Stock material or miscellaneous articles – All metal or with adjacent metals – Embodying fibers interengaged or between layers
Reexamination Certificate
1999-02-09
2001-02-27
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Embodying fibers interengaged or between layers
C428S634000, C428S626000, C428S660000, C428S670000, C428S416000, C428S418000, C428S223000, C156S307700, C156S307300
Reexamination Certificate
active
06194081
ABSTRACT:
BACKGROUND
Aircraft primary structures are predominately made from non-composite metals. However, the aerospace industry has been increasingly using light weight, advanced composite materials in place of metals to produce primary structures because of the high specific strength of advanced composites materials. Nevertheless, advanced composite materials have not entirely replaced metals in primary structures because advanced composites are more sensitive to damage, have lower bearing strength, and are more susceptible to fastener failure than metals.
Several improved composites have been designed, including Arall, as disclosed in U.S. Pat. No. 4,500,589, and Glair, as disclosed in U.S. Pat. No. 5,039,571. Disadvantageously, however, the layers of both Arall and Glair have a mismatch of the ratio between their modulus of elasticity and their yield strength.
For example, Arall is a composite of aluminum skins adhesively bonded to a core of Aramid fiber/epoxy composite. The Aramid fiber of Arall has a unidirectional yield strength of about 172,000 psi and a modulus of 12.2×10
6
psi, while the aluminum layer has a yield strength of 50,000 psi and modulus of 10.0×10
6
psi. Thus, stressing the Aramid fiber layer to its maximum yield strength would stress the aluminum layer to 141,000 psi, which is well above the maximum limit for the aluminum layer. Conversely, stressing the aluminum layer to its maximum yield strength of 50,000 psi stresses the Aramid fiber layer to 61,000 psi, which is well below the maximum limit for the Aramid fiber layer. Thus, the strength of the Aramid fiber layer is underutilized. Similarly, the layers of composite laminates of standard alpha-beta alloys of titanium, such as Ti6Al-4V, and carbon fiber composites have a mismatch of the ratio between their modulus of elasticity and their yield strength.
The aerospace industry has not used the newer beta alloys of titanium, such as TIMETAL® 15-3 (Ti-15V-3Cr-3Sn-3Al) and TIMETAL® 21s (Ti-15Mo-3Al-3Nb), for composite laminates even though these beta alloys of titanium have higher strength and a lower modulus of elasticity because commonly used adhesives will not stick adequately to the titanium oxide surface layer present on these alloys. While methods have been developed to bond the standard alpha-beta alloys of titanium to carbon fiber composites, these methods do not work with the beta alloys of titanium.
Therefore, there is a need for improved composite laminates for the primary structures of aircraft which utilize the full strength of each layer. Further, there is a need for a method of preparing these composite laminates.
SUMMARY
According to one embodiment of the present invention, there is provided a method of preparing a beta titanium-composite laminate. The method comprises providing a first layer of beta titanium alloy having a yield strength to modulus of elasticity ratio and providing a first layer of composite having a yield strength to modulus of elasticity ratio. Then, the first layer of beta titanium alloy is adhered to the first layer of composite, thereby forming a beta titanium-composite laminate. The yield strength to modulus of elasticity ratio of the first layer of beta titanium alloy matches the strength to modulus of elasticity ratio of the first layer of composite such that the first layer of beta titanium alloy will reach its stress limit and the first layer of composite will reach its stress limits at about the same total strain.
In one embodiment, the beta titanium alloy provided is selected from the group consisting of (Ti-15V-3Cr-3Sn-3Al) and (Ti-15Mo-3Al-3Nb). In a preferred embodiment, the composite provided is a carbon fiber/epoxy composite. In another preferred embodiment, the composite provided is an S2-glass/epoxy composite.
In one embodiment, adhering comprises applying an adhesive to the beta titanium alloy. In another embodiment, adhering comprises bonding the composite by heating the composite.
In a particularly preferred embodiment, the yield strength to modulus of elasticity ratio of the first layer of beta titanium alloy is between about 5% of the strength to modulus of elasticity ratio of the first layer of composite. In another particularly preferred embodiment, the method additionally comprises cold reducing the beta titanium alloy before adhering. In yet another particularly preferred embodiment, the method additionally comprising heating the beta titanium alloy at a temperature for a time to produce an aged beta titanium alloy before adhering, such as a temperature of approximately 950° F. and a time of approximately 8 hours.
In a particularly preferred embodiment, the method additionally comprises cold reducing the beta titanium alloy and then aging the beta titanium alloy before adhering. In another particularly preferred embodiment, the method additionally comprises coating the surface of the beta titanium alloy with a metal selected from the group consisting of platinum and the functional equivalent of platinum as a coating material, to produce a coated titanium alloy before adhering. In another particularly preferred embodiment, the method additionally comprises abrading the surface of the beta titanium alloy before adhering.
In another particularly preferred embodiment, the method additionally comprises, after adhering, providing a second layer of beta titanium alloy having a yield strength to modulus of elasticity ratio and adhering the second layer of beta titanium alloy to the beta titanium-composite laminate, where the yield strength to modulus of elasticity ratio of the second layer of beta titanium alloy matches the strength to modulus of elasticity ratio of the first layer of composite such that the second layer of beta titanium alloy will reach its stress limit and the first layer of composite will reach its stress limits at about the same total strain. In yet another particularly preferred embodiment, the method additionally comprises, after adhering, providing a second layer of composite having a strength to modulus of elasticity ratio and adhering the second layer of composite to the beta titanium-composite laminate, where the strength to modulus of elasticity ratio of the second layer of composite matches the yield strength to modulus of elasticity ratio of the first layer of beta titanium alloy such that the second layer of composite will reach its stress limit and the first layer of beta titanium alloy will reach its stress limits at about the same total strain.
The present invention also includes a method of making an airplane part comprises preparing a beta titanium-composite laminate according to the present invention and incorporating the beta titanium-composite laminate into an airplane part. The present invention also includes a method of making an airplane comprising preparing an airplane part according to the present invention and incorporating the part into an airplane. The airplane part can be selected from the group consisting of airplane skin, a spar, a plate and a tube.
In a preferred embodiment, the present invention includes a beta titanium-composite laminate produced according to a method of the present invention.
In another preferred embodiment, the present invention includes a beta titanium-composite laminate comprising a first layer of beta titanium alloy having a yield strength to modulus of elasticity ratio, and a first layer of composite having a strength to modulus of elasticity ratio adhered to the first layer of beta titanium alloy. The yield strength to modulus of elasticity ratio of the first layer of beta titanium alloy matches the strength to modulus of elasticity ratio of the first layer of composite such that the first layer of beta titanium alloy will reach its stress limit and the first layer of composite will reach its stress limits at about the same total strain. For example, the yield strength to modulus of elasticity ratio of the first layer of beta titanium alloy can be between about 5% of the strength to modulus of elasticity ratio of the first layer of composite. The beta titanium-composite
Farah David A.
Sheldon & Mak
Ticomp. Inc.
Zimmerman John J.
LandOfFree
Beta titanium-composite laminate does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Beta titanium-composite laminate, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Beta titanium-composite laminate will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2604507