Mcdonnell Douglas Corporation

Richard G Pettit

Ken K Yasui

Douglas J Waldron

A method for reducing material property degradation during friction stir welding. More specifically, the method includes the steps of solution heat treating first and second structural members at a first predetermined temperature schedule. The first and second structural members are then quenched to a predetermined temperature at which the structural members are in a nonequilibrium state and have an incomplete temper. The first structural member is then positioned adjacent to the second structural member, thereby defining an interface therebetween. Thereafter, the first and second structural members are joined to form a structural assembly by friction stir welding the material along the interface prior to precipitation heat treating the structural assembly. The structural assembly is then aged, such as by precipitation heat treating, at a second predetermined temperature schedule to stabilize the material properties of the resulting structural assembly, thereby completing the temper of the material. The method requires fewer manufacturing steps than conventional techniques for friction stir weld precipitation-hardened parent materials. In addition, the method minimizes the degradation of the material properties during friction stir welding, and produces a structural assembly with improved strength, hardness, and corrosion resistance, as well as dimensional quality.

High strength friction stir welding

An apparatus and method for forming an aircraft fuselage having at least one doubly curved portion. A plurality of fuselage panels are extruded with integrally formed stiffening portions extending preferably longitudinally the full length of each fuselage panel. The stiffening portions are further formed so as to be generally parallel to one another. The fuselage panels are then formed into skin panels having a desired curvature and trimmed into gores, and the stiffening portions trimmed at end portions that run out toward longitudinal edges of the panels. When adjacent panels are affixed together, the stiffening portions run out toward longitudinal edges of adjacent panels. The longitudinal edges are secured by splice longerons which are riveted or welded to the longitudinal edges of the skin panels. Independent fastening members are then secured to the stiffening portions and the splice longerons at the points where the stiffening portions run out to positions closely adjacent the splice longerons. The apparatus and method permits aircraft fuselages having doubly curved portions to be formed from extruded panels which is more cost efficient and makes use of a greater percentage of raw materials than conventional methods of machining such panels out of non-near-net stock such as plate.

Aircraft fuselage and method of forming same

Currently, fiber/metal laminate sheets are limited in width due to restrictions in the width of thin metal sheets available. This invention solves that problem by providing an integral splice concept and a method for manufacturing a laminate employing the inventive concept. Specifically, a fiber/metal laminate sheet is provided having at least two metal plies and at least one fiber layer. Each of the metal plies comprises at least two metal sheets which are arranged side-by-side and have sheet metal breaks therebetween. All of the sheet metal breaks lie within the integral splice. An important feature of the invention is that the sheet metal breaks in each metal ply are staggered widthwise across the laminate with respect to the sheet metal breaks in the remaining metal plies, in accordance with a predetermined metal break staggering pattern, thereby maximizing the bond engagement of the discontinuous metal plies with the adjacent fiber layers. Another important inventive feature is that the fiber layers are continuous through the integral splice region. The resultant spliced laminate may have any desired width, and is strong, fatigue-resistant, durable, and easy to manufacture.

Fiber/metal laminate splice

In a crack arresting structure the crack arresting feature is located in the transition from one thickness to another, or a region of increased thickness can be intentionally introduced for the purpose of inhibiting crack growth propagation. The crack arresting feature comprises two different structural configurations. These structures include a thickness transition region where a portion of the structure is plastically deformed at or immediately adjacent to the thickness transition region. Alternatively, an overhang is provided where an appendage to the thicker part extends back over the thinner part at a thickness transition region. A high strength fiber or wire, preferably of non-constant cross-section may be inserted into a gap underneath the overhang and held in place by crimping due to plastic deformation. Fiber or wire reinforced interface may be adhesively bonded into place prior to or in lieu of deformation or crimping. The plastic deformation is preferably accomplished by strip or localized coining of the part by feeding the part through rollers or by other means such as localized shot peening, or laser shock peening or other suitable methods which apply high local stresses and result in a local thickness reduction at or adjacent the thickness transition point (or on either or both sides thereof). This results in a local compressive residual stress region, which has been shown to impede or even turn crack growth.

Crack arresting structure

The structure and process for making a metallic panel structure from a plurality, e.g. two, core elements each comprised of a pair of sheets of superplastic material welded together along a plurality of weld lines, the weld lines of one core element being spaced differently or of different shape from the weld lines of the other core element. The core elements are joined together, with the weld lines of one core panel positioned at an angle, e.g., normal, to the weld lines of the adjacent core element. The resulting panel assembly is placed in a die. The die is heated to superplastic forming temperature, and gas pressure is applied to the spaces between the sheets of the respective core elements, causing superplastic forming and expansion of the sheets of each core panel to form a first series of bulges between weld lines of one core element, and a second series of bulges dissimilar in shape, e.g. larger, than the first series of bulges, between weld lines of the adjacent core element, the bulges expanding inwardly toward each other. The two series of bulges are orthogonally disposed, the bulges from the two core elements contacting and forming around each other. Further pressurization is applied to cause diffusion bonding at the contacting areas of the two series of bulges. The resulting structure is formed of two normally disposed series of bulges, one series larger than the other, with face sheets connected to such bulges.

Panel structure fabrication

A process for forming single piece metal alloy panel structures includes both superplastic forming and braze bonding steps, and is particularly adapted to superplastically formable materials which are not particularly diffusion bondable, such as aluminum alloys. The process involves constructing a worksheet assembly from a plurality of worksheets which are associated with a brazing alloy capable of brazing the worksheets. At least two of the worksheets are joined in facing contact with each other by welding in a preselected pattern. The perimeter of the joined worksheets is then sealed, with the provision of means for permitting the admission of pressurized gas therebetween, after which the worksheet assembly is placed in a forming die. The actual structure forming process begins by heating the die and its associated worksheet assembly to a temperature suitable for superplastic forming, and simultaneously applying gas pressure at the means for admission of pressurized gas. The pressurized gas is applied to cause expansion of the sheets until the desired geometry of the structure has been attained. Following the superplastic forming step, the structure is braze bonded by ensuring that the die temperature is at or above the minimum brazing temperature of the brazing alloy for a specified period of time, thereby bonding at least some of the contacting surfaces of the structure together.

Method of superplastically forming and braze bonding a structure

A fiber/metal laminate composite material is comprised of a plurality of metallic layers, reinforced with a plurality of fiber layers. The metallic layers are preferably aluminum, while the fibers in the fiber layers are preferably comprised of an aramid. The fibers are bi-directionally oriented. To provide the laminate with superior fiber failure resistance characteristics, the laminate is post-stretched along a post-stretch axis which bisects the two fiber axes.

Fiber/metal laminate

The structure and process for making a metallic panel structure from a plurality of core panels each comprised of a pair of sheets of superplastic material welded together along a plurality of weld lines. The core panels are joined together, with the weld lines of one core panel positioned normal to the weld lines of the adjacent core panel. The resulting assembly is placed in a die. The die is heated to superplastic forming temperature, and gas pressure is applied to the spaces between the sheets of the respective core panels, causing superplastic forming and expansion of the sheets of each core panel to form a series of bulges between weld lines of one core panel, and a series of similar bulges between weld lines of the adjacent core panel, the bulges expanding inwardly toward each other. The two series of bulges are orthogonally disposed, the bulges from the two core panels contacting and forming around each other. Further pressurization is applied to cause diffusion bonding at the contacting areas of the two series of bulges. The resulting structure is formed of two normally disposed series of bulges, with face sheets connected to such bulges. According to another embodiment, three core panels can be employed, resulting in a structure following superplastic forming and diffusion bonding, formed of two outer series of inwardly extending parallel bulges and an intermediate series of bulges between the two series of outer bulges.

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La Habra, CA, United States of America

Richard G Pettit