DE7917624U1 - Shape memory alloy connector - Google Patents

Description

Shape memory alloy connector

The innovation concerns the frictional connection of the Ends of elongated individual parts, in particular glass fibers / with connecting elements made of shape memory alloy (hereinafter also referred to as FG alloys for short).

Shape memory alloys are known as a class of materials and in various compositions (see e.g. US Pat 3,012,882 and 3,174,852). What these materials have in common the ability to undergo a thermally inducible sudden change in shape during the transition from the martensitic to the austenitic condition; For example, if a body made of FG alloy in an austenitic state is formed, then by Temperature reduction brought into the martensitic state and mechanically deformed in this state, so increases he rewarmed with regression of the austenitic

In practice again the shape ("memory form")

that it had before the deformation in the martensitic state.

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In general, an FG alloy can be characterized by a "critical temperature range" in which the martensitic state changes to the austenitic state, and vice versa; this temperature range (hereinafter referred to as martensite / austenite transformation temperature or critical temperature T.) is the range between the temperatures (T) at which the martensitic structure of the FG alloy is stable (M-) and the Temperatures at which the austenitic structure is stable (A _f ), ie (T) M _f <T _fe <(T) A _f .

If this shape memory effect practically only occurs at the transition (T) M- -> (T) A- and not the other way round, is it called a "one-way effect"? is he at least partially thermally reversible, d. H. he kicks

both at (T) M _f > (T) A _f and at (T) A _f > (T) M-

on, it is referred to as a "two-way effect" (see z. B. DE-OS 27 24 255 of the applicant).

Fasteners made from various FG alloys in Form of sleeves or sleeve-like pipe structures are

z. B. from DE-OS 20 65 651 for connecting pipes, for. B. fuel lines, known. Connecting sleeves FG alloys have also already been used by the applicant for the vacuum-tight metal / ceramic connection of pipes and rods have been proposed (CH patent application no.

8509/78).

In the known sleeve-shaped connecting elements this Art, the wall thickness of the socket is less than or at most about as large as the clear width of the socket opening. The resilience required for the connection of pipes or rods with sleeves made of FG alloy.

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speed of the connecting element is achieved by that the socket manufactured in an austenitic state (e.g. at normal ambient temperature) by cooling, z. B. with liquid nitrogen, cooled to M - temperature and at M - temperature by pulling a mandrel through is widened so much that the ends of the pipes or rods to be connected into the socket opening can be inserted. Excessive stretching must be avoided, otherwise it would be necessary for a firm connection required resilience is no longer achievable.

In this case, the subsequent expansion of the sleeve is problematic in terms of production engineering and the achievable accuracy of fit of the sleeve is limited. The resetting f "relaxation") of the connecting element for frictional contact with the individual parts used _{at M f temperatures during the subsequent reheating of the socket to A.} by only up to about 8% (with one-way effect) or up to about 1.5% (with two-way effect) when T is exceeded and the A, state is reached. Therefore, a relatively high accuracy of fit of the connecting elements, in particular with regard to the perforations, is desirable.

The known technology for connecting individual parts with sleeve-like perforated elements made of FG alloy are therefore initially limited by the fact that practically only tubes or rods with a certain minimum diameter of a few mm can be connected. A disadvantage of the known sleeve-shaped connecting elements

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ten from FG alloy is also that practically ηατ the Technically unsatisfactory widening of the socket opening with thorns or the like for mechanical tension (at M temperature) is suitable and that furthermore for each connection of the ends of a pipe and / or rod pair in each case a socket made of FG lees is required.

The object of the invention is a new connection technology with shape memory alloys, with which technology also practically any thin individual parts, e.g. B. glass fibers, wires, filaments and the like connect to each other let, the connection of a plurality of individual particles with a single connecting element can be achieved is, the mechanical tension of the connecting element according to different, comparatively simpler or better controllable methods can be achieved and an improved accuracy of fit is made possible.

The object is achieved according to the invention in that one in a method of the type described above as a connecting element for example a plate or Sheet-shaped body made of shape memory alloy used, the two approximately parallel and practical has outer surfaces running perpendicular to the longitudinal axis of the at least one opening, each of which has smallest dimensions by a multiple, d. H. are more than twice as large as the clear width (diameter transversely to the axial direction) of the at least one opening, and that the body is used for mechanical Tension of the connecting element in the martensitic state (M) of the shape memory alloy under biaxial expansion in the main or parallel to the outer surfaces Deformed reference plane of the body.

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The shape of the named outer surfaces of the body can regularly, e.g. B. rectangular, polygonal, circular or oval or irregular as long as the smallest dimension of these outer surfaces is several times larger is than the opening diameter.

The "thickness" of the connector; H. the distance between the named outer surfaces of the body is on are not particularly critical as long as a corresponding connection length of the individual parts is guaranteed and the body in the Μ, state can be strained by deforming. As a rule, the thickness of the connecting element is at least as great as and preferably larger than the diameter of the opening (s).

Such a connecting element made of FG alloy can be _{tensioned in the M f} state, ie under T, of the alloy used in each case by very different methods which produce a biaxial expansion of the connecting element in the plane parallel to the aforementioned outer surfaces. For example, a sheet-metal or plate-shaped connecting element according to the invention in the M _f state can be mechanically tensioned by upsetting, pressing (force action practically perpendicular to the outer surfaces) or by cross rolling or stretching in two directions, preferably normal to each other (force effects practically parallel to the main plane). In general, a practically useful stress is achieved with biaxial elongation of a few percent, ie 1-8% increase in length in each of the two axes .

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The opening (s) of the one used according to the invention Connecting element is (are) for receiving the ends the structures or pairs of structures to be connected, e.g. B. glass fibers or glass fiber pairs, in the mechanical tensioned M state of the connecting element and for the force-fit connection of the structures or pairs of structures in the Af- (memory form) state of the connecting element determined and can be dimensioned accordingly. The opening (s) can or can in principle both in the mechanically tensioned or untensioned M_ state and in the A_ state of the connecting element are formed.

According to a preferred embodiment, the opening (s) of the connecting element in the martensitic State of the FG alloy, namely after tensioning, formed; this can result in an undesirable subsequent Distortion of, for example, cylindrical openings due to mechanical tensioning is avoided will. The M - state of the FG alloy should be preserved remain what by, appropriate cooling and / or choice of appropriate processing methods, z. B. thermal Laser drilling, eroding, ECM processes and the like, can be achieved.

The method according to the invention is particularly suitable for the frictional connection of glass fibers with typical thicknesses of 50-1000 micrometers or more. Such glass fibers are important for optical conductors, among other things, and connecting elements according to the invention can, for. B. used to connect the ends of a fiber pair or a plurality of fiber pairs.

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For most applications it is useful that the T. temperature, ie the range between (T) M_ and (T) A-, is below room temperature, preferably below 0 C and mostly below -20 ⁰ C.

Suitable FG alloys for the connecting element can can be selected from the publications on the state of the art of FG alloys. Examples of special groups of FG alloys are alloys that have Ni / Ti or Ni / Ti / Cu or Cu / Al / Ni or Cu / Zn / Contain Al. The latter group is preferred for many purposes.

The invention is explained with reference to the drawings. It demonstrate:

1 the semi-schematic, perspective illustration of a body made of FG alloy before mechanical clamping,
FIG. 2 shows the body from FIG. 1 after clamping in the martensitic state,

3 shows the body of FIG. 2 with the opening as a connecting _{element f}

4 shows the connecting element from FIG. 3 with glass fibers inserted into the opening,

FIG. 5 shows the connecting element from FIG. 4 after restoring the body made of FG alloy, 6 shows a pair of bodies made of FG alloy with one fiber end in each body of the pair, and FIG 7 shows the pair of bodies from FIG. 6 in a retaining sleeve.

The plate-shaped or block-shaped body 10, shown semi-schematically and enlarged in FIG. 1, consists of a shape memory alloy, ζ. B. made of Cu / Al / Zn (T, -20 ⁰ C)

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The body 10 present at normal temperature in the austenitic state is, for. B. by immersing in liquid nitrogen, on a (T) M_ z. B. cooled from about -200 C and mechanically deformed in this state without it reaching the T, temperature. For this purpose, the body 10 can be _{deformed, v / grounded, optionally with cooling t} by an upsetting or pressing force acting in the direction of the arrow 19, ie approximately perpendicular to the main plane of the body 10, to form the deformed body 20 shown in FIG. Alternatively, the body can also be deformed to form the body 20 by cross-rolling or stretch drawing at (T) M, in which case the one rolling or stretching. The stretching direction corresponds to the double arrow 15, 16 and the other rolling or stretching direction corresponds to the double arrow 17, 18. The directions of the double arrows 15, 16 and 17, 18 preferably intersect at an angle of 90 degrees.

The body 20 is then _f in (t) M, optionally after re-immersion in liquid nitrogen or under continuous cooling and in any case under T., provided with at least one substantially cylindrical opening 30 whose longitudinal axis runs approximately perpendicular to the main plane of the body 20, preferably by thermal drilling, in particular with the aid of a laser beam.

The diameter of the opening 30 corresponds to a fraction of the smallest dimension of the surface 21, here the distance between the edges 23, 24 of the body 20; In particular, the smallest dimension of the surface 21 is more than twice as large and preferably at least five times larger than the diameter of the opening 30. In a typical case, the diameter of the opening is 50-1000 micrometers.

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Furthermore (one-way effect) or again (two-way effect) in the martensitic state of the body 20, the ends of a pair of glass fibers 41, 42 are pushed into its opening. The outside diameter of the glass fibers 41, 42 is by some, e.g. B. 5, micrometers smaller than the diameter of the opening 30 (at (T) M _f ), but a few micrometers larger than the diameter of the opening at (T) A-.

When T ^ is exceeded in the direction (T) M _f -> (T) A _f of the connecting element 20 shown in FIG ", ie practically the outer configuration of the body 10 of FIG. 1, springs back and thereby connects the glass fibers 41, 42 to one another in a force-locking manner in the body 51 of FIG. 5.

With fasteners !! with two-way effect, the resulting compound 50 is cooled again below T,

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ie at (T) M _f , releasable again because the body then spontaneously jumps back into the tensioned shape 20.

In the case of connections with a one-way effect, the resulting Compound 50 can no longer be released by cooling below T.

Instead of a single opening 30, the body 20 can also be provided with a plurality of such openings. Furthermore, the body 20 shown in FIG. 2 can be brought back to (T) A _f and provided in this state with one or more perforations if the body is made of FG alloy with a two-way effect.

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In this case, however, the opening diameter must be a few microns smaller than the outer diameter of the glass fibers 41, 42 or corresponding other individual parts for the connection 50. The _{body provided with openings in this way at (T) A f} jumps again because of the two-way effect Cooling below T, back into the clamped form 20 of FIG. 3 and is then capable of receiving the individual parts 41, 42 to be connected and their frictional holding when it warms up to temperatures above T after the individual parts 41, 42 have been inserted is left.

Both in connection elements with a one-way effect and in those with a two-way effect, the opening can already be in the body 10 prior to tensioning, d. H. prior to formation of the body 20, e.g. B. by usual mechanical Drill at (T) A_. In this case, however, it must be ensured that the desired shape of the opening at (T) M not significantly affected by the deformation, z. B. is not distorted or sprained. A breakthrough produced at (T) A ~ must, as mentioned above, be a few micrometers smaller than the outer diameter of the individual parts to be connected.

The cuboid design of the body 10, 20, 51 shown in FIGS. 1-5 is not, as indicated at the beginning critical and the thickness of the body can be larger or smaller than shown. Furthermore, the surfaces must 11, 12 not be completely flat and can e.g. B. be provided with grooves, ribs, knobs or the like. In the end the inner wall of the opening (s) can also be made with grooves or ribs using appropriate machining methods be provided to increase the strength of the connection.

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In FIGS. 6 and 7, one of two holding bodies in the form of circular disks is shown in a semi-schematic sectional view 62, 62 existing pair shown. In each of the bodies 61, 62 made of FG alloy, the end region is a glass fiber 63, 64 attached, analogously as described in connection with Figs. 1-5, but with the modification, that only one glass fiber is pushed into the opening 30 (Fig. 3) of the tensioned holding body and through Relaxation of the FG alloy is attached in the respective associated holding body.

The end faces 611, 621 of the holding body 61, 62 with the glass fibers 63, 64 fastened therein are then above T. (i.e. at A ^ temperature) ground flat and z. B. in the arrangement 70 shown in Fig. 7 for formation a planar contact coupling of the fibers 63, - 64 joined together. The holding bodies 61, 62 can be made of FG alloy exist with the same or different T. values.

In the coupling arrangement 70 in FIG. 7, the two bodies 61, 62 are provided with one from the hollow cylindrical outer sleeve 71 and the circular disc-shaped internal screw connection 72 existing conventional sleeve connected, but are

. also other coupling elements including those made of FG alloy, preferably with a different T. than that the body 61, 62 is suitable. It goes without saying that each of the bodies 61, 62 also has the ends of several Can hold fibers on one side, so that an arrangement 70 with flat contact surfaces 612, 621 for coupling the ends of two fiber groups can be used.

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The method according to the invention is explained using the following example:

For example, rectangular specimens were produced from shape memory alloys with dimensions of 3 mm × 5 mm × 10 mm, namely from an FG alloy with 73.5% by weight Cu, 16.5% by weight Zn, 8% by weight Al and 2 % By weight Ni (alloy A, M _f = -60 C) and an FG alloy with 75% by weight Cu, 15% by weight Zn, 8% by weight Al and 2% by weight Ni (alloy B, M. * +50 C). The specimens were in a martensitic to stood in a hand press; in the direction of its largest Dimensions compressed by about 5%, i.e. H. the cuboid height mechanically reduced from 10 mm to 0.5 mm. Alloy A specimens were previously placed in an alcohol cooling bath cooled to -10 C and compressed at this temperature, the specimens of alloy B, however, is compressed at +20 ⁰ C.

Then, while keeping the martensitic state, the FG alloy specimens were inserted into each of the specimens Hole 0.85 mm in diameter drilled, approximate in the middle of the face of 3 χ 5 mm and practical perpendicular to this. Then, still in the martensitic state of the respective FG alloy, steel wires, Copper wires and glass fibers (each with a diameter of 0.8 mm) pushed into the holes and the respective Test piece with inserted wire or with inserted glass fiber heated above the ^ temperature (alloy A to room temperature, alloy B to +100 ⁰ C). Each of the test pieces practically jumps back into its shape before the upsetting, which causes the bore narrows and holds the inserted wire or the inserted glass fiber.

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The compounds thus obtained were used to test the | j

Bond strength under tension. With the test pieces made of alloy B, a tensile load of 3 kg is required to pull out the copper wire pieces, and a tensile load of 5 kg to pull out the steel wire pieces. The glass; fibers did not pull themselves out, but went _; previously broken.

In the case of the test pieces made of alloy A, the amounts to. '

Pulling the wires out of the test pieces required tensile loads several times (up to five times) the values measured on the test pieces made of alloy B; but also with the test pieces made of alloy A crack the fiber when trying to unplug it. In both cases, the tensile strength was thus the Connection of glass fiber and FG alloy greater than the tensile strength of the glass.

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List of reference symbols "-

10 FG alloy body

11 upper surface of 10

12 lower surface of 10

15 Direction of the first elongation axis

16 inversion of 15

17 Direction of the second expansion axis

18 reversal of 17

19 Direction of pressing or upsetting force

20 bodies after deforming

21 upper surface of 20

23 side edge of 20

24 "η ι»

3 0 breakthrough

41 fiberglass

42 fiberglass

50 connection

51 connecting element

61 first body of a body pair made of FG alloy 611 contact surface of 61

62 second body of the body pair 621 contact surface of 62

63 fiberglass

64 fiber

70 connecting element with body pair

71 sleeve outer sleeve

7 2 Socket screw connection.

Claims (8)

BBC Baden .. ♦ - Oil - PROTECTION CLAIMS 1. Connecting element made of shape memory alloy for connecting elongated individual parts with at least one Connection element made of shape memory alloy, which connection element is at least one substantially cylindrical Has opening for receiving end areas of individual parts to be connected and in the martensitic State of the shape memory alloy can be mechanically stressed, so that in this state there are end regions the items can accommodate and hold in the austenitic state non-positively, with at least one End region of an individual part into which at least one opening of the connecting element is introduced can, while the shape memory alloy is in the mechanically stressed martensitic state, and the connecting element then converted into the austenitic state of the shape memory alloy by the action of temperature can be, characterized in that the connecting element a body (10) made of shape memory alloy possesses, the two approximately parallel and practically perpendicular to the longitudinal axis of the at least one opening (30) extending outer surfaces (11, 12), whose the smallest dimensions in each case are several times larger than the clear width of the at least one opening (30), and that the body (10) by biaxial expansion (15, 16; 17, 18) in the martensitic state of Porm memory alloy in the one parallel to the outer surfaces Main plane of the body can be stretched. 47/79 ■ ··· «· f ■« ι - 02 - 2. Connecting element according to claim 1, characterized in that the connecting element is a sheet-metal or plate-shaped Body (10, 20) and at least one practically cylindrical opening (30) perpendicular to the sheet metal or Has plate plane, the smallest dimension of the body (10, 20) in the sheet metal or plate plane at least is about five times larger than the diameter of the at least one opening (30). 3. Connecting element according to claim 2, characterized in that that the shape memory alloy contains copper, aluminum and zinc as main components. 4. Connecting element according to claim 2, characterized in that the shape memory alloy nickel and titanium as Contains main ingredients. 5. Connecting element according to claim 2, characterized in that the shape memory alloy is nickel, titanium and copper contains as main ingredients. 6. Connecting element according to one of claims 1-5, thereby characterized in that the shape memory alloy has a martensite / austenite conversion temperature of below C C owns. 7. Connecting element according to one of claims 1-6, characterized characterized in that it contains at least two glass fibers (41, 42) in a non-positive connection with the body (51) made of shape memory alloy. 8. Connecting element according to claim 7, characterized in that the glass fibers (63, 64) are non-positively connected in a multi-part body (61, 62).