Patent Publication Number: US-2018038779-A1

Title: Embedded strain sensor network

Description:
FIELD OF THE INVENTION 
     The present subject matter relates generally to systems and methods for monitoring and measuring component strain, and more particularly to systems and methods which provide full local and global strain capture of all strain components. 
     BACKGROUND OF THE INVENTION 
     Throughout various applications, components are subjected to numerous extreme conditions (e.g., high temperatures, high pressures, large stress loads, etc.). In such applications, an apparatus&#39;s individual components may suffer creep and/or deformation over time that may reduce the component&#39;s usable life. Such concerns might apply, for instance, to some turbomachines, such as gas turbine systems. During operation of a turbomachine, various components (collectively known as turbine components) within the turbomachine and particularly within the turbine section of the turbomachine, such as turbine blades, may be subject to creep due to high temperatures and stresses. For turbine blades, creep may cause portions of or the entire blade to elongate so that the blade tips contact a stationary structure, for example a turbine casing, and potentially cause unwanted vibrations and/or reduced performance during operation. 
     Accordingly, components such as turbine components may be monitored for creep. One approach to measure and monitor components for creep is to configure strain sensors with a plurality of nodes on or embedded in the surface of the components, and analyze the nodes of the strain sensors at various intervals to monitor for deformations associated with creep strain. Such sensors only measure strain in and along the two-dimensional surface. Further, such sensors, and in particular the nodes thereof are exposed to the operating environment of the component. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention. 
     In a first exemplary embodiment, a component for a gas turbine is provided. The component includes an outer surface, an interior volume, the interior volume comprising a first material having a first radiopacity, a plurality of nodes embedded within the interior volume and spaced from the outer surface, the plurality of nodes defining a three-dimensional array, each of the plurality of nodes comprising a second material having a second radiopacity. The second radiopacity is different from the first radiopacity. 
     In a second exemplary embodiment, a method of making a turbine component having an interior volume is provided. The method includes forming the interior volume using a first material having a first radiopacity and forming a three-dimensional array of nodes within the interior volume, each node of the three-dimensional array comprising a second material having a second radiopacity, wherein the second radiopacity is different from the first radiopacity. 
     In a third exemplary embodiment, a method of monitoring strain in a component is provided. The method includes determining a first location of a plurality of internal nodes within the component based on the radiopacity of the nodes, recording the first location of the nodes, subjecting the component to at least one duty cycle, determining a second location of the plurality of nodes after the at least one duty cycle, comparing the second location of the plurality of nodes to the first location of the plurality of nodes, calculating a displacement of the nodes from the first location to the second location, and calculating local strain on the component based on the displacement of the nodes. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures. 
         FIG. 1  provides a perspective view of an exemplary component including an embedded strain sensor network comprising a plurality of nodes according to various embodiments of the present disclosure. 
         FIG. 2  provides a longitudinal section view of an exemplary component according to various embodiments of the present disclosure. 
         FIG. 3  provides a transverse section view of the exemplary component of  FIG. 2 . 
         FIG. 4  provides a longitudinal section view of another exemplary component according to various embodiments of the present disclosure. 
         FIG. 5  provides a transverse section view of still another exemplary component according to various embodiments of the present disclosure. 
         FIG. 6  is a flow chart illustrating a method according to various embodiments of the present disclosure. 
         FIG. 7  is a flow chart illustrating another method according to various embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     Referring now to  FIGS. 1 through 5 , various example components  10  are illustrated, each with a plurality of embedded nodes  40  configured therein. The component  10  can comprise a variety of types of components used in a variety of different applications, such as, for example, components utilized in high temperature applications. In some embodiments, the component  10  may comprise an industrial gas turbine or steam turbine component such as a combustion component or hot gas path component. In some embodiments, the component  10  may comprise a turbine blade, compressor blade, vane, nozzle, shroud, rotor, transition piece or casing. In other embodiments, the component  10  may comprise any other component of a turbine such as any other component for a gas turbine, steam turbine or the like. In some embodiments, the component may comprise a non-turbine component including, but not limited to, automotive components (e.g., cars, trucks, etc.), aerospace components (e.g., airplanes, helicopters, space shuttles, aluminum parts, etc.), locomotive or rail components (e.g., trains, train tracks, etc.), structural, infrastructure or civil engineering components (e.g., bridges, buildings, construction equipment, etc.), and/or power plant or chemical processing components (e.g., pipes used in high temperature applications). 
     As may be seen in the example embodiments illustrated by  FIGS. 1 through 5 , the component  10  has an exterior surface  12  beneath which nodes  40  may be configured, and further includes an interior volume  14  formed from a first material, which is the predominant material of the component  10 . Exterior surface  12  generally comprises the outermost extent of component  10 , and may be of the same material as the first material of interior volume  14  or may be a distinct material, e.g., an applied surface coating. A plurality of nodes  40  may be embedded within the interior volume  14 . The nodes  40  may be formed from a second material that is different from the first material of the interior volume  14 . In particular, the second material of the nodes  40  may differ from the first material of the interior volume  14  in radiographic properties, that is, any material property which can be readily detected by radiographic scans. As discussed herein, the nodes  40  form a strain sensor network and are advantageously utilized to measure the strain of the component  10 . 
     The component  10  can take a variety of shapes, such as polygonal, curvilinear, tapered, prismatic, e.g., cylinder or rectangular prism, solid or hollow. The nodes  40  can be of any shape, regular or irregular, e.g., circular, oblong, ovoid, polygonal, elongate or other shapes. The nodes  40  define a three-dimensional array which can take a variety of forms, e.g., the nodes  40  may be positioned in a regularly-spaced grid or the nodes  40  may be positioned more or less arbitrarily and/or the relative locations of the nodes  40  may be constrained by, e.g., a minimum value for distance X between nodes  40  or a minimum value for distance Y from the outer surface  12  of the component  10  to any node  40 . For example, the minimum value for distance X between nodes  40  can be selected based on the fracture mechanics of the predominant material (i.e., the first material of the interior volume  14 ) of the component  10  and in such embodiments the nodes  40  can be arrayed in a regular manner or the distance between adjacent nodes may vary so long as it is at least the minimum. Additionally, the characteristics of the second material of the nodes  40  may influence the determination of the minimum value for distance X between nodes  40 . 
     In various embodiments, and in particular when the second material of the nodes  40  is less dense than the first material of the interior volume  14 , and in particular where the nodes  40  are air-filled voids, nodes  40  that are too large, too numerous, and/or too close together can create a weak spot in the component  10  which may be considered a mechanical defect in the component  10 . Thus, it is preferred to maintain at least minimum value for distances X between nodes  40  and at most maximum sizes of the nodes  40  in such embodiments. 
     As mentioned above, the second material of the nodes  40  may differ from the first material of the interior volume  14  in radiographic properties. For example, in some embodiments, the first material and the second material may differ in radiodensity or radiopacity. One skilled in the art will recognize that radiopacity is influenced primarily by the density and atomic number of a material. Thus, the first material and the second material may differ in their density and/or atomic number in order to provide nodes  40  with a radiopacity that is distinct from that of interior volume  14 . 
     As may be seen in, e.g.,  FIGS. 2 and 3 , component  10  may in some embodiments be a hollow component, such as a nozzle, transition piece, or duct. In the particular example illustrated by  FIGS. 2 and 3 , component  10  is tapered with straight walls forming a generally conical or frustoconical shape. As illustrated in  FIGS. 2 and 3 , in some embodiments, the second material of the nodes  40  may be a solid material of differing radiopacity, either greater or lesser, than that of the first material of the interior volume  14 . As illustrated in  FIGS. 2 and 3 , in some embodiments, the nodes  40  may be regularly shaped, e.g., spherical. 
     As may be seen in, e.g.,  FIG. 4 , component  10  may in some embodiments be a hollow component, such as a nozzle, transition piece, or duct. In the particular example illustrated by  FIG. 4 , component  10  is configured with curved walls, e.g., as in a transition piece which may be provided between a combustor and a nozzle. In some embodiments, the second material of the nodes  40  may be a material having lesser radiopacity than the first material of the interior volume  14 , e.g., as illustrated in  FIG. 4 , the nodes  40  may be voids in the interior volume  14 . As illustrated in  FIG. 4 , in some embodiments, the nodes  40  may be of various differing shapes, which can include regular or irregular shapes. 
     As may be seen in, e.g.,  FIG. 5 , component  10  may in some embodiments be a solid component, such as an airfoil, rotor vane, or stationary vane. In the particular example illustrated by  FIG. 5 , exterior surface  12  of component  10  is predominantly curved, although it is equally possible to provide a component with a straight line exterior, or some combination of straight and curved. It is to be understood that any form or profile of exterior surface  12  may be used, and in certain embodiments the shape of the exterior surface  12  may influence the configuration of the nodes  40  and the three-dimensional array defined thereby, e.g., as illustrated in  FIG. 5 , fewer nodes  40  are provided in the more sharply curved portions of component  10  in order to maintain a minimum value for distance Y between outer surface  12  and nodes  40 . As illustrated in  FIG. 5 , in some embodiments, the nodes  40  may have oblong or elliptical cross-section. It is also possible within the scope of the disclosure that the nodes  40  may be elongated (e.g., extending in the direction perpendicular to the view illustrated in  FIG. 5 ). Such elongate members may be, e.g., reinforcing fibers which may have the second material of nodes  40  implanted therein. 
     The various embodiments disclosed herein may be combined such that features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. For example, the component  10  of  FIG. 5  may also or instead have nodes  40  which are voids (as illustrated in  FIG. 4 ), and the nodes  40  arranged to define a regularly-spaced array of  FIG. 5  may be provided in components  10  such as illustrated in any of the other  FIGS. 2 through 4 , and/or the component  10  of  FIG. 5  may have nodes  40  arrayed in a different pattern, such as a hexagonal grid rather than a rectangular grid, or various other patterns which may be regular, arbitrary with minimum constraints, or random. The foregoing examples are for illustration only and without limitation, numerous other combinations of features will be apparent to one of ordinary skill in the art and all such variations are considered within the scope of the present disclosure. 
     In some embodiments, when the three-dimensional array is sufficiently large, a portion of the three-dimensional array defined by the nodes  40  can be dedicated to serialization, i.e., binary encoding of data in a serialization area. For example, if the array is defined by a ten-by-ten-by-ten grid of nodes  40 , then the middle five-by-five-by-five area can be dedicated for serialization and the rest for strain measurement. In such embodiments, the presence of a node in the serialization area can equate to binary number 1 while the absence of a node in the serialization area can equate to binary number 0. Thus, many different data such as a component number, sensor number, sensor location and so forth can be coded in binary form and implanted in the three-dimensional array defined by the nodes  40 . 
     Suitable materials for component  10  (and more specifically the first material of the interior volume  14  of the overall component  10 ) can include nickel or cobalt based superalloys, e.g., in high-temperature applications. Additional materials which can be employed include stainless steel or ceramic matric composite (“CMC”). A CMC generally comprises a ceramic matrix with ceramic reinforcing fibers embedded therein. In some embodiments wherein the component  10  is a CMC, the first material of the interior volume  14  may comprise the ceramic matrix and the second material of the nodes  40  can be implanted in the fibers before infiltration of the matrix material. Still further materials are possible as well. 
     In some embodiments when the first material of the interior volume  14  is stainless steel, the second material of the nodes  40  can also be a stainless steel having a differing radiopacity. For example, a stainless steel alloy comprising Cobalt, Chromium, and Molybdenum (CoCrMo steel) having a density of about 0.298 pounds per cubic inch can be used as the first material of the interior volume  14  of the component  10 . Further in such embodiments, the second material of nodes  40  may be class 304 stainless steel having a density of about 0.285 pounds per cubic inch. 
     As illustrated in  FIG. 7 , in some embodiments, a method  200  of making a component  10  comprises a designing step  210  of designing a three-dimensional array of nodes  40 , a forming step  220  of forming an outer surface, a forming step  230  of forming an interior volume predominantly of a first material  14  having a first radiopacity, and a forming step  240  of forming the designed three-dimensional array of nodes  40  within the interior volume with each node  40  spaced at least a predetermined minimum distance from the outer surface  12  and each node  40  spaced at least a predetermined minimum distance from every other node  40 , wherein the nodes  40  comprise a second material having a second radiopacity and the second radiopacity is not equal to the first radiopacity. 
     Nodes  40  in accordance with the present disclosure may be incorporated into component  10  using any suitable techniques, including direct metal laser melting (DMLM); other suitable additive manufacturing techniques; or identifying pre-existing internal characteristics (e.g., naturally-occurring voids) of the component  10  that can function as the nodes  40 . For example, the nodes  40  can be microstructural features of the material. These features can be non-metallic inclusions or voids, large precipitates in metallic materials, nodular graphite particles in cast irons, non-metallic or metallic features in composite materials, and other microstructural features. Additionally, component  10  can be manufactured by casting such that nodes  40  can be embedded beneath exterior surface  12  by introducing nodes  40  into the mold before the interior volume  14  has solidified, in which case nodes  40  can become fixed in position within the interior volume  14  once solidification is complete. 
     Component  10  can be made by additive manufacturing, e.g., DMLM, and nodes  40  can be formed by manipulating the manufacturing process. For example, the laser can be configured to provide lack of fusion in the base powder material, either randomly or in selected locations, to form an array of nodes  40  that comprise voids, e.g., as in the example illustrated in  FIG. 4 . Additionally, a combination of voids and other node materials may be used. 
     As another example using additive manufacturing, the first material of the interior volume  14  (which can be, e.g., CoCrMo steel) may predominate the powder bed with between about 0.001% and about 10% by weight of the second material of the nodes  40  (which can be, e.g., class 304 steel) added in. In such embodiments, the second material of the nodes  40  can be specifically placed in designated locations, e.g., by a robotic arm. Thus, it is possible to predesign the location of the nodes  40  and provide a predetermined initial configuration for the three-dimensional array defined thereby. 
     As illustrated in  FIG. 6 , in some embodiments, a method  100  of monitoring strain in a component, comprises a determining step  110  of determining a first location of a plurality of internal nodes  40  within the component  10 , a recording step  120  of recording the first location of the nodes  40 , a subjecting step  130  of subjecting the component  10  to at least one duty cycle, a determining step  140  of determining a second location of the plurality of nodes  40  without removing the component  10  from service, a comparing step  150  of comparing the second location of the plurality of nodes  40  to the first location of the plurality of nodes  40 , a calculating step  160  of calculating a displacement of the nodes  40  from the first location to the second location, and a calculating step  170  of calculating local strain on the component  10  based on the displacement of the nodes  40 . 
     Various scanning techniques, including radiography such as x-ray or computerized tomography (CT) scans may be used to discern the initial configuration of the three-dimensional array within component  10  formed by nodes  40 . The initial configuration can include the relative distances X between one node  40  and the next most proximate node  40  in each direction, and/or the relative distances Y from the exterior surface  12  for each node or for those nodes  40  which comprise the exterior of the array, i.e., those nodes  40  which are relatively closer to the exterior surface  12  than other nodes  40 . In embodiments wherein the initial configuration of the node array is predetermined, e.g., when a regular grid is designed and specifically implemented, the designed configuration may be used as the initial configuration, or the finished component  10  may be scanned to determine the initial configuration as well as for quality control of the manufacturing process. Once determined, the initial configuration may then be stored or recorded, e.g., in a computer memory, and the component  10  placed in service. It should be noted that because component  10  is to be placed in service, the array of nodes  40  may be designed so that the mechanical properties, e.g., fracture mechanics, of the component  10  are not altered in a way that would cause a deleterious effect on the serviceability of component  10 . In other words, the array of nodes may be designed taking into account the fracture mechanics of the first material of the interior volume  14  so that no known mechanical defect is created as a result of the nodes  40 . As noted above, in order to avoid creating a known mechanical defect, a minimum value for the distances X between nodes  40  can be selected based on the fracture mechanics of the first material of the interior volume  14  of the component  10 , and in such embodiments distance X between adjacent nodes  40  may be at least the minimum distance value. 
     As mentioned above, various scanning techniques may be used within the scope of the present subject matter. In some embodiments, CT scanning can be particularly advantageous. For example, when nodes  40  comprise microstructural features, as discussed above, a CT scanner known as micro and nano CT can then be used to extract very fine information regarding such microstructural distributed sensor nodes. As a result, much more accurate local strain information may be obtained which can help development of new materials and evaluate materials in micro and nano scale. 
     Suitable apparatus for scanning the component  10 , e.g., while performing the step  110  of determining a first location of a plurality of internal nodes  40  within the component  10  and/or the determining step  140  of determining a second location of the plurality of nodes  40 , can be a personal computer, x-ray scanner, or other scanning device which includes a suitable processor. In general, as used herein, the term “processor” refers not only to integrated circuits referred to in the art as being included in a computer, but also refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits. Suitable processors may also include various input/output channels for receiving inputs from and sending control signals to various other components with which the processor is in communication, such as an imaging device, data acquisition device, etc. Such processors may generally perform various steps as discussed herein. Further, it should be understood that a suitable processor may be a single master processor in communication with the other various components of a scanner or scanning system, and/or may include a plurality of individual component processors, i.e. an imaging device processor, a data acquisition device processor, a robotic arm processor, etc. The various individual component processors may be in communication with each other and may further be in communication with a master processor, and these components may collectively be referred to as a processor. 
     Once component  10  is placed in service, it may be subjected to a variety of environmental conditions, the result of which over time can be strain deformation and creep. Such deformation may be detected by determining a second configuration of the three-dimensional array defined by nodes  40  based on the location of nodes  40  using radiography or other scanning techniques. The second configuration may include, e.g., changes in the relative distances X between nodes  40  and/or changes in the distances Y from exterior surface  12  for at least a portion of the nodes  40 . Because the configuration of the three-dimensional array defined by nodes  40  and changes thereto can be determined by scanning, indirect internal strain measurement (e.g., without destructive testing) is provided. By comparing the second configuration of the three-dimensional array defined by nodes  40  to the recorded initial configuration based on the location of nodes  40 , displacement of the nodes  40  from their initial locations can be determined. Further, the local strain on the component can be calculated based on the displacement of the nodes  40 . Because the array is three-dimensional and the configurations thereof are measured and compared in all directions, the displacement can be measured in three dimensions, which permits full local strain capture, i.e., calculation of all strain components. In particular, the three-dimensional strain can include six independent components, three normal strains and three shear strains, e.g., both normal and shear strains in each of longitudinal, radial, and circumferential directions. 
     So long as the calculated strain and deformation are within acceptable operating parameters, the component  10  may be kept in service after the strain is calculated. Subsequently, the above steps may be repeated to determine and compare a third configuration, a fourth configuration, and so on. Thus, by iterating the steps of determining a second (or third, fourth, or other subsequent) location of the plurality of nodes, comparing the subsequent location of the plurality of nodes to one or more prior location(s) of the plurality of nodes, calculating a displacement of the nodes, and calculating local and/or global strain on the component based on the displacement of the nodes, strain monitoring may be provided over the useful life of the component. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.