REWORK DETERMINATION FOR COMPOSITE STRUCTURES WITH HEAT

INDUCED INCONSISTENCIES

BACKGROUND OF THE INVENTION

This invention relates generally to composite structures, and more particularly, to determining the remaining service life of composite structures with inconsistencies.

Increasingly components and structures for aircrafts are being made of composite materials. These composite structures may develop inconsistencies due to heat, de-lamination, puncture, scrapes and gouges. With the exception of heat induced inconsistencies, there are established procedures to address composite structures with non-heat heat induced inconsistencies.

It is not uncommon for aircraft composite structures (may also be referred to as "parts" or "components") to be exposed to elevated temperature conditions. Composite parts heat up when the aircraft is subjected to various situations such as lightning strikes, fires within the fuselage, wing structure and landing gear wells, heat impingement due to numerous or improper composite reworks, damaged thrust reversers, and broken hot air ducts.

Although the foregoing scenario is illustrated with respect to aircrafts, similar situatuins can exist in other assemblies (for example, ships, space shuttle, automobiles and others).

Current assessment techniques can detect structural inconsistencies but cannot predict the remaining service life of a part or the part's ability to perform its design function. Typically, all composite structures with heat induced inconsistencies are immediately reworked or replaced. In some instances, the rework or replacement may be pre-mature. This can result in monetary loss because an aircraft can be grounded for rework, when it may not need to be reworked. Also, a component is under utilized when it is replaced before its service life is over.

A rework or the ability to confidently defer the rework or replacement of a composite structure with inconsistencies until a major maintenance check would result in increased revenue and a decrease in unneeded reworks. In view of the above, what is needed is a method and system for assessing composite structure with heat induced inconsistencies to determine the remaining life of the structure.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a method for assessing the ability to rework a composite structure with heat induced inconsistencies is provided. The method includes acquiring information related to the composite structure with heat induced inconsistencies;

comparing this information with assessment signatures of composite structures with heat induced inconsistencies stored in a look up table; correlating the output of the compared information with material master curves; analyzing the composite structure with heat induced inconsistencies to determine its remaining capability; determining if the composite structure requires immediate rework or replacement; and displaying these results.

In another aspect of the present invention, a system for assessing the ability to rework a composite structure with heat induced inconsistencies is provided. The system includes an analysis module; a database; a compare module that communicates with a look up table in the database for comparing information to the composite structure with heat induced inconsistency assessment signatures located in the look up table; and an output module, in communication with an output interface module within the analysis module, for displaying any matches.

In yet another aspect of the present invention, computer-executable process steps stored on a computer-readable medium, the computer-executable process steps for assessing the ability to rework a composite structure with heat induced inconsistencies, the computer-executable process steps executable to perform a method comprising: acquiring information related to the composite structure with heat induced inconsistencies; comparing the information of the composite structure with heat induced inconsistencies with assessment signatures stored in a look up table; correlating the output of the compared information with material master curves; analyzing the composite structure with heat induced inconsistencies to determine its remaining capability; determining if the composite structure with heat induced inconsistencies requires immediate rework or replacement; and displaying the results of the assessment.

This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiments thereof in connection with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features and other features of the present invention will now be described with reference to the drawings of a preferred embodiment. The illustrated embodiment is intended to illustrate, but not to limit the invention. The drawings include the following:

Figure 1 shows a block diagram of a computing system for executing process steps, according to one aspect of the present invention;

Figure 2 shows the internal architecture of the computing system of Figure 1 ;

Figure 3A shows a block diagram of a system for assessing a composite structure with heat induced inconsistencies, according to one aspect of the present invention;

Figure 3B shows a lookup table in a database, according to one aspect of the present invention;

Figure 4 is a flow diagram showing the steps of populating the database, according to one aspect of the present invention; and

Figure 5 is a flow diagram showing the steps of assessing the inconsistencies and determining needed rework of a composite structure, according to one aspect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an automated method/system for assessing inconsistencies in a composite structure. The system can be implemented in software and executed by a computing system. To facilitate an understanding of the preferred embodiment, the general architecture and operation of a computing system will be described first. The specific process under the preferred embodiment will then be described with reference to the general architecture.

Computing System:

Figure 1 is a block diagram of a computing system for executing computer executable process steps according to one aspect of the present invention. Figure 1 includes a host computer 10 and a monitor 11. Monitor 11 may be a CRT type, a LCD type, or any other type of color or monochrome display.

Also provided with computer 10 are a keyboard 13 for entering data and user commands, and a pointing device (for example, a mouse) 14 for processing objects displayed on monitor 11.

Computer 10 includes a computer-readable memory storage device 15 for storing readable data. Besides other programs, storage device 15 can store application programs including web browsers and computer executable code, according to the present invention.

According to one aspect of the present invention, computer 10 can also access computer- readable removable storage device storing data files, application program files, and computer executable process steps embodying the present invention or the like via a removable memory device 16 (for example, a CD-ROM, CD-R/W, flash memory device, zip drives, floppy drives and others).

A modem, an integrated services digital network (ISDN) connection, or the like also

provide computer 10 with a network connection 12 to the World Wide Web (WWW), to the intranet - the network of computers within a company or entity within the company, or to the aircraft itself. The network connection 12 allows computer 10 to download data files, application program files and computer-executable process steps embodying the present invention.

It is noteworthy that the present invention is not limited to the Figure 1 architecture. For example, notebook or laptop computers, or any other system capable of connecting to a network and running computer-executable process steps, as described below, may be used to implement the various aspects of the present invention.

Figure 2 shows a top-level block diagram showing the internal functional architecture of computing system 10 that may be used to execute the computer-executable process steps, according to one aspect of the present invention. As shown in Figure 2, computing system 10 includes a central processing unit (CPU) 121 for executing computer-executable process steps and interfaces with a computer bus 120.

Also shown in Figure 2 are an input/output interface 123 that operatively connects output display device such as monitors 11, input devices such as keyboards 13 and a pointing device such as a mouse 14.

A storage device 133 (similar to device 15) also interfaces to the computing device 10 through the computer bus 120. Storage device 133 may be disks, tapes, drums, integrated circuits, or the like, operative to hold data by any means, including magnetically, electrically, optically, and the like. Storage device 133 stores operating system program files, application program files, computer-executable process steps of the present invention, web-browsers and other files. Some of these files are stored on storage device 133 using an installation program. For example, CPU 121 executes computer-executable process steps of an installation program so that CPU 121 can properly execute the application program.

Random access memory ("RAM") 131 also interfaces with computer bus 120 to provide CPU 121 with access to memory storage. When executing stored computer-executable process steps from storage device 133, CPU 121 stores and executes the process steps out of RAM 131.

Read only memory ("ROM") 132 is provided to store invariant instruction sequences such as start-up instruction sequences or basic input/output operating system (BIOS) sequences.

The computing system 10 can be connected to other computing systems through the network interface 122 using computer bus 120 and a network connection (for example 12). The network interface 122 may be adapted to one or more of a wide variety of networks, including local area networks, storage area networks, wide area networks, the Internet, and the like.

In one aspect of the invention, composite assessment software may be supplied on a CD- ROM or a floppy disk or alternatively could be read from the network via a network interface 122. In yet another aspect of the invention, the computing system 10 can load the composite assessment software from other computer readable media such as magnetic tape, a ROM, integrated circuit, or a magneto-optical disk.

Alternatively, the composite assessment software is installed onto the storage device 133 of the computing system 10 using an installation program and is executed using the CPU 121.

In yet another aspect, the composite assessment software may be implemented by using an Application Specific Integrated Circuit that interfaces with computing system 10.

According to the present invention, a method and system for assessing a composite structure with heat induced inconsistencies is provided. Although the system and method of the present invention are implemented using an aircraft, those skilled in the art will recognize that the principles and teachings described herein may be applied to a variety of structures made with composite materials, such as automobiles, trains and ships.

Figure 3A shows a block diagram of a system 300 for assessing a composite structure with heat induced inconsistencies. System 300 comprises a database 301 having a look up table 302 containing photographs of composite structures with heat induced inconsistencies (or "structure") samples. A photograph or picture of a composite structure with heat induced inconsistencies is taken creating a heat induced inconsistency assessment signature for that particular structure. The heat induced inconsistency assessment signature shows the possible changes to a known composite structure when exposed to heat for a known amount of time. Heat induced inconsistency assessment signatures are obtained at various temperatures, such as 350° F, 400° F, 450° F, 500° F, 550° F and 600° F.

When fabricating the composite structures with heat induced inconsistencies samples, heat induced inconsistency assessment signatures can be obtained from a variety of nondestructive inspection (NDI) techniques commonly applied to aircraft structures to detect heat induced charring, de-lamination, voids, material softening etc. and physical material changes in structural components. These techniques include transmission ultrasonics, pulse echo ultrasonics, lamb wave UT, high frequency eddy current, laser fluorescence, hardness testers and microwave inverse scattering.

In a preferred embodiment of the present invention, microwave inverse scattering is utilized to measures changes in the bulk matrix material and discrete anomalies in a composite structure. The dielectric characteristics of a composite structure can change as the result of

chemical composition or physical change. These changes can result from excessive heating, curing, hardening, residual stress and temperature gradients. By knowing the changes in a value of a known dielectric constant, characteristics related to heat induced inconsistencies can be determined. This technique uses the measurement of a scattered microwave energy field to determine dielectric constants in a material that relate to its polymerization.

Turning back to Figure 3 A, an analysis module 303 is coupled to database 301. A compare module 304, within analysis module 303, compares a composite structure with heat induced inconsistencies to the assessment signatures in look up table 302. Comparison occurs by overlaying the picture of the composite structure with heat induced inconsistencies to the structure with inconsistencies in contained in look up table 302 or by a comparison of performance data. Once the comparison is completed, any matches that were obtained are communicated to an output module 306 via an output interface module 305 within analysis module 303. Output module 306 may be any device with a monitor or any device capable of receiving a communication.

A match occurs when the picture of the composite structure with heat induced inconsistencies is the same as, or similar to, (i.e. has a certain number of characteristics in common determined by the user of the system) an assessment signature in look up table 302. The number of matches that can occur is not limited. Once a list of possible matches is generated, the user manually filters (or compares) each match in the list to the picture of composite structure with heat induced inconsistencies. By manually filtering each match, the user can determine the assessment signature that most closely matches the picture of the composite structure with heat induced inconsistencies.

It is noteworthy that the foregoing modular structure of system 300 is simply to illustrate the adaptive aspects of the present invention. The various modules can be integrated into a single piece of code, subdivided into further sub-modules or implemented in an ASIC. System 300 can be implemented in a computing system similar to computing system 10.

Figure 3 B shows lookup table 302 in database 301 which stores the assessment signatures of the fabricated composite structure with heat induced inconsistencies, according to one aspect of the present invention. Look up table 302 comprises a first column 302A and a second column 302B. First column 302 A lists NDI test results, i.e. the assessment signatures, of the fabricated composite structure with heat induced inconsistencies and second column 302B lists the corresponding remaining service life of the composite structure with heat induced inconsistencies.

Figure 4 is a flow diagram showing the steps of populating database 301, according to one aspect of the present invention. In step S400, composite structure with heat induced inconsistency samples are fabricated by applying heat to accelerate the life cycle of the materials and create heat induced inconsistencies the structure. Instead of looking at what happens to a material in 10 years, the material is assessed after a specific number of hours of use, such as 100 hours. In step S401, a NDI inspection of the fabricated composite structure with heat induced inconsistencies is performed and photographs/pictures of the fabricated composite structure with heat induced inconsistencies are taken. The NDI inspection is performed using techniques that are well known in the art, such as those described above. In step S402, the NDI signature assessments are correlated with known material aging results, i.e. the material master curves, of the material, used in the composite structure to ensure the assessment of the extent of fabricated heat induced inconsistencies of the composite structure are accurate. In step S403, the remaining life of the composite structure with heat induced inconsistencies is predicted based on the correlation in step S402. In step S404, the composite structure with heat induced inconsistencies samples are tested to verify the remaining service life. In step S405, database 301 is populated with the assessment signatures of the fabricated composite structure with heat induced inconsistencies.

Figure 5 is a flow diagram showing the steps of assessing the heat induced inconsistencies and determining needed reworks to a composite structure, according to one aspect of the present inventions. In step S500, information about a composite structure with heat induced inconsistencies is acquired. This information may include, but is not limited to, photographs/pictures and performance data.

In step S501, the photograph of a composite structure with heat induced inconsistencies is compared to heat induced inconsistency signatures in look up table 302 to determine if there are any matches. Comparison occurs by overlaying the picture of a composite structure with heat induced inconsistencies with information contained in table 302 of a composite structure with heat induced inconsistencies or by a comparison of data. A match occurs when the picture of the composite structure with heat induced inconsistencies is the same as, or similar to, (i.e. has a certain number of characteristics in common determined by the user of the system) to a heat induced inconsistency assessment signature in look up table 302. The number of matches that can occur is not limited. Once a list of possible matches is generated, the user can manually filter (or compare) each match in the list to the picture of composite structure with heat induced inconsistencies. By manually filtering each match, the user can determine the heat induced

inconsistencies assessment signature that most closely matches the picture of the composite structure with heat induced inconsistencies.

In step S502, the output of step S501 is correlated with the material master curve. In other words, if a match occurs in step S501, the performance data of the composite structure with heat induced inconsistencies is compared with the performance data in the material master curves to determine the remaining service life of the composite structure with heat induced inconsistencies.

In step S503, the remaining service life of the structure is analyzed by techniques well known in the art. In step S504, a determination is made as to whether the structure requires immediate rework or if the rework can be deferred based on the analysis in step S503. In step S505, the composite structure with heat induced inconsistencies is reworked or replaced if there is a determination in step S 504 that rework or replacement should be performed immediately. In step S506, rework or replacement of the composite structure with heat induced inconsistencies is deferred as it has been determined that the composite structure with heat induced inconsistencies has not degraded or decayed to a point where rework or replacement is necessary as the structure will still perform its designed function. In step S507, rework or replacement of the composite structure with heat induced inconsistencies is not required.

While the present invention is described above with respect to what is currently considered its preferred embodiments, it is to be understood that the invention is not limited to that described above. To the contrary, the invention is intended to cover various modifications and equivalent arrangements within the spirit and scope of the appended claims.