Title: Method, device and machine for pure bending test optionally alternating
Abstract: The present invention provides a method, apparatus, and a machine for testing in pure bending, optionally in alternating bending. Two mutually identical testpieces are subjected to optionally alternating opposing bending movements while conserving mutual symmetry about a point, under drive from two controlled motor assemblies that are free to move relative to each other. Interfering forces induced in the two testpieces during testing are minimized, and the performance of the testpieces in pure bending can be studied with increased accuracy.
Patent Number: 7,017,423 Issued on 03/28/2006 to Calloch, et al.
| Inventors:
|
Calloch; Sylvain (Antony, FR);
Dureisseix; David (Cachan, FR);
Arnold; Gilles (Bagneux, FR);
Zudaire Rovira; Inaki (Molins de Rei, ES)
|
| Assignee:
|
Centre National de la Recherche Scientifique (CNRS) (FR)
|
| Appl. No.:
|
524474 |
| Filed:
|
August 12, 2003 |
| PCT Filed:
|
August 12, 2003
|
| PCT NO:
|
PCT/FR03/02515
|
| 371 Date:
|
February 11, 2005
|
| 102(e) Date:
|
February 11, 2005
|
| PCT PUB.NO.:
|
WO2004/017047 |
| PCT PUB. Date:
|
February 26, 2004 |
Foreign Application Priority Data
| Current U.S. Class: |
73/849 |
| Current Intern'l Class: |
G01N 3/20 (20060101) |
References Cited [Referenced By]
U.S. Patent Documents
| 3786673 | Jan., 1974 | Weissmann.
| |
| 3952572 | Apr., 1976 | Mergler et al.
| |
| 5284058 | Feb., 1994 | Jones.
| |
| Foreign Patent Documents |
| 197 29 438 | Feb., 1999 | DE.
| |
| 2 247 139 | May., 1975 | FR.
| |
| 627 501 | Aug., 1949 | GB.
| |
| 714 221 | Feb., 1980 | SU.
| |
Other References
Brunet et al: "Nonlinear Kinematic Hardening . . . ", Journal of Engineering
Materials, vol. 123, No. 4, Oct. 2001, pp. 378-383.
Yoshida et al. "Identification of Materials . . . ", INT. Journal of Mech. Sci.,
vol. 40, No. 2-3, 1998, pp. 237-249.
S. Calloch et al, "A Pure Bending Machine to Identify the Mechanical Behaviour
of thin sheets", 6th International Esaform Conference on Material Forming,
Apr. 28-30, 2003.
|
Primary Examiner: Noori; Max
Assistant Examiner: Davis; Octavia
Attorney, Agent or Firm: Lerner, David, Littenberg, Krumholz & Mentlik, LLP
Claims
What is claimed is:
1. A method of testing in pure bending or alternating bending, the method comprising
the following succession of steps:
a) making or selecting a testpiece having two mutually opposite end grip zones
and a bending zone interconnecting the two grip zones the testpiece presenting,
in a rest state, a first mean plane crossing the bending zone and each of the grip
zones and constituting a first plane of symmetry at least for the bending zone,
and a mean surface for the bending zone and each of the grip zones, wherein the
mean surface is perpendicular to the first mean plane;
b) leaving the testpiece in the rest state rigidly securing its two grip zones
so as to define for each of them a respective pivot axis perpendicular to the first
mean plane and occupying a determined first position relative to the respective
grip zones and a second position relative to the mean surface; and
c) imparting controlled opposing turning movements to the two grip zones of the
testpiece, optionally in alternation, about the respective pivot axes and away
from the rest state, while leaving the pivot axes free to move towards each other
or apart from each other, so as to impart optionally alternating bending to the
bending zone and so as to study the behavior of the bending zone in pure bending; wherein
the method is simultaneously performed on two mutually identical testpieces (1)
by implementing
step b) in such a manner that the first mean planes of the two testpieces are
mutually parallel and the mean surfaces of the two testpieces are mutually symmetrical
about a point when the two testpieces are in the rest state, and in such a manner
that the pivot axes of the two testpieces are common and mutually symmetrical about
the point; and by implementing
step c) in such a manner that optionally alternating opposing torques in controlled
manner are applied about each pivot axis to the respective corresponding grip zones
so as to impose optionally alternating opposing bending movements to the bending
zones of the two testpieces, while allowing the pivot axes to move freely relative
to each other.
2. A method according to claim 1, the testpiece presenting as its mean surface
in its rest state, a second mean plane constituting a second plane of symmetry
at least for the bending zone, the method being characterized in that step b) is
implemented in such a manner that the second mean planes of the two testpieces
coincide when the two testpieces are in the rest state and the pivot axes are placed
in the second mean planes, which thus coincide.
3. A method according to claim 1, the testpiece presenting in its rest state
a third mean plane which is perpendicular to the first mean plane which is crossed
by the bending zone with the grip zones being disposed on respective opposite sides
thereof, and constitutes a third plane of symmetry, at least for the bending zone,
the method being characterized in that step b) is implemented in such a manner
that the third mean planes of the two testpieces coincide and the pivot axes are
mutually symmetrical about the third mean planes which thus coincide.
4. A method according to claim 1, wherein during step c), the behavior of the
bending zone of the testpieces in pure bending is studied by measuring the resistance
opposed to the turning by at least one of the grip zones, in particular to deduce
therefrom changes in the resistance to bending of the bending zone.
5. A method according to claim 1 wherein step b) is implemented by connecting
each of the grip zones to the corresponding respective pivot axis by plurality
of arms, the plurality of arms corresponding to the grip zones of the two testpieces
being mutually symmetrical about the point, and by connecting the plurality of
arms corresponding to a given pivot axis using respective controlled motors suitable
for imparting optionally alternating opposing turning movements to the plurality
of arms about the corresponding pivot axis, the controlled motors corresponding
to the two pivot axes being mutually identical and being allowed to move freely
relative to each other.
6. A method according to claim 5 wherein step b) is further implemented by causing
each arm of the plurality of arms to be elastically flexible in the first mean
plane of the corresponding testpiece with stiffness that is greater than the stiffness
of the bending zone of the testpiece, while otherwise being rigid, and wherein
during step c) the resistance opposed to turning is measured by measuring the bending
stresses to which at least one of the plurality of arms is subjected in the first
mean plane of the corresponding testpiece.
7. A method according to claim 5, wherein the plurality of arms and the controlled
motors are arranged in such a manner that during step b) the pivot axes are mutually
parallel and disposed respectively on either side of the point.
8. A method according to claim 7, wherein the third mean plane of the testpiece
comprises a mutual plane of symmetry for the grip zones of the testpiece, and wherein
the plurality of arms which correspond to the grip zones of the two testpieces
are mutually identical.
9. A method according to claim 5, wherein the plurality of arms and the controlled
motors are arranged in such a manner that during step b), the pivot axes coincide
and pass through the point.
10. A method according to claim 1, wherein during step a) each testpiece is made
or selected in such a manner as to be in the form of a plate of thickness (
e)
extending perpendicular to the mean surface.
11. A method according to claim 10, wherein during step a) each testpiece is
made or selected in such a manner that the thickness (
e)
is also constant, at least in the bending zone.
12. A method according to claim 10, wherein during step a), each testpiece is
made or selected in such a manner that it presents a dimension (L
1)
perpendicular to the first mean plane that is constant, at least in the bending zone.
13. A method according to claim 10, wherein during step a) each testpiece is
made or selected in such a manner as to present a respective transition perpendicular
to the first mean plane between the bending zone and each of the grip zones.
14. Test apparatus for testing a testpiece in pure bending or alternating bending,
the testpiece comprising two mutually opposite end grip zones and a bending zone
interconnecting the two grip zones the testpiece presenting, in a rest state, a
first mean plane crossing the bending zone and each of the grip zones, and constituting
a first plane of symmetry at least for the bending zone, and a mean surface for
the bending zone and for each of the grip zones, wherein the mean surface is perpendicular
to the first mean plane, the apparatus comprising:
a pair of clamps each defining a slot for securely gripping a respective grip
zone of the testpiece, the slots presenting, in a relative rest position corresponding
to the testpiece being in the rest state, a first mean plane which crosses each
of the slots, and a mean surface for each of the slots wherein each slot presents
on either side of the mean surface a respective clamping face for clamping the
corresponding grip zone of the testpiece and with the mean surface extending perpendicular
to the first mean plane of the slots;
means for defining a respective pivot axis for each clamp in such a manner that
in the relative rest position of the clamps, the pivot axes are perpendicular to
the first mean planes of the slots, and occupy determined positions relative to
the corresponding clamps and are free to move towards each other or apart from
each other;
controlled means for imparting opposing, optionally alternating turning movements
to the clamps about the corresponding pivot axes away from the relative rest position
of the clamps, while leaving the pivot axes free to move towards each other or
apart from each other; and
means for measuring the behavior of the bending zone of the testpiece in pure
bending; wherein,
the apparatus implements the method according to claim 1 by including:
two mutually identical sets of the pair of clamps, the two sets of the clamps
having the first mean planes of their slots mutually parallel and having the mean
surfaces of the slots mutually symmetrical about a point when the two sets are
occupying respective rest position, in which the two sets are suitable for receiving
a respective testpiece in the rest position with the two testpieces being in a
relative position such that they are mutually symmetrical about the point;
the means for defining the pivot axes of the pair of clamps are arranged so that
the pivot axes are common to the two sets, being mutually symmetrical about the
point when the two sets are in their rest positions, and being free to move relative
to each other; and
the controlled means for imposing opposing and optionally alternating turning
movements on the clamps of the two sets comprising controlled motor means for applying
opposing, optionally alternating torques about each pivot axis to the corresponding clamps.
15. Apparatus according to claim 14, wherein each testpiece presents as its mean
surface in its rest state, a second mean plane constituting a second mean plane
of symmetry at least for the bending zone, the slots of pair of clamps possessing
as mean surface respective second mean planes between the clamping faces of each
clamp when in the rest position,
the apparatus being characterized in that the second mean planes of the two sets
of the pair are mutually symmetrical about the point when the two sets are in the
rest position.
16. Apparatus according to claim 15, wherein each testpiece in its rest state
presents a third mean plane that is perpendicular to the first mean plane, that
is crossed by the bending zone when the grip zones are disposed respectively on
either side thereof, and that constitutes a third plane of symmetry at least for
the bending zone, and the slots of the pair of clamps present, in the rest position,
a third mean plane on either side of which they are disposed and which is perpendicular
to their first mean plane,
the apparatus being characterized in that the third mean planes of the two sets
of the pair are mutually symmetrical about the point when the two sets are in the
rest position.
17. Apparatus according to claim 14, wherein the means for measuring the behavior
of the bending zone of the testpieces in pure bending comprise:
means for measuring the resistance opposed to the alternating turning movements
by at least one of the clamps; and, where appropriate
means for deducing therefrom how the resistance of the testpiece to bending between
the clamps changes.
18. Apparatus according to claim 14, wherein
the means for defining the pivot axes of the two sets comprises:
on each of the pivot axes, two respective shafts on the same axis and mounted
to turn relative to each other about the corresponding pivot axis; and
at least four arms that are mutually symmetrical about the point, each connecting
a respective one of the shafts to a respective one of the clamps corresponding
to the same pivot axis; and
the controlled motor means for applying opposing, optionally alternating torques
about each pivot axis to the corresponding clamp comprise two mutually identical
controlled motors arranged in such a manner as to be capable of moving freely relative
to each other, each of the motors being associated with a respective one of the
pivot axes and being suitable for imparting opposing, optionally alternating, turning
movements to the two respective corresponding shafts.
19. Apparatus according to claim 18, wherein the motors are electric stepper motors.
20. Apparatus according to claim 18, wherein each arm of the plurality of arms
is elastically flexible in the first mean plane of the slot of the corresponding
clamp with stiffness greater than the stiffness of the bending zone of the corresponding
testpiece, and is otherwise rigid, and in that the measurement means comprise means
for measuring the bending stresses to which at least one of the plurality of arms
is subjected in the first mean plane of the slot of the corresponding clamp.
21. Apparatus according to claim 20, wherein the plurality of arms present in
mutually symmetrical positions about the point at least one respective zone that
is weakened in bending in the first mean plane of the slot of the corresponding
clamp, and wherein
the means for measuring bending stresses are located in the zone of at least
one of the plurality of arms.
22. Apparatus according to claim 18, wherein the plurality of arms, the shafts,
and the motors are arranged in such a manner that in the rest position the pivot
axes are mutually parallel and disposed respectively on either side of the point.
23. Apparatus according to claim 22, wherein the plurality of arms of the apparatus
are mutually identical and each testpiece presents as its mean surface in its rest
state a second mean plane and a third mean plane,
the second mean plane comprising a second mean plane of symmetry at least for
the bending zone, the slots of the pair of clamps possessing as mean surface respective
second mean planes between the clamping faces of each clamp when in the rest position,
and wherein the second mean planes of the two sets of the pair are mutually symmetrical
about the point when the two sets are in the rest position, and
the third mean plane of each testpiece comprising a plane of mutual symmetry
for the grip zones and being perpendicular to the first mean plane, that is crossed
by the bending zone when the grip zones are disposed respectively on either side
thereof, and that comprises a third plane of symmetry at least for the bending
zone, and the slots of the pair of clamps present, in the rest position, a third
mean plane on either side of which they are disposed and which is perpendicular
to their first mean plane, and wherein the third mean planes of the two sets of
the pair of clamps are mutually symmetrical about the point when the two sets are
in the rest position.
24. Apparatus according to claim 18, wherein some of plurality of the arms, the
shafts, and the motors are arranged in such a manner that, in the rest position,
the pivot axes coincide and pass through the point.
25. Apparatus according to claim 14, wherein the clamps are chamfered so as to
taper towards each other when the clamps are in the rest position.
26. A testing machine for performing testing in pure bending, optionally in alternating
bending, for implementing the method according to claim 1, wherein the machine comprises:
two mutually identical motor assemblies that are mechanically mutually independent,
each of the identical motor assemblies further comprising:
two clamps each of which is suitable for securely receiving a respective grip
zone of a corresponding testpiece;
means for defining a relative pivot axis for the two clamps and occupying a determined
position relative to each of the two clamps while in a relative rest position; and
controlled motor means for imparting relative and optionally alternating turning
movements to the clamps about the relative pivot axis away from the relative rest
position; and
common means for controlling the motor means of the two motor assemblies to impart
relative, optionally alternating turning movements to the respective clamps about
the respective relative pivot axes.
27. A machine according to claim 26, characterized in that it comprises:
means for measuring the resistance to relative turning opposed by at least one
of the clamps.
28. A machine according to claim 26, wherein for each of the motor assemblies respectively,
the means for defining the relative pivot axes of the two clamps comprises:
two shafts mounted on the same axis to turn relative to each other about the
relative pivot axis; and
two arms, each of which secures one of the clamps to a respective one of the
shafts; and
the controlled motor means for imparting relative, optionally alternating turning
movement to the clamps about the relative pivot axes, comprise a controlled motor
that is mechanically independent of the control motor of the other motor assembly
and that is suitable for imparting relative, optionally alternating, turning movements
to the two shafts.
29. A machine according to claim 28, wherein each controlled motor is an electric
stepper motor.
30. A machine according to claim 28, wherein
each of the plurality of arms is elastically flexible in a mean plane perpendicular
to the pivot axis and is otherwise rigid, and the measurement means comprise means
for measuring the bending stresses to which at least one of the plurality of arms
is subjected in the mean plane.
31. A machine according to claim 30, wherein each of the plurality of arms presents
at least one zone that is weak in bending in the mean plane, and wherein the means
for measuring bending stresses are located in the zone of at least one of the arms.
32. A machine according to claim 26, wherein the plurality of arms are mutually identical.
33. A machine according to claims 26, wherein the clamps are chamfered.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is a national phase entry under 35 U.S.C. § 371
of International Application No. PCT/FR03/02515 filed Aug. 12, 2003, published
in France, which claims priority from French Application No. 02/10261 filed Aug.
31, 2002, all of which are incorporated herein by reference.
This application is a 371 of PCT/FR03/02515.
The present invention relates to a method of testing in pure bending, optionally
in alternating bending, the method comprising the following succession of steps:
a) making or selecting a testpiece having two mutually opposite end grip zones
and a bending zone interconnecting the two grip zones, said testpiece presenting,
in a rest state, a first mean plane crossing the bending zone and each of the grip
zones and constituting a first plane of symmetry at least for the bending zone,
and a mean surface for the bending zone and each of the grip zones, which mean
surface is perpendicular to the first mean plane;
b) while leaving the testpiece in the rest state, rigidly securing its two grip
zones so as to define for each of them a respective pivot axis perpendicular to
the first mean plane and occupying a determined position firstly relative to the
respective grip zone and secondly relative to the mean surface; and
c) imparting controlled opposing turning movements to the two grip zones of the
testpiece, optionally in alternation, about the respective pivot axes and away
from the rest state, while leaving the pivot axes free to move towards each other
or apart from each other, so as to impart optionally alternating bending to the
bending zone and so as to study the behavior of the bending zone in pure bending,
for example by measuring the resistance opposed to said turning movement by at
least one of the grip zones of the testpiece in order to deduce therefrom how the
resistance to pure bending of the bending zone changes.
BACKGROUND OF THE INVENTION
By convention, it is considered that a bending test in pure bending is a bending
test that is implemented while inducing as little parasitic force as possible into
the bending zone of the testpiece, i.e. more specifically as little normal and/or
intersecting force as possible.
In the context of the present application, when it is said that the turning movement
is optionally alternating, or that a test in pure-bending is optionally in alternating
bending, that constitutes a convenient shorthand for specifying in particular that:
- the changes in turning during a test may be monotonic, i.e. always in
the same direction, or with one or more reversals of direction; and
- if there is a reversal of direction, the maximum amplitudes in opposite
directions may be equal or different.
Such a method is described in an application to performing alternating pure
bending tests by M. Brunet, F. Morestin, and S. Godereaux (2001, "Non-linear kinematic
hardening identification for anistropic sheet metals with bending-unbending tests",
Journal of Engineering Materials and Technology, Vol. 123, pp. 378-383), who also
describe apparatus and a machine for implementing the method.
That known method is applied to a single testpiece, as do all previously-known
methods of alternating bending testing. Nevertheless, in a manner specific to that
method, each of the grip zones of the testpiece is held securely in a respective
clamp mounted to pivot about a respective axis in a respective slider and engaged
with a common device for driving both clamps and suitable for imparting thereto,
and also to the grip zones of the testpiece to which they are respectively secured,
alternating opposite turning movements about the respective pivot axes relative
to the respective sliders so as to impart alternating bending to the bending zone
of the testpiece between the clamps. The pivot axes of the two clamps are mutually
parallel and the two sliders are mounted to slide on a common slideway in a direction
perpendicular to the two pivot axes, thus allowing the axes to move towards each
other or apart from each other along said direction as a function of variation
in the apparent length of the testpiece between the two grip zones, i.e. between
the two clamps, depending on the bending state of its bending zone.
The pivotal mounting of each clamp about the respective pivot axis in the respective
slide takes place via a respective shaft, which shaft is secured to each clamp
to lie on the corresponding pivot axis, and is engaged in two bearings of the corresponding
slide. Between these two bearings, the shaft meshes via a respective gear train
with a respective drive shaft, itself mounted to turn in two bearings of the corresponding
slide about an axis that is parallel to the respective pivot axis and that is disposed
relative thereto in such a manner that the axes of rotation of the drive shafts
corresponding to the two slides, i.e. corresponding to the two clamps, are further
apart from each other than are the pivot axes of the clamps. Each drive shafts
itself acts via an Oldham joint disposed opposite from the corresponding clamp
relative to the corresponding slide, to engage a respective outlet shaft of the
drive device which is constituted by an electric motor associated with a torque limiter.
The bending zone of the testpiece can thus be subjected to bending alternately
in one direction and in the other, through an amplitude that is adjusted by adjusting
the magnitude of the turning of each clamp about the corresponding pivot axis relative
to the corresponding slide, said magnitude of turning being identical at all times
for both clamps because they are driven in common.
In that known apparatus, the resistance opposed by the clamps and by the grip
zones of the testpiece against alternating turning is measured by sensors disposed
on the drive shafts between the Oldham joints and the slides, in order to measure
the twisting stresses of the drive shafts, where changes in such resistance serve
to deduce changes in the resistance to bending of the bending zone.
That prior art apparatus makes it possible continuously to control the pivoting
of each grip zone about its pivot axis, i.e. the bending of the bending zone between
the grip zones, thereby constituting a significant advance over earlier apparatuses,
in particular over the apparatus which appears previously to have been the most
satisfactory in terms of maximum bending amplitude, in particular on a testpiece
of small thickness, as measured perpendicularly to its mean surface, i.e. the apparatus
described by F. Yoshida, M. Urabe, and V. V. Toropov (1998, "Identification of
material parameters in constitutive model for sheet metals from cyclic bending
test", International Journal for Mechanical Sciences, Vol. 40, pp. 237-249).
The apparatus described by Yoshida et al. acts positively by means of a drive
motor in alternating turning only on a first one of the grip zones of the testpiece,
while the second grip zone is merely held at a determined orientation relative
to a frame that also carries the motor by means of slideway-and-slider assemblies
allowing it to move along two mutually perpendicular directions in order to allow
the first grip zone to change its direction and in order to accommodate variations
in the apparent length of the bending zone between the two grip zones while alternating
bending is being applied.
In the apparatus of Yoshida et al., the bending zone thus serves as means for
transmitting movement from the grip zone that is directly connected to the motor
for drive in alternating turning motion to both the other grip zones, and also
the slider-slideway assemblies that serve to maintain a constant orientation, and
as a result the non-negligible friction that appears in the connections between
the sliders and the slideways leads to non-negligible interfering forces appearing
in the testpiece and more precisely in its bending zone, so bending conditions
remain remote from ideal conditions of pure bending. This leads to a non-negligible
amount of error in determining the changing resistance to bending of the bending
zone from a measurement of the resistance opposed to the alternating turning movements
by the grip zone that is connected to the motor.
Simultaneous positive action in pivoting on both grip zones of the testpiece
enables the two grip zones to be guided in a single direction only, i.e. in practice
it enables the two clamps to be guided to slide relative to each other in a single
direction only in the apparatus of Brunet et al., thereby enabling friction to
be reduced in comparison with the apparatus of Yoshida et al., and consequently
reducing the parasitic forces induced in the bending zone by the friction and the
disturbances that follow therefrom when studying changes in the bending resistance
of the bending zone, with the study thus being less remote from pure bending, but
with the friction and the parasitic forces still remaining perceptible. In other
words, the twisting stresses measured on the drive shafts of the apparatus of Brunet
et al. are due not only to the bending resistance of the bending zone, but also
to the resistance due to friction that the slides encounter against the slideway
whenever they need to move towards each other or apart from each other as a function
of variations in the apparent length of the bending zone between the grip zones,
i.e. between the clamps; in addition, the twisting stresses are also associated
in part with the resistance opposed to turning by the shafts carrying the clamps
in their bearings in the slides, by the gearing transmitting motion between these
shafts and the drive shafts, and by the drive shafts in their own bearings in the
slides, and that too can lead to a non-negligible amount of error in interpreting
these twisting stresses in terms of the bending resistance of the bending zone.
SUMMARY OF THE INVENTION
The object of the present invention is to remedy at least some of the drawbacks
of the method and apparatus described by Brunet et al., and in preferred implementations
of the present invention, to remedy all of those drawbacks.
To this end, the present invention provides a method of testing in pure bending,
optionally in alternating bending, the method comprising the following succession
of steps:
a) making or selecting a testpiece having two mutually opposite end grip zones
and a bending zone interconnecting the two grip zones, said testpiece presenting,
in a rest state, a first mean plane crossing the bending zone and each of the grip
zones and constituting a first plane of symmetry at least for the bending zone,
and a mean surface for the bending zone and each of the grip zones, which mean
surface is perpendicular to the first mean plane;
b) while leaving the testpiece in the rest state, rigidly securing its two grip
zones so as to define for each of them a respective pivot axis perpendicular to
the first mean plane and occupying a determined position firstly relative to the
respective grip zone and secondly relative to the mean surface; and
c) imparting controlled opposing turning movements to the two grip zones of the
testpiece, optionally in alternation, about the respective pivot axes and away
from the rest state, while leaving the pivot axes free to move towards each other
or apart from each other, so as to impart optionally alternating bending to the
bending zone and so as to study the behavior of the bending zone in pure bending,
for example by measuring the resistance opposed to said turning movement by at
least one of the grip zones of the testpiece in order to deduce therefrom how the
resistance to pure bending of the bending zone changes,
as described by Brunet et al., this method being characterized, according to
the
present invention, in that it is applied simultaneously to two mutually identical
testpieces by implementing:
- step b) in such a manner that the first mean planes of the two testpieces
are mutually parallel and the mean surfaces of the two testpieces are mutually
symmetrical about a point when the two testpieces are in the rest state, and in
such a manner that the pivot axes of the two testpieces are common and mutually
symmetrical about said point; and
- step c) by applying optionally alternating opposing torques in controlled
manner about each pivot axis to the respective corresponding grip zones so as to
impose optionally alternating opposing bending movements to the bending zones of
the two testpieces, while allowing the pivot axes to move freely relative to each other.
Under such conditions, it is each testpiece which acts via its grip zones interconnected
by the bending zone and opposes bending resistance to the bending zone of the other
testpiece between its grip zones, without it being necessary to provide any kind
of guidance for the grip zones relative to any kind of structure, and consequently
avoiding any risk of inducing parasitic forces due to friction into the bending
zone of either testpiece. Thus, the measurement of the resistance opposed to turning
by at least one of the grip zones is much more representative of the resistance
opposed by the bending zone in pure bending, it being understood that by having
identical testpieces with the optionally alternating pure bending test being performed
simultaneously on both of them makes it possible to conserve symmetry permanently,
at least to within a good approximation, between the two testpieces in the state
when they are bent in opposite directions and also when in the rest state, said
symmetry being about the point or center of symmetry, i.e. both testpieces have
their bending zones subjected to the same bending state, if any, and consequently
the bending zones of the two testpieces oppose substantially identical resistance
to pure bending.
In association with the characteristics of the method of the invention and with
the advantageous consequences to which they give rise in this way, the present
invention also provides apparatus for testing a testpiece of the type described
in the introduction, the testing being in pure bending, optionally in alternating
bending, and the apparatus comprising:
- a pair of clamps each defining a slot for securely gripping a respective
grip zone of the testpiece, the slots presenting, in a relative rest position corresponding
to the testpiece being in the rest state, a first mean plane which crosses each
of the slots, and a mean surface for each of the slots, with each slot presenting
on either side of the mean surface a respective clamping face for clamping the
corresponding grip zone of the testpiece and with the mean surface extending perpendicularly
to the first mean plane of the slots;
- means for defining a respective pivot axis for each clamp in such a
manner that in the relative rest position of the clamps, the pivot axes are perpendicular
to the first mean planes of the slots, and occupy determined positions relative
to the corresponding clamps and are free to move towards each other or apart from
each other;
- controlled means for imparting opposing, optionally alternating turning
movements to the clamps about the corresponding pivot axes away from the relative
rest position of the clamps, while leaving the pivot axes free to move towards
each other or apart from each other; and
- means for measuring the behavior of the bending zone of the testpiece
in pure bending, e.g. comprising:
- means for measuring the resistance opposed to said turning movement
by at least one of the clamps, and where appropriate;
- means for deducing therefrom the changes in the bending resistance
of the testpiece between the clamps,
as proposed by Brunet et al., said apparatus being characterized in that, in
order
to implement the method of the invention,
- it includes two mutually identical sets of said pair of clamps, having
the first mean planes of their slots mutually parallel and having the mean surfaces
of the slots mutually symmetrical about a point when the two sets are occupying
their rest positions in which each of them is suitable for receiving a respective
testpiece in the rest position with the two testpieces being in a relative position
such that they are mutually symmetrical about said point;
- the means for defining the pivot axes of the clamps of the two sets
are arranged in such a manner that the pivot axes are common to both sets, being
mutually symmetrical about said point when the two sets are occupying their rest
positions, and being free to move relative to each other; and
- the controlled means for imposing opposing and optionally alternating
turning movements on the clamps of the two sets comprise controlled motor means
for applying opposing, optionally alternating torques about each pivot axis to
the corresponding clamps.
In the meaning of the present invention, mutual symmetry of the mean surfaces
of the slots about the point or center of symmetry includes the special case in
which said mean surfaces are plane and coincide in a plane that includes the point
or center of symmetry.
In the apparatus, the two testpieces constitute the only mechanical connections
between two mutually identical motor assemblies, each of which comprises:
- two clamps, each of which is suitable for securely receiving a respective
grip zone of a corresponding testpiece;
- means for defining a relative pivot axis for the two clamps and occupying
a determined position relative to each of the two clamps while in a relative rest
position; and
- controlled motor means for imparting relative and optionally alternating
turning movements to the clamps about the relative pivot axis away from the relative
rest position, and
these two motor assemblies, together with control means for the motor means
of the two motor assemblies serving to impose relative turning movement, optionally
in alternation, on the respective clamps about the respective relative pivot axes,
and possibly also together with means for measuring the resistance opposed to the
relative turning movement by at least one of said clamps, constitute a machine
for testing in pure bending, possibly in alternation, itself characteristic of
the present invention and for implementing the method of the invention.
Naturally, it is necessary to carry or support the apparatus of the invention
constituted by the machine as designed in this way together with the two testpieces,
by carrying or supporting each of said mutually identical motor assemblies, however
it is possible for this purpose to use means that induce interfering forces in
the two testpieces that are much smaller and much less harmful than those induced
by friction between slides and slideways in the prior art apparatuses described
above, and thus leading to much less disturbance of the pure bending state in the
bending zones and thus to much less disturbance in the study of changes in the
bending resistance opposed by the bending zones on the basis of measuring the resistance
opposed by at least one of said clamps to being turned.
By way of example, it is possible for this purpose to use an air cushion or a
hydraulic mat on which the entire apparatus is allowed to rest freely, or the motor
assemblies of the machine can be suspended via flexible ties from a point that
is situated as high as possible above the machine, or one of the motor assemblies
can be rigidly supported by a rigid support while the other one is suspended in
the above-specified manner so that its weight is not transmitted to the first motor
assembly via the two testpieces, where these examples are not limiting in any way.
It should be observed that the method, the apparatus, and the machine of the
invention
may be used with testpieces presenting a variety of shapes in the rest state, and
in particular:
- any shape of constant section, perpendicularly to the first mean plane
and to the mean surface, in particular in the bending zone;
- shapes that are curved or plane for their mean surfaces which when plane,
may optionally constitute a second plane of symmetry, at least for the bending zone;
- or indeed shapes that are optionally symmetrical, at least for the bending
zone, about a third mean plane that is perpendicular to the first mean plane and
crossed by the bending zone, with the grip zones being disposed respectively on
either side thereof, these examples not being limiting.
Thus, as non-limiting examples, two mutually identical testpieces may be subjected
to a bending method of the invention, optionally an alternating bending method,
each of which testpieces is in the form of a plate of constant thickness as measured
perpendicularly to its mean surface, and each of which is flat, in particular in
its bending zone, as can be the case for a sample of raw sheet metal, or else it
can be curved or corrugated, in particular in its bending zone, as can be the case
for a sample of the wall of a metal receptacle or of sheet metal unwound from a
coil, or a sample of wall for a metal bellows, or indeed a testpiece in the form
of a rod that is curved or rectilinear, of section that is constant, at least in
its bending zone, or indeed a testpiece in the form of a plate or a rod in which
the bending zone tapers from one of the grip zones to the other.
In contrast, it would appear that the method described by Brunet et al., given
the way in which the two clamps are driven to pivot about their pivot axes and
the way in which the slides are guided in a direction perpendicular to said axes,
is capable of being applied only to testpieces that present in the rest state,
and that conserve in the bent state, at least two mutually perpendicular planes
of symmetry, one of which is the above-mentioned first plane of symmetry and the
other of which is the above-mentioned third plane of symmetry oriented perpendicularly
to the sliding direction of the two slides and permanently constituting a plane
of symmetry between the clamps in the apparatus of Brunet et al.
In this respect, in the context of the present application, the terms "first",
"second", and "third" planes of symmetry are used for convenience of language,
and in particular:
- mention of a first plane of symmetry does not necessarily imply that
there are any other planes of symmetry; and
- mention of a third plane of symmetry does not necessarily imply that
there is a second plane of symmetry.
If, as is often the case, the testpiece in its rest state presents a mean surface
constituting a second mean plane that constitutes a second plane of symmetry at
least for its bending zone, as applies for example to a testpiece in the form of
a rectilinear rod or a testpiece in the form of flat plate, then:
- step b) is implemented-in such a manner that the second mean planes
of the two testpieces coincide when the two testpieces are in the rest state and
the pivot axes are placed in the second mean planes, which thus coincide; and
- in the apparatus-of the invention, if the slots of each pair of clamps
present as their mean surfaces respective second mean planes of symmetry between
the clamping faces of each clamp, when in a rest position, then the machine is
arranged in such a manner that the second mean planes of the two sets of said pair
of clamps are mutually symmetrical about the point or center of symmetry when the
two sets are in the rest position, said mutual symmetry including the special case
in which said second mean planes of the two sets of pairs of clamps coincide and
include the point or center of symmetry.
Similarly, if the testpiece in its rest state presents a third mean plane
that is perpendicular to the first mean plane, is crossed by the bending zone when
the grip zones are disposed respectively on either side thereof, and constitutes
a third plane of symmetry at least for the bending zone, which is also frequently
the case, e.g. if the testpiece is in the form of a rectilinear rod of constant
section as corresponds to the most frequent case of testpieces that are in the
form of a plate that is flat or curved:
- step b) is implemented in such a manner that the third mean planes of
the two testpieces coincide and the pivot axes are mutually symmetrical about the
third mean planes which thus coincide; and
- for the machine of the invention, when the slots of each pair of clamps
in the rest position present respective third mean planes which are perpendicular
to their first mean planes and on either side of which they are disposed, the third
mean planes of the two sets of said pairs are mutually symmetrical about the point
or center of symmetry when the two sets of clamps are in the rest position, said
mutual symmetry of the third mean planes of the two sets of the pairs of clamps
including the special case in which the third mean planes coincide and include
the point or center of symmetry.
Various methods of connecting each of the grip zones to the corresponding
pivot axis can be envisaged, but it is preferred to use a connection that is as
direct as possible, so as to avoid inducing interfering forces between each testpiece
and the means for measuring the bending resistance opposed to the turning movement
by the bending zone of each of them.
In this respect, in a preferred implementation of the method of the invention,
step b) is implemented by connecting each of the grip zones to the corresponding
respective pivot axis by an arm, the arms corresponding to the grip zones of the
two testpieces being mutually symmetrical about said point, and by connecting the
two arms corresponding to a given pivot axis by means of a respective controlled
motor suitable for imparting optionally alternating opposing turning movements
to the two arms about the corresponding pivot axis, the controlled motors corresponding
to the two pivot axes being mutually identical and being allowed to move freely
relative to each other.
To this end, and respectively for each of the motor assemblies of the machine
of the invention:
- the means for defining the relative pivot axes of the two clamps comprise:
- two shafts mounted on the same axis to turn relative to each other
about the relative pivot axis; and
- two arms, each of which secures one of the clamps to a respective
one of the shafts; and
- the controlled motor means for imparting relative optionally alternating
turning movement to the clamps about the relative pivot axes, comprise a controlled
motor that is mechanically independent of the control motor of the other motor
assembly and that is suitable for imparting relative, optionally alternating turning
movements to the two shafts,
such that the test apparatus of the invention is then characterized in that:
- the means for defining the pivot axes of the two sets comprise:
- on each of the pivot axes, two respective shafts on the same axis
and mounted to turn relative to each other about the corresponding pivot axis; and
- four arms that are mutually symmetrical about said point, each connecting
a respective one of the shafts to a respective one of the clamps corresponding
to the same pivot axis; and
- the controlled motor means for applying opposing, optionally alternating
torques about each pivot axis to the corresponding clamps comprise two mutually
identical controlled motors arranged in such a manner as to be capable of moving
freely relative to each other, each of the motors being associated with a respective
one of the pivot axes and being suitable for imparting opposing, optionally alternating
turning movements to the two respective corresponding shafts,
with each of the controlled motors advantageously being constituted by an electric
stepper motor, in particular for the purpose of facilitating selection of the pivot
amplitude of each clamp, i.e. of each grip zone, about the respective pivot axis
relative to the clamp and to the grip zone corresponding to the same pivot axis,
i.e. making it easier to adjust the bending amplitude for each of the bending zones,
even though other means may be selected for this purpose.
It is then possible to measure the resistance opposed to turning by at least
one
of the grip zones of at least one of the testpieces by measuring the twisting stresses
on at least one of the shafts of at least one of the motor assemblies, in which
case it is possible to choose to make each arm in such a manner that it is rigid
in bending in any mean plane and also in twisting.
Nevertheless, it is preferred to ensure that each arm is elastically
bendable in the first mean plane of the corresponding testpiece, i.e. in the first
mean plane of the slot of the corresponding clamp, i.e. in a mean plane perpendicular
to the corresponding pivot axis, with stiffness that is greater than the stiffness
of the bending zone of the testpiece, while being rigid otherwise, thus making
it possible to measure the bending stresses to which at least one of the arms is
subjected in a direction that is circumferential relative to the corresponding
pivot axis, which bending stresses are much more directly representative of the
bending resistance of the bending zone, in which case the measurement means comprise
means for measuring the bending stresses to which at least one of the arms is subjected
in said mean plane.
For this purpose, it may be tempting to measure the bending stresses to which
each of the arms is subjected, by providing appropriate measurement means on each
of them, however testing to validate the method of the invention and performed
on an apparatus and a machine of the invention has shown that measuring the bending
stresses to which only one of the arms is subjected gives a result that is meaningful
and that has sufficient accuracy concerning the resistance to bending of the bending
zone in each of the testpieces, and concerning changes in said bending resistance
as alternating bending progresses, i.e. when performing fatigue testing in bending.
In order to make it easier to measure the bending stresses to which at least
one
of the arms is subjected, it is preferable to provide for each of the arms to present
at least one zone that is weakened in bending in said mean plane perpendicular
to the corresponding pivot axis, i.e. in a direction that is circumferential relative
to said corresponding pivot axis, with the zones thus weakened in bending being
mutually symmetrical about the point or center of symmetry, and with the means
for measuring the bending stresses of at least one of the arms being placed in
said zone.
As the person skilled in the art will readily understand, the symmetry in the
treatment given to the two testpieces and in the apparatus of the invention about
a point or center of symmetry while the testpieces are in their rest state and
the clamps are in their rest position is characteristic of the present invention
and can be obtained in two main manners, by appropriately arranging the arms, the
shafts, and the motors.
This arrangement may be such that in the rest state of the testpieces and in
the rest position of the clamps:
- the pivot axes are mutually parallel and disposed respectively on either
side of the point or center of symmetry, in which case, if each testpiece in its
rest state presents a third mean plane as specified above and if said mean plane
constitutes not only a plane of symmetry for the bending zone but also a plane
of mutual symmetry for the grip zones, the arms corresponding to the grip zones
of the two testpieces may advantageously be mutually identical; or else
- the pivot axes coincide and pass through the point or center of symmetry,
this relative positioning being considered as constituting a special case of mutual
symmetry for the pivot axes about the point or center of symmetry in the meaning
of the present invention.
In both cases, the machine and the apparatus of the invention may be very simple
to implement, such that in spite of using two motors, the cost price remains competitive
compared with that of prior art apparatuses, and reliability is, in contrast, considerably increased.
Although as stated above, testpieces of very different shapes can be subjected
to bending tests in accordance with the present invention, each testpiece is made
or selected during step a) of the method of the invention in such a manner as to
present the shape of a plate of thickness that extends perpendicularly to its mean
surface, in which case:
- said thickness is preferably constant, at least in the bending zone;
- each testpiece preferably presents a dimension that is constant perpendicularly
to the first mean plane, at least in the bending zone; and
- each testpiece preferably presents a respective transition perpendicular
to the first mean plane between the bending zone and each of the grip zones.
A testpiece as made in this way in the form of a plate is particularly suitable
for bending tests of large amplitude, and in order to be able to access bending
amplitudes of about 90° between the grip zones, it is preferable to provide
for the clamps of the machine or the apparatus of the invention to be chamfered
so as to taper towards each other, when the clamps are seen in the rest position.
Other characteristics and advantages of the various aspects of the present
invention appear from the description below relating to two non-limiting implementations,
and also from the accompanying drawings which form an integral portion of the description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are perspective views showing a non-limiting example of the shape
of a testpiece suitable for use in implementing the method of the invention, the
testpiece in this non-limiting example being generally in the shape of a flat plate,
e.g. obtained by being cut out from a flat metal sheet, and prepared in two different
ways in order to enable it to be integrated in test apparatus of the invention.
FIG. 3 is a diagrammatic side elevation view of apparatus for implementing the
method of the invention, comprising a machine of the invention and two mutually
identical testpieces, e.g. as shown in FIG. 1 or in FIG. 2, or indeed having any
other shape suitable for enabling a bending test to be performed, the apparatus
being shown in a rest position with the two testpieces being in the rest state.
FIG. 4 is a view from above seen looking along the direction identified by IV
in FIG. 3, showing the same apparatus likewise in the rest position with the two
testpieces being in the rest state.
FIG. 5 is a view from above similar to that of FIG. 4, showing the apparatus
after it has left its rest position and the two testpieces have been subjected
to bending in opposing manners.
FIGS. 6 to 8 are diagrammatic views similar to FIGS. 3 to 5 respectively, showing
apparatus having a variant embodiment of the machine, FIG. 7 being a view from
above seen looking along VII of FIG. 6.
FIG. 9 is a side elevation view similar to that of FIG. 6 showing a concrete
embodiment of the apparatus shown in FIG. 6 while in the rest position with the
two testpieces being in the rest state.
FIG. 10 is a view from above seen looking in a direction referenced X in FIG.
9, showing how surface deformation gauges are positioned on a zone of one of the
arms of the apparatus that is a zone of weakness in bending, the gauges constituting
means for measuring the bending stresses to which said arm is subjected because
of the strength of the two testpieces in bending.
FIG. 11 is a connection diagram of the apparatus.
FIG. 12 is a perspective view of the apparatus shown in FIG. 9, the apparatus
being in the rest position with the testpieces being in the rest state.
FIG. 13 is a perspective view of one of the two mutually identical motor assemblies
constituting the test machine of the invention in this case.
FIGS. 14 and 15 are perspective views showing respectively one of the mutually
identical arms of the machine and a variant embodiment of one of these mutually
identical arms.
FIGS. 16 and 17 are perspective views showing the two jaws of one of the mutually
identical clamps of the test machine of the invention in a shape adapted to the
shape of the testpiece shown in FIG. 1 or in FIG. 2, it being understood that each
shape of testpiece to be tested in bending corresponds to a clamp having a specific
shape, as will easily be designed by a person skilled in the art as a function
of the shape of the testpiece.
FIG. 18 is a perspective view of the apparatus after it has left the rest state,
the two ends of the testpiece being in the oppositely-bent state, e.g. being bent
through a right angle.
FIG. 19 is a diagrammatic elevation view similar to that of FIGS. 3 and 6 showing
another embodiment of apparatus of the invention in the rest position with the
two testpieces being in the rest state.
FIGS. 20 and 21 are views of the apparatus in section on planes marked XX—XX
and XXI—XXI in FIG. 19, showing the two testpieces in the rest state while
the apparatus is in the rest position.
FIGS. 22 and 23 are views similar to those
