WO1998039197A1

WO1998039197A1 - Controlled deformability of aluminum, or other metal structure

Info

Publication number: WO1998039197A1
Application number: PCT/US1998/004233
Authority: WO
Inventors: Joseph C. Benedyk
Original assignee: Alcoa Inc.
Priority date: 1997-03-04
Filing date: 1998-03-04
Publication date: 1998-09-11
Also published as: AU6446898A

Abstract

A controllably deformable frame structure comprising a structural member (50) and a member for controllably deforming the frame structure. The controllably deforming structure comprises at least one energy-absorbing zone (57) disposed within the structural member. In turn, the structural member will deform controllably when subjected to loads of lesser magnitude than required to plastically deform the remainder of the at least one structural member. The invention likewise comprises a method of manufacturing a frame structure.

Description

TITLE OF THE INVENTION

Controlled Deformability of Aluminum, or Other Metal Structure

BACKGROUND OF THE INVENTION

1 . The Technical Field

The present invention relates in general to frame structures. In particular, the^'

present invention relates to aluminum and other metal frame structures which are

capable of bearing substantial static and dynamic structural loads, yet which are

controllably deformable in the event they are subjected to loads of greater than a

predetermined value.

2. The Prior Art

Aluminum and other metal frame structures have been known in the art for

many years. Such frame structures have long been used in the design of storage

racks, containers, and other applications. In particular, such frame structures have

been extensively used in the production of vehicles, such as aircraft, automobiles,

and trucks, where it is particularly desirable to provide a frame structure which is

sturdy, uses materials efficiently so as to be relatively lightweight and inexpensive,

and is commercially practical to produce. In addition to exhibiting these qualities,

vehicle frame structures are typically designed to deform when subjected to loads,

particularly compressive and bending loads resulting from a collision with another

vehicle or a stationary object, which exceed predetermined structural design limits.

By deforming when subjected to such loads, the frame structure can absorb a

significant amount of the collision impact energy which would otherwise be transmitted to the passenger cell, thus preventing many potentially serious injuries

to the vehicle's occupants.

In the past, it has been standard automotive industry practice to insert

certain components into a vehicle structure specifically so that they will

preferentially deform during a collision. In this manner, designers have been able

to design collision energy management into a vehicle structure. However, in the

past, vehicle designers have generally been limited to using conventional structural

materials. Although the properties of such materials are well-known and well-

documented, it is difficult to design a frame structure using such materials that is

sturdy enough to support the requisite structural loads, yet capable of absorbing a

sufficient amount of collision energy to protect the vehicle's occupants after an

accident, without adversely affecting the structure's weight, cost, and ease of

production.

Retrogression heat treatment (RHT) technology, as disclosed by Benedyk,

U.S. Pat. No. 5,458,393, has been used in the past to reduce the number of

elements and discontinuities in a vehicle structure. Benedyk discloses a space

frame and manufacturing method involving the use of induction heating to locally

soften distinct points on vehicle frame components, thus significantly increasing the

formability of the metal. The locally softened areas are then worked, formed, and

assembled, as desired. After these operations have been completed, the effected

areas are generally hardened towards their pre-softened hardness. The apparatus

and method of Benedyk yield an efficiently assembled frame structure which is

comprised of relatively fewer components than a conventional frame structure, yet which exhibits structural characteristics which are comparable or superior to those

of a conventional structure.

Accordingly, it is an object of the present invention to use localized induction

heating technology to locally soften certain locations on aluminum and other metal

structures to establish a pattern or pre-softened "trigger points" that constitute one

or more energy absorbing zones within the overall structure. It is also an object of

the present invention to use localized induction heating technology to soften certain

locations on aluminum and other metal structures to enable establishment of a

predetermined pattern of pre-buckled "trigger points" that constitute one or more

energy absorbing zones within the overall structure. It is further an object of the

present invention to orient such trigger points in a manner that allows for controlled

deformation of the energy absorbing zone after an impact.

These and other objects of the present invention will become apparent in

light of the present specification, claims, and drawings.

SUMMARY OF THE INVENTION

The invention comprises a controllably deformable frame structure comprising

at least one structural member and means for controllably deforming the frame

structure. The controllable deforming means comprises at least one energy

absorbing zone operably disposed within at least one of the at least one structural ^'

member to, in turn, controllably deform when subjected to loads of lesser

magnitude than required to plastically deform the remainder of the at least one

structural member.

In a preferred embodiment, the at least one structural member comprises a

metal material. In such an embodiment, the metal material may comprise

aluminum.

In another preferred embodiment, the at least one structural member

comprises an extruded member. In another preferred embodiment, the at least one

structural member comprises a stamped member.

Preferably, the frame structure comprises at least a portion of an automobile

frame structure. In such an embodiment, the automobile frame structure may

comprise a bumper support.

In yet another preferred embodiment, the at least one energy absorbing zone

of the at least one structural member comprises a locally heat treated region. In

another preferred embodiment, the at least one energy absorbing zone of the at

least one structural member comprises at least one of a mechanically pre-deformed

region and a locally heat treated region. In another preferred embodiment, the at least one energy absorbing zone of

the at least one structural member comprises a region which has been locally heat

treated, mechanically pre-deformed, and rehardened.

The invention further comprises the method for manufacturing a frame

structure which is controllably deformable when subjected to mechanical loads in

excess of a predetermined load. The method comprises steps of: (a) arranging at

least one structural member in a predetermined orientation; and (b) introducing at

least one energy-absorbing zone in a predetermined region of the at least one

structural member. This, in turn, facilitates controlled deformation of the structural

member when subjected to loads of lesser magnitude than are required to deform

the remainder of the at least one structural member.

In a preferred embodiment, the step of introducing the at least one energy-

absorbing zone in a predetermined region of the at least one structural member

comprises the step of softening predetermined regions of the at least one structural

member through localized heat treatment.

In another preferred embodiment, the step of introducing at least one energy

absorbing zone in a predetermined region of the at least one structural member

comprises the step of mechanically pre-deforming predetermined regions of the at

least one structural member in a desired, predetermined orientation.

In yet another preferred embodiment, the step of introducing at least one

energy absorbing zone in a predetermined region of the at least one structural

member further comprises the steps of: (a) softening the predetermined region of

the at least one structural member through localized heat treatment; (b) mechanically pre-deforming the softened regions of the at least one structural

member in a predetermined orientation; and (c) hardening a portion of the

predetermined region of the at least one structural member toward its pre-softened

hardness.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view of a frame structure comprised of a plurality of

structural members;

Fig. 2 is a perspective view of an embodiment of a specially treated

structural member having an energy absorbing zone; and

Fig. 3 is a perspective view of an embodiment of a specially treated

structural member having a plurality of energy absorbing zones.

DETAILED DESCRIPTION OF THE DRAWINGS

While this invention is susceptible of embodiment in many different forms,

there is shown in the drawings and described in detail herein several preferred

embodiments with the understanding that the present disclosure is to be considered

as an example of the principles of the invention, and is not intended to limit the

invention to the illustrated embodiments.

Controllably deformable frame structure 20 is shown in Fig. 1 as including

a plurality of structural members, such as structural members 22, 24 and 26, and

controllable deformation means 57 (as shown in Figs. 2 an 3) . As can be seen in

Fig. 1 , when the structural members are used, for example, as part of an

automotive space frame, such structural member may comprise side members 22,

cross members 24, and vertical members 26, among others. Controllably

deformable frame structure 20 may also be comprised of more or fewer structural

members than are shown in Fig. 1 , and the structural members may be configured

in any desired, predetermined orientation, which may be different from that shown

in Fig. 1 .

In the embodiment of Fig. 1 , it is contemplated that at least a portion of the

structural members include controllable deformation means 57 (Figs. 2 and 3),

while other ones of the structural members omit such controllable deformation

means. Indeed, as will be more fully explained and understood to those having

ordinary skill in the art, operative and relative location of such controllable

deformation means will serve to enable controlled deformation of the particular frame structure when excessive impact is imparted upon the particular frame

structure.

Fig. 2 illustrates a specially treated structural member 50 according to the

invention. In such an embodiment, Structural member 50 comprises an elongated,

hollow member of rectangular cross section, having a first end 51 , a second end

52, and four side walls 53 through 56. Each side wall includes a respective end

surface 53a through 56a, defining each side's thickness. Structural member 50

further includes controllable deformation means 57, which, as will be understood,

comprises an "energy-absorbing" zone. Controllable deformation means 57

comprises a region which has been subjected to a retrogression heat treatment

process. As will be explained, such a process enables a localized region (of the

frame) to become softened and then rehardened toward its original hardness.

Indeed, based upon the time of heating and cooling, structural characteristics of the

region can be altered to, for example, result in a structure that is more malleable at

the localized region as compared to the remainder of the structure. Additionally,

as will also be explained, such localized regions can be machineably altered prior to

hardening - so as to, for example, enable structural indentations to be imparted into

the structure toward facilitation of controlled deformation of the structure upon

excessive impact.

As shown in Fig. 2, controllable deformation means 57 further comprises a

plurality of indentations 58 having a desired, predetermined size, shape, and depth.

Although indentations 58 are shown as oblong, they may be of other suitable

shapes as well, such as, for example, square or circular. The number, shape, size, and orientation of the indentations relative to each other and to the overall

dimensions of any side 53 through 56 of structural member 50 may be varied as

required to provide the structural member 50 with the desired deformability

characteristics. For example, Fig. 2 illustrates controllable deformation means 57

as comprising a uniform pattern of indentations 58 on each of side walls 53

through 56. In other embodiments, indentations 58 may be applied in a uniform or

non-uniform pattern to any of, or all of, sides 53 through 56 of structural member

50.

As previously explained, controllable deformation means 57 may comprise

specific regions wherein the structural member has been locally softened through

the use of a retrogression heat treatment. The manner and extent of the heat

treatment may be varied to achieve the desired deformability characteristics. In

particular, the energy-absorbing characteristics of structural member may be

established in a desired, predetermined manner by applying such a retrogression

heat treatment in varying manners, including varying temperatures and durations,

at various predetermined locations on any or all of the sides of the structural

member.

Additionally, each structural member may comprise more than one energy-

absorbing zone (controllably deformation means) 57. For example, in the

embodiment illustrated in Fig. 3, structural member 50 has two separate energy-

absorbing zones, each comprising a pattern of circular indentations. In such a

structural member, it is possible for one or more of such zones to be comprised of a pattern of indentations, while one or more other such zones are comprised of

specially heat treated regions.

Although not required, in a preferred embodiment, structural member 50

comprises a 6000-series aluminum alloy formed by an extrusion process. However,

it is also contemplated that various other suitable materials and other commercial^'

processes, such as stamping be used. Furthermore, although structural member 50

is illustrated as being hollow, it is likewise contemplated that the structural member

be of solid or varying cross section, as well as having a plethora of different overall

geometries.

In operation, controllably deformable frame structure 20, may be subjected

to an impact load that exceeds a desired, predetermined value. Such an impact

load may place a load on one or more of the treated structural members 50. When

subjected to a load which exceeds a predetermined value, energy-absorbing zone

57 (controllable deformation means) will begin to deform at a load of lesser

magnitude than is required to deform the other portions of the structural member.

Each energy absorbing zone 57 associated with each structural member may be

designed to deform in a desired, predetermined rate and in a desired, predetermined

orientation — regardless of the point, magnitude, or direction of impact. In frame

structures comprising automobile frames, for example, a frame structure may be

designed to deform, in response to a predetermined range of impact load, in a

manner that absorbs an optimal amount of collision energy, in order to protect the

passengers and critical components of a vehicle, such as a fuel tank. The process for fabricating a controllably deformable frame structure 20

comprises first forming a structural member (such as structural members 22, 24,

26 and 50) in a conventional manner, as would be known to one skilled in the art.

For example, a typical structural member may be formed by extruding an elongated,

hollow member of rectangular cross section according to known mill processes, and

then annealing the extruded member to a desired, predetermined hardness.

Alternatively, the structural member may be initially formed as a solid extrusion, a

stamping, a combination of extrusions and/or stampings, or by other suitable

means.

Next, energy-absorbing zones 57 are added to the extruded member. As will

be understood, such energy absorbing zones can be imparted during or after

extrusion.

Energy-absorbing zones 57 may be created in the form of indentations

stamped into any or all of the side walls in selected predetermined regions of the

structural member. Preferably, energy-absorbing zones 57 may be created by

locally softening, or making more malleable, the material comprising the structural

members in selected predetermined regions of the structural member. In a preferred

embodiment, selected predetermined regions of structural member 50 may be

locally softened to facilitate the stamping of indentations; indentations may then

be stamped into any or all of the side walls, and finally, the softened region may

then be hardened, as desired, towards its pre-softened hardness.

For those embodiments wherein predetermined regions of the structural

member(s) are locally softened, it is contemplated such softening be effected by using a retrogression heat treatment as disclosed in U.S. Pat. No. 4,766,664 issued

to Joseph C. Benedyk, for a Process for Formation of High Strength Ladder

Structures and U.S. Pat. No. 5,458,393, issued to Joseph C. Benedyk, for a Space

Frame Apparatus and Process for the Manufacture of Same, both of which are

incorporated herein by reference. Using this process, an induction coil is placed in

operable contact with the specific area to be heated and, in turn, softened, with

only minimal heat being conducted to areas adjacent to the predetermined regions.

A controllably deformable frame structure (such as frame structure 20) may

then be assembled from one or more structural members, using any suitable

process. At least a portion of the individual structural members are contemplated

to comprise structural members having energy-absorbing zones. One such

acceptable process for assembling the frame structure, when multiple frame

structures are used, is described in the previously identified patents to Joseph C.

Benedyk. Of course, other processes known in the art, such as the use of

mechanical nodes or welding, may also be used to assemble multiple frame

structures.

If desired, energy absorbing zones 57 may be added to the individual

structural members comprising the frame structure after the individual structural

members have been assembled into the frame structure. It may be desirable to do

so to avoid subjecting energy absorbing zones 57 to undesired loads which may be

encountered during assembly of the frame structure.

The frame structure treated with the particular described controllable

deformation means greatly facilitates controlled energy absorbtion through deformation of the frame structure upon impact of predetermined loads.

Additionally, as will be readily recognized, by isolating, or preselecting regions to

be heated by the retrogression heat treatment, not only will controlled deformation

occur upon impacts at predetermined loads, but such deformation will likewise

occur in a controlled deformation pattern.

The foregoing description and drawings are merely to explain and illustrate

the invention and the invention is not limited thereto except insofar as the appended

claims are so limited, as those skilled in the art who have the disclosure before

them will be able to make modifications and variations therein without departing

from the scope of the invention.

Claims

1 . A controllably deformable frame structure comprising:

at least one structural member; and

means for controllably deforming the frame structure, the

controllable deforming means comprising at least one energy-

absorbing zone operably disposed within at least one of the at

least one structural member, to, in turn, controllably deform

when subjected to loads of lesser magnitude than required to

plastically deform the remainder of the at least one structural

member.

2. The invention according to claim 1 wherein the at least one structural

member comprises a metal material.

3. The invention according to claim 2 wherein the metal material includes

aluminum.

4. The invention according to claim 1 wherein the at least one structural

member comprises an extruded member.

5. The invention according to claim 1 wherein the at least one structural

member comprises a stamped member.

6. The invention according to claim 1 wherein the frame structure comprises at

least a portion of an automobile frame structure.

7. The invention according to claim 6 wherein the at least a portion of an

automobile frame structure comprises a bumper support.

8. The invention according to claim 1 wherein the at least one energy absorbing

zone of the at least one structural member comprises a locally heat treated region.

9. The invention according to claim 1 wherein the at least one energy absorbing

zone of the at least one structural members comprises at least one of a

mechanically pre-deformed region, and a locally heat treated region.

1 0. The invention according to claim 1 wherein the at least one energy absorbing

zone of the at least one structural member comprises a region which has been

locally heat treated, mechanically pre-deformed, and rehardened.

1 1 . A method for manufacturing a frame structure which is controllably

deformable when subjected to mechanical loads in excess of a predetermined load,

the method comprising the steps of:

arranging at least one structural member in a predetermined

orientation; and

introducing at least one energy-absorbing zone in a

predetermined region of the at least one structural member, to

in turn, facilitate controlled deformation when subjected to

loads of lesser magnitude than are required to deform the

remainder of the at least one structural member.

1 2. The method according to claim 1 1 wherein the step of introducing the at

least one energy-absorbing zone in a predetermined region of the at least one

structural member comprises the step of softening predetermined regions of the at

least one structural member through localized heat treatment.

1 3. The method according to claim 1 1 wherein the step of introducing at least

one energy absorbing zone in a predetermined region of the at least one structural

member comprises the step of mechanically pre-deforming predetermined regions

of the at least one structural member in a desired, predetermined orientation.

1 4. The method according to claim 1 1 wherein the step of introducing at least

member further comprises the steps of:

softening the predetermined region of the at least one structural

member through localized heat treatment;

- mechanically pre-deforming the softened regions of the at least

one structural member in a predetermined orientation; and

hardening a portion of the predetermined region of the at least

one structural member toward its pre-softened hardness.