Mechanical connector for structural members

The invention is a connector to join structural members. In particular, the invention is a connector to assemble and join structural members where the members can be formed from dissimilar materials; for example, an aluminum plate joined by the connector to a steel plate. The connector can be formed in part or in whole from a shape memory metal that exhibits dimensional change upon assembly to complete the joint.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
There are several methods presently used to join structural members, 
particularly those members that are plates formed of dissimilar metals; 
for example, plates used in the construction of ships. The use of thin 
plate and the extensive inclusion of aluminum inserts in steel structure 
on the new ships being designed today has presented a difficult and labor 
intensive condition for the Naval architects and the construction trades. 
2. Description of the Known Related Art 
Current methods to join plates include: to weld causing the material of the 
plates to fuse together, or to bond using adhesives which attach via 
properties of the bonding agent(s), or to mechanically fasten by the use 
of physical force. For example, one current method of welding joins 
dissimilar metals, such as aluminum structure to steel structure, by an 
explosion bonded piece of "Deta Couple" which is aluminum on one side and 
steel on the other. Another mechanical method can be an externally applied 
deformation or penetration of the plates through the use of bolts, rivets, 
or clamps. Each of these methods has its limitations and disadvantages: 
1. Welding requires that the materials of two or more plates to be joined 
be compatible metallurgically or molecularly to the fusion process. The 
heat generated by welding, or by brazing, may result in degradation of 
some material properties. 
2. Adhesive bonding requires that the material of the plate and the bonding 
agent be chemically compatible and environmentally controlled for proper 
curing. 
3. Mechanical fasteners are both labor and material intensive, and require 
specialized equipment and training. Mechanical fastening does not produce 
an optimum structural connection, particularly in the construction of 
ships. 
Further, current methods to join structural members formed of dissimilar 
metals have the continuing requirement either to inhibit or, preferably, 
eliminate galvanic action developed by and between the dissimilar metals. 
SUMMARY OF THE INVENTION 
Briefly, in accordance with the invention, a compressive connector assembly 
for fastening or joining structural members includes an element formed 
from a PRIOR ART material that has a shape memory which undergoes a 
transformation both in crystal structure and thereby in critical 
dimensions when the material is exposed to selected high temperature 
excursions and to low temperature gradients which develops a compressive 
force acting upon a channel member in the assembly where the channel in 
the member has opposing walls spaced-apart by a distance D1 subsequent to 
a high temperature excursion and by a distance D2 at the low temperature 
gradients where D1&lt;D2 so that a structural member having a thickness T1 
positioned partially within the compressive channel prior to the high 
temperature excursion is clamped or retained by the channel member when 
D1&lt;T1&lt;D2. 
Accordingly, one object of the invention is to join structural members by 
compressive force. 
Another object of the invention is to join structural members formed from 
dissimilar materials by compressive force without direct contact of the 
structural members with each other. 
Another object of the invention is to join structural members by 
compressive force with a universal connector. 
Another object of the invention is to join structural members by 
compressive force with a resulting joint formed by other than fusion 
welding or mechanical fasteners. 
Further objects, features and the attending advantages of the invention 
will be apparent when the following description is read with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In accordance with the invention, one embodiment of connector 20 that finds 
use in the method of joining one or more structural members is shown by 
FIGS. 1 and 2. The longitudinally extending connector 20, which is 
configured in a generally H-shaped cross section with its major dimension 
extending in the longitudinal direction, is preferably formed from a 
memory metal alloy such as nickel-titanium. This and other memory metal 
alloys are available from several U.S. suppliers including Shape Memory 
Applications, Inc., Sunnyvale, Calif. 
Shape Memory Applications' literature states: "Memory Alloys undergo a 
transformation in their crystal structure when cooled from the stronger 
high temperature form (Austenite) to the weaker, low temperature form 
(Martensite). The martensite is easily deformed to a new shape. When the 
alloy is heated through its transformation temperature, it reverts to 
austenite and goes back to its previous shape with great force. This 
process is repeatable." 
"The temperature at which the alloy `remembers` its high temperature form 
when heated can be adjusted by slight changes in alloy composition. In the 
Nickel-Titanium alloys for instance, it can be changed from above 
+100.degree. C. to below -100.degree. C. The shape recovery occurs over 
just a few degrees and can be controlled within a degree or two." 
Both austenite and martensite forms of the memory alloy are ductile with 
tensile strengths to 200,000 pounds per square inch (psi), are 
bio-compatible, and are extremely corrosion resistant. These memory alloys 
have a yield strength in the austenite form of from 35,000 to 70,000 psi; 
and, in the martensite form, a deformation stress of from 10,000 to 20,000 
psi. The martensite form can absorb up to eight percent (8%) recoverable 
strain. 
The connector 20 of FIG. 1 is formed from a memory metal alloy, such as 
that described, in its austenite form or phase. Lands 22 formed in 
opposing walls of respective gripping channels 24 and 26 are spaced-apart 
by a distance D1. This manufactured connector is then expanded (deformed) 
to its martensite phase so that the opposing lands are spaced-apart by a 
distance D2 as shown by FIG. 2, where D1 is less than D2 (D1&lt;D2). The 
gripping channels 24 and 26 of the connector 20 remain substantially 
constant in configuration and dimensions in each of these alloy phases. 
In FIGS. 3 and 4, one or more structural members, such as flat plates 28 
and 30, are positioned in the respective gripping channels 24 and 26 of 
connector 20 as described and shown by FIG. 2. The flat plates can be of 
similar materials; however, for purposes of describing the embodiment of 
FIGS. 1 through 5 and its use of dissimilar materials as structural 
members, plate 28 can be aluminum and plate 30 can be steel. Both plates 
have a dimensional thickness (T1) greater than the distance D1 but less 
than distance D2. With the plates 28 and 30 in position, the connector 20 
is heated which results in a phase transformation from the martensite 
phase of FIG. 2 back to the austenite phase of FIG. 1. As the connector 20 
undergoes this transformation and attempts to return to the austenite 
phase dimensions as described and shown by FIG. 1, the connector 20 grips 
the plates 28 and 30 under relatively strong compressive forces developed 
between the pairs of opposing lands 22. The connector 20 rigidly clamps 
the plates as shown by FIG. 4 into a final joint having excellent 
structural integrity. 
FIG. 5 illustrates an assembly of structural members and connectors such as 
connector 20, formed in accordance with the invention. The assembly 
includes a T-beam member 34 that butts into and is joined by conventional 
welds to a panel member 36. The T-beam member is formed from a flange 
panel 38 and a stem panel 40. 
The flange panel 38 is a composite subassembly built-up from a pair of 
structural plates 42 and 44 that are joined by connector 20. The stem 
panel 40 is also a subassembly of a pair of structural plates 46 and 48 
joined by connector 50. The panel member 36 is another subassembly that 
has a pair of structural plates 52 and 54 joined by connector 56. 
Connectors 50 and 56 are functionally like connector 20 although each need 
not be of the same physical dimensions or structural configuration; for 
example, other connector embodiments formed in accordance with the 
invention as will be described could be used where structurally applicable 
and desirable. 
The T-beam member 34 of FIG. 5 is assembled by joining, e.g., welding, stem 
panel 40 to flange panel 38 along T-joint 58 where plates 46 and 48 butt 
into plates 42 and 44. The stem panel 40 of the T-beam member 34 is 
similarly joined to the panel member 36 along T-joint 60 where plates 46 
and 48 butt into plates 52 and 54. A suitable cut-out, such as cut-out 62, 
can be used at each end of connector 50 so that the connector does not 
physically interfere with connectors 20 and 56 at the respective T-joints. 
Alternatively, a portion of each connector can be machined away or 
otherwise removed to accept an abutting surface. The size of cut-out 62 
relative to the large size of the final assembly results in minimal, if 
any, loss of structural rigidity. Yet this assembly, which is relatively 
common in ship construction, can be readily manufactured through use of 
the connectors and method of the invention thereby eliminating relatively 
difficult weld joints that need to be made along intricate weld lines, and 
frequently under severely constrained welding tip orientations. 
In accordance with the invention, another embodiment of a connector 66 is 
shown by FIG. 6. Connector 66 is formed from a memory alloy and functions 
like connector 20 as described. Connector 66 is structurally 
distinguishable, however, from connector 20 since it is configured in a 
generally U-shaped cross section. Operatively, flange edges 68 and 70 of 
abutting plates 72 and 74, respectively, are clamped together in a 
connector channel 76 when the connector 66 under goes transformation to 
the austenite phase. 
Referring now to FIG. 7, yet another embodiment of a connector 80 can be 
formed from a memory alloy. The connector 80 has channels 82 and 84 that 
have smooth, opposing walls; that is, without lands such as the lands 22 
of connector 20 as described. A liner 86 formed from a non-memory alloy is 
positioned within each of the channels 82 and 84. There are operating 
environments where the channel of a connector has a lip edge, such as lip 
edge 85 for channel 84, to retain the liner 86 within the channel. The 
liner 86 has internal gripping lands 88 similar to lands 22 of FIG. 1. 
The use of liner 86 provides several advantages not readily available with 
the connectors of FIGS. 1-6 which have integrally formed landed channels. 
These advantages include: 
1) A connector can be manufactured in standard sizes and used with various 
liner sizes, i.e., with various gap widths between the opposing lands but 
with common outer dimensions to compensate for different plate thicknesses 
to be retained by the connector. 
2) The liner can be manufactured from a highly machinable material and 
could even be extruded. 
3) Where structural members are formed from dissimilar materials, the 
selection of an appropriate liner material will further inhibit galvanic 
corrosion. 
In accordance with another embodiment of the invention, a compressive 
connector assembly 90 as shown by FIG. 8 has a connector body 92 that is 
preferably formed from a metal or metal alloy which is not a memory metal 
alloy. However, it is contemplated that in certain applications of the 
connector assembly the connector body could be formed from a memory metal 
alloy where increased compressive or gripping forces are required. 
The connector body 92 has one or more openings, such as longitudinally 
extending channel 94 which has inwardly tapering walls 96 and 98. The 
generally U-shaped channel 94, therefore, has a dimensional width at the 
bight 100 that is greater than the width at the mouth 102 as defined by 
the opposing walls 96 and 98. 
Channel 94 is formed to receive a liner 104. Liner 104 has a gripping 
channel 106 with outer wall surfaces 108 and 110. These surfaces have a 
taper that is generally parallel with and complementary to the taper of 
the respective inner surfaces of walls 96 and 98. The liner 104 is also 
preferably formed from a metal or metal alloy which is not a memory metal 
alloy. However, like the liner 86 of FIG. 7, liner 104 has internal 
gripping lands 112 that are preferably positioned in opposing pairs as 
illustrated by FIG. 8. An actuator member 116 completes the compressive 
connector assembly 90. 
The actuator 116 of FIG. 8 is formed from a memory metal alloy and 
preferably configured in a generally arc- or crescent-shaped cross 
section. The actuator is positioned between the bight surface 100 of 
channel 94 and the bottom surface 118 of liner 104. The dimension D.sub.T 
between the spaced-apart tips 120 and 122 of the actuator 116 is at a 
maximum in the martensite phase of the selected memory metal alloy. 
Referring to FIG. 9, the compressive connector assembly 90 of FIGS. 8 and 9 
is illustrated as it appears subsequent to a high temperature 
transformation from the martensite phase, as represented by FIG. 8, to the 
austenite phase. During the transformation, as has been described with 
reference to FIGS. 1 through 4, the actuator 116 attempts to return to its 
austenite dimensions; i.e., the dimension D.sub.T moves from a maximum 
toward its minimum dimension as measured between the tips 120 and 122. As 
the actuator tips move toward each other, the cross-sectional 
configuration of the actuator changes (compare the actuator 116 of FIG. 8 
in its martensite phase to that of FIG. 9 subsequent to its austenite 
phase.) This tip movement generates a dislocating force between the bight 
surface 100 of channel 94 and the bottom surface 118 of liner 104 so that 
the liner is moved away from the bight surface toward the mouth 102 of the 
channel 94 and is, therefore, placed in compression. Thus, as the liner 
moves, the tapering inner surfaces of the channel walls 96 and 98 
complement with the liner outer wall surfaces 108 and 110 to force the 
liner walls to move toward each other. This compressive force moves the 
opposing lands 112 of gripping channel 106 towards each other so that they 
clamp or grip an edge portion of a structural member, such as plate 126, 
positioned within the gripping channel. These relatively strong 
compressive forces are developed as a result of the actuator 116 
functioning as a force generator. 
The compressive connector assembly 90 of FIGS. 8 and 9 can be joined to a 
structural member, such as plate 128; for example, by a conventional 
welded joint 130. Although the plates 126 and 128, which are connected by 
the connector assembly 90, can be of similar materials, the plates can be 
formed of dissimilar metals so that, for example, one plate can be steel 
and the other plate aluminum. 
In accordance with yet another embodiment of the invention, a compressive 
connector assembly 134 as shown by FIG. 10 is structurally and 
functionally similar to the connector assembly 90 of FIGS. 8 and 9, but 
here the longitudinally extending connector body 136 is configured 
generally as an H-shaped cross section. A pair of 
longitudinally-extending, outwardly- opening, and Janus-positioned 
channels 140 and 142 contain respective liners 144 and 146. These liners 
receive and are configured, like the liner 104 of FIG. 8, to grip 
associated structural members such as plates 148 and 150. Again like the 
connector assembly 90 of FIG. 8, the plates 148 and 150 are clamped into 
the assembly by the forces generated by similar actuator members 154 and 
156 as has been described for assembly 90. Again, the structural members 
can be formed of similar or dissimilar materials in accordance with the 
teachings of the invention. 
In an assembly process, the connector formed in accordance with the 
invention as described and illustrated, has several distinct advantages: 
1) Except when cryogenic alloys are used, no special equipment is required 
for the assembly. 
2) Elevated temperatures which may degrade material characteristics and 
induce warping are not incurred during the assembly process. 
3) Use of a special explosive-bonded dissimilar material is not required 
for joining plates of different or dissimilar materials. 
4) Training requirements for the assembly process are minimal. 
5) The assembly process is not labor intensive. 
6) The quality of the final assembly is excellent and repeatable. 
As will be evidenced from the foregoing description, certain aspects of the 
invention are not limited to the particular details of construction as 
illustrated, and it is contemplated that other modifications and 
applications will occur to those skilled in the art. It is, therefore, 
intended that the appended claims shall cover such modifications and 
applications that do not depart from the true spirit and scope of the 
invention.