Patent Publication Number: US-7211767-B1

Title: Techniques for treating a surface crack on a component

Description:
BACKGROUND 
   Surface cracks in materials pose reliability concerns in a broad range of industries. For example, in the aircraft industry, a weak point on an aircraft wing flap may begin as a micro-crack which is virtually undetectably by the naked eye. Over time, the micro-crack may grow due to stresses from normal use. In particular, the ends of the crack expand outwardly, and the tip of the crack (i.e., the deep point of the crack) extends even deeper. Eventually, the micro-crack grows into a larger visible crack which is hopefully detected and fixed before a failure results. 
   One conventional approach to fixing a surface crack in a part (e.g., tiny cracks on aircraft components such as propulsion system plumbing) is to repair the crack by welding. In this approach, welding equipment fuses the two sides of the crack back together. In particular, the welding equipment applies extreme heat to make the area around the crack soft and pasty so that the material along the two sides of the crack melts back together again. In some situations, additional metallic material fuses into or above the crack to provide reinforcement. 
   Another conventional approach to fixing a surface crack in a part is to drill holes into the part at the ends of the crack. Such drilling rounds out the crack ends thus preventing the crack the growing outwardly any further. 
   Yet another conventional approach to fixing a surface crack in a part is to simply replace the part. For example, in the context of a wing flap, a team of mechanics simply removes the failed wing flap and installs a new wing flap in its place. 
   SUMMARY 
   Unfortunately, there are deficiencies to the above-described conventional approaches to fixing a part having a surface crack. For example, in the above-described conventional welding approach, the welding operation is capable of damaging the part and thus introducing weak points in other locations. In particular, the welding process often involves the application of extreme heat which not only provides desired fusing, but also provides weakening in neighboring areas of the heat-affected zone due to distortion and welding stresses. Also, due to the extreme heat, the welding process is not appropriate for fixing many types of materials such as silicon-based components. 
   Additionally, in connection with the above-described conventional hole drilling approach, the drilling of holes simply prevents the crack from spreading. This process does not strengthen the part. Rather, if anything, this process weakens the part by removing additional material from the part. 
   Furthermore, in connection with the above-described conventional part replacement approach, part replacement is very expensive. In effect, significant expense are incurred because the cost of the new part is incurred, as well as the cost to remove the cracked part and install the new part. Moreover, the possibility exists that removal of the cracked part and installation of the new part will cause damage to another part in the vicinity, e.g., fatigue in adjacent supporting structures that are overstressed during the removal and/or installation processes. 
   In contrast to the above-described conventional approaches to fixing a surface crack in a part, there is a component treatment system which is capable of utilizing electric current to repair a surface crack on a component (e.g., a conductive body). The electric current (e.g., a series of high-density, short electric pulses) is configured to melt tips of the crack (i.e., embedded narrow portions of the crack). Such current is capable of generating localized heating in high-resistance dislocations at the crack tips to repair the crack as the current passes from one side of the crack to the other. Accordingly, such current heals the crack and inhibits the crack from spreading. Furthermore, the effect of the current remains localized thus enabling the current to strengthen the material around the crack while easily avoiding damaging or weakening other portions of the component. 
   One embodiment is directed to a system for treating a conductive component. The system includes a power source, an interface configured to electrically contact with a surface of the conductive component, and a controller coupled to the power source and the interface. The controller is configured to pass electric current (e.g., electric pulses) from the power source through the interface and the component to melt tips of a set of cracks along the surface of the component. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
       FIG. 1  is a perspective view of a system for treating a component with electric current. 
       FIG. 2  is a cross-sectional view of a portion of the component as electric current passes around a surface crack. 
       FIG. 3  is a subsequent cross-sectional view of the component after the electric current has passed around the surface crack for a period of time. 
       FIG. 4  is a top view of the portion of the component when an interface of the system of  FIG. 1  is in contact with a surface of the component but at a different orientation. 
       FIG. 5  is a top view of the component when multiple portions are treated in an organized and controlled manner. 
       FIG. 6  is a flowchart of a procedure which is performed by a user of the system of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   A component treatment system is capable of utilizing electric current to repair a surface crack on a component (e.g., a conductive body). The electric current (e.g., a series of high-density, short electric pulses) is configured to melt tips of the crack (i.e., embedded narrow portions of the crack). Such current is capable of generating localized heating in high-resistance dislocations at the crack tips to repair the crack as the current passes from one side of the crack to the other. Accordingly, such current heals the crack and inhibits the crack from spreading. Furthermore, the effect of the current remains localized thus enabling the current to strengthen the material around the crack while easily avoiding damaging or weakening other portions of the component. 
     FIG. 1  shows a component treatment system  20  which is suitable for treating a set of surface cracks  22  (i.e., one or more cracks  22 ) on a surface  24  of a conductive component  26  (e.g., a planar metallic part, a silicon-based part, etc.). The component treatment system  20  includes a component interface  28 , a controller  30  and a power source  32 . The component interface  28  includes a pair of electrodes  34 (A),  34 (B) (collectively, electrodes  34 ) and an insulator  36  (shown only generally by the arrow  36 ) which is disposed between the electrodes  34 . The controller  30  couples to the interface  28  and to the power source  32  (e.g., through a set of cables). Preferably, the power source  32  and the connecting media are capable of delivering a significant amount of current (e.g., well above 80 Amperes per square millimeter). 
   During operation of the component treatment system  20 , the controller  30  is configured to take electric current  38  from the power source  32  and pass that current through the component interface  28  and the component  26  in response to commands from a user. In particular, the controller  30  is configured to send a series of high-density, short electric pulses  40  through the interface  28  and through the conductive component  26 . This results in application of non-uniform Joule energy at a highly stressed area around the crack tip (i.e., the deepest portions of the surface cracks  22 ) where the highest dislocation density is present. Accordingly, there is significant heat release in these focused area only, resulting in localized melting and mending of the crack tips. 
   The electric current  38  flows from one electrode  34 (A) to the other electrode  34 (B) through the component  22 . Preferably, the electric current  38  exceeds 80 Amperes/mm 2  in order to generate significant heating effects within the component interface  28 . In some arrangements, the electrodes are substantially linear in shape and parallel to each other (e.g., 0.5 inches to 1.0 inches apart) to distribute the electric pulses  40  in a relatively uniform manner along the X-axis across the component surface  24 . Due to such uniform distribution, the series of short electric pulses  40  provides effective localized heating down to a depth of about 2 millimeters. In some arrangements, the electric current  38  is direct current. In other arrangements, the electric current  38  is alternating current. 
   The insulator  36  of the component interface  28  (e.g., a rubber separator) is configured to inhibit the electric current  38  from arcing directly between the electrodes  38  and thus forcing the electric current  38  through the conductive component  26 . As the electric pulses  40  pass through the component  26 , the series of short electric pulses  40  generates localized heating at points of dislocations substantially at a depth of 2 millimeters or less within the component  26 . In particular, the tips of the surface cracks  22  have higher resistances than at other portions of the component  26  due to defects in the crystalline structure of the material at the tips of the cracks  22 . As a result, localized melting and repairing occurs at the crack tips thus strengthening the component  26 . Moreover, since such heating is tightly focused at the points of dislocations only, there is no extreme heating of the bulk material and, thus, there is no weakening of other portions of the component  26  as in conventional approaches such as welding, drilling holes or part replacement. Further details will now be provided with reference to  FIGS. 2 and 3 . 
     FIGS. 2 and 3  show a cross-sectional view of a portion  50  of the conductive component  26  at various stages of treatment by the component treatment system  20 . In particular,  FIG. 2  shows the portion  50  as the electric current  38  (i.e., a series of short electric pulses  40 ) passes through the component  26 .  FIG. 3  shows the portion  50  shortly after treatment (e.g., after a period of at most a few seconds of treatment has passed). As shown, the portion  50  includes a crack  22  having a tip  52  which extends in the negative Z-direction from the surface  24  of the component  26 . An area  54  immediately around the crack tip  52  initially includes dislocations  56  ( FIG. 2 ) due to breaks in the lattice of the material and thus has lower conductivity, i.e., higher resistance. That is, the area  54  has an extremely high density of dislocations  56  relative to other locations due to high plastic deformation and other stressing in that area  54 . 
   As the electric current  38  passes through the component  26  during operation of the system  20 , the area  54  tends to generate localized heating. In particular, at least some of the electric current  38  flows beneath the crack  22  from one side of the crack  22  to the other and through the area  54  causing tightly focused heating at the dislocations  56 . Taking the skin effect into account, the amount of electric current  38  flowing beneath the crack  22  and through the tip  22 , rather than around the crack  22  and along the surface  24 , may vary depending on the orientation of the crack  22  relative to the angular orientation of the electrodes  34  (also see  FIG. 1 ). Thus, the amount of electric current  38  is preferably set high enough (e.g., at least 80 Amperes/mm 2 ) to generate enough heat to cause melting at the crack tips  52  regardless of electrode orientation, but low enough so as not to cause melting of the bulk material. In some arrangements, the aggregate temperature rise in the bulk structure (i.e., the overall temperature of the component  26 ) remains small, or is negligible, during treatment. 
   As a result of the applied series of short electric pulses  40 , there is little or no distortion or inadvertent work hardening in the component  26 . Rather, only the area  54  immediately at the dislocations  56  tends to melt and thus repair itself.  FIG. 3  illustrates a mended section  58  in place of the original tip  52  (shown in phantom in  FIG. 3 ). Test data has shown situations in which up to 70% of a crack is repairable in this manner. Accordingly, the component  26  is now stronger and removal of the tip  52  inhibits further crack growth. Further details will now be provided with reference to  FIG. 4 . 
     FIG. 4  is a top view  60  of a portion of the component  26  when the component interface  28  of the system  20  is in contact with the surface  24  of the component  26 . By way of example, the electrodes  34  are shown in a different orientation compared to that shown in  FIG. 1 . In one arrangement the area covered by the electrodes  34  is approximately 0.5 square inches. 
   It should be appreciated that, in some situations, a user has visually detected a crack  22  (e.g., due to the large size of the crack  22 , due to magnification or X-ray sensing of the component  26 , etc.). In these situations, the user may prefer to position the component interface  28  in the manner shown in  FIG. 1 . That is, the user orients the electrodes  34  to be substantially parallel to the majority of the cracks  22 . Accordingly, the electric current  38  flows in a direction which is substantially perpendicular to the majority of the cracks  22  and a significant amount of the electric current  38  flows beneath the cracks  22  (i.e., along the X-axis in  FIG. 1 ). 
   It should be further appreciated that, in some situations, the user is capable of omitting visual detection of the cracks, but nevertheless may wish to treat the component  26  (e.g., to remove any hidden defects, to treat the component  26  under the assumption that the component  26  may contain micro-cracks, etc.). In these situations, the user may position the component interface  28  as shown in  FIG. 1 , or alternatively as shown in  FIG. 4  where the electrodes  34  are substantially perpendicular to the majority of the cracks  22  (or even perhaps diagonally). Of course, the user may purposefully position the interface  28  as shown in  FIG. 4  for a particular desired effect as well (e.g., thorough and comprehensive application of the series of short electric pulses  40  in multiple directions such a first treatment in along the X-axis and a subsequent treatment along the Y-axis). 
   In  FIG. 4 , the electric current  38  flows along the Y-axis which is substantially parallel to the majority of cracks  22 . Nevertheless, even in this situation, the electric current  38  repairs the tips  52  of the cracks  22  because the characteristics of the electric current  38 , a series of electric pulses  40  with sufficient density/magnitude, results in melting of the crack tips  52  ( FIGS. 2 and 3 ). Accordingly, it should be understood that the treatment process is capable of being applied for component strengthening whether cracks  22  have been initially detected or not. Further details will now be provided with reference to  FIG. 5 . 
     FIG. 5  is a top view  70  of the component  26  when multiple portions  72  of the component surface  24  are treated in an organized and controlled manner (e.g., one portion at a time) to form a matrix coverage pattern  74  (e.g., in two dimensions). Here, the user places the component interface  28  over a first portion  72 ( 1 ) and applies the electric current  38  through the first portion  72 ( 1 ). In some arrangements, the series of short electric pulses  40  is provided for a duration of a few hundred milliseconds. The user then moves the component interface  28  over a second portion  72 ( 2 ) and applies the electric current  38  in the same manner. The user repeats this process along a row  76 ( 1 ) (i.e., the X-axis) and then repeats this process for another row  76 ( 2 ), and so on. Since treatment of each portion  72  takes at most a few seconds, the user is ultimately capable of treating a relatively large surface area of the component  26  in a very short amount of time. 
   Preferably, the user partially overlaps sections  72  as shown in  FIG. 5 . Such overlapping provides a thorough and comprehensive treatment of the component  26  in total. Accordingly, any surface cracks  22  are repaired and further crack growth is inhibited. Further detail will now be provided with reference to  FIG. 6 . 
     FIG. 6  is a flowchart of a procedure  80  which is performed by a user (e.g., a person, automated equipment, etc.) using the component treatment system  20  when treating the conductive component  26 . In step  82 , the user places the component interface  28  into electrical contact with the surface  24  of the component  26  (also see  FIG. 1 ). 
   In step  84 , the user passes electric current  38  through the interface  28  and the component  26 . As the electric current  38  flows through the component  26 , the electric current melts tips of cracks  22  along the surface  24  of the component  26 . Preferably, step  84  occurs under clean and controlled environmental conditions to ensure the electric current  38  robustly flows through the component  26  and no arcing occurs directly between the electrodes  34  of the interface  28 . 
   In step  86 , the user moves the interface  28  out of electrical contact with the surface  24  of the component  26 . This may involve moving the interface  28  to another location  72  for further treatment of the component  26 , or removal of the interface  28  from the component  26  completely if treatment is complete. 
   As described above, the component treatment system  20  is capable of utilizing electric current  38  to repair a surface crack  22  on a component  26  (e.g., a conductive body). The electric current  38  (e.g., a series of high-density, short electric pulses  40 ) is configured to melt tips  52  of the crack  22  (i.e., embedded narrow portions of the crack). Such current  38  is capable of generating localized heating in high-resistance dislocations  56  at the crack tips  52  to repair the crack  22  as the current  38  passes from one side of the crack to the other. Accordingly, such current  38  heals the crack  22  and inhibits the crack  22  from growing. Additionally, the effect of the current  38  remains localized thus enabling the current  38  to strengthen the material around the crack  22  while easily avoiding damaging or weakening other portions of the component  26 . 
   While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 
   For example, it should be understood that an exemplary material for the component  26  is metal such as powder metal (PM) aluminum alloys. However, the component  26  is capable of being formed from other materials as well such as other metals (e.g., steel, etc.). Moreover, the material of the component  26  does not need to be metallic. Rather, the system  20  is capable of working on non-metallic conductive materials as well such as silicon-based materials.