U.S. patent application number 09/935949 was filed with the patent office on 2002-01-24 for rectangular bursting energy absorber.
This patent application is currently assigned to Safety By Design Company. Invention is credited to Reid, John D., Rohde, John R., Sicking, Dean L..
Application Number | 20020007994 09/935949 |
Document ID | / |
Family ID | 26926023 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020007994 |
Kind Code |
A1 |
Reid, John D. ; et
al. |
January 24, 2002 |
Rectangular bursting energy absorber
Abstract
A bursting energy absorber system having an impact head, and
energy absorption mechanism. The energy absorbing mechanism has a
generally rectangular mandrel for rupturing cooperating thin-wall
generally rectangular tubes in a controlled rupture to absorb
impact forces for a colliding vehicle. A frame may be used to mount
the system to a truck, trailer, guardrail, median barrier end
treatment, or a crash cushion. Stress concentrators such as saw
cuts or scoring may be incorporated into the absorption tubes to
selectively control rupturing and energy dissipation. The mandrels
may be tapered, rectangularly shaped with beveled edges to reduce
frictional forces along the interior corners of the tubes.
Lubricants may be applied to further control frictional
influences.
Inventors: |
Reid, John D.; (Lincoln,
NE) ; Rohde, John R.; (Lincoln, NE) ; Sicking,
Dean L.; (Lincoln, NE) |
Correspondence
Address: |
Thomas E. Sisson
JACKSON WALKER L.L.P.
Suite 2100
112 E. Pecan Street
San Antonio
TX
78205
US
|
Assignee: |
Safety By Design Company
|
Family ID: |
26926023 |
Appl. No.: |
09/935949 |
Filed: |
August 23, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09935949 |
Aug 23, 2001 |
|
|
|
09307235 |
May 7, 1999 |
|
|
|
6308809 |
|
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60232465 |
Sep 13, 2000 |
|
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Current U.S.
Class: |
188/377 |
Current CPC
Class: |
F16F 7/125 20130101;
E01F 15/146 20130101; E01F 15/143 20130101 |
Class at
Publication: |
188/377 |
International
Class: |
F16F 007/12 |
Claims
1. An energy absorption system comprising: an impact head; an
energy absorption mechanism affixed to said head, said mechanism
further comprising: a first mandrel; and a tubular member, said
tubular member receivable within a first end of said tubular member
such that upon impact forces being applied to said impact head,
said first mandrel is urged through said tubular member propagating
cracks or fractures in said tubular member, said cracks controlling
the dissipation of said impact forces.
2. The system of claim 1 wherein said first mandrel has a tapering
rectangular shape with bevels at each corner.
3. The system of claim 1 wherein said generally rectangular tubular
member has rounded interior corners.
4. The system of claim 1 further comprising a means for selectively
controlling said crack propagation along a length of said tubular
member.
5. The system of claim 4 wherein said means for selectively
controlling said crack propagation further comprises a cut in an
end of said tubular member.
6. The system of claim 5 wherein said cut has a length
approximately twice as long as the wall thickness of said tubular
member.
7. The system of claim 4 wherein said means for selectively
controlling said crack propagation further comprises a score in
said tubular member.
8. The system of claim 7 wherein said score is in an end of said
tubular member.
9. The system of claim 7 wherein the depth of said score is
approximately 10% to approximately 20% the thickness of said
tubular member.
10. The system of claim 1 further comprising a lubricant applied to
an inner surface of said tubular member.
11. The system of claim 3 where in said lubricant is selected from
the group consisting of zinc, oil, grease, paint, rust particles,
and ceramic compositions.
12. An energy absorption system comprising: an impact head; an
energy absorption mechanism affixed to said head, said me chanism
further comprising: a first generally rectangular mandrel; and a
generally rectangular tubular member, said tubular member
receivable within a first end of said tubular member such that upon
impact forces being applied to said impact head, said first mandrel
is urged through said tubular member propagating cracks or
fractures in said tubular member, said cracks controlling the
dissipation of said impact forces.
13. The system of claim 12 wherein said means for selectively
controlling said crack propagation further comprises a cut in an
end of said generally rectangular tubular member.
14. The system of claim 13 wherein said cut is further in the
center of a rounded interior corner of said tubular member.
15. The system of claim 13 wherein said cut has a length
approximately twice as long the wall thickness of said tubular
member.
16. The system of claim 11 wherein said means for selectively
controlling said crack propagation further comprises a score of
said generally rectangular tubular member.
17. The system of claim 16 wherein said score is in an end of said
tubular member.
18. The system of claim 16 wherein said score is further in the
center of a rounded interior corner of said tubular member.
19. The system of claim 16 wherein the depth of said score is
approximately 10% to approximately 20% the thickness of said
tubular member.
Description
[0001] This is a continuation-in-part application based upon
co-pending U.S. Pat. application Ser. No. 09/307,235, filed May 7,
1999. Further, this application claims priority to U.S. Provisional
Patent Application SN 60/232,465, filed Sep. 13, 2000.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a traffic crash attenuation
system. More particularly, the present invention includes a system,
method and apparatus for absorbing the kinetic energy from an
impacting vehicle in a controlled and safe manner with roadside
safety devices such as: guardrails and median barrier end
treatments, crash cushions, and truck mounted attenuators.
Specifically, the present invention provides a system for the
controlled rupturing of a tubular member by a mandrel whereby
forces of an impacting vehicle are absorbed. More particularly, the
present inventive system utilizes a rectangular mandrel and a
corresponding rectangular tubular member.
[0003] U.S. Pat. No. 4,200,310 illustrates an energy absorbing
system which utilizes a number of cylindrical energy absorbing
members placed in a series-type relationship on a frame mounted to
a truck. The system is provided with an alignment or guidance
frame. However, there is nothing which teaches any selectively
controlling the rupture of the cylindrical members. The mechanism
of energy dissipation is significantly different than that of the
present invention.
[0004] U.S. Pat. No. 3,143,321, teaches the use of a frangible tube
for energy dissipation. As with the present invention, the
apparatus disclosed in U.S. Pat. No. 3,143,321 uses a mandrel
receivable within a tubular member. However, there is no teaching
of a means for selectively controlling the rupturing along a length
of the tubular member.
SUMMARY OF THE INVENTION
[0005] The crash attenuation system of the present invention
provides an impact head attached to an energy absorption mechanism.
The energy absorption mechanism has one or more mandrels with a
certain tensile strength or hardness attached to the impact head.
Attached to the head are one or more tubular members which have
second tensile strengths or hardnesses, generally lower than those
of the mandrels. The mandrels are receivable in a first end of the
tubular members such that upon impact forces being applied to the
impact head, the mandrels are forced through the tubular members
rupturing, rather than fragmenting, the tubular members and
absorbing the impact forces. The rupturing may be controlled by any
number or combination of stress concentrating elements such as
placing holes, notches, cuts, scores, preferential material
orientation, or slots in the tubular members, providing gussets (or
any strengthening member) along the length of the tubular members,
or providing the mandrels with stress concentrators such as gussets
or mandrel geometry so that as the mandrels are urged through the
tube the rupturing is controlled. Specifically, the present
invention focuses on rectangular mandrel and rupture tube
geometry.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1A is an isometric view of a mandrel and tubular member
of the present invention before impact forces are applied.
[0007] FIG. 1B illustrates the rupturing of the tubular member by
the mandrel upon impact.
[0008] FIG. 2A is a side elevation view of an embodiment of the
present invention having a mandrel with a forward tubular extension
and a tubular member with a second mandrel.
[0009] FIG. 2B is an end view of the illustration of FIG. 2A.
[0010] FIG. 2C is a side elevation view of an embodiment of the
present invention with the first and second mandrels having stress
concentrators.
[0011] FIG. 2D is an end view of the illustration of FIG. 2C.
[0012] FIG. 3A shows a top plan view of the present invention with
the controlled fracture energy absorbers attached to the impact
head and trailer or truck mounted frame elements.
[0013] FIG. 3B is a side elevation view of the illustration of FIG.
3A.
[0014] FIG. 4A shows a top plan view of the present invention with
an alignment member attached to the trailer or truck mounted
frame.
[0015] FIG. 4B is a side elevation view of the illustration of FIG.
3C.
[0016] FIG. 5A illustrates the rectangular mandrel of the present
invention.
[0017] FIG. 5B shows the rectangular tubular member of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] The controlled fracture or rupturing mechanism of the
present invention is based on the concept that, when an over-sized
plunger with a tapered surface (mandrel 12) is forced into a
thin-wall tubing 14 of the generally same shape, pressure is
exerted on the edge of the tubing from the inside, as illustrated
in FIGS. 1A and 1B. The pressure initially expands the size of the
thin-wall tubing, first elastically until the yielding strength of
the metal is reached and then plastically. The tubing eventually
fractures or ruptures 16 at the edge when the ultimate tensile
capacity of the material is exceeded. This process of expanding and
fracturing the thin-wall tubing 14 is repeated and energy
dissipated as the mandrel 12 proceeds forward. This process can be
applied to tubes manufactured from a variety of materials,
including, but not limited to, steel, aluminum, fiber reinforced
plastic (FRP), polymers such as high density polyethylene, and
concrete or other ceramics.
[0019] Although this concept may be used with both brittle
materials and ductile materials, brittle materials, such as
frangible aluminum, ceramics, or concrete, fragment during the
process and produce shrapnel that could pose a hazard to nearby
traffic or pedestrians. Therefore, the present invention
anticipates the use of ductile materials or brittle materials which
are appropriately coated so as not to produce shrapnel-like
fragments. Ductile materials, such as steel, polymers, or FRP
materials with longitudinal reinforcement, tear into a number of
longitudinal strips that remain attached to the undeformed portions
of the tubular energy absorber.
[0020] The amount and rate of energy dissipation can be controlled
by varying the shape, size, thickness, and strength ofthe thin-wall
tubing 14 and the number of tubes. The location and required force
level of the rupture can be controlled by incorporating stress
concentrators on the tubing, using holes 17, slots 18, notches,
cuts, scores and strengtheners such as gussets 19, shown in FIGS.
3A and 4A, or on the mandrel 12, using raised edges 30 as shown in
FIG. 2C, or varying the geometrical shape of the mandrel. Further
stress concentrators may include the use of preferential material
orientation such as fiber alignment in fiber reinforced plastics or
cold rolling of metals to produce elongated grain boundaries.
[0021] FIG. 2A shows a two-stage splitting system that involves
splitting first one tube 14 and then another 22. The first tube 14
is attached to a roadside safety device (not shown). Initially upon
impact of a vehicle with an impact head (not shown in FIG. 2A), the
hollow tube extension 22 on mandrel 12 on the right is pushed into
the outer tube 14. The mandrel 12 engages outer tube 14, causing it
to split or rupture as illustrated in FIG. 1. After further
displacement, the hollow tube extension 22 contacts a second,
conical shaped mandrel 24 on the far end 26 of the outer tube 14
and is itself split. Each rupturing allows for controlled
absorption of impact energy. Mandrel 24 is supported to outer tube
14 by gussets 25.
[0022] FIG. 2C illustrates a two stage system with gusset plates or
raised edges 30 and 32 extending outward from the mandrels 12 and
24, respectively. These gusset plates 30 and 32 illustrate an
example of a stress concentrator placed on the outer tube. The
tubes may be provided with slots or strengthening members to
control the rupturing process.
[0023] In addition, the controlled fracturing mechanism can be used
in combination with other means of energy dissipation. Energy
absorbing materials 40A and 40B (FIG. 2C) (e.g., aluminum honeycomb
or composite tube, etc.) can also be placed inside of the tubes to
increase the energy dissipation capacity as shown in FIG. 2C.
[0024] For end-on impacts, the vehicle will contact the impact
plate 50,.i.e., end of the impact head, and push it forward. This
in turn will push the mandrel forward into the thin-wall tubing and
start the process of expanding and fracturing/bursting of the
tubing. This process will continue until: (a) the impacting vehicle
is brought to a safe and controlled stop; (b) the entire length of
the tubing is fractured; or (c) the impacting vehicle yaws out and
disengages from the impact head.
[0025] For impacts that are end-on at a large angle, the impacting
vehicle will initiate the controlled fracturing/bursting process
until the thin-wall tubing is bent out of the way or the mandrel
disengages from the thin-wall tubing, and then gate behind the
device. Similarly, the impacts on the side of the thin-wall tubing
14 near the end of the device cause the thin-wall tubing will be
bent out of the way, allowing the vehicle to gate behind the
device. Thus, when struck on the corner, either on the end or the
side of the cushion, the energy absorbing mechanism begins to
collapse longitudinally providing lateral resistance as it begins
to bend out of the way.
[0026] For impacts into the side of the thin-wall tubing downstream
of the beginning of length-of-need, the thin-wall tubing will act
like a barrier and contain and redirect the impacting vehicle. An
anchoring mechanism will be necessary to resist the tensile forces
acting on the tubing to contain and redirect the vehicle. Note that
this requirement of containment and redirection is applicable only
for devices that have redirective capability, such as a terminal or
a redirective crash cushion.
[0027] A roadside safety device utilizing the controlled fracture
mechanism consists of a few major components, as illustrated in
FIGS. 3A and 4A. Thin-wall tubing 14 is utilized. The tubing may
have a circular, square, or rectangular cross-section. The edge of
the front end of the tubing (i.e., the end into which the mandrel
is attached) may have notches or slots to control the location(s)
of the fracture for the tubing. The tubing may also have
longitudinal slots cut along portions of its length to control the
rate of energy dissipation.
[0028] An impact head/plate 50 is provided. Details of the impact
head/plate are shown in FIGS. 3B and 4B. The impact head 50
consists of an impact plate 51; a means to provide mechanical
interlock 52 between the impact head and the front of the impacting
vehicle, such as raised edges around the impact plate 50; and a
mandrel 12 welded to the back of the impact plate 50.
[0029] The mandrel 12 is much stronger (having a greater tensile
strength, a greater thickness, or greater hardness) than the
splitting tube 14 to prevent the mandrel from deforming. The
mandrel 12 need not have the same cross-sectional shape as the
thin-wall tubing, however, there must be only small clearances
between the mandrel and the tubing in order to prevent
misalignment. For example, channel or wide flange shapes could be
used with rectangular frame rail elements as long as the height and
depth of the open sections were close to the same as the clear
opening in the tube.
[0030] The head 13 of the mandrel 12 is tapered so that only the
leading portion of the mandrel head 13 initially will fit into the
thin-wall tubing. The mandrel 12 may have stress concentrators,
e.g., a particular geometrical shape or raised edges, to control
where the thin-wall tubing will fracture. For square or rectangular
tubes, the mandrel may have a corresponding square or rectangular
shape that flares outward. This type of tube/mandrel combination,
as discussed below in relation to FIGS. 5A and 5B, assures that the
tube splits at the corners where strain hardening during
manufacturing has made the metal less ductile.
[0031] As mentioned previously, the controlled fracture mechanism
of the present invention may be used in combination with other
forms of energy dissipation. One such design (FIG. 2C) may include
the placement of some form of energy absorbing material 40A and
40B, such as aluminum honeycomb or composite tube inside the
thin-wall tubing. As the mandrel proceeds forward, the mandrel will
fracture the thin-wall tubing as well as crush or compress the
energy absorbing material inside the tubing for additional energy
absorption.
[0032] A composite tube trailer or truck mounted attenuator
utilizes a crushable composite beam as its primary energy
dissipation mechanism. There are two embodiments of this device,
shown in FIGS. 3A and 4A. One embodiment, shown in FIG. 4A, uses
telescoping frame rail elements 70 and 72 to maintain lateral
stability and alignment for the attenuator and utilizes the
controlled fracture concept with composite tubes to provide the
energy dissipation. Frame 60 is mounted to the trailer or truck to
support the head 50 and energy absorption mechanism 75. It is
envisioned that cables or thin steel straps (not shown) may be used
to brace the frame 60. Cables may be attached to the back of the
frame on one side and to the front of the frame on the other side
to prevent lateral "racking" of the frame system.
[0033] Another embodiment utilizes controlled fracture frame rail
elements in addition to composite tube energy absorbers as shown in
FIG. 3A. The present invention may have energy absorbers placed
inside of the telescoping tubes or outside.
[0034] As previously stated, the tube bursting energy absorber
works on the principal that the energy associated with the
propagation of cracks along the length of a tube can be carefully
controlled and utilized to dissipate the energy of an impacting
vehicle. This invention incorporates a tapered mandrel that is
forced inside an energy absorbing tube of slightly smaller
dimensions. As the tapered mandrel is forced inside the tube, hoop
stresses develop in the energy absorbing tube and these stresses
are then used to propagate cracks along the length of the tube. The
cracks propagate in front of the mandrel such that there is no
direct contact between the mandrel and the crack surfaces, thereby
limiting friction. The system's operation is somewhat different
when incorporated for round and square energy absorbing tubes.
[0035] Although a number of energy absorbing systems utilized
collapsing round tubes, none ofthe prior inventions have
incorporated square tubes. The corners of square tubes make these
energy absorbers perform much differently than round tubes. Because
square tubes have rounded corners, a tapered square mandrel forced
inside a square tube will tend to contact the tube only in the
vicinity of the corners. Although such a system would eventually
produce ruptures in the corners ofthe tube, the sharp corners of
the mandrel would contact the crack surfaces and high friction
forces would be generated.
[0036] The tube bursting energy absorber avoids this situation by
using a tapered mandrel with bevels at each corner. As shown in
FIG. 5A, the preferred mandrel 12A for square tubes 14A (FIG. 5B)
involves welding four steel plates (13a, 13b, 13c, and 13d)
together to form a pyramid. The interior edges of the plates are
placed together and the valley 16 is fillet welded to form a
relatively flat, beveled surface 17 at each corner (only one corner
is shown in FIG. 5A with the flat, beveled surface 17). As shown in
FIG. 5B, this configuration allows the mandrel 12A to contact the
square tube 14A everywhere but the rounded corners 18A. As the tube
is pushed onto the mandrel, the rounded corners will be placed in
tension and straightened out. As this happens, stress
concentrations where the tube walls bend around the beveled edges
of the mandrel will initiate cracks. These cracks will then
propagate in front of the mandrel 12A to produce a controlled
energy absorbing system. The mandrel will not contact the crack
surfaces and therefore friction between the mandrel and the energy
absorbing tube is minimized. Because there are two crack initiators
at each corner, two cracks can start and propagate simultaneously.
Normally only one of these two cracks will dominate and the other
crack will stop propagating. However, when this occurs, one side of
the tube is actually a very shallow channel shape, which tends to
dissipate more energy when the cracked walls are curled back. Saw
cut manufactured cracks placed in the center of each corner can
force the crack to run down the center of the tube corner. Thus,
initial manufactured cracks can lower the energy dissipation
associated with square tubes to some extent. The energy dissipation
rate for this system is controlled by a number of factors,
including the thickness of the energy absorbing tube, bevel angle
on the mandrel, lubrication applied to the inside of the energy
absorbing tube, and the material used in the energy absorber.
Energy is dissipated by the tube bursting energy absorber through
three primary mechanisms: crack propagation, curling of the cracked
sections of tube, and friction. Crack propagation energy in a
square or rectangular tube is controlled primarily by the type and
thickness of the material used in the energy absorbing tube. More
ductile and tougher metals have higher strain energy release rates
and thus dissipate more energy. Likewise, thicker tubes also absorb
more energy in the crack propagation process.
[0037] Energy dissipated as the cracked sections of a rectangular
tube are curled back is controlled by the taper angle of the
mandrel and the thickness of the material. Higher mandrel taper
angles decrease the radius of the curled sections of cracked tube
and thereby increase the energy dissipated in the bending process.
However, lower taper angles do increase friction slightly, thereby
offsetting the decreased bending energy to some extent. Tube
thickness also affects the energy required to curl the cracked
sections of the tube.
[0038] Friction is the other major source of energy dissipation.
Lubricants placed inside the energy absorbing tube can greatly
reduce friction energy. Although conventional lubricants such as
grease or oil, and other hydrocarbon compositions, can serve this
purpose, other lubricants could include zinc used in the
galvanizing process, paints, ceramic composition surfaces, and even
rust particles.
[0039] Round tubes made from ductile materials, such as low carbon
steel, will deform greatly when a tapered mandrel is driven inside.
If the energy absorber does not include weakening mechanisms as
described by Smith (1973), the tube will expand sufficiently to
completely engulf the mandrel. In this case, the forces required to
push the mandrel inside the energy absorber rise rapidly and the
system is ineffective. Smith teaches that, by using a pattern of
slots in the energy absorbing tube, it can be made to deform
outwardly away from the mandrel and fold back upon itself. In this
situation the energy absorbing forces are controlled, but the cost
of producing the large numbers of slots, holes, or other weakening
mechanisms is high. As described above, the tube bursting energy
absorber involves propagating cracks along the length of the tube.
For round tubes, these cracks must be manufactured in the end or
along the side of the tube. The cracks are manufactured by placing
small saw cuts at strategic points around the tube or by scoring
the surface of the tube along its length. FIG. 5A shows a saw cut
20A in the center of one of the rounded comers. Optimally, saw cuts
should be twice as long as the wall thickness of the energy
absorbing tube. FIG. 5A shows a score 22A in the center of one of
the rounded corners. Scores need only be 10-20% of the thickness of
the energy absorbing tube in order to propagate the crack. Scoring
refers to a shallow notch, cut, mark, or scratch down the side of
the tubes. Typically, they look like little grooves down the sides
of the four corners in the rectangular tube configuration. However,
the scores could be placed any place along the tube to enhance or
promote crack propagation and/or reduce the bursting force levels.
Scores may be placed on the outside or inside of the tubes. When
forced inside the energy absorbing tube, the mandrel creates high
hoop stresses which will cause the cracks to grow in a opening
mode.
[0040] There are two primary advantages of this system. The first
advantage is that small saw cuts and/or shallow surface scores are
very inexpensive to produce. The second advantage of this approach
is that the cracks propagate in front of the mandrel in a manner to
prevent direct contact between the mandrel and the crack tip. By
keeping the mandrel out of the crack tip, friction is greatly
reduced and the energy dissipation rate is controlled.
[0041] Just as in the case with the square tube, the energy
dissipation rate of the absorber can be influenced by the thickness
of the energy absorbing tube, bevel angle on the mandrel,
lubrication applied to the inside of the energy absorbing tube, and
the material used in the energy absorber. The primary difference in
energy dissipation between round and square tubes is that round
tubes can have a number of different crack configurations. The
crack propagation energy is directly related to the number of
cracks induced in the tube. The energy dissipated as the cracked
sections of tube are curled back is controlled by the taper angle
of the mandrel and the number of cracks induced in the tube. When
more cracks are induced in the tubes, the moment of inertia of each
cracked section is reduced. By reducing the section modulus, the
energy required to bend each section back is reduced. Energy
dissipation by round tubes is also controlled by all of the factors
mentioned previously for the square tube.
[0042] For any given tube configuration, energy dissipation rates
are relatively constant. However, for many safety applications it
is desirable to design energy absorbers with multiple energy
absorption stages. Another advantage of the tube bursting energy
absorber is that multiple stages are easily implemented by nesting
energy absorbing tubes of varying lengths. For example, a two-stage
energy absorbing system can be set up by inserting a longer tube
inside a shorter tube of larger dimension. The first stage would
consist of a single tube while the second stage would consist of
two nested tubes. When the mandrel reaches the nested tube, cracks
will be propagated down both the inner and outer tubes and the
energy dissipation increases to a higher level. The energy
dissipation rate for the two combined tubes is generally less than
the sum of the rate for each tube bursted separately. This decrease
can be attributed to reduced friction associated with the combined
bursting process.
[0043] Another means of developing a two-stage energy absorbing
system is to score only the front portion of a tubular section. The
scored section of the tube typically has a lower energy dissipation
rate than the un-scored portion of the tube, thus forming a
two-staged energy absorbing system.
[0044] Although the invention has been described with reference to
a specific embodiment, this description is not meant to be
construed in a limiting sense. On the contrary, various
modifications of the disclosed embodiments will become apparent to
those skilled in the art upon reference to the description of the
invention. It is therefore contemplated that the appended claims
will cover such modifications, alternatives, and equivalents that
fall within the true spirit and scope ofthe invention.
* * * * *