurality of connected arcuate sections that are symmetrical about a transverse center line of the bend-inducing structure perpendicular to the bend line, and the opposite ends of the bend-inducing structure have radii of curvatures less than the radii of curvature of the return portions.    
   
   
       11 . The sheet of material as defined in  claim 10  wherein, 
 the radii of curvature of the return portions are at least about 5 times the radii of curvature of the opposite ends of the bend-inducing structure.    
   
   
       12 . The sheet of material as defined in  claim 2  wherein, 
 each return portion has a length equal to between about 2 to about 4 times the thickness dimension of the sheet of material and a radius of curvature between about 2 and about 4 times the thickness dimension of the sheet of material.    
   
   
       13 . The sheet of material as defined in  claim 12  wherein, 
 each end portion has a radius of curvature not greater than approximately the thickness dimension of the sheet of material.    
   
   
       14 . The sheet of material as defined in  claim 4  wherein, 
 the bend-inducing structures are configured and positioned to produce edge-to-face engagement of the sheet of material on opposite sides of the bend-inducing structures during bending.    
   
   
       15 . A sheet of material formed for bending along a bend line comprising: 
 a sheet of material having a plurality of bend-inducing slits positioned in longitudinally staggered relation on alternating sides of the bend line and configured to produce edge-to-face contact of the sheet of material on opposite sides of the slits during bending, the slits each being arcuate with convex sides closest to the bend line and having arcuate return portions at opposite ends of the slits extending back along the slits toward the other return portion, and the arcuate return portions having a length dimension and radius of curvature reducing stress concentrations.    
   
   
       16 . The sheet of material as defined in  claim 15  wherein, 
 the arcuate return portions have chords oriented substantially parallel to the bend line.    
   
   
       17 . The sheet of material as defined in  claim 16  wherein, 
 the radii of curvature of the arcuate return portions are at least about 2 times a thickness dimension of the sheet of material.    
   
   
       18 . The sheet of material as defined in  claim 17  wherein, 
 the radii of curvature of the return portions are between about 2 and about 4 times the thickness dimension of the sheet of material.    
   
   
       19 . The sheet of material as defined in  claim 15  wherein, 
 the sheet of material is bent along the bend line.    
   
   
       20 . The sheet of material as defined in  claim 19  wherein, 
 the sheet of material is bent along the bend line into a three-dimension structure suitable for loading transversely to the bend line.    
   
   
       21 . A method of increasing the fatigue resistance of a structure formed by bending a sheet of material along a bend line having by a plurality of bend-inducing structures positioned and configured to cause bending along the bend line, the method comprising the step of: 
 forming the bend-inducing structures to extend along the bend line and have arcuate return portions extending away from opposite ends of the bend-inducing structures and back along the bend-inducing structures toward the other return portion, the return portions having a length dimension along the bend line and a radius of curvature selected to be sufficiently large to significantly reduce stress concentration and significantly increase resistance to fatigue upon cyclical loading of the bent sheet of material the transverse to the bend line.    
   
   
       22 . The method as defined in  claim 21  wherein, 
 the step of forming the bend-inducing structures with arcuate return portions is accomplished by forming the arcuate return portions to have a radius of curvature between about 2 and about 4 times the thickness dimensions of the sheet of material.    
   
   
       23 . The method as defined in  claim 22  wherein, 
 during the forming steps, forming the bend-inducing structures as one of slits, grooves and steps in the sheet of material.    
   
   
       24 . The method as defined in  claim 23  wherein, 
 during the forming steps, forming the bend-inducing structures with a configuration producing edge-to-face engagement of the sheet of material on opposite sides of the bend-inducing structures during bending.    
   
   
       25 . A method of preparing a sheet of material for bending along a bend line into a three-dimensional structure and subsequent loading of the structure transverse to the bend line, comprising the steps of: 
 forming a plurality of bend-inducing structures along the bend line, the bend-inducing structures being at least one of slits, grooves and steps in the sheet of material positioned proximate the bend line; and    during the forming step, forming the bend-inducing structures with return portions extending from opposite ends of the bend-inducing structures away from the bend line and back along the bend-inducing structures toward the other return portion with each return portion having a length dimension along the bend line sufficient to substantially increase the resistance to fatigue failure when the structure undergoes transverse loading.    
   
   
       26 . The method as defined in  claim 25  wherein, 
 during the forming step, forming the arcuate return portions with chords oriented substantially parallel to the bend line.    
   
   
       27 . The method as defined in  claim 26  wherein, 
 during the forming step, forming the arcuate return portions with a radius of curvature at least equal to about 2 times the thickness dimension of the sheet of material.    
   
   
       28 . The method as defined in  claim 27 , and the step of: 
 after the forming step, bending the sheet of material into a three-dimensional structure.    
   
   
       29 . The method as defined in  claim 28 , and the step of: 
 after the bending step, loading the three-dimensional structure transversely to the bend line.    
   
   
       30 . A method of forming a structure from a sheet of material to resist cyclical loading comprising the steps of: 
 forming a sheet of material with a plurality of bend-inducing structures configured and positioned along a bend line to produce bending of the sheet of material along the bend line;    bending the sheet of material along the bend line to produce a three-dimensional bent structure; and    during the forming step forming each bend-inducing structure as a continuous arcuate slit having opposite ends curving away from the bend line and having arcuate return portions extending from the opposite ends and curving back along the slit toward the other return portion with distal ends of the return portions curving back toward the bend line.    
   
   
       31 . The method as defined in  claim 30 , and the step of: 
 after the bending step, cyclically loading the bent structure transversely of the bend line.    
   
   
       32 . The method as defined in  claim 31  wherein, 
 the step of forming each bend-inducing structure is accomplished by forming the arcuate return portions with a chord length extending along the bend line by at least about 20 percent of the length of the bend-inducing structure along the bend line.