Patent Publication Number: US-2020282698-A1

Title: Panel and method of forming a three-sheet panel

Description:
PRIORITY 
     This application is a divisional of U.S. Ser. No. 15/443,235 filed on Feb. 27, 2017. 
    
    
     FIELD 
     The present application relates to multilayer structures, and is particularly directed to a panel and a method of forming a three-sheet panel. 
     BACKGROUND 
     Multilayer structures are typically formed from a core sheet sandwiched between two face sheets. The core sheet of a multilayer structure defines substantial void space and has an effective cross-sectional thickness that is substantially greater than the cross-sectional thicknesses of the adjacent face sheets. Therefore, multilayer structures typically possess relatively high strength and stiffness at relatively low weight. As such, multilayer structures are used in various aerospace applications. 
     Superplastic forming is a known technique for manufacturing multilayer structures, such as expanded two-sheet panels (no core sheet) and expanded three-sheet panels (a core sheet positioned between two face sheets), which may be used as alternatives to traditional honeycomb multilayer structures. Superplastic forming is a metal forming process that takes advantage of the superplasticity of certain materials, such as titanium alloys, aluminum alloys and nickel alloys, at elevated temperatures. When such materials are heated to a superplastic state, they become pliable and can be expanded (e.g., by gas pressure) against a mold to achieve a desired shape. During expansion, the material can experience elongation of several hundred percent. 
     While the void space in multilayer structures advantageously reduces density (increases bulk), it presents a complication when a multilayer structure is subjected to thermally induced stress due to thermal gradients in the multilayer structure. For example, the multilayer structure may comprise a three-sheet panel (i.e., a core sheet positioned between two face sheets) that is used in a thrust reverser of an aircraft engine. In this example implementation, one face sheet (i.e., the inner sheet) faces toward the aircraft engine, and the other face sheet (i.e., the outer sheet) on the other side of the core sheet faces away from the aircraft engine. Since the inner sheet is closer to the aircraft engine than the outer sheet, the inner sheet is exposed to higher temperatures than the outer sheet during operation of the aircraft engine. The thermal gradient between the inner sheet and the outer sheet results in thermally induced stress in the three-sheet panel. 
     Accordingly, those skilled in the art continue with research and development efforts in the field of multilayer structures including three-sheet panels. 
     SUMMARY 
     In one aspect, a panel comprises a first face sheet and a second face sheet spaced apart from the first face sheet. The panel further comprises a core sheet intercoupled between the first face sheet and the second face sheet. Each of the first and second face sheets is made of a material having a thermal expansion that is different from the thermal expansion of the other face sheet. 
     In another aspect, a method is provided of forming a three-sheet panel. The method comprises selecting a first face sheet made of a first thermal expansion material, and selecting a second face sheet made of a second thermal expansion material that is different from the first thermal expansion material. The method also comprises attaching each of the selected first and second face sheets to a core sheet to sandwich the core sheet between the first and second face sheets to provide a precursor panel. The method further comprises processing the precursor panel to form the three-sheet panel. 
     In yet another aspect, a method is provided of forming a three-sheet panel. The method comprises selecting a first face sheet made of INCOLOY Alloy 909, and selecting a second face sheet made of INCONEL Alloy 625. The method also comprises selecting a core sheet made of INCONEL Alloy 625, and attaching each of the selected first and second face sheets to the core sheet to sandwich the core sheet between the first and second face sheets to provide a precursor panel. The method further comprises processing the precursor panel to form the three-sheet panel. 
     In still another aspect, a method is provided of forming a three-sheet panel. The method comprises attaching a first face sheet and a second face sheet to a core sheet to sandwich the core sheet between the first and second face sheets. The method also comprises superplastic forming the first face sheet at a different rate of expansion than the second face sheet to form the three-sheet panel. 
     Other aspects will become apparent from the following detailed description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is cross-sectional view of a superplastic three-sheet panel constructed in accordance with an example embodiment. 
         FIG. 2  is a thermal expansion profile of example suitable materials that can be used to make the superplastic panel of  FIG. 1 . 
         FIG. 3  is cross-sectional view of a superplastic three-sheet panel constructed in accordance with another example embodiment. 
         FIG. 4  is a flow diagram illustrating an example method of superplastic forming a three-sheet panel in accordance with an example embodiment. 
         FIG. 5  is a flow diagram illustrating another example method of superplastic forming a three-sheet panel in accordance with another example embodiment. 
         FIG. 6  is a flow diagram illustrating another example method of superplastic forming a three-sheet panel in accordance with another example embodiment. 
         FIG. 7  is a flow diagram of an aircraft manufacturing and service methodology. 
         FIG. 8  is a block diagram of an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
     The present application is directed to panels and methods of forming three-sheet panels. The specific panel, forming method, and the industry in which the panel and forming method are implemented may vary. It is to be understood that the disclosure below provides a number of embodiments or examples for implementing different features of various embodiments. Specific examples of components and arrangements are described to simplify the present disclosure. These are merely examples and are not intended to be limiting. 
     By way of example, the disclosure below describes superplastic panels and methods of superplastic forming three-sheet panels for aircraft. More specifically, the disclosure below describes a superplastic formed three-sheet panel for use in a thrust reverser of an aircraft engine. The three-sheet panel and method of superplastic forming the three-sheet panel may be implemented by an original equipment manufacturer (OEM) for manufacturing superplastic panels in compliance with military and space regulations. 
     Referring to  FIG. 1 , a superplastic panel  100  constructed in accordance with an example embodiment is illustrated. Superplastic panel  100  includes a first face sheet  110 , a second face sheet  120  spaced apart from the first face sheet  110 , and a core sheet  130 . The first face sheet  110 , the second face sheet  120 , and the core sheet  130  form a multi-layered structure  140 . 
     While the multi-layered structure  140  of the superplastic panel  100  is shown and described having three layers (i.e., the first face sheet  110 , the second face sheet  120 , and the core sheet  130 ), additional layers, such as additional core sheets, additional face sheets and/or additional other sheets, may be included in the layered structure  140  without departing from the scope of the present disclosure. 
     The core sheet  130  of the superplastic panel  100  includes a first major side  131  and an opposed second major side  132 . The first face sheet  110  may be connected (e.g., adhered, welded, braised, mechanically fastened etc.) to the first major side  131  of the core sheet  130  and the second face sheet  120  may be connected (e.g., adhered, welded, braised, mechanically fastened etc.) to the second major side  132  of the core sheet  130 , thereby sandwiching the core sheet  130  between the first face sheet  110  and the second face sheet  120 , and forming the layered structure  140 . 
     Compositionally, each of the first and second face sheets  110 ,  120  of the superplastic panel  100 , which may be single ply or multi-ply, may be formed from various materials or combinations of materials. The composition of each of the first and second face sheets  110 ,  120  may be the same as, similar to, or different from the composition of the core sheet  130 . As one example, each of the first and second face sheets  110 ,  120  may be formed from a metal or metal alloy, such as steel, titanium, a titanium alloy, aluminum or an aluminum alloy. As another example, each of the first and second face sheets  110 ,  120  may be formed from a composite, such as a carbon fiber-reinforced composite or a fiberglass composite. As yet another example, each of the first and face sheets  110 ,  120  may be formed from a ceramic material. The composition of the first face sheet  110  may be the same as, similar to, or different from the composition of the second face sheet  120 . 
     Each of the first and second face sheets  110 ,  120  is made of a material having a thermal expansion that is different from the thermal expansion of the other face sheet. The material of the first face sheet  110  comprises a low thermal expansion material, and the material of the second face sheet  120  comprises a high thermal expansion material. In some embodiments, the material of the first face sheet  110  comprises an iron alloy comprising 35.0 weight percent (wt %) to 40.0 wt % nickel, 12.0 wt % to 16.0 wt % cobalt, 4.3 wt % to 5.2 wt % niobium, and 1.3 wt % to 1.8 wt % titanium, commonly known as INCOLOY® Alloy 909. In some embodiments, the material of the second face sheet  120  comprises a nickel alloy comprising at least 58.0 wt % nickel, 20.0 wt % to 23.0 wt % chromium, at most 5.0 wt % iron, 8.0 wt % to 10.0 wt % molybdenum, and 3.15 wt % to 4.15 wt % niobium, commonly known as INCONEL® Alloy 625. INCOLOY and INCONEL are trademarks of Special Metals Corporation. 
     In some embodiments, the first face sheet  110  has a coefficient of thermal expansion between about 4.0 parts-per-million per degrees Fahrenheit (ppm/° F.) and about 5.5 ppm/° F. The first face sheet  110  has a thickness between about 0.01 inches (0.025 centimeters) and about 0.125 inches (0.318 centimeters). The first face sheet  110  has a density between about 0.25 lbs/in 3  and about 0.40 lbs/in 3 . 
     In some embodiments, the second face sheet  120  has a coefficient of thermal expansion between about 7 ppm/° F. and about 10 ppm/° F. The second face sheet  120  has a thickness between about 0.01 inches (0.025 centimeters) and about 0.125 inches (0.318 centimeters). The second face sheet  120  has a density between about 0.25 lbs/in 3  and about 0.40 lbs/in 3 . 
     In some embodiments, the core sheet  130  has a coefficient of thermal expansion between about 7 ppm/° F. and about 10 ppm/° F. The core sheet  130  is intercoupled between the first face sheet  110  and the second face sheet  120 . The core sheet  130  has a thickness between about 0.01 inches (0.025 centimeters) and about 0.10 inches (0.254 centimeters). The core sheet  130  has a density between about 0.25 lbs/in 3  and about 0.40 lbs/in 3 . An example core sheet material is commercially available as part number CarTech® 625 Alloy. CarTech is a trademark of Carpenter Technology Corporation. Other materials that can be used for the core sheet  130  are possible. 
     In some embodiments, the cross-sectional thickness of the core sheet  130  may be relatively thick, as compared to the cross-sectional thickness of the first face sheet  110  and the cross-sectional thickness of the second face sheet  120 . In some embodiments, despite being relatively thick, the core sheet  130  has a relatively lower density (basis weight divided by cross-sectional thickness), as compared to the densities of the first face sheet  110  and the second face sheet  120 . 
     Referring to  FIG. 2 , an example thermal expansion profile  200  of suitable materials (i.e., for the first and second face sheets  110 ,  120 ) that can be used to make the superplastic panel  100  of  FIG. 1  is illustrated. First solid diagonal line  210  represents the lower thermal expansion of the first face sheet  110 , and second solid diagonal line  220  represents the higher thermal expansion of the second face sheet  120 . Dashed horizontal line  230  intersects the second diagonal line  220  at a lower temperature T 1 , and intersects the first diagonal line  210  at a higher temperature T 2 . The difference between the higher temperature T 2  and the lower temperature T 1  is up to 800° F. 
     The combination of the first face sheet  110 , the second face sheet  120 , and the core sheet  130  cooperate to enable superplastic panel  100  to withstand a temperature up to or above 1000° F. without degradation of the superplastic panel  100  when the first face sheet  110  is exposed to more heat than the second face sheet  120 , such as when the superplastic panel  100  is installed and in service on a thrust reverser of an aircraft engine. 
     Those skilled in the art will appreciate that only a portion of the superplastic panel  100  is shown in  FIG. 1 , and that the overall size and shape of the superplastic panel  100  may depend on the end application. For example, the disclosed superplastic panel  100  may be used as a wall panel forming the inlet inner wall, fan duct and/or exhaust nozzle of a bypass gas turbine aircraft engine and, therefore, may be sized, shaped and contoured accordingly. Additionally, while the superplastic panel  100  is shown in  FIG. 1  as being a substantially curved structure, planar superplastic panels, such as superplastic panel  300  shown in  FIG. 3 , are also contemplated. As shown in  FIG. 3 , superplastic panel  300  includes first face sheet  310 , second face sheet  320 , and core sheet  330  between first and second face sheets  110 ,  120  to form multi-layered structure  340 . Other cross-sectional profiles of superplastic panels are possible. 
     The following example illustrates a method of superplastic forming a three-sheet panel in accordance with an embodiment. The example superplastic forming method is intended to illustrate, but in no way limits, the scope of the invention. 
     Referring to  FIG. 4 , a flow diagram  400  is shown illustrating an example method of superplastic forming example superplastic three-sheet panel  100  of  FIG. 1  (or example superplastic panel  300  of  FIG. 3 ) in accordance with an embodiment. The superplastic forming method  400  disclosed herein may be employed according to FAA regulations, for example. Specifications of FAA regulations for forming superplastic panels are known and, therefore, will not be described. 
     In block  402 , a first face sheet made of a first thermal expansion material is selected. In block  404 , a second face sheet made of a second thermal expansion material that is different from the first thermal expansion material is selected. In some embodiments, the selecting of the first face sheet made of the first thermal expansion material includes selecting material of the first face sheet to be a low expansion material, and the selecting of the second face sheet made of the second thermal expansion material that is different from the first thermal expansion material includes selecting material of the second face sheet to be a high expansion material. 
     In some embodiments, the selecting material of the first face sheet to be a low expansion material includes selecting material of the first face sheet to be INCOLOY Alloy 909, and the selecting material of the second face sheet to be a high expansion material includes selecting material of the second face sheet to be INCONEL Alloy 625. 
     Then, in block  406 , each of the selected first and second face sheets is attached to a core sheet to sandwich the core sheet between the first and second face sheets to provide a precursor panel. In some embodiments, the core sheet is selected with a thickness that is greater than thickness of each of the selected first and second face sheets. In some embodiments, the material of the core sheet is selected to be INCONEL Alloy 625. In some embodiments, the attaching each of the selected first and second face sheets to a core sheet to sandwich the core sheet between the first and second face sheets to provide a precursor panel includes welding each of the selected first and second face sheets to the core sheet to provide the precursor panel. In block  408 , the precursor panel is processed to form the three-sheet panel. Since the first thermal expansion material of the first face sheet and the second thermal expansion material of the second face sheet are different from each other, the core sheet is pulled into a desired shape. More specifically, the differential thermal expansion of the two materials pulls the core sheet into a desired shape. The process then ends. 
     Referring to  FIG. 5 , a flow diagram  500  is shown illustrating a method of superplastic forming example superplastic three-sheet panel  100  of  FIG. 1  (or example superplastic panel  300  of  FIG. 3 ) in accordance with another embodiment. The superplastic forming method  500  disclosed herein may be employed according to military and space regulations, for example. 
     In block  502 , a first face sheet made of INCOLOY Alloy 909 is selected. In block  504 , a second face sheet made of INCONEL Alloy 625 is selected. In block  506 , a core sheet made of INCONEL Alloy 625 is selected. Then, in block  508 , each of the selected first and second face sheets is attached to the core sheet to sandwich the core sheet between the first and second face sheets to provide a precursor panel. In block  510 , the precursor panel is processed to form the three-sheet panel. Since the first face sheet is made of INCOLOY Alloy 909 and the second face sheet is made of INCONEL Alloy 625, the core sheet is pulled into a desired shape. More specifically, the differential thermal expansion of the INCOLOY Alloy 909 and the INCONEL Alloy 625 pulls the core sheet into a desired shape. The process then ends. 
     Referring to  FIG. 6 , a flow diagram  600  is shown illustrating a method of superplastic forming example superplastic three-sheet panel  100  of  FIG. 1  (or example superplastic panel  300  of  FIG. 3 ) in accordance with yet another embodiment. The superplastic forming method  600  disclosed herein may be employed according to military and space regulations, for example. 
     In block  602 , a first face sheet and a second face sheet are attached to a core sheet to sandwich the core sheet between the first and second face sheets. Then, in block  604 , the first face sheet is superplastic formed at a different rate of expansion than the second face sheet to form the three-sheet panel. In some embodiments, the superplastic forming the first face sheet at a different rate of expansion than the second face sheet to form the three-sheet panel includes expanding one of the first and second face sheets at a first time and then expanding the other one of the first and second face sheets at a second time which is after the first time to pull the core sheet into a desired shape. In some embodiments, the superplastic forming the first face sheet at a different rate of expansion than the second face sheet to form the three-sheet panel includes expanding the first and second face sheets at the same time to pull the core sheet into a desired shape. 
     The above-described example superplastic forming methods may be carried out using manufacturing systems or apparatus suitable for making multilayer structures such as three-sheet panels. Numerous manufacturing systems or apparatus for making three-sheet panels are known and, therefore, will not be described. 
     Examples of the present disclosure may be described in the context of an aircraft manufacturing and service method  700  as shown in  FIG. 7  and an aircraft  800  as shown in  FIG. 8 . During pre-production, the illustrative method  700  may include specification and design, as shown at block  702 , of the aircraft  800  and material procurement, as shown at block  704 . During production, component and subassembly manufacturing, as shown at block  706 , and system integration, as shown at block  708 , of the aircraft  800  may take place. Thereafter, the aircraft  800  may go through certification and delivery, as shown block  710 , to be placed in service, as shown at block  712 . While in service, the aircraft  800  may be scheduled for routine maintenance and service, as shown at block  714 . Routine maintenance and service may include modification, reconfiguration, refurbishment, etc. of one or more systems of the aircraft  800 . 
     Each of the processes of illustrative method  700  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  FIG. 8 , the aircraft  800  produced by illustrative method  700  ( FIG. 7 ) may include an airframe  802  with a plurality of high-level systems  804  and an interior  806 . Examples of high-level systems  804  may include one or more of propulsion system  808 , electrical system  810 , hydraulic system  812 , and environmental system  814 . Any number of other systems may be included. Superplastic panels and superplastic forming methods shown or described herein may be employed in any combination of these systems. 
     Moreover, superplastic panels and superplastic forming methods shown or described herein may be employed during any one or more of the stages of the manufacturing and service method  700 . For example, components or subassemblies corresponding to component and subassembly manufacturing (block  706 ) may be fabricated or manufactured in a manner similar to components or subassemblies produced while aircraft  800  is in service (block  712 ). Also, one or more examples of superplastic panels and superplastic forming methods, or combination thereof, may be utilized during production stages (blocks  708  and  710 ). Similarly, one more examples of superplastic panels and superplastic forming methods, or a combination thereof, may be utilized, for example and without limitation, while aircraft  800  is in service (block  712 ) and during maintenance and service stage (block  714 ). 
     It should be apparent that a superplastic panel produced in accordance with above-described example methods is suitable for any type of application. The superplastic panel is especially advantageous when there is a thermal gradient during use of the superplastic panel, such as in a thrust reverser of an aircraft engine, for example. The difference in thermal expansion between the inner face sheet (i.e., the inner wall with the lower thermal expansion coefficient and closer to the aircraft engine) and the outer face sheet (i.e., the outer wall with the higher thermal expansion coefficient and farther away from the aircraft engine) reduces thermally induced stress in the superplastic panel. As such, the superplastic panel is capable of operating at higher temperatures with reduced thermally induced stress. The result is a superplastic panel that does not need to be replaced as often due to potential delamination of the inner and outer face sheets. This lowers maintenance and service costs. 
     It should also be apparent that the difference in thermal expansion between the first and second face sheets  110 ,  120  of the superplastic panel  100  eliminates the need for a thick laminate of the first face sheet  110 . This is because the thermal stress induced in the first face sheet  110  is reduced due to the lower thermal expansion of the first face sheet  110 . The result is a weight-efficient superplastic panel (as compared to known superplastic panels) with a capability to handle temperatures up to or above 1000° F. without degradation of the superplastic panel when the superplastic panel is installed and in service in a particular application. Accordingly, the superplastic panel  100  has not only high-temperature capability, but also has low weight (i.e., weight-competitive). 
     It should further be apparent that the material of the first face sheet  110  and the material of the second face sheet  120  of the superplastic panel  100  can each be selected and tailored to reduce thermally induced stress in the superplastic panel  100  depending upon the particular application of the superplastic panel (e.g., in an inner wall/outer wall of a thrust reverser of an aircraft engine). 
     Although an aerospace example is shown, the principles disclosed herein may be applied to other industries, such as the automotive industry, the marine industry, and the construction industry. Accordingly, in addition to the aircraft  800 , the principles disclosed herein may apply to other vehicles (e.g., land vehicles, marine vehicles, space vehicles, etc.) as well as to other types of structures. 
     Although the above description describes a three-layer structure in which the middle layer comprises a core sheet construction, it is conceivable that the middle layer may comprise a construction that is other than a core sheet. As an example, the middle layer may comprise a brazed honeycomb construction. Other constructions of the middle layer of the three-layer structure are possible. 
     Although the above description describes example superplastic panels and example methods of superplastic forming three-sheet panels for OEMs in accordance with military and space regulations, it is conceivable that the example superplastic panels and superplastic forming methods may be implemented in any industry in accordance with the applicable industry standards. 
     Also, although the above description describes a superplastic forming method to make a three-sheet panel, it is conceivable that other forming methods may be used. 
     Further, although various embodiments of the disclosed superplastic panels and superplastic forming methods have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.