Patent Application
20230302527
The present disclosure relates generally to fasteners and more particularly to fasteners for joints in dynamic temperature environments.
Fastened joints subjected to extreme changes in temperature, such as those in hypersonic missile applications, typically experience detrimental effects as a result of thermal expansion. For example, such joints may experience detrimental changes in clamping force as a result of such thermal expansion, as the fastener (e.g., a bolt, a screw, or other fastening device) and the fastened elements (e.g., flanges on a missile airframe or other components of the missile) thereof typically have different rates of thermal expansion. These differences in rates of thermal expansion may result in a decreased clamping force on the joint, which may lead to a loosening of the joint, or an increased clamping force of the joint, which may lead to excessive stress and deformation or fracture of the fastener and/or the fastened elements.
Such detrimental thermal expansion effects are typically mitigated by the design of the fastened joints. For example, some conventional designs use fasteners that sufficiently match the coefficients of thermal expansion (CTE’s) of the fastened elements such that the rates of thermal expansion of the fastened elements and the fasteners are sufficiently similar in an effort to maintain the clamping force of the fastened joint relatively consistent throughout exposure to extreme changes in temperature. Additionally or alternatively, some designs add a spring or other resilient member in compression, such as a Belleville washer, to the fastened joints to accommodate for the differences in rates of thermal expansion between the fastened elements and the fasteners in an effort to reduce the resultant change in clamping force of the fastened joint.
For many applications, however, these designs are not feasible. For example, in hypersonic missile airframe applications, the materials required for hypersonic missile airframe joints typically do not have sufficiently similar CTE’s (such as ceramic matrix composite (CMC) flanges attached with refractory metal fasteners). Even if they did, however, temperature changes in such applications may be transient, leading to differences in rates of thermal expansion of the fastened elements and the fasteners regardless of them having sufficiently similar CTE’s. Furthermore, the addition of spring or other resilient members to the fastened joints adds significant height to the fastened joint. Many applications, however, do not have the available space allocation for such added height.
An improved fastener system for fastening at least two elements together is described herein. The fastener system includes a fastener and a fastener insert. The fastener system solves the above-mentioned problems associated with conventional solutions to the detrimental thermal expansion effects of fastened joints subjected to extreme changes in temperature by incorporating the fastener insert having a resilient shaft portion integrally connected to and coaxially aligned with an internally threaded shaft portion of a hollow shaft of the resilient fastener insert. The resilient shaft portion of the fastener insert is continuous, unitary and formed as a single piece with the internally threaded shaft portion of the hollow shaft of the fastener insert, without adding significant height to the fastener system in the axial direction. The resilient shaft portion of the fastener insert is placed in tension while the fastener system fastens the at least two elements together (for example, with a threaded shaft of the fastener secured to the internally threaded shaft portion of the hollow shaft of the fastener insert) such that it can deform to accommodate for thermal expansion of at least one of the fastener, the fastener insert, and at least one of the at least two elements. This effectively maintains the clamping force formed by the fastener system on the at least two elements and therefore, excessive deformation or fracture of the fastener system (including the fastener and the fastener insert) and/or the at least two elements can be prevented.
According to an aspect of this disclosure, a fastener insert includes a hollow shaft extending in an axial direction and configured to receive a threaded fastener at a first axial end of the hollow shaft. The fastener also includes a supporting flange extending radially outward from a second axial end of the hollow shaft. The hollow shaft includes an internally threaded shaft portion. The internally threaded shaft portion is configured to secure the threaded fastener received in the hollow shaft. The hollow shaft also includes a resilient shaft portion formed as a unitary single piece with the internally threaded shaft portion.
According to an embodiment of any paragraph(s) of this disclosure, the resilient shaft portion is formed between the internally threaded shaft portion of the hollow shaft and the supporting flange.
According to another embodiment of any paragraph(s) of this disclosure, the resilient shaft portion is formed by at least one cutout in the hollow shaft.
According to another embodiment of any paragraph(s) of this disclosure, the at least one cutout includes a plurality of cutouts arranged circumferentially around the hollow shaft.
According to another embodiment of any paragraph(s) of this disclosure, at least one of the at least one cutout is triangular in shape.
According to another embodiment of any paragraph(s) of this disclosure, at least one of the at least one cutout is circular in shape.
According to another embodiment of any paragraph(s) of this disclosure, at least one of the at least one cutout is linear in shape.
According to another embodiment of any paragraph(s) of this disclosure, a thickness of a circumferential wall of the resilient shaft portion is less than a thickness of the circumferential wall of the internally threaded shaft portion.
According to another embodiment of any paragraph(s) of this disclosure, a circumferential wall of the resilient shaft portion is axially corrugated.
According to an aspect of this disclosure, a fastener system includes a fastener insert. The fastener insert includes a hollow shaft extending in an axial direction from a first axial end to a second axial end of the hollow shaft. The fastener insert also includes a supporting flange extending radially outward from the second axial end of the hollow shaft. The hollow shaft includes an internally threaded shaft portion and a resilient shaft portion formed as a unitary single piece with the internally threaded portion. The fastener system also includes a fastener having a threaded shaft received in the hollow shaft of the fastener insert at the first axial end and secured to the internally threaded shaft portion of the hollow shaft.
According to another embodiment of any paragraph(s) of this disclosure, a length of the threaded shaft of the fastener is less than or equal to a length of the internally threaded shaft portion of the hollow shaft of the fastener insert.
According to another embodiment of any paragraph(s) of this disclosure, a length of the threaded shaft of the fastener is greater than a length of the internally threaded shaft portion of the hollow shaft of the fastener insert and equal to or less than a length of the hollow shaft of the fastener insert.
According to another embodiment of any paragraph(s) of this disclosure, the resilient shaft portion is formed between the internally threaded shaft portion of the hollow shaft and the supporting flange.
According to another embodiment of any paragraph(s) of this disclosure, the resilient shaft portion is formed by at least one cutout in the hollow shaft.
According to another embodiment of any paragraph(s) of this disclosure, the at least one cutout is at least one of triangular, circular, and linear in shape.
According to another embodiment of any paragraph(s) of this disclosure, a thickness of a circumferential wall of the resilient shaft portion is less than a thickness of the circumferential wall of the internally threaded shaft portion.
According to another embodiment of any paragraph(s) of this disclosure, a circumferential wall of the resilient shaft portion is axially corrugated.
According to an aspect of this disclosure, a method of fastening at least two elements together includes the step of inserting a first axial end of a hollow shaft of a fastener insert into a through hole extending through the at least two elements such that a supporting flange extending radially outward from a second axial end of the hollow shaft abuts an outer surface of a first element of the at least two elements. The method also includes the step of inserting a threaded shaft of a fastener into the first axial end of the hollow shaft and securing the threaded shaft of the fastener into an internally threaded shaft portion of the hollow shaft such that a head of the fastener abuts an outer surface of a second element of the at least two elements. The method also includes the step of further securing the threaded shaft of the fastener into the internally threaded shaft portion of the hollow shaft such that tension is created on a resilient shaft portion of the hollow shaft. The resilient shaft portion of the hollow shaft is formed as a unitary single piece with the internally threaded shaft portion of the hollow shaft. The method then includes the step of forming a resilient clamping force on the at least two elements.
According to another embodiment of any paragraph(s) of this disclosure, the method further includes the step of accommodating for an axial thermal expansion of at least one of the fastener, the fastener insert, and at least one of the at least two elements when exposed to a change in temperature.
According to another embodiment of any paragraph(s) of this disclosure, the step of accommodating includes axially deforming the resilient shaft portion of the hollow shaft when the at least one of the fastener, the fastener insert, and at least one of the at least two elements undergoes the axial thermal expansion.
The following description and the annexed drawings set forth in detail certain illustrative embodiments described in this disclosure. These embodiments are indicative, however, of but a few of the various ways in which the principles of this disclosure may be employed. Other objects, advantages and novel features will become apparent from the following detailed description when considered in conjunction with the drawings.
The annexed drawings show various aspects of the disclosure.
Described herein is fastener system for fastening at least two elements together. The fastener system includes a fastener and a fastener insert which is configured to accommodate for thermal expansion of at least one of the fastener, the fastener insert, or at least one of the at least two elements which are fastened together with the fastener system, when they are subjected to changes in temperature. Specifically, the fastener insert includes a resilient shaft portion that is configured to deform in the axial direction so that it can accommodate any such thermal expansion. The resilient shaft portion of the fastener insert is continuous, unitary and formed as a single piece with an internally threaded shaft portion that is configured to secure the fastener to the fastener insert. With the accommodation of thermal expansion by the resilient shaft portion of the fastener insert, a clamping force of the fastener system on the at least two elements being fastened therewith is effectively maintained throughout variable thermal expansion of at least one of the fastener, the fastener insert, or at least one of the at least two elements.
Turning to
The fastener insert 18 includes a hollow shaft 20 configured to extend in the axial direction 22 through a through hole 24 of the at least two elements, including the first element 12 and the second element 14. The hollow shaft 20 has a first axial end 26 and a second axial end 28 and may be cylindrical in shape. A length of the hollow shaft 20 in the axial direction may be in the range of 0.64 centimeters (0.25 inches) to 15.24 centimeters (6.0 inches), for example 1.65 centimeters (0.65 inches). An internal diameter of the hollow shaft 20 may be in the range of 0.48 centimeters (0.19 inches) to 2.54 centimeters (1 inch), for example 0.79 centimeters (0.31 inches). The fastener insert 18 also includes a supporting flange 30 extending radially outward from the second axial end 28 of the hollow shaft 18 such that when the first axial end 26 of the hollow shaft 18 is inserted into the through hole 24, the supporting flange 30 abuts an outer surface 32 of the first element 12. A diameter of the supporting flange 30 may be in the range of 0.64 centimeters (0.25 inch) to 7.62 centimeters (3 inches), for example 1.91 centimeters (0.75 inches). As will be described in more detail with reference to
The fastener 16 is a threaded fastener having a head 38 and a threaded shaft 40 extending in the axial direction 22 from the head 38. The hollow shaft 20 of the fastener insert 18 is configured to receive the threaded shaft 40 of the fastener 16 at the first axial end 26 of the hollow shaft 20. Accordingly, a diameter of the threaded shaft 40 of the fastener 16 may correspond to the inner diameter of the hollow shaft 20 and may therefore be in a range of 0.48 centimeters (0.19 inch) to 2.54 centimeters (1 inch), for example 0.79 centimeters (0.31 inches). As with the dimensions of the hollow shaft 20, however, it is understood that the dimensions of the fastener 16 described herein are provided as non-limiting examples, and other dimensions of the fastener 16 may be applicable. The internally threaded shaft portion 34 of the hollow shaft 20 is configured to secure the threaded shaft 40 of the fastener 16 such that the head 38 of the fastener abuts an outer surface 42 of the second element 14. The threaded shaft 40 of the fastener 16 may have a length sufficient to ensure a strong and secure connection between the fastener 16 and the internally threaded shaft portion 34 of the hollow shaft 20 of the fastener insert 18 when the threaded shaft 40 is secured by the internally threaded shaft portion 34. That is, the length of the threaded shaft 40 may be less than or equal to a length of the internally threaded shaft portion 34 of the hollow shaft 20 of the fastener insert 18. However, the length of the threaded shaft 40 may alternatively be greater than the length of the internally threaded shaft portion 34 of the hollow shaft 20. In either case, the length of the threaded shaft 40 may be equal to or less than a length of the hollow shaft 20 of the fastener insert 18.
When the threaded shaft 40 of the fastener 16 is further secured in the internally threaded portion 34 of the hollow shaft 20 of the fastener insert 18, with the supporting flange abutting the outer surface 32 of the first element 12 and the head 38 of the fastener 16 abutting the outer surface 42 of the second element 14, an axial preloaded tension is created on the resilient shaft portion 36 of the hollow shaft 20 of the fastener insert 18. This tension imparts a clamping force on the at least two elements including the first element 12 and the second element 14, fastening the at least two elements together. As will be described in more detail below, due to the resiliency of the resilient shaft portion 36 (in particular, the ability of the resilient shaft portion 36 to deform in the axial direction), the clamping force is a resilient clamping force that accommodates axial thermal expansion of at least one of the fastener 16, the fastener insert 18 and at least one of the at least two elements (e.g., the first element 12 and/or the second element 14).
The fastener insert 18 is configured to have adequate strength to support an axial preloaded tension in order to achieve the required clamping force on the at least two elements 12, 14. As the axial preloaded tension may be sustained at elevated temperatures, the fastener insert 18 may be made with a suitable high temperature/high strength material. For example, for temperatures up to approximately 3,000° F., the fastener insert 18 may be made with ultra-high temperature ceramics (UHTC’s) and/or refractory metals such as tungsten, molybdenum alloys (e.g., TZM), columbium (niobium), and/or tantalum alloys. For temperatures up to approximately 1,800° F., the fastener insert 18 may be made with nickel super alloys such as Inconel. For temperatures up to approximately 1,200° F., the fastener insert 18 may be made with titanium and/or stainless-steel alloys. Each of these materials have coefficients of thermal expansion (CTE’s) in an approximate range of 3 to 10 micro-in/in/°F. This can exceed the CTE’s of the at least two elements, including the first element 12 and the second element 14, which are fastened together. For example, for high temperature applications, the at least two elements may be anisotropic ceramic matrix composite materials (CMC’s). It will be understood, however, that the specific materials and CTE’s described above are provided as non-limiting examples, and that other materials and CTE’s may be applicable to the fastener insert 18 depending on the environment and application for which it is used.
The resilient shaft portion 36 of the hollow shaft 20 of the fastener insert 18 may have a variety of forms that allow it to sustain the axial preloaded tension and make it deformable in the axial direction. For example, with reference to
Additionally or alternatively, the circumferential wall 46 of the resilient shaft portion 36 may be formed to have different properties than a circumferential wall 50 of the internally threaded shaft portion 34 of the hollow shaft 20 that make it deformable in the axial direction. For example, with reference to
With reference to
The method 100 then includes a step 106 of further securing the threaded shaft of the fastener into the internally threaded shaft portion of the hollow shaft such that tension is created on a resilient shaft portion of the hollow shaft. The resilient shaft portion of the hollow shaft is formed as a unitary single piece with the internally threaded shaft portion of the hollow shaft, as described previously with the resilient shaft portion 36 and the internally threaded shaft portion 34 of the hollow shaft 20. The tension imparts a resilient clamping force on the at least two elements.
The method 100 may therefore include accommodating for an axial thermal expansion of at least one of the fastener, the fastener insert, and at least one of the at least two elements when exposed to a change in temperature. The accommodating includes axially deforming the resilient shaft portion of the hollow shaft when the at least one of the fastener, the fastener insert, and at least one of the at least two elements undergoes the axial thermal expansion.
Although the above disclosure has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments. In addition, while a particular feature may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.
This invention was made with government support. The government has certain rights in the invention.
