Note: Descriptions are shown in the official language in which they were submitted.
CA 02615277 2008-01-14
Device for Testing a Fuselage Structure With Longitudinal and Circumferential
Curvature
The present invention relates to a testing apparatus associated with a
fuselage
structure having double curvature.
More particularly, the present invention is aimed at providing a testing
apparatus
that permits testing the static strength, fatigue strength and tolerance to
damage of
fuselage structures having double curvature, or in other words longitudinal
and
circumferential curvature.
In practice, these fuselage structures are fuselage rings typically used to
construct the aft or fore fuselage of an airplane.
It is known that such a testing apparatus can be used to apply to the fuselage
structure, by means of a force-application system, stresses representative of
the
stresses undergone by the fuselage structure during its use. These stresses
are
typically tensile or compressive forces exerted in the longitudinal direction
of the
structure, torsional forces around the circumference of the structure and
pressure
forces related to the pressure difference existing between the interior and
exterior of the
aircraft.
For example, there is known a testing apparatus making it possible to apply
pressure forces and an axial mechanical load to a structure having simple
curvature, of
the same type as a cylindrical ring, as described in the document "Development
of a
test fixture for fuselage curved panels", by M. Langon and C. Meyer, CEAT,
ICAF 1999,
pages 745 to 753.
Nevertheless, such a testing apparatus cannot be applied to a fuselage
structure
having double curvature and still be representative of the real stresses
experienced by
the airplane's fuselage structure.
The objective of the present invention is to resolve the aforesaid
disadvantages
and to provide an apparatus for testing a fuselage structure having double
curvature.
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To this end, the testing apparatus associated with a fuselage structure
having longitudinal and circumferential curvature comprises an assembly of
means for applying forces to the fuselage structure.
According to the invention, it comprises support means capable of
supporting the said fuselage structure and the assembly of force-application
means, this assembly of force-application means being mounted between the
support means and the force-introduction means interlocked with the said
fuselage structure, and being capable of applying collinear forces to the
fuselage
structure.
According to one embodiment of the invention, there is provided a testing
apparatus associated with a fuselage ring having longitudinal and
circumferential
curvature, comprising an assembly of means for applying forces to the said
fuselage ring, characterized in that it comprises support means capable of
supporting the said fuselage ring and the assembly of force-application means,
and in that the assembly of force-application means is mounted between the
said
support means and the force-introduction means, interlocked with the said
fuselage ring and is capable of applying torsional and tensile or compressive
forces to the fuselage ring, said forces being tangential at the point of
application
to the fuselage ring.
By applying forces in collinear manner to the fuselage structure in this way,
which forces therefore remain tangential to the structure having double
curvature
at their point of application, it is possible to apply representative airplane
stresses
undergone by the fuselage structure during its use.
In practice, the force-introduction means are formed by a substantially
circular structure interlocked with the fuselage structure along a
circumferential
line.
By applying forces via a substantially circular structure, it is possible to
apply stresses that are uniformly distributed over the circumference of the
fuselage structure.
According to one characteristic of the invention, the force-introduction
means are fixed to an upper end of the fuselage structure.
In this way, the entire fuselage structure, and not merely one portion, is
subjected to the applied forces.
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2a
Preferably the upper end is an end of larger diameter of the fuselage
structure.
Thus local variations at the force-application point are not very significant
compared with the entirety of the fuselage structure.
According to another advantageous characteristic of the invention, the
force-introduction means comprise pinch-type fixation means capable of
interlocking the force-introduction means with the upper end of the fuselage
structure in tension and in torsion.
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Pinch-type fixation of the upper end of the fuselage structure makes it
possible to
avoid any fixation element that could damage the fuselage structure.
In addition, mounting and demounting of the structure in these fixation means
are facilitated, especially during actions for inspection of the fuselage
structure after it
has been stressed.
In practice, the means for applying forces of a first type are capable of
applying a
tensile or compressive force to the fuselage structure, and the means for
applying
forces of a second type are capable of applying a torsional force to the
fuselage
structure.
Other features and advantages of the invention will become more apparent in
the description hereinafter.
In the attached drawings, provided by way of non-limitative examples:
- Fig. 1 is a schematic perspective view of a fuselage structure having
double
curvature;
- Fig. 2 illustrates, in perspective, a testing apparatus according to one
embodiment of the invention;
- Fig. 3 is a simplified partial view in elevation illustrating the
principle of the
testing apparatus of Fig. 2;
- Fig. 4 is a perspective view of a means for applying forces of a first type
in the
testing apparatus of Fig. 2;
- Fig. 5 is a perspective view of a means for applying forces of a second type
in
the testing apparatus of Fig. 2;
- Fig. 6 is a perspective view of support means of the testing apparatus of
Fig. 2;
- Fig. 7 is a view in partial cross section of the support means of Fig. 6;
- Fig. 8 is a view in partial section of means for fixing the fuselage
structure to the
support means of Fig. 6;
- Fig. 9 is an overhead view of an element of the fixation means of Fig. 8;
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- Fig. 10 is a view in cross section along line X-X of the element of Fig. 9;
- Fig. 11 is a perspective view of a second element of the fixation means
of Fig.
8;
- Fig. 12 is a view in partial cross section of a third element of the
fixation means
of Fig. 8;
- Fig. 13 is an overhead view of the force-introduction means of the apparatus
of
Fig. 2;
- Fig. 14 is a view in partial cross section along line XIV-XIV of Fig. 13;
- Fig. 15 is a perspective view of pressurizing means of the testing
apparatus of
Fig. 2; and
- Fig. 16 is a view in longitudinal section of the pressurizing means of
Fig. 15.
Referring now to the figures, there will be described a practical example of
an
apparatus for testing a fuselage structure.
The testing apparatus to be described hereinafter makes it possible to test a
structure 10 having double curvature as illustrated in Fig. 1.
For example, it may be a fuselage ring having both longitudinal curvature and
circumferential curvature, as illustrated by the arrows in Fig. 1.
The testing apparatus makes it possible to test the static strength, fatigue
strength and damage tolerance of such a structure.
In general, it makes it possible to apply stresses representative of those
experienced by an airplane structure, and especially tensile or compressive
forces in
the longitudinal direction, torsional forces relative to the longitudinal axis
or even
pressure forces due to the pressure difference between the interior of the
structure and
the outside.
It will be understood that it is necessary to be able to combine all of these
types
of forces to be exerted on the structure.
At present, the behavior of a fuselage structure having double curvature is
learned by means of tests and numerical simulations on structures having
single
curvature.
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Test data are therefore necessary to validate and calibrate the numerical
models
used for the configurations having double curvature, in order to learn the
behavior
thereof.
The testing apparatus such as described hereinafter also makes it possible to
evaluate and study the behavior of new materials (metallic and composites) as
well as
to study new technologies.
A testing apparatus according to one embodiment of the invention is
illustrated in
general manner in Figs. 2 and 3.
In principle, the testing apparatus includes force-application means 30, 40
mounted around fuselage structure 10 on support means 50.
As clearly illustrated schematically in Fig. 3, fuselage structure 10 is
mounted at
the center of support means 50 by virtue of fixation means 60. Force-
application means
30, 40 are mounted at the periphery between support means 50 and force-
introduction
means 70 fixed to fuselage structure 10.
In this embodiment, force-application means 30 are capable of applying a force
of a first type, corresponding to a longitudinal tensile or compressive force,
applied in
the longitudinal direction of the fuselage structure.
Force application means 40 are means for applying forces of a second type, and
are capable of applying a torsional force to fuselage structure 10, in the
circumferential
direction of fuselage structure 10.
In practice, to ensure that stresses on the fuselage structure will be
uniformly
distributed, these force-application means 30, 40 are composed of a plurality
of force-
application structures disposed regularly at the periphery of the fuselage
structure.
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As an example, the means for applying longitudinal forces in this embodiment
include sixteen identical structures 30 for application of longitudinal
forces.
One of those is illustrated in detail in Fig. 4.
It comprises a hydraulic jack 31 mounted substantially vertically and capable
of
exerting a compressive or tensile force along the axis of the rod of the jack.
By means
of a pivot joint, this hydraulic jack 31 is mounted around a horizontal axis
at its ends
31a, 31b.
In particular, at lower end 31a, hydraulic jack 31 is mounted pivotally in an
eye
joint link 32 intended to be fixed to support means 50.
Hydraulic jack 31 includes an actuating end 31b, corresponding in this case to
the upper end of hydraulic jack 31. This actuating end 31b is fixed by means
of an eye
joint link 33 to a first end 34a of a lever arm 34.
First end 34a includes fixation means 35 intended to fix lever arm 34 to force-
introduction means 70. A second end 34b of lever arm 34 is fixed, also by
means of a
pivot joint 36, to a pylon 37, intended to be mounted on support means 50.
Mounting of pylon 37 on fixation devices 38 is achieved again by means of
pivot
joints of the same type as eye joint links 32 and 33. Preferably, in order to
make pylon
37 rigid, it is composed of two legs 37a inclined relative to the vertical
axis and joined at
end 37b, which is fixed to second end 34b of lever arm 34 via pivot joint 36.
Legs 37a of pylon 37 are fixed respectively by fixation devices 38 to support
means 50, a crossbeam 37c extending between legs 37a in order to increase the
rigidity
of the structure of pylon 37.
This special structure of pylon 37 is particularly capable of absorbing the
stresses exerted by jack 31 on the fuselage structure by means of lever arm
34.
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As described hereinabove, jack 31, lever arm 34 and pylon 37 are fixed to one
another and to support means 50 by virtue of joints pivoting respectively
around
mutually parallel horizontal axes.
The said jack, lever arm and pylon therefore constitute a deformable
quadrilateral in particular making it possible, by inclining jack 31 around
fixation eye
joint link 32, to move jack 31, lever arm 34 and pylon 37 aside from fuselage
structure
to facilitate access thereto, especially to inspect the structure after
application of a
set of stresses or to permit fuselage structure 10 to be placed on support
means 50.
It will be noted that all of the fixations to support means 50 are achieved by
virtue
of nut-and-bolt assemblies of sufficient dimension and size that they can
withstand the
longitudinal stresses applied to the fuselage structure.
Furthermore, this structure 30 for application of longitudinal forces is
supplemented by an auxiliary arm 39 extending between pylon 37 and support
means
50.
This auxiliary arm 39 makes it possible to hold together the deformable
assembly
comprising jack 31, lever arm 34 and pylon 37 when lever arm 34 is detached
from
force-introduction means 70, and to ensure that the deformable quadrilateral
does not
become completely inclined to the horizontal.
By virtue of the mounting of jack 31 in eye joint links 32, 33, the direction
of
operation of the rod of hydraulic jack 31 can follow the longitudinal
deformation of the
fuselage structure, in such a way that the force exerted remains collinear
with fuselage
structure 10, or in other words that the force applied is at all times
tangential to its point
of application on the longitudinally curved surface of the fuselage structure.
Referring now to Fig. 5, there will be described the means 40 for application
of
forces of a second type capable of applying a torsional force to the fuselage
structure.
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These means for applying forces of a second type include eight identical force-
application structures, one of which is illustrated in detail in Fig. 5.
Means 40 for application of forces of a second type include a hydraulic jack
41
mounted on a support structure 42. This support structure 42 is composed in
this
embodiment of two triangular plates 42a disposed parallel to one another and
fixed to a
support plate 42b intended to be fixed to support means 50.
Hydraulic jack 41 has a lower end 41a mounted via pivot joint 43 between
plates
42a of support structure 42.
A lever arm 44 forming a coupler link is also fixed on the one hand to an
actuating end 41b of hydraulic jack 41 and on the other hand to a support
bearing 45
interlocked with support structure 42.
The fixations of actuating end 41b and support bearing 45 to lever arm 44
forming a coupler link are pivot joints that permit pivoting of lever arm 44
forming a
coupler link around support bearing 45 during translational movement of the
rod of jack
41.
This pivoting action is transmitted to an auxiliary lever arm 46, which is
also
mounted pivotally, at one of its ends 46a, around a pivot axis 47 on lever arm
44
forming a coupler link.
Free end 46b of the auxiliary lever arm is equipped with a spherical plain
bearing
and is capable of being fixed to force-introduction means 70. By virtue of
this spherical
plain bearing having three rotational degrees of freedom, the force applied by
auxiliary
lever arm 46 under the action of hydraulic jack 41 is a force tangential to
the
circumferentially curved surface of fuselage structure 10, even after
deformation thereof
in its longitudinal or circumferential directions.
Referring now to Figs. 6 and 7, there will be described support means 50.
As illustrated in Fig. 6, support means 50 includes a central platform 51
designed
to support fuselage structure 10. In this regard, the platform has at its
center a disk 52,
on which the fuselage structure is fixed by fixation means to be described
later.
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In addition, platform 51 includes extensions 53 beyond disk 52, capable of
supporting force-application means. In the present case, there are eight such
extensions 53. Platform 51 therefore has overall octagonal shape, each
extension 53
forming one side of the octagon.
In this embodiment, in which the means for applying tensile/compressive forces
include sixteen hydraulic jacks, each extension 53 includes two fixation
supports 53a on
which there can be fixed respectively two hydraulic jacks 31 for application
of a
tensile/compressive fixation force, by means of a fixation eye joint link 32.
Support means 50 additionally include a peripheral structure composed of
extensions 54 extending radially relative to central platform 51.
More particularly, this peripheral structure in the present case includes
eight
adjacent extensions 54, fixed respectively to the eight sides of central
platform 51.
Each extension 54 is composed of profile sections, and in particular includes
two
radially extending profile sections 54a and one profile section 54b
substantially inclined
relative to radial profile sections 54a.
Inclined profile section 54b is capable of supporting means 40 for application
of
torsional forces.
To this end, each profile section 54b has a series of bores permitting a
support
plate 42b of a structure 40 for application of torsional forces to be fixed by
nuts and
bolts.
In addition, each extension 54 is provided at the periphery with pads 55
intended
to receive fixation devices 38 of pylons 37 of means 30 for application of
tensile or
compressive forces.
In this way support means 50 make it possible to absorb all loads applied to
fuselage structure 10 mounted at its center.
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These support means 50 therefore have overall circular shape suitable for
mounting, on the periphery of fuselage structure 10, different means 30, 40
for
application of forces.
As clearly illustrated in Figs. 6 or 7, support means 50 include a series of
pillars
56 with which the structure can be embedded in the floor.
As clearly illustrated in Fig. 7, support means 50 house a conduit 57 through
which there can be supplied a pressurized fluid to means of pressurizing the
interior of
fuselage structure 10, which means will be described later with reference to
Figs. 15
and 16.
Fixation of fuselage structure 10 on support means 50 is achieved by pinching
(or clamping), Making it possible to keep fuselage structure 10 pinched
between an
inner ring and an outer ring, merely by exerting a clamping force, the
fuselage structure
being held by friction. This type of fixation has the advantage that it does
not damage
fuselage structure 10 during the tests.
Fuselage structure 10 is fixed at its small diameter by fixation means 60 on
support means 50.
Fixation means 60 include essentially an outer ring 61, a contour ring 62, a
pinch
ring 63 and an inner ring 64.
As clearly illustrated in Fig. 8, lower end 10a of fuselage structure 10 is
placed
between outer ring 61 and contour ring 62. Fuselage structure 10 is held in
place solely
by friction. To increase the coefficient of friction between its parts, the
surfaces facing
contour ring 62 and outer ring 61 can be treated to increase their roughness.
Outer ring 61 is capable of absorbing the stresses applied to fuselage
structure
10 by force-application means 30, 40.
In order to support the longitudinal forces, particularly of tension, outer
ring 61
has a series of bores 61a through which fixation bolts can be passed. The
fixation bolts
are capable of being fixed in seats 52a of disk 52 of central structure 51 of
support
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means 50.
Furthermore, as clearly illustrated in Fig. 9, outer ring 61 is provided with
radial
throats, in this case four radial throats 61b disposed 900 apart from one
another.
As an example, these radial throats 61b have rectangular cross section, and
their shape is complementary to that of radial ribs 52b, also provided at 900
apart from
one another on disk 52 of central structure 51 of support means 50 illustrated
in Fig. 6.
By virtue of this connection achieved by embedding ribs 52b in throats 61b,
the
torsional forces introduced into fuselage structure 10 and absorbed by outer
ring 61 can
be transmitted to support means 50 fixed on the floor.
As clearly illustrated in Fig. 10, outer ring 61 has overall cylindrical outer
shape
and overall frustoconical inner shape, its inner face 61c being capable of
conforming to
the outer face of lower end 10a of the fuselage structure.
Contour ring 62 is preferably constructed in several parts in order to permit
assembly of this contour ring 62 with outer ring 61. In this example, contour
ring 62 is
formed from four sectors extending over 90 .
As clearly illustrated in Fig. 8, contour ring 62 includes a frustoconical
outer face,
complementary to inner face 61c of outer ring 61, in order that lower end 10a
of
fuselage structure 10 can be held by pinch action.
In order to be able to adjust the frictional force, a pinch ring 63 such as
illustrated
in Figs. 11 and 12 is mounted against contour ring 62.
Pinch ring 63 is provided with two cone-shaped rings 63a, 63b. These cone-
shaped rings 63a, 63b are placed between two concentric cylindrical portions
63c, 63d,
which define between them a seat for cone-shaped rings 63a, 63b.
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More particularly, cone-shaped rings 63a, 63b have a cylindrical inner wall,
intended to cooperate with the surface of inner cylindrical portion 63d of
pinch ring 63.
Cone-shaped rings 63a, 63b additionally have frustoconical outer walls
intended
to come in contact with inclined inner faces of outer cylindrical portion 63c
of pinch ring
63.
The two cone-shaped rings 63a, 63b are placed in upside-down relationship
such that each frustoconical face forms an angle of approximately plus 5 or
minus 5
respectively relative to the vertical axis.
Over the entire periphery of pinch ring 63 there is provided a series of
tensioning
bolts 63e intended to pass into bores provided for this purpose in cone-shaped
rings
63a, 63b.
In addition, a circular guide piece 63f interlocked with concentric
cylindrical
portions 63c, 63d makes it possible to ensure vertical guidance of each
tensioning bolt
63e.
During operation, tensioning bolts 63e are displaced along a vertical axis to
move cone-shaped rings 63a, 63b further apart or closer together in such a way
that the
force exerted by outer frustoconical portion 63c of pinch ring 63 against
contour ring 62
can be adjusted.
In this way it is possible to adjust the clamping force exerted by fixation
means
60 on fuselage structure 10.
Finally, as illustrated in Fig. 8, an inner ring 64 is mounted inside pinch
ring 63. It
makes it possible to absorb all the radial forces generated toward the
interior of fixation
means 60 by pinch ring 63.
Referring now to Figs. 13 and 14, there will be described force-introduction
means 70. In principle, these force-introduction means 70 are formed from a
substantially circular structure capable of being fixed to fuselage structure
10 along a
circumferential line thereof.
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As clearly illustrated in Fig. 3, force-introduction means 70 are preferably
fixed to
upper end 10b of fuselage structure 10. Thus the application of forces is
achieved on a
part of larger cross section of fuselage structure 10 in such a way that the
variations at
the local point of application of forces has only little impact on the
behavior of fuselage
structure 10 in its entirety.
As clearly illustrated in Fig. 14, force-introduction means 70 include means
80 for
fixation by pinch action that are capable of interlocking, in tension and in
torsion, force-
introduction means 70 and upper end 10b of fuselage structure 10.
Just as for fixation means 60 of the lower end 10a of fuselage structure 10,
fixation means 80 of upper end 10b are provided with an outer ring 81, a
contour ring
82, a pinch ring 83 and an inner ring 84.
The fixation of upper end 10b by pinch action is identical to that described
hereinabove with reference to Fig. 11 and does not need to be described again
here.
However, in contrast to fixation means 60 of lower end 10a, fixation means 80
are not fixed to support means 50.
Consequently, a support ring 85, which is interlocked with contour ring 82,
for
example, is intended to support pinch ring 83 and inner ring 84.
Furthermore, fixation means 80 are provided with robust fixation elements to
ensure fixation on the one hand of fixation elements 35 of each means 30 for
application of longitudinal forces and on the other hand of auxiliary lever
arm 46, by
means of spherical plain bearing 46b of the means for applying torsional
forces.
In particular, outer ring 81 is provided with threaded holes 81a, in which
there are
screwed high-strength bolts 71. These bolts are capable of being fixed to
fixation
element 35.
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As clearly illustrated in Fig. 13, outer ring 81 is provided with sixteen
bolts 71
intended to receive sixteen respective fixation elements 35 of means 30 for
application
of longitudinal forces.
For application of torsional forces, end 48b of auxiliary lever arm 46 is
fixed by a
spherical plain bearing at the location of nuts 72 disposed on the periphery
of outer ring
81.
As clearly illustrated in Fig. 13, outer ring 81 is provided with eight
fixation
bearings 81b disposed uniformly on the periphery.
These fixation bearings 81b are therefore disposed 45 apart from one another
on the periphery of outer ring 81. Each bearing 81b is in this case a
triangular tooth
81b, each vertical face 81c forming an angle of 45 with a radius of means 70
for
introduction of forces passing through the apex of tooth 81b.
Finally, the testing apparatus comprises means 90 for pressurizing the
interior of
fuselage structure 10.
As clearly illustrated in Figs. 15 and 16, pressurizing means 90 in principle
comprise covers 90a, 90b fixed sealingly to lower end 10a and upper end 10b of
fuselage structure 10.
In practice, a lower cover 90a is fixed sealingly to the center of support
means
50. An upper cover 90b is fixed by a series of peripheral bolts to means 70
for
introduction of forces, the bolts in this embodiment being disposed in
corresponding
bores provided in contour ring 82.
Between covers 90a, 90b, pressurizing means 90 are additionally provided with
a
cage-like structure 91 and vertical partitions 92, which separate the interior
space from
cage-like structure 91.
These vertical partitions 92 make it possible to reduce the volume to be
pressurized and thus to increase the safety of the personnel in the event of a
large leak
or possibly of an explosion.
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Cage-like structure 91 and partitions 92 are therefore capable of being
expanded
in the interior of the fuselage structure.
The compressed-air supply is admitted at lower cover 90a, which includes an
aperture for admission of compressed air being conveyed through conduit 57,
which
was described hereinabove with reference to Fig. 7.
Because force-application means 30, 40 are mounted by pivot joints on the one
hand and spherical plain bearing on the other hand, the mechanical stresses
applied by
force-application means 30, 40 are collinear with the doubly curved surface of
the
fuselage structure, and they remain collinear with this surface even when the
fuselage
structure is deformed.
By virtue of the different force-application means and of pressurizing means,
it is
possible to apply to the structure all the mechanical stresses representative
of real
behavior of the fuselage structure.
In particular, it is possible to apply the following maximum stresses:
Static test Fatigue test
1: Pressure + tension Fmax = 17,000 kN Fmax =
10,000 kN
2: Pressure + compression APmax = 3.7 bar APmax =
1.9 bar
3: Pressure + torsion Mmax = 7,300 kN Mmax =
4,300 kN
APmax = 3.7 bar APmax = 1.9 bar
4: Pressure + torsion + Fmax = 17,000 kN Fmax =
17,000 kN
compression Mmax = 7,300 kN Mmax = 4,300 kN
APmax = 3.7 bar APmax = 1.9 bar
By virtue of the design of the apparatus such as described hereinabove, means
30 for application of longitudinal forces can be moved aside by deformation of
the
parallelogram formed by each jack 31, lever arm 34 and pylon 37, thus ensuring
that
the space outside the fuselage structure can be made available and that the
said
structure can be inspected from the outside.
In addition, since the fuselage structure is mounted by clamping, it is easily
possible to demount the said structure and also to inspect the interior of the
structure
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after the application of stresses.
It will be noted in addition that demounting of the structure in the course of
testing can also be avoided by using methods of nondestructive inspection in
traditional
manner and by using sensors placed beforehand at different points of the
fuselage
structure.
This test structure makes it possible to study the damage tolerance as well as
fatigue and static strength of a structure having double curvature. In
particular, it is
possible to measure the constraints applied to fuselage structure 10, recorded
by strain
gauges, and to observe all the deflections in the fuselage structure in all
spatial
directions.
It will be understood that the present invention is not limited to the
practical
example such as described hereinabove.
In particular, the number of hydraulic jacks used both to apply a torsional
force
and to apply a compressive or tensile force is in no way limitative. In
addition, force-
application means other than hydraulic jacks could be used.
Furthermore, other types of fixation of the fuselage structure at its ends
could be
used rather than those based on clamping as described hereinabove.
