Abstract:
The present application provides a method of inspecting a bond joint. The method may include the steps of applying an exothermic adhesive to a first shell and/or a second shell, attaching the first shell to the second shell via the exothermic adhesive to create the bond joint, allowing the exothermic adhesive to cure, and imaging the heat released by the exothermic adhesive along the bond joint. The bond joint may be a turbine blade bond joint.

Description:
TECHNICAL FIELD 
     The present application and resultant patent relate generally to wind turbine blades and inspection systems thereof and more particularly relate to a thermographic inspection system for a composite wind turbine blade bond joint using an exothermic adhesive. 
     BACKGROUND OF THE INVENTION 
     Modern wind turbine blades generally combine low weight and low rotational inertia with high rigidity and high resistance to fatigue and wear so as to withstand the various forces and the extreme conditions encountered over a typical life cycle. Generally described, the turbine blades may be formed from two shell halves. A critical step in the manufacture of the turbine blade is the closing of the two shell halves of the blade at a leading edge, a trailing edge, and at a spar cap union with a shear web via an adhesive to create a bond joint. Verifying the width and the overall integrity of this adhesive bond is required to ensure that the turbine blade will meet performance and lifetime requirements. Failure of the turbine blade along the bond joint could lead to significant damage. 
     Current methods for the inspection of this adhesive bond joint include visual inspection and various types of non-destructive imaging inspection techniques such as ultrasonic testing. Such ultrasonic testing, however, may be time consuming and relatively costly. Moreover, some of the blade materials may be difficult to penetrate via ultrasound. Specifically, certain areas of the blade may be obscured from ultrasonic testing because of the use of foam, balsa, or other types of core materials that may not pass typical ultrasonic frequencies therethrough. Certain types of microwave inspection techniques also are known. Such microwave inspection, however, may be limited by exposure to radiation. 
     There is thus a desire for improved systems and methods of inspecting an adhesive bond joining the halves of a wind turbine blade. Preferably such systems and methods may accurately and reliably inspect the entire adhesive bond joint without requiring expensive and time consuming ultrasonic testing and the like. 
     SUMMARY OF THE INVENTION 
     The present application and the resultant patent thus provide a method of inspecting a bond joint. The method may include the steps of applying an exothermic adhesive to a first shell and/or a second shell, attaching the first shell to the second shell via the exothermic adhesive to create the bond joint, allowing the exothermic adhesive to cure, and imaging the heat released by the exothermic adhesive along the bond joint. The bond joint may be a turbine blade bond joint. 
     The present application and the resultant patent further provide a turbine blade inspection system. The turbine blade inspection system may include a number of turbine blades with a bond joint of an exothermic adhesive and a thermographic device. The thermographic device may image the heat released by the exothermic adhesive to determine the integrity of the bond joint. 
     The present application and the resultant patent further provide a turbine blade inspection system. The turbine blade inspection system may include a number of turbine blades with a bond joint of an exothermic adhesive about a first shell and a second shell and an infrared camera. The infrared camera may image the heat released by the exothermic adhesive to determine the integrity of the bond joint. 
     These and other features and improvements of the present application and the resultant patent will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a wind turbine blade. 
         FIG. 2  is a side sectional view of a portion of the wind turbine blade of  FIG. 1 . 
         FIG. 3  is a schematic diagram of thermographic inspection system for use with a wind turbine blade having an exothermic adhesive bond joint as may be described herein. 
         FIG. 4  is an expanded view of the wind turbine blade of  FIG. 3  with the exothermic adhesive bond joint. 
         FIG. 5  is a further expanded view of the wind turbine blade of  FIG. 3  with the exothermic adhesive bond joint. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, in which like numerals refer to like elements throughout the several views,  FIGS. 1 and 2  show a wind turbine blade  100  as may be described herein. Generally described, the wind turbine blade  100  may be constructed of layers of an outer skin supported by a primary spar. Specifically, the wind turbine blade  100  may extend from a tip  110  to an opposing root  120 . Extending between the tip  110  and the root  120  may be a spar cap  130  and a shear web  140 . The shear web  140  may serve as the main structural support within the wind turbine blade  100 . The spar cap  130  may be a glass portion running the length of the wind turbine blade  100  coincident with the shear web  140  so as to accommodate the tensile load on the wind turbine blade  100 . The wind turbine blade  100  and the components thereof may have any size, shape, or configuration. Other components and other configurations also may be used herein. 
     As described above, the wind turbine blade  100  may be formed in shells. For example, a first shell  150  may extend from a first shell leading edge  160  to a first shell trailing ledge  170  and may define a suction surface  180 . The first shell  150  may be bonded to a second shell  190 . The second shell  190  may extend from a second shell leading edge  200  to a second shell trailing edge  210  and may define a pressure surface  220 . The shells  150 ,  190  may be made out of fiber reinforced materials as well as core materials. Specifically, the layers of the shells  150 ,  190  may include a fiber-resin matrix. The core materials may include foam, balsa wood, engineered core materials, and the like. Other types of materials may be used herein. 
     In this example, the shells  150 ,  190  may be bonded together via an exothermic adhesive  230  to create a bond joint  240 . Examples of suitable exothermic adhesives  230  may include a methyl methacrylate monomer (MMA), different types of cyanoacrylates, and similar types of materials. Generally described, an exothermic adhesive  230  will create heat during curing due to an exothermic chemical reaction upon the addition of a catalyst and the like. Many two part epoxies are exothermic at least in part. The layers of the shells  150 ,  190  and the exothermic adhesive  230  of the bond joint  240  may be cured in a conventional fashion. 
     A defect  245  in the bond joint  240  formed by the exothermic adhesive  230  may have an impact on the overall operation and lifetime of the wind turbine blade  100 . Areas of concern for such a defect include the leading edges  160 ,  200 ; the trailing edges  70 ,  210 ; and about the spar cap  130 . Each of these areas carries at least a portion of the tensile load on the blade  100  such that any bending of the fibers in these areas may reduce the strength of the fiber. 
     The wind turbine blade  100  thus may be inspected via a wind turbine blade thermographic inspection system  250  as may be described herein. The wind turbine blade thermographic inspection system  250  may be a type of non-destructive testing using thermography. Specifically, the wind turbine blade thermographic inspection system  250  may include an infrared camera  260  and the like as is shown in  FIGS. 3 and 4 . An example of an infrared camera  260  capable of providing the thermal images herein may be offered by FLIR Systems, by Fluke Corporation, by Omega Engineering, and by other entities. Any type of heat imaging and/or sensing device may be used herein. In addition to visual inspection of the thermal images, the thermal images produced by the infrared camera  260  may be processed by different types of software and/or algorithms to ensure overall compliance with predetermined parameters and the like. Other components and other configurations may be used herein. 
     In use, the wind turbine blade  100  may be assembled as described above with the exothermic adhesive forming the bond joint  240  between the shells  150 ,  190 . As the exothermic adhesive  230  cures, heat may be released in a known manner. This heat may be visualized via the infrared camera  260  or other type of heat imaging device of the wind turbine blade thermographic inspection system  250 . The wind turbine blade thermographic inspection system  250  thus may ensure the integrity of the bond joint  240 . Moreover, the wind turbine blade thermographic inspection system  250  may verify the width  270  of the bond joint  240  at the leading edge  160 ,  200 , the trailing edge  170 ,  210 , and elsewhere as is shown in  FIG. 5 . These areas are often obscured by the foam, balsa, or other types of core materials that typically do not pass ultrasonic frequencies therethrough. 
     Further, the use of the exothermic adhesive  230  has the benefit of positioning a heat source exactly at the area of interest without the influence of an operator. The amount of heat generated must be controlled so as to avoid damage to the materials involved. The exothermic reaction provided by the exothermic adhesive  230  thus reduces the potential for an operator to overheat the area of interest. Specifically, the use of the wind turbine blade  100  and the wind turbine blade thermographic inspection system  250  provides a rapid and low cost inspection system with increased overall reliability and repeatability. Moreover, the inspection may be carried out in the field for “in situ” repairs where other types of testing may not be feasible. 
     Although the use of the exothermic adhesive  230  and the wind turbine blade thermographic inspection system  250  has been discussed in the context of the turbine blade bond joint  240  many other types of bond joints may be inspected herein. Any connection or bonding of two components may be evaluated herein. 
     It should be apparent that the foregoing relates only to certain embodiments of the present application and the resultant patent. Numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.