Note: Descriptions are shown in the official language in which they were submitted.
CA 03086808 2020-06-23
Method and Device for Predicting Residual Stress of Metal Plate Based on
Measuring of Residual Stress Release Warpage
Technical Field
The disclosure relates to a method for predicting residual stress of a metal
plate based
on measuring of residual stress release warpage and a device for measuring
residual
stress release warpage of the metal plate.
Background Art
Aluminum alloy thick plates are widely used in aerospace and other large
equipment.
In order to improve the mechanical properties of the plates during manufacture
of
aeronautical aluminum alloy plates, the processes of solution treatment,
quenching
and aging treatment are usually used. In the quenching process, due to the
fact that the
central portion is cooled slower than the surface, the surface of the aluminum
alloy
thick plate is subjected to compressive stress after quenching, and the
central portion
is subjected to tensile stress. The existence of residual stress makes the
aluminum
alloy thick plate deform in the process of machining aeronautical parts.
Although the
residual stress can be reduced by pre-stretching treatment after quenching,
the
dimensional accuracy of aeronautical parts is required to be high, and the
requirement
for controlling the residual stress of the aluminum alloy thick plate is very
strict.
Large residual stress easily causes the dimensional accuracy of parts to be
unable to
meet the requirements. Only by controlling the residual stress within a
certain range
of values, can the deformation in the machining process of aluminum alloy
thick plate
be reduced, and qualified parts can be obtained. The detection of residual
stress of
aluminum alloy thick plate is the premise to ensure the machining of
aeronautical
parts to meet the deformation requirements.
7050, 7075 and 7085 aluminum alloy thick plates are widely applied to large-
scale
equipment such as aerospace equipment due to high specific strength and
excellent
mechanical properties. In order to improve the mechanical properties of the
plates
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during manufacturing of aluminum alloy thick plates, solution quenching and
aging
treatment are usually used. However, in the process of solution quenching, the
surface
and the central portion of the thick plate are not uniformly cooled, so that
the
aluminum alloy thick plate has very high residual stress. Since the central
portion is
cooled more slowly than the surface, the surface after final quenching is
subjected to
compressive stress, while the central portion is subjected tensile stress, and
the
residual stress exists. The aluminum alloy thick plate is deformed in the
process of
machining the aluminum alloy thick plate into aeronautical parts, so that
deformation
failure of the parts is caused. In order to reduce the residual stress of the
aluminum
alloy thick plate, the pre-stretching treatment is carried out after solution
quenching.
The plastic stretching generated by the pre-stretching process will release
the residual
stress partially, and the residual stress is controlled within a certain value
range, so
that the deformation generated in the machining process of the aluminum alloy
thick
plates can be reduced, and qualified parts can be manufactured.
However, the existing residual stress testing equipment is expensive in
manufacturing
cost and harsh in testing environment requirements, and is not suitable for
detecting
the residual stress of aluminum alloy thick plates in industrial production,
especially
aluminum alloy thick plates such as 7050, 7075, 7085 and the like in a
quenching
state, a pre-stretching state and an aging state. Therefore, there is a need
for a low-cost
and high-precision testing method and special equipment for residual stress in
the
industrial production process of aluminum alloy thick plates.
Summary of the Disclosure
In order to solve the above technical problems: the disclosure provides a
method and a
device for predicting residual stress of a metal plate based on measuring of
residual
stress release warpage, which are suitable for effective characterization of
residual
stress in industrial production of aeronautical aluminum alloy thick plates.
The device
for measuring the residual stress release deformation amount of the thick
metal plate
is special equipment for detecting the linear cutting deformation measurement
of
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aluminum alloy thick plates such as 7050, 7075, 7085 and the like in a
quenching
state, a pre-stretching state and an aging state so as to obtain the residual
stress level
of the aluminum alloy plate.
The disclosure is realized by the following technical solution:
A method for predicting residual stress of a metal plate based on residual
stress
release warpage, comprising:
(1) adopting one of an X-ray method, a blind hole method, an ultrasonic
method, a
crack flexibility method or a finite element analysis method to test residual
stress of
plates with different thicknesses;
(2) cutting a sample by a machining method along a plate thickness direction,
releasing residual stress to cause warpage of the plate, and testing warpage
by a
displacement sensor to obtain a relationship between the residual stress and
the
warpage of the plates with different thicknesses; obtaining, by fitting a
curve, a
quadratic equation: y=ax2+bx+c, wherein x is residual stress, y is warpage,
and a, b
and c are fitting coefficients;
(3) testing, upon cutting the metal plate on the basis of established
functional
relationship between the residual stress and the warpage, the warpage y under
a
specific linear cutting percentage, and calculating the residual stress
according to a
¨b 4b2 ¨ 4a (c ¨ y)
formula x ¨ ______________ .
2a
According to the method, in step (2) the machining method is preferably a
linear
cutting method.
According to the method, in step (2), the sample is cut by fixing one end of
the metal
plate, a length of a fixed portion being less than 1/2 of a length of the
sample, a
cutting position being preferably selected at 1/2 of the length of the sample,
and the
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cutting being performed along the plate thickness direction.
According to the method, in step (2) the warpage is measured at an end remote
from a
clamping position.
According to the method, in step (3) the specific linear cutting percentage is
a linear
cutting percentage controlled at a position where the warpage tends to be
gentle.
According to the method, in step (3) a cutting depth is 62.5-75% of the plate
thickness,
then it is recommended that the cutting depth is 75-95% of the plate
thickness, and
then it is recommended that the cutting depth is 50-62.5% of the plate
thickness, and
finally it is recommended that the cutting depth is 30-50% of the plate
thickness.
According to the method, predicted residual stress is the residual stress of
the metal
plate.
A device for measuring residual stress release deformation amount of a thick
metal
plate, comprising a clamping apparatus, wherein the clamping apparatus
comprises a
base, a fixing rod, a displacement testing seat and a displacement testing
means; the
base comprising a first base plate, two vertical baffles, a connecting plate
and a
pressing plate, both ends of the first base plate being fixedly connected with
one
vertical baffle respectively, bolt holes being formed in the two vertical
baffles, one
side edge of the first base plate being fixedly connected with one end of the
connecting plate to form a T shape, and the pressing plate being positioned
above the
two vertical baffles, the pressing plate being provided with through holes
corresponding to the bolt holes of the two vertical baffles in position, the
pressing
plate being connected with the two vertical baffles through bolts; a lower end
of the
fixing rod being fixedly connected with the other end of the connecting plate;
one end
of the displacement testing seat being sleeved outside the fixing rod, and the
other end
of the displacement testing seat being connected with a lower end of a dial
gauge.
According to the device, the device further comprises a deformation testing
platform
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including a second base plate, a fixing plate, a first clamping block and a
second
clamping block; a lower end of the fixing plate being fixedly connected with
one end
of the second base plate, a connecting hole being formed in a plate surface of
the
fixing plate; one end of the first clamping block being fixedly connected with
one end
of the plate surface of the fixing plate, a lower end of the first clamping
block being
fixedly connected with the second base plate; the second clamping block being
opposite to the first clamping block, one end of the second clamping block
being
provided with a bolt hole corresponding to the connecting hole of the fixing
plate in
position, one end of the second clamping block provided with the bolt hole
being
connected with the plate surface of the fixing plate through a bolt, a lower
end of the
second clamping block being fixedly connected with the second base plate; the
clamping apparatus being positioned on an upper surface of the second base
plate, and
one end of the base of the clamping apparatus being positioned between the
first
clamping block and the second clamping block.
According to the device, the displacement testing seat comprises a supporting
plate,
both ends of the supporting plate being provided with through holes, a lower
end of
the displacement testing means being inserted into the through hole at one end
of the
supporting plate; the fixing rod being inserted into the through hole at the
other end of
the supporting plate.
According to the device, the through holes at both ends of the supporting
plate are
bolt holes, a lower end of the displacement testing means being provided with
a
thread, the lower end of the displacement testing means being screwed into the
bolt
hole at one end of the supporting plate to be connected with the supporting
plate;
the fixing rod being provided with a thread and being screwed into the bolt
hole at the
other end of the supporting plate to be connected with the supporting plate.
According to the device, the displacement testing seat comprises a first
collet and a
second collet connected to each other, the first collet being clamped to a
lower portion
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of the displacement testing apparatus and the second collet being clamped to
the
fixing rod.
According to the device, the displacement testing means employs a dial gauge.
According to the device, the vertical baffle has two bolt holes formed
therein.
According to the device, the connecting plate is an elongated plate, and an
upper plate
surface of the elongated plate is stepped.
Beneficial technical effects of the present disclosure,
The disclosure has the beneficial technical effects that: the method
establishes the
relationship between residual stress and warpage by accumulating a large
amount of
experimental data, and can evaluate the residual stress level only by
measuring the
warpage of the sample. The method is simple and intuitive to operate, high in
measurement efficiency and suitable for detection in an industrial production
process.
The disclosure provides a device for measuring the residual stress release
deformation
amount of a thick metal plate. By means of the device, the magnitude of the
internal
residual stress of a material and the fluctuation of the residual stress among
different
batches of plates can be rapidly evaluated, so that the effective monitoring
of the
residual stress of the plates is realized. The establishment of a plate
residual stress
control standard is facilitated, and the uniformity of the residual stress of
the plates is
improved. The method and the equipment are not only suitable for testing the
residual
stress of plates, but also can be used for testing of structures such as
profiles, pipes,
bars and the like.
Brief Description of the Drawings
FIG 1 is a schematic diagram of a linear cutting process of an aluminum alloy
thick
plate;
FIG 2 is a schematic diagram showing the residual stress distribution along
the
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thickness of an aluminum alloy thick plate;
FIG 3 is a schematic diagram showing the warpage displacement for an aluminum
alloy thick plate at different linear cutting depth percentages;
FIG 4 is a schematic diagram showing the residual stress prediction for an
aluminum
alloy thick plate at different plate thicknesses and warpages;
FIG 5 is a schematic diagram showing a structure of a device for measuring a
residual
stress release warpage of a thick metal plate according to an embodiment of
the
present disclosure;
FIG 6 is a side view showing the device for measuring residual stress release
warpage
of a thick metal plate according to an embodiment of the present disclosure;
FIG 7 is a schematic diagram showing a structure of a device for measuring
residual
stress release warpage of a thick metal plate according to an embodiment of
the
present disclosure when a sample to be tested is loaded;
FIG 8 is a schematic diagram showing another structure of a device for
measuring the
residual stress release warpage of a thick metal plate according to an
embodiment of
the present disclosure.
In the drawings: base -1; fixing rod -2; displacement testing seat -3;
displacement
testing means -4; first base plate -5; two vertical baffles -6, 6'; connecting
plate -7;
pressing plate -8; first collet -9; second collet -10; second base plate -11;
fixing plate
-12; first clamping block -13; second clamping block -14; sample to be tested -
15;
linear cutting machine -16; bolt-17; bolt-18.
Detailed Description of the Disclosure
The present disclosure will now be described in further detail with reference
to the
accompanying drawings and detailed description.
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The embodiment of the disclosure provides a method for measuring residual
stress of
a metal plate based on residual stress release warpage, which comprises the
following
steps:
(1) adoping one of an X-ray method, a blind hole method, an ultrasonic method,
a
crack flexibility method or a finite element analysis method to measure
residual stress
of aluminum alloy plates with different thicknesses, wherein the residual
stress
distribution of the aluminum alloy thick plate is shown in FIG 2.
(2) fixing one end of an aluminum alloy thick plate, such as a section line
portion in
FIG 1, wherein a length of the fixed portion is less than 1/2 of a length of a
sample,
then placing a displacement sensor such as a dial gauge or a laser sensor at a
point a at
a central portion of an edge at one end of the sample 15 to be tested,
recording an
initial value, and performing linear cutting along the thickness of the plate
by using a
linear cutting machine 16 at the position of 1/2 of the length of the sample.
According
to the warpage displacement schematic diagram of the aluminum alloy thick
plate
under different linear cutting depth percentages, as shown in FIG 3, the
percentage
depth when the warpage tends to be gentle is taken as the linear cutting
percentage.
Preferably, the cutting depth is selected as 62.5%-75% of the plate thickness.
The
numerical value at point a after cutting is recorded, and the change amount of
the
value at the point a is obtained as the warpage of the plate.
(3) measuring the warpage of plates with different thicknesses to obtain a
relationship
between the residual stress and the warpage; obtaining, by fitting a curve, a
quadratic
equation: y=ax2+bx+c, where x is residual stress, y is warpage, and a, b, c
are fitting
coefficients.
(4) cutting the metal plate on the basis of established functional
relationship between
the residual stress and the warpage, measuring the warpage y under a specific
linear
cutting percentage, and calculating the residual stress according to a
formula, wherein,
as shown in FIG 4, the distribution of the residual stress under different
plate
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thicknesses and warpages can be obtained.
As shown in FIGs 5-8, a device for measuring residual stress release
deformation
amount of a thick metal plate comprises a clamping apparatus, wherein the
clamping
apparatus comprises a base 1, a fixing rod 2, a displacement testing seat 3
and a
displacement testing means 4. The base comprises a first base plate 5, two
vertical
baffles 6 and 6', a connecting plate 7 and a pressing plate 8, wherein the
first base
plate is a horizontally arranged rectangular plate, and the two vertical
baffles are
vertical rectangular plates, one end of the first base plate being fixedly
connected with
the vertical baffle 6, the other end of the first base plate being fixedly
connected with
the vertical baffle 6', and bolt holes being formed in the two vertical
baffles,
respectively, one side edge of the first base plate being fixedly connected
with one
end of the connecting plate, the first base plate and the connecting plate
forming a T
structure, the connecting plate being an elongated plate, an upper plate
surface of the
elongated plate being stepped, the other end of the connecting plate being
provided
with a connecting hole, the pressing plate being a rectangular plate, the
pressing plate
being positioned on an upper surface of the two vertical baffles, the pressing
plate
being provided with a through hole corresponding to the bolt hole of the two
vertical
baffles in position, the pressing plate being connected with the two vertical
baffles
through bolts 17, and the bolts being preferably hexagon screws, wherein the
connecting plate can also cushion the sample to be tested by adopting a
cushion block
and other methods, so that additional deformation of the sample to be tested
caused by
the pressing force of the pressing plate is avoided. The fixing rod is
preferably a
cylindrical rod, while a lower end of the fixing rod is inserted into the
connecting hole
of the connecting plate to be fixedly connected with the other end of the
connecting
plate. One end of the displacement testing seat is sleeved outside the fixing
rod, and
the other end of the displacement testing seat is connected with a lower end
of the
displacement testing means. In particular, the displacement testing seat has a
structure
which comprises a supporting plate, both ends of the supporting plate being
provided
with through holes, the lower end of the displacement testing means being
inserted
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into the through hole at one end of the supporting plate, and the fixing rod
being
inserted into the through hole at the other end of the supporting plate.
Preferably, the
through holes at both ends of the supporting plate are bolt holes, the lower
end of the
displacement testing means being provided with a thread, and the lower end of
the
displacement testing means being screwed into the bolt hole at one end of the
supporting plate to be connected with the supporting plate. The fixing rod is
provided
with a thread, and is screwed into the bolt hole at the other end of the
supporting plate
to be connected with the supporting plate.
Another structure of the displacement testing seat is provided that: the
displacement
testing seat comprises a first collet 9 and a second collet 10 connected with
each other,
the clamping ends of the two collets facing outwards, the first collet being
clamped to
a lower portion of the displacement testing means, the second collet being
clamped to
the fixing rod, and the ends of the two collets being fastened through
fastening bolts
18. The displacement testing means can adopt other contact and non-contact
displacement testing means, preferably a dial gauge.
The device further comprises a deformation testing platform, wherein the
deformation
testing platform comprises a second base plate 11, a fixing plate 12, a first
clamping
block 13 and a second clamping block 14; the second base plate being a
horizontal
rectangular plate, the fixing plate being a vertical rectangular plate, a
lower end of the
fixing plate being fixedly connected with one end of an upper plate surface of
the
second base plate, and a plurality of connecting holes being formed in a plate
surface
of the fixing plate. The first clamping block and the second clamping block
are
vertical plates, one end of the first clamping block being fixedly connected
with one
end of a plate surface of the fixing plate, and a lower end of the first
clamping block
being fixedly connected with an upper plate surface of the second base plate.
The
second clamping block is arranged opposite to the first clamping block, one
end of the
second clamping block being provided with a bolt hole corresponding to the
connecting hole of the fixing plate in position, one end of the second
clamping block
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provided with the bolt hole being connected with the plate surface of the
fixing plate
through a bolt, and a lower end of the second clamping block being fixedly
connected
with an upper plate surface of the second base plate. The clamping apparatus
is
positioned on the upper plate surface of the second base plate, and one end of
the base
of the clamping apparatus is positioned between the first clamping block and
the
second clamping block.
In use, the sample 15 to be tested is placed in the base of the clamping
apparatus, and
the connecting bolts of the pressing plate and the two vertical baffles are
screwed
tightly. The sample to be tested is fixed in the base of the clamping
apparatus, and a
position of the dial gauge is adjusted by adjusting a position of the
displacement
testing base, so that a measuring head of the dial gauge contacts a surface of
the
sample to be tested, and the measuring head is preferably slightly pressed
down by
1-3 mm. Then the clamping apparatus is placed on the second base plate of the
deformation testing platform horizontally, one end of the base of the clamping
apparatus being positioned between the first clamping block and the second
clamping
block, and a position of the second clamping block being adjusted to clamp the
device.
Then the sample to be tested is cut using a linear cutting machine 16, wherein
the
residual stress of the sample to be tested (in a quenching state, a pre-
stretching state
and an aging state) is a surface compressive stress and a central tensile
stress state
distribution, so that the sample to be tested is bent towards one side which
is cut first.
The compression and bending deformation triggers the dial gauge, and the
deformation amount of the sample to be tested at a specific linear cutting
depth is
obtained by calculating a reading difference of the dial gauge before and
after linear
cutting. An integral level of the residual stress inside the aluminum alloy
thick plate is
judged according to the deformation difference under the same linear cutting
depth.
The materials which can be tested by the device are structures such as cutting
plates,
belts, extruded materials and pipes, and are not limited to specific sizes.
The tested
materials are all materials that can be removed using low external forces and
are not
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limited to specific metal material and non-metal material varieties. The
method for
releasing residual stress adopts a method for removing materials with low
external
force, and comprises linear cutting and electric spark.
The foregoing description is only one example of implementation of the present
disclosure and is not intended to limit the disclosure. It should be noted
that other
equivalent modifications may be made by those skilled in the art in light of
the
technical teachings of this disclosure, or the present disclosure can be
applied to other
occasions without modification, which can also achieve the technical objects
of the
present disclosure and shall be covered by the protection scopes thereof.
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