Process to fracture connecting rods and the like with resonance-fatigue

Abstract

A process to fracture connecting rods and the like, that are made of high strength materials, comprises of the following mechanisms: (a) Fatigue: fluctuation of stresses in a pre-notched connecting rod due to the use of harmonic excitation will extend the notch tip in the connecting rod and will weaken the predetermined fracture plane by creating micro-cracks, (b) Resonance: resonance occurs when the frequency of the used harmonic excitation matches a natural frequency of the connecting rod, idealized as a structural system, (c) Pre-stressing forces: by applying pre-stressing forces acting in the same loading mode, the stresses in the connecting rod due to several force components can be superimposed, (d) Dynamic force: applying a dynamic force will raise the stress intensity factor, exceeding the fracture toughness of the material.

We claim:  
     
         1 . A process for the fracture separation, into a cap and a rod, of an integrally formed connecting rod having a bore therein along a predetermined fracture plane, the process comprising: 
 a) fixing a part of the connecting rod that intended to become the rod, selectively, over a stationary lower jaw, a part of the connecting rod that intended to become the cap, selectively, over an upper jaw movable along a straight line perpendicular to the predetermined fracture plane,    b) applying two harmonic forces to two sides of the connecting rod, where at any time instant, the two harmonic forces are equal in magnitude, opposite in direction, and act along a straight line that is substantially parallel to the predetermined fracture plane and perpendicular to the axis of the bore cylindrical surface, said applying being accomplished by urging two contacts against the two sides, and    c) applying a dynamic force, by urging the upper jaw away from the lower jaw to thereby fracture the connecting rod into said cap and rod.    
     
     
         2 . A process as claimed in  claim 1 , wherein step b) is preceded by applying a pre-stressing force to the upper jaw, urging said upper jaw away from the lower jaw and thereby pre-stressing the connecting rod.  
     
     
         3 . A process as claimed in  claim 1 , wherein step b) is preceded by applying two pre-stressing forces to the two sides of the connecting rod, where the two pre-stressing forces are equal in magnitude, opposite in direction, and act along a straight line that is substantially parallel to the predetermined fracture plane and perpendicular to the bore axis, said applying being accomplished by urging the two contacts against the two sides.  
     
     
         4 . A process as claimed in  claim 1 , wherein step b) is preceded by: 
 a) applying a pre-stressing force to the upper jaw, urging said upper jaw away from the lower jaw and thereby pre-stressing the connecting rod, and    b) applying two pre-stressing forces to the two sides of the connecting rod, where the two pre-stressing forces are equal in magnitude, opposite in direction, and act along a straight line that is substantially parallel to the predetermined fracture plane and perpendicular to the bore axis, said applying being accomplished by urging the two contacts against the two sides.    
     
     
         5 . A process as claimed in any one of  claims 1  to  4 , wherein the frequency of the harmonic forces is substantially the same as a selected natural frequency of a structural system that idealizes the connecting rod with all movements and rotations constraints imposed on said connecting rod during the fracturing process, said selected natural frequency is the natural frequency associated with a natural vibration mode that has substantially the same configuration of the characterizing deformed shape of said structural system under the effect of the harmonic forces.  
     
     
         6 . A process as claimed in any one of  claims 1  to  5 , wherein said dynamic force is applied during a time period centered on a time instant at which the deformed shape of the connecting rod is the closest to its original shape.  
     
     
         7 . A process as claimed in any one of  claims 1  to  5 , wherein said dynamic force is an impulsive force applied substantially at a time instant at which the deformed shape of the connecting rod is the closest to its original shape.  
     
     
         8 . A process as claimed in any one of  claims 1  to  5 , wherein said dynamic force is applied during a time period centered on a time instant at which the stress intensity factor corresponding to the harmonic forces has a maximum value.  
     
     
         9 . A process as claimed in any one of  claims 1  to  5 , wherein said dynamic force is an impulsive force applied substantially at a time instant at which the stress intensity factor corresponding to the harmonic forces has a maximum value.