Method for fastening a part to another part using electrically deformable rivets

Abstract

Methods for fastening two fiber composite parts to each other with a fastener that includes electroactive polymer material. The parts have an opening within an inner circumferential surface. Fibers protrude from the inner circumferential surface into the opening and interlock with chains of micrograins of the electroactive polymer material. The fastener may switch between an activated state and a deactivated state and in the deactivated state, the fastener engages the exposed fibers.

Claims

1. A method for fastening a first fiber composite part to a second fiber composite part each fiber composite part including a matrix material and fibers embedded therein, the method comprising: a) forming an opening, that has an inner circumferential surface, in the first and second fiber composite parts; b) removing matrix material from the inner circumferential surface so as to expose fibers; c) activating a fastener, that includes electroactive polymer material, so as to reduce a diameter of the fastener and inserting the activated fastener into the opening; d) deactivating the fastener inside the opening so that the diameter of the fastener increases and an outer circumferential surface of the deactivated fastener engages the exposed fibers.

2. The method according to claim 1, wherein step a) comprises cutting the opening into the first and second fiber composite parts.

3. The method according to claim 1, wherein step b) comprises evaporating the matrix material.

4. The method according to claim 3, wherein the matrix material is evaporated by electromagnetic radiation.

5. The method according to claim 1, wherein step c) comprises activating the fastener by applying a voltage to the electroactive polymer material.

6. The method according to claim 1, wherein step c) comprises inserting the activated fastener by a robotic arm.

7. The method according to claim 6, wherein the electroactive polymer material is supplied with voltage through the robotic arm.

8. The method according to claim 1, wherein in step c) the activated fastener is inserted to protrude from the opening and wherein in step d) the deactivated fastener recedes to be flush with or recessed from a surface of the first, the second, or both fiber composite parts.

9. The method according to claim 1, wherein in step c) the activated fastener engages the exposed fibers.

10. The method according to claim 9, wherein the activated fastener engages the exposed fibers with a portion that includes electroactive polymer material such that the exposed fibers and micrograins of the electroactive polymer material are able to slide against each other.

11. The method according to claim 1, wherein in step d) the deactivated fastener engages the exposed fibers with a portion that includes electroactive polymer material such that the exposed fibers and micrograins of the electroactive polymer material are interlocked.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention are described in more detail with reference to the accompanying schematic drawings that are listed below

(2) FIG. 1 depicts opening forming in fiber composite parts;

(3) FIG. 2 depicts fiber exposing in the opening circumference;

(4) FIG. 3 depicts fastener insertion into the opening;

(5) FIG. 4 depicts fastener expansion in the opening;

(6) FIG. 5 depicts detail A of FIG. 4 with the fastener in an active state; and

(7) FIG. 6 depicts detail A of FIG. 4 with the fastener in a passive state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(8) Referring to FIG. 1, a first fiber composite part 10 and a second fiber composite part 12 are depicted. The fiber composite parts 10, 12 are intended to be fastened together. Each fiber composite part 10, 12 includes a matrix material 14 and fibers 16 that are embedded therein. As exemplified in FIG. 1, each fiber composite part 10, 12 includes two layers that have a different orientation of the embedded fibers 16. In a first layer 18, the fibers 16 are aligned in parallel to the drawing plane. In a second layer 20 the fibers 16 are aligned perpendicular to the drawing plane. It should be noted that the fiber composite parts 10, 12 may have several more layers that also may have different orientations. The invention is applicable regardless.

(9) The fiber composite parts 10, 12 may be structural parts of an aircraft, for example frames that are going to be fastened together, or a frame and a skin panel, or any other structural parts of an aircraft that are typically riveted together.

(10) As shown in FIG. 1, an opening 22 is created in both fiber composite parts 10, 12, preferably using a mechanical drill 24. The opening 22 includes an inner circumferential surface 26.

(11) Referring to FIG. 2, laser milling is performed. As depicted, a laser mill 28 may include a robotic arm that has a laser source 30 that is connected to a work implement 32 which outputs a laser beam 34 towards the inner circumferential surface 26. The power of the laser beam 34 is chosen such that the matrix material 14 can be evaporated, while leaving the fibers 16 unaffected. As a result, a new inner circumferential surface 26 is generated, from which the fibers 16 protrude into the opening. In other words, the fibers 16 are exposed and protrude from the inner circumferential surface 26 into the opening 22.

(12) As depicted in FIG. 3, a fastener 36 is inserted into the opening 22. The fastener 36 comprises an electroactive polymer and may thus be deformed by applying a voltage to the electroactive polymer material. For a detailed explanation reference is made to DE 10 2019 128 914 A1, FIGS. 2a and 2b, paragraphs [0047]-[0049], the disclosure is explicitly incorporated herein by reference.

(13) The fastener 36 is handled by another work implement 38 that is preferably arranged at a robotic arm 40. Furthermore, the fastener 36 is connected to a voltage source 42. While not depicted here, the leads 44 connecting the fastener 36 to the voltage source 42, may be integrated into the work implement 38 and/or the robotic arm 40.

(14) After forming the opening 22 and subsequent to removing the matrix material, the fastener 36 is supplied from the voltage source 42. As a result of the electroactive polymer material, the fastener contracts in the radial direction and expands in the axial direction. Consequently, the diameter of the fastener 36 is smaller than the diameter of the opening 22. The fastener 36 is inserted such that it protrudes from the opening on both sides relative to an outer surface 46 of each fiber composite part 10, 12.

(15) As depicted in FIG. 4, the fastener 36 is separated from the voltage source 42. Thereby, the electroactive polymer material reverts back to its normal configuration. As a result, the fastener expands in the radial direction and contracts in the axial direction. The fastener 36 is dimensioned such that in this deactivated state, the fastener top surface 48 and the fastener bottom surface 50 are flush with the outer surface 46 of the fiber composite parts 10, 12. It is also possible, that the fastener 36 is dimensioned such the top and bottom surfaces 48, 50 are slightly recessed relative to the outer surface 46.

(16) Referring to FIG. 5 and FIG. 6, the interface region between the fastener 36 and the inner circumferential surface 26 is described in more detail (circle A in FIG. 4).

(17) FIG. 5 depicts on the left a portion of the second fiber composite part 12. The fibers 16 protrude from the inner circumferential surface 26 that is formed by the matrix material 14. To the right of FIG. 5, a portion of the fastener 36 is depicted. As described herein, the electroactive polymer material includes two different polymers, namely PEDOT and PSS. Both these polymers form micrograins 52. As depicted in FIG. 5, the micrograins 52 form small chains that extend towards the inner circumferential surface 26 and are arranged in an alternating manner with the exposed fibers 16.

(18) In FIG. 5, the fastener 36 or rather the electroactive polymer material is supplied from the voltage source 42. In this activated state, the temperature of the fastener 36 rises and the bond between the micrograins 52 is weakened. As a result, the exposed fibers 16 and the electroactive polymer material are able to slide relative to each other, which results in the fastener 36 being able to be inserted into the opening 22.

(19) Referring to FIG. 6, the fastener 36 is separated from the voltage source 42 and the bond between the micrograins 52 of the electroactive polymer material has strengthened again. In this configuration the exposed fiber 16 and the chains formed by the micrograins 52 are interlocked and cannot be moved relative to each other without substantial force being introduced. Consequently, the fastener 36 is positively locked with the first and second fiber composite parts 10, 12 and prevents their separation along the axial direction of the fastener 36. Thus, the first and second fiber composite parts are fastened to each other.

(20) In order to reverse this process, the fastener 36 is connected to the voltage source 42 again, which reduces the diameter of the fastener 36 and weakens the bond between the micrograins 52 thereby allowing a pushing of the fastener 36 out of the opening 22.

(21) In contrast to a usual rivet connection, this rivet like connection can be engaged and disengaged without destroying any of the parts 10, 12 or fasteners 36.

(22) In order to improve fastening of structural parts to each other that are usually riveted, the invention proposes a fastener (36) that includes electroactive polymer material. The parts (10, 12) have an opening (22) within an inner circumferential surface (26). Fibers (16) protrude from the inner circumferential surface (26) into the opening (22) and interlock with chains of micrograins (52) of the electroactive polymer material.

(23) The systems and devices described herein may include a controller or a computing device comprising a processing and a memory which has stored therein computer-executable instructions for implementing the processes described herein. The processing unit may comprise any suitable devices configured to cause a series of steps to be performed so as to implement the method such that instructions, when executed by the computing device or other programmable apparatus, may cause the functions/acts/steps specified in the methods described herein to be executed. The processing unit may comprise, for example, any type of general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, a central processing unit (CPU), an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, other suitably programmed or programmable logic circuits, or any combination thereof.

(24) The memory may be any suitable known or other machine-readable storage medium. The memory may comprise non-transitory computer readable storage medium such as, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. The memory may include a suitable combination of any type of computer memory that is located either internally or externally to the device such as, for example, random-access memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like. The memory may comprise any storage means (e.g., devices) suitable for retrievably storing the computer-executable instructions executable by processing unit.

(25) The methods and systems described herein may be implemented in a high-level procedural or object-oriented programming or scripting language, or a combination thereof, to communicate with or assist in the operation of the controller or computing device. Alternatively, the methods and systems described herein may be implemented in assembly or machine language. The language may be a compiled or interpreted language. Program code for implementing the methods and systems described herein may be stored on the storage media or the device, for example a ROM, a magnetic disk, an optical disc, a flash drive, or any other suitable storage media or device. The program code may be readable by a general or special-purpose programmable computer for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein.

(26) Computer-executable instructions may be in many forms, including modules, executed by one or more computers or other devices. Generally, modules include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types. Typically, the functionality of the modules may be combined or distributed as desired in various embodiments.

(27) It will be appreciated that the systems and devices and components thereof may utilize communication through any of various network protocols such as TCP/IP, Ethernet, FTP, HTTP and the like, and/or through various wireless communication technologies such as GSM, CDMA, Wi-Fi, and WiMAX, is and the various computing devices described herein may be configured to communicate using any of these network protocols or technologies.

(28) While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms comprise or comprising do not exclude other elements or steps, the terms a or one do not exclude a plural number, and the term or means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.

LIST OF REFERENCE SIGNS

(29) 10 first fiber composite part 12 second fiber composite part 14 matrix material 16 fibers 18 first layer 20 second layer 22 opening 24 mechanical drill 26 inner circumferential surface 28 laser mill 30 laser source 32 work implement 34 laser beam 36 fastener 38 work implement 40 robotic arm 42 voltage source 44 leads 46 outer surface 48 fastener top surface 50 fastener bottom surface 52 micrograins