This application is related to co-pending U.S. patent application Ser. No. 13/310,333, filed on Dec. 2, 2011, and co-pending U.S. patent application Ser. No. 13/310,539, filed on Dec. 2, 2011, both of which applications are incorporated by reference herein in their entireties.
1. Field
The present disclosure generally relates to processes for manufacturing and/or repairing composite structures, and deals more particularly with monitoring composite structures as they are being cured.
2. Background
Fiber reinforced thermoset resin structures, such as carbon fiber epoxy, may be cured through the application of heat and pressure using autoclave or out-of-autoclave processes. In order to optimize properties of the cured structure, it is sometimes desirable to monitor temperature and/or pressure during curing to determine whether either of these process parameters are outside of specified ranges.
Several techniques have been employed to monitor temperature and/or pressure during the cure process, however each has disadvantages. For example, thermocouples may be located at specific locations on a composite structure or a composite repair in order to monitor temperature, however thermocouples only provide temperature information at specific locations and may not reveal out-of-range temperature information at other locations. Thermocouples may have less than desired reliability, and may not be practical for use on large, complex structures or composite repairs that extend over a relatively large area. In some applications, thermocouples may also interfere with the cure process itself, particularly where thermocouples are placed in incorrect areas beneath vacuum bagging material.
IR (infrared) cameras may be used to monitor temperature within exposed areas of a composite structure during curing, however infrared cameras are relatively expensive, are limited to line-of-sight monitoring, and are not capable of monitoring areas of a structure beneath the vacuum bags.
Techniques have been devised to measure the pressure being applied to a composite structure or composite repair during curing using discrete pressure sensors. However, the sensed pressure information is limited to the location of the pressure sensors, consequently, this technique does not provide useful information concerning pressure over large areas of the structure. Moreover, the use of pressure sensors can, themselves result in undesirable mark-off when installed in highly convex or concave regions of a structure where pressure measurements may be particularly useful. Furthermore, it may be impractical to use pressure sensors with certain types of curing equipment, such as press claves.
Accordingly, there is a need for a method and apparatus for monitoring process parameters, such as temperature and pressure, over large areas of a composite structure during curing. There is also a need for a method and apparatus as described above which provide a permanent visual map of temperature and pressure over the entire area of a composite structure during curing, and which may be employed to alter process parameters in real-time during the curing process, thereby optimizing the properties of the cured composite structure or repair.
The disclosed embodiments provide a system and method for monitoring processing of a composite structure to determine whether one or more processing parameters is outside of preselected limits which may affect properties of the completed structure. The embodiments provide a visual map of the entire area of the composite structure, allowing operating personnel to quickly and easily detect whether process parameters, such as temperature and pressure, are outside of preselected limits. Mapping is achieved using a chromatic film containing at least one of a thermochromatic dye and a mechanochromatic dye that is tailored to respond to specific thermal or time-temperature ranges and/or pressures. The chromatic material may be embedded into a film, or may be sprayed or otherwise applied as a coating on a sheet of paper or plastic. The chromatic film may also be in the form of a caul sheet. Process parameters may be monitored continuously during a fabrication process such as curing, and a permanent record of the map may be generated for analysis and/or comparison to a set of reference data, or maps of other composite structures. The embodiments may improve qualities of composite structures and reduce scrap.
According to one disclosed embodiment, a method is provided of monitoring at least one process parameter affecting processing of a composite structure, comprising placing a chromatic film in proximity to the composite structure, processing the composite structure, including subjecting the composite structure to heat and pressure, and using the chromatic film to monitor at least one of a temperature and pressure in real-time during the processing. Placing the chromatic film includes placing a sheet of the chromatic film over the composite structure layup. Using the chromatic film to monitor at least one of temperature and pressure includes detecting visual changes in the chromatic film to determine whether at least one of the temperature and pressure is outside a preselected range during the processing. Placing the chromatic film may include adhesively attaching each of a plurality of chromatic film segments around the perimeter of the composite structure. Using the chromatic film to provide a visual indication includes illuminating the chromatic film with light, recording an image of the chromatic film with a camera, and analyzing the recorded image to determine whether the at least one of the temperature and pressure is outside of the preselected range. The method may further comprise altering the process based on the results of the analysis of the recorded image. The chromatic film includes at least one of a thermochromatic dye, and a mechanochromatic dye. Using the chromatic film to provide a visual indication includes detecting a fluorescence or non-fluorescence of the chromatic film. The method may also comprise sealing a vacuum bag over the chromatic film and the composite structure.
According to another embodiment, a method is provided of monitoring curing of a composite structure. The method comprises placing a chromatic film in proximity to the composite structure which visually changes in response to application thereto of at least one of heat and pressure outside of preselected temperature and pressure ranges. The method also comprises curing the composite structure using heat and pressure, illuminating the chromatic film with light, and, monitoring visual changes in the illuminated chromatic film. The method further comprises recording an image of the illuminated chromatic film, and analyzing the recorded image to determine whether at least one of the heat and pressure is outside the preselected range of temperatures and pressures. The method also comprises
altering the curing of the composite structure based on the analysis of the recorded image. Placing the chromatic film includes placing the chromatic film over and extending completely across the composite structure. The composite structure may be a repair patch, and placing the chromatic film includes placing the chromatic film around the periphery of the repair patch.
According to still another embodiment, apparatus is provided curing a composite structure, comprising a tool adapted to have a composite structure layup placed thereon, and a chromatic film located in proximity to the composite structure layup for monitoring at least one of heat and pressure to which the composite structure layup is subjected. The chromatic film includes at least one of a thermochromatic dye, and a mechanochromatic dye. The chromatic film overlies and substantially covers the entire area of the composite structure. In one variation, the chromatic film substantially surrounds the periphery of the composite structure. The apparatus may further comprise a source of illumination for illuminating the chromatic film with light, and a camera for recording an image of the illuminated chromatic film. The apparatus may further comprise a vacuum bag adapted to be sealed over the composite structure layup for applying compaction pressure to the composite structure layup during curing, wherein the chromatic film is integrated with the vacuum bag. The chromatic film is responsive to at least one of heat and pressure applied to the composite structure layup during curing to provide a visual indication of whether the at least one of heat and pressure is outside a range of preselected values during the curing.
The features, functions, and advantages can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments in which further details can be seen with reference to the following description and drawings.
The novel features believed characteristic of the illustrative embodiments are set forth in the appended claims. The illustrative embodiments, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment of the present disclosure when read in conjunction with the accompanying drawings, wherein:
The composite layup 20 is consolidated by curing it in a cure apparatus 24 which may comprise, for example and without limitation, an autoclave or an oven, in which the composite layup 20 is subjected to a combination of heat 25 and pressure 27. Consolidation may be aided by use of vacuum bag 58 which applies compaction pressure to the composite layup 20.
It may be desirable in some applications to monitor certain process parameters, such as at least one of temperature of the heat 25 and pressure 27, in order to verify that the composite layup 20 has not been subjected to temperatures and pressures 27 outside of specified values or ranges of values for prescribed time periods. Subjecting the composite layup 20 to temperatures or pressures outside of the specified values may have undesired affects on the completed composite structure 20.
In accordance with the disclosed embodiments, process parameters such as at least one of temperature of the heat 25 and the pressure 27 may be continuously monitored and recorded during a fabrication process such as curing, or verified after the process has been completed. The process parameters may be monitored over the entire area, if desired, of the composite structure layup 20 in order to verify that all sections of the layup 20 have been properly processed according to specifications. In order to monitor whether the process parameters are out-of-range, a chromatic film 22 is placed in proximity to the composite structure layup 20 within the vacuum bag 58, and is thus subjected to the same temperatures and pressures within the cure apparatus 24 that are used to process the composite layup 20. The chromatic film 22 is illuminated 33 by a suitable radiation source 26 which may comprise, for example and without limitation a UV source (ultraviolet), IR (infrared) source or other radiation source of a suitable wavelength. As will be discussed below in more detail, the chromatic film 22 may visually change in response to the application thereto of heat and/or pressure during a processing cycle.
Depending upon the application, and the particular process parameters to be monitored, the chromatic film 22 may comprise a material that includes thermochromatic and/or mechanochromatic dyes that are respectively tailored to respond to specific thermal or time-temperature ranges and/or pressures. When triggered by exposure to the temperatures and/or pressures to which they have been tailored, these dyes undergo fluorescent shifts. When illuminated by a light source of a suitable wavelength, these fluorescent shifts in the chromatic film 22 become visible, manifesting themselves as a change in color or color intensity, or a turning on or off of fluorescence. As will be discussed below in more detail, the dyes may be mixed with other materials to form a film, applied as a coating (not shown) to paper or plastic, or integrated into materials used as vacuum bags.
A camera 28, which may comprise a solid-state digital camera or other suitable recording device, records images 37 of the chromatic film 22 which result from reflection or backscattering 35 of light from the chromatic film 22. Each image 37 recorded by the camera 28 is processed by a suitable computer 30 and is output to a display 34. Certain areas 36 of the chromatic film where the process parameters, such as temperature and/or pressure, are out-of-range and result in fluorescent shifts in the chromatic film 22, are made visible in the image 37 displayed to the operator 41 or may be processed directly by the computer 30. This visible, process out-of-range indication may be in the form of a change in color, color intensity or fluorescence within certain areas 36 of the chromatic film 22. Thus, an operator may visually verify that process parameters have remained within the proper range of values during an entire process cycle, or that certain areas of the chromatic film 22, and thus of the composite structure 20, have been subjected to temperatures and/or pressures that are outside of the prescribed ranges.
The computer 30 may store images 37 recorded of previously fabricated composite structures 20, or other reference data in a memory 32. The stored image 37 or reference data may be retrieved by the computer 30 and compared to later recorded images 37 for purposes of quality control or process control. Based on the image 37 recorded by the camera 28, the computer 30 may provide information to a process controller 38 that may adjust process parameters, such as temperature and/or pressure, on a real-time basis if desired, used by the apparatus 24, or in preparation for processing the next composite layup 20.
As previously discussed, the monitoring process may be carried out by recording images 37 of the chromatic film 22 and monitoring these recorded images 37 for visual changes. Image monitoring may be carried out by an operator 41, such as a human (
Attention is now directed to
Referring particularly to
During curing, a vacuum is drawn in the vacuum bag 58 to consolidate the composite rework patch 20a while heat is applied to the composite rework patch 20a. The heat may be supplied by an oven (not shown), or by local radiation sources, such as infrared lamps, or heating blankets (not shown). As in the example previously described in connection with
Attention is now directed to
Referring now to
Embodiments of the disclosure may find use in a variety of potential applications, particularly in the transportation industry, including for example, aerospace, marine, automotive applications and other applications involving processing of composite structures. Thus, referring now to
Each of the processes of method 72 may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on.
As shown in
Systems and methods embodied herein may be employed during any one or more of the stages of the production and service method 72. For example, components or subassemblies corresponding to production process 80 may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft 74 is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages 80 and 82, for example, by substantially expediting assembly of or reducing the cost of an aircraft 74. Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft 74 is in service, for example and without limitation, to maintenance and service 88. During maintenance and service 88, the disclosed embodiments may be employed to monitor curing of composite patches used to carry out repairs on the airframe 90, such as repair of a composite skin (not shown).
As used herein, the phrase “at least one of”, when used with a list of items, means different combinations of one or more of the listed items may be used and only one of each item in the list may be needed. For example, “at least one of item A, item B, and item C” may include, without limitation, item A, item A and item B, or item B. This example also may include item A, item B, and item C or item B and item C. The item may be a particular object, thing, or a category. In other words, at least one of means any combination items and number of items may be used from the list but not all of the items in the list are required.
The description of the different illustrative embodiments has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different illustrative embodiments may provide different advantages as compared to other illustrative embodiments. The embodiment or embodiments selected are chosen and described in order to best explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.
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