CN111950096B - Method for identifying influence coefficient of ultrasonic vibration on material stress - Google Patents

Method for identifying influence coefficient of ultrasonic vibration on material stress Download PDF

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CN111950096B
CN111950096B CN202010687291.1A CN202010687291A CN111950096B CN 111950096 B CN111950096 B CN 111950096B CN 202010687291 A CN202010687291 A CN 202010687291A CN 111950096 B CN111950096 B CN 111950096B
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stress
area
boundary
shear
ultrasonic vibration
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CN111950096A (en
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陈雪林
何道广
丁撼
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Central South University
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    • G06—COMPUTING; CALCULATING OR COUNTING
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    • G06F30/00—Computer-aided design [CAD]
    • G06F30/10—Geometric CAD
    • G06F30/17—Mechanical parametric or variational design
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    • G16C—COMPUTATIONAL CHEMISTRY; CHEMOINFORMATICS; COMPUTATIONAL MATERIALS SCIENCE
    • G16C60/00—Computational materials science, i.e. ICT specially adapted for investigating the physical or chemical properties of materials or phenomena associated with their design, synthesis, processing, characterisation or utilisation
    • G—PHYSICS
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    • G06F—ELECTRIC DIGITAL DATA PROCESSING
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Abstract

The invention discloses a recognizerThe method for determining the influence coefficient of the ultrasonic vibration on the stress of the material comprises the following steps of: s1, dividing the chips contacted with the cutter rake face into a shearing area and a sliding area according to the contact characteristics of the cutter rake face and the chips, and obtaining the stress of the contact area of the cutter rake face and the chips; s2, obtaining a boundary A of the shearing area and the sliding area1A2Positive stress σ ofA1A2And shear stress τA1A2(ii) a S3, obtaining a boundary CA1Normal stress of
Figure DDA0002588034520000011
And shear stress
Figure DDA0002588034520000012
S4, acquiring the positive stress sigma of the boundary BCBCAnd shear stress τBC(ii) a S5, according to boundary BC, CA1，A1A2And obtaining the influence coefficient of the ultrasonic vibration. According to the invention, the stress state of each shearing unit under ultrasonic vibration is established by analyzing the influence rule of the ultrasonic vibration on the stress-strain state of each unit in the shearing area, and the influence coefficient of the ultrasonic vibration on the material flow stress is quickly and accurately identified, so that a foundation is laid for analyzing the physical phenomenon in the cutting process, predicting the cutting force and cutting heat.

Description

Method for identifying influence coefficient of ultrasonic vibration on material stress
Technical Field
The invention relates to the field of machining, in particular to a method for identifying an influence coefficient of ultrasonic vibration on material stress.
Background
The ultrasonic vibration assisted machining can obviously reduce the cutting force and the cutting temperature, improve the stability in machining, prolong the service life of a cutter and improve the machining efficiency, and is widely used for machining various high-strength and high-hardness materials. In order to accurately evaluate the cutting force and the cutting heat in the ultrasonic vibration assisted machining, the influence coefficient of the ultrasonic vibration on the material stress in the cutting process needs to be accurately obtained. The existing prediction models of cutting force and cutting heat are all cutting force coefficients obtained through cutting experiments, and the cutting force and the cutting heat are calculated according to the cutting force coefficients. The cutting force coefficients of different ultrasonic vibration parameters are different, and the cutting parameters under the influence of the ultrasonic vibration also have obvious difference on the cutting force and the heat. In order to improve the prediction accuracy of cutting and heat, the influence coefficient of the ultrasonic vibration on the material stress needs to be accurately obtained. The influence coefficients of the existing ultrasonic vibration on the material are obtained through ultrasonic vibration stretching and compressing experiments, a plurality of specific samples need to be prepared to carry out a plurality of groups of ultrasonic stretching and compressing experiments, the ultrasonic vibration is obtained through comparing with the change data of the material stress along with strain under the conventional condition, and the obtained flow stress influence coefficients of the ultrasonic vibration on the material and the material stress coefficients in the ultrasonic vibration auxiliary cutting processing have certain difference.
Disclosure of Invention
The present invention is directed to solving at least one of the problems of the prior art. Therefore, the invention provides a method for identifying the stress influence coefficient of the material caused by ultrasonic vibration, which can accurately and conveniently obtain the stress influence coefficient.
The method for identifying the influence coefficient of the ultrasonic vibration on the stress of the material comprises the following steps: s1, dividing the chips contacted with the cutter rake face into a shearing area and a sliding area according to the contact characteristics of the cutter rake face and the chips, and obtaining the stress of the contact area of the cutter rake face and the chips; s2, obtaining a boundary A of the shearing area and the sliding area1A2Positive stress σ ofA1A2And shear stress τA1A2(ii) a S3, obtaining a boundary CA of the contact between the shearing area and the front cutter face of the cutter1Normal stress of
Figure BDA0002588034500000021
And shear stress
Figure BDA0002588034500000022
S4, obtaining the positive stress sigma of the boundary BC of the shearing areaBCAnd shear stress τBC(ii) a S5, according to boundary BC, CA1，A1A2And obtaining the influence coefficient of the ultrasonic vibration.
According to some embodiments of the invention, in step S1, the stress state of the tool rake face and chip contact area is as follows:
under a normal stress of
Figure BDA0002588034500000023
Shear stress of
Figure BDA0002588034500000024
Wherein sigmasIs the positive stress yield strength of the material;
lxthe distance from the target point to the end point of the contact length of the cutter and the chip;
τsis the yield shear stress of the workpiece material, and k is a constant;
l1the contact length of the shearing area and the front cutter face of the cutter is shown;
l2the contact length of the slippage area and the front tool face of the tool is shown; mu.ssIs the coefficient of friction of the material.
According to some embodiments of the invention, in step S2, the boundary a1A2Positive stress σ ofA1a2And shear stress τA1A2The calculation process of (2) is as follows:
s21, according to the stress state of the contact area between the tool rake face and the cutting chips obtained in the step S1, the compressive stress sigma of the sliding area between the tool and the cutting chips can be obtained4And shear stress τ4，
Figure BDA0002588034500000031
Figure BDA0002588034500000032
S22, by applying σ thereto4And τ4Is integrated to obtain FσAnd FτI.e. by
Figure BDA0002588034500000033
Figure BDA0002588034500000034
S23, obtaining F according to the stress balance of the chip areaτ4And Fσ4；
S24, dividing the boundary A1A2Comparing the normal force with the tangential force and the area of the boundary, σ is obtainedA1A2And τA1A2I.e. by
Figure BDA0002588034500000035
Figure BDA0002588034500000036
Wherein A is1A2Is a boundary A1A2B is the width of the tool;
Fσand FτRespectively positive force and tangential force of the tool to the chip sliding area;
Fσ4and Fτ4The boundary A1A2 is the positive force and the tangential force, respectively, for the chip slip region.
According to some embodiments of the present invention, the force balance formula of the x direction and the y direction can be derived according to the force balance of the shearing area as follows:
stress in the x direction: fx＝0＝Fσcosα+Fτsinα-Fσ4sinφfi-Fτ4cosφfi；
Force is applied in the y direction: fy＝0＝Fσsinα+Fτcosα-Fσ4cosφfi-Fτ4sinφfi；
Solving the following steps:
Figure BDA0002588034500000037
Figure BDA0002588034500000038
φfialpha is the cutter rake angle, the shear angle of the material flow.
According to some embodiments of the invention, length A1A2Can be obtained from the following equation:
Figure BDA0002588034500000041
φinh is the undeformed chip thickness for the inflow angle of the sheared material.
According to some embodiments of the invention, in step S4, the positive stress σ of the boundary BCBCAnd shear stress τBCThe calculation process of (2) is as follows:
according to the stress balance of the shear zone region, there are
0＝Fx＝(Fσ4sinφfi-Fτ4cosφfi)+(Fσ5cosα-Fτ5sinα)+(-Fσ1sinφin+Fτ1cosφin)
0＝Fy＝(Fσ4cosφfi-Fτ4sinφfi)+(Fσ5sinα-Fτ5cosα)+(-Fσ1sinφin+Fτ1sinφin) And positive pressure F of boundary BC can be obtainedσ1With tangential force Fτ1Then applying a positive pressure Fσ1With tangential force Fτ1Dividing by the area of the boundary BC to obtain the positive stress sigma of the boundary BCBCAnd shear stress τBCI.e. by
Figure BDA0002588034500000042
Figure BDA0002588034500000043
h is the undeformed chip thickness, phi is the shear angle, and b is the tool width.
According to some embodiments of the invention, the specific steps of step S5 are as follows:
acquiring normal stress and shear stress on the shear band according to the parameters acquired in the steps S2, S3 and S4; obtaining a relational expression of the influence coefficients of the normal stress, the shear stress and the material stress according to the correction model of the normal stress and the shear stress;
and calculating the material stress influence coefficient according to the relational expression.
According to some embodiments of the present invention, the normal stress and the shear stress on the shear band are obtained according to the parameters obtained in steps S2, S3 and S4 as follows:
Figure BDA0002588034500000051
Figure BDA0002588034500000052
lsto length of the cutting zone, /)x1Is the vertical distance from the point on the cropped area to the boundary CA 1.
According to some embodiments of the invention, the corrected models for normal stress and shear stress are:
Figure BDA0002588034500000053
Figure BDA0002588034500000054
Tm，Tr，Eu，
Figure BDA0002588034500000055
εvrespectively the melting point, room temperature, ultrasonic vibration energy density, strain rate and strain of the material;
Figure BDA0002588034500000056
is a reference strain rate; a is the yield strength, T, of the materialvIs ultrasonic vibrationTemperature of the sheared area in the motion-assisted machining; b is the hardening modulus of the material, C is the strain rate coefficient of the material, n is the hardening coefficient of the material, m is the thermal softening coefficient of the material, and d and e are the influence coefficients of the ultrasonic vibration on the flow stress of the material.
The method for identifying the influence coefficient of the ultrasonic vibration on the stress of the material according to the embodiment of the invention at least has the following technical effects: by analyzing the influence rule of the ultrasonic vibration on the stress-strain state of each unit in the shearing area, the stress state of each shearing unit under the ultrasonic vibration is established, and the influence coefficient of the ultrasonic vibration on the material flow stress is quickly and accurately identified, so that a foundation is laid for analyzing the physical phenomenon in the cutting process, predicting the cutting force and cutting heat.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The invention is further illustrated by the following examples in conjunction with the drawings.
FIG. 1 is a schematic view of the contact area between the chip, the workpiece, and the tool;
FIG. 2 is a schematic view of the chip portion of the chip sliding region in contact with the tool under force;
FIG. 3 is a schematic view of a deformation of a sheared area;
FIG. 4 is a force diagram of a shear band;
fig. 5 is a force state diagram of the shearing area unit.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.
In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "transverse," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," "circumferential," and the like are used in an orientation or positional relationship indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the device or element so referred to must have a particular orientation, be constructed and operated in a particular orientation, and are not to be construed as limiting the invention. Furthermore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified.
Referring to fig. 1 to 5, a method for identifying an influence coefficient of ultrasonic vibration on a stress of a material according to an embodiment of the present invention includes the following steps:
s1, dividing the chips contacted with the cutter rake face into a shearing area and a sliding area according to the contact characteristics of the cutter rake face and the chips, and obtaining the stress of the contact area of the cutter rake face and the chips;
s2, obtaining a boundary A of the shearing area and the sliding area1A2Positive stress σ ofA1A2And shear stress τA1A2；
S3, obtaining a boundary CA of the contact between the shearing area and the front cutter face of the cutter1Normal stress of
Figure BDA0002588034500000071
And shear stress
Figure BDA0002588034500000072
S4, obtaining the positive stress sigma of the boundary BC of the shearing areaBCAnd shear stress τBC；
S5, according to boundary BC, CA1，A1A2And obtaining the influence coefficient of the ultrasonic vibration.
The method comprises the following specific steps:
the method is characterized in that an ultrasonic vibration assisted cutting machining test is firstly carried out, wherein a cutter is made of high-speed steel, color change is easy to occur in the high-temperature accumulated in a shearing area of the high-speed steel, obvious scratch is easy to occur in a friction area between cutting chips and the cutter, and data can be conveniently identified and obtained.
At a certain cutting speed, the length of the cutter with obvious color change of the cutting edge of the front cutter surface in the cutter is analyzed, namely the distance extending from the cutting edge to the cutter body. This is due to the fact that the chip is in contact with the rake face of the tool, which inevitably increases the friction between the tool and the chip, the temperature of the frictional contact of which inevitably increases, which inevitably changes the color of the cutting edge of the tool, i.e. the length of the cutting edge which changes color but has no scratch marks, is set to ln. The length of the rake face of the tool extending from the cutting edge to the tool body direction with a significant scratch is analyzed as lfThe discoloration reaction corresponds to the shear zone of the chip, corresponding to the bond zone of the tool.
Because the workpiece material of the cutter and the chip bonding area is subjected to shear deformation and is a main cutting force concentration area, a large amount of cutting heat is accumulated at the position, the surface color of the cutter is changed due to the cutting heat, and the chips and the cutter do not slide relatively, so that no scraping mark exists, and the length l of the cutter and chip bonding area of the part of area is equal to the length l of the cutting tool1I.e. by
ln＝l1。
Because the workpiece material in the contact friction area of the cutter and the chips generates certain shearing deformation, the chips slide on the cutter, the temperature is increased to a certain extent, but the color of the front cutter surface of the cutter cannot be changed, the chips slide on the cutter, and the cutter has scraping marks, namely the depth of the scraping marks from the cutting edge to the cutter body direction is the sliding friction length of the chips on the cutter, namely lf＝l2。l1And l2Can be obtained by cutting experiments and then directly measuring on the cutter, and the average value can be obtained by multiple groups of experiments. This slip friction corresponds to the slip region of the chip, corresponding to the scraping region on the tool.
In a first step S1, the stress of the contact area of the tool and the chip in the ultrasonic vibration-assisted machining is calculated. During the cutting processThe contact area of the tool and the chip (chip) can be divided into two parts, wherein the first part is a bonding area, the bonding area is an area on the tool corresponding to a chip shearing area, the shearing area is an area where the material to be removed is subjected to shearing deformation in the cutting process, the bonding area is in contact with the shearing area, the bonding area is an area on the tool, the contact length of the area and the tool is set to be l1The length of this portion is set to the distance from the edge to the midpoint of the contact length. In this region, the positive pressure perpendicular to the tool rake face is sufficiently great that the chip can undergo bending deformation, the frictional stress reaching the yield stress of the material, the plastic deformation occurring in this part of the region. The second partial area is a scraping area and corresponds to a chip sliding area. The contact stress distribution of the two regions is as follows, and the positive stress is shown by the formula:
Figure BDA0002588034500000081
the shear stress is as follows:
Figure BDA0002588034500000091
wherein sigmasThis parameter is the positive stress yield strength of the material for maximum compressive stress, which is determined by the material properties and is known. Mu.ssThe coefficient of friction of the material is usually taken to be 0.03,lxτ is the distance from the end point of the contact length of the workpiece (workpiece) and the cutting tool (cutting tool) to the target pointsIs the yield shear stress of the material of the workpiece, is the material property of the material, determined by the material, and k is a constant determined by the property between the workpiece and the tool.
In a second step S2, the stress of the boundary A1A2 of the cut region (shear band area) is solved.
In the chip slip region, the chip portion in contact with the cutter, which is mainly subjected to the force applied thereto by the shear band (shear band), has a positive stress and a shear stress which are respectively:
Figure BDA0002588034500000092
Figure BDA0002588034500000093
σ4and τ4The normal stress and the shear stress applied to the slip region at the boundary A1A2 are respectively.
The positive and tangential forces in the slip region of the tool against the chip are respectively:
Figure BDA0002588034500000094
Figure BDA0002588034500000095
dlxis a whole and represents the contact length infinitesimal.
According to the force balance of the chip area, the force is synthesized into an x-y coordinate system for balancing, and the x direction has the following components:
Fx＝0＝Fσcosα+Fτsinα-Fσ4sinφfi-Fτ4cosφfi；
the y direction is as follows:
Fy＝0＝Fσsinα+Fτcosα-Fσ4cosφfi-Fτ4sinφfi；
the positive force and the tangential force in the slip region of the chip at the boundary A1A2 are Fτ4And Fσ4To find out
Figure BDA0002588034500000101
Figure BDA0002588034500000102
Since the shear angle difference is very small, 0-3 °, its effect on the sine-cosine value is very small, neglecting its effect on the chip thickness. The length of the boundary A1A2 is approximately:
Figure BDA0002588034500000103
Figure BDA0002588034500000104
wherein, a rapid stop test in the cutting process is carried out, and the microstructure is analyzed and tested, and the shearing angle difference is found, delta phi = phifi-φmid＝φmid-φinWhen the temperature is 3 degrees, the temperature is consistent with the experimental result. I.e. delta phi =3o。φfi、φmidAnd phiinRespectively is the material outflow shearing angle in the cutting process, the shearing angle in the inflow process and the shearing material inflow angle.
Figure BDA0002588034500000105
Where α is the tool rake angle, h is the undeformed chip thickness, hcThe thickness of the machined chip can be averaged by continuously measuring the thickness of the chip 25. Phi is the shear angle, phimidAnd (4) equivalence. From which phi can be obtainedmidDue to Δ φ =3oThen phi can be further obtainedfiAnd phiinThe value of (c).
Comparing the normal force and the tangential force of the boundary A1A2 with the area of the boundary, the normal stress and the tangential stress can be obtained, namely
Figure BDA0002588034500000111
Figure BDA0002588034500000112
And step 3, solving the stress of the shearing area boundary CA 1.
In the shearing region corresponding to the bonding region in the chip-tool contact region, which is a deformation region where the chip contacts the workpiece, the positive and tangential forces are Fσ5，Fτ5And then.
Figure BDA0002588034500000113
Figure BDA0002588034500000114
The stress of CA1 can be obtained according to the formula of the first step, i.e. its positive stress
Figure BDA0002588034500000115
As shown in the formula:
Figure BDA0002588034500000116
shear stress
Figure BDA0002588034500000117
As follows:
Figure BDA0002588034500000118
l2≤lx≤l1+l2
and step 4, solving the stress of the shearing area boundary BC.
According to the stress balance of the shearing area, there are
0＝Fx＝(Fσ4sinφfi-Fτ4cosφfi)+(Fσ5cosα-Fτ5sinα)+(-Fσ1sinφin+Fτ1cosφin)
0＝Fy＝(Fσ4cosφfi-Fτ4sinφfi)+(Fσ5sinα-Fτ5cosα)+(-Fσ1sinφin+Fτ1sinφin)
Depending on the force balance of the shear band, a positive pressure F at the boundary BC may be obtainedσ1With tangential force Fτ1。
The area s of the boundary BC is
Figure BDA0002588034500000121
Wherein the tool also has a width, defined as b, and an area, s, corresponding to the boundary BC, of the area of the tool in contact with the chip.
Comparing the normal force and the tangential force with the area, the positive stress sigma can be obtainedBCAnd shear stress tauBC。
Figure BDA0002588034500000122
Figure BDA0002588034500000123
And step 5, solving the influence coefficient of the ultrasonic vibration on the material stress.
And (4) obtaining the ultrasonic vibration influence coefficient according to the stress states of the boundaries BC, CA1 and A1A 2.
According to the stress state of the boundary BC, CA1, A1A2, the average normal stress and shear stress on the shearing area are obtained, and the length l of the shearing areasIs composed of
Figure BDA0002588034500000124
The positive stress (strength) and the shear stress (strength) on the shear band are respectively:
Figure BDA0002588034500000125
Figure BDA0002588034500000126
wherein lx1Is the vertical distance of the point on the clipping region to the boundary CA 1.
The number of points on the shear band is determined according to the unknown number, namely n unknown numbers are provided, and n points on the shear band are taken to ensure equation solution and obtain the influence coefficient of the ultrasonic vibration on the material stress.
The shear strength of the material is corrected by the model
Figure BDA0002588034500000127
Tau is the shearing stress intensity of the material, and the formula is to calculate the shearing stress intensity of a certain point in a shearing area.
The stress intensity of the material is corrected by the model
Figure BDA0002588034500000131
The formula is the stress intensity of a certain point in a shearing area for the positive stress intensity of the material. Where a, B, C, n, m are parameters in the model, respectively, are known and are determined by the properties of the material. T ism，Tr，Eu，
Figure BDA0002588034500000132
εvRespectively the melting point, room temperature, ultrasonic vibration energy density, strain rate and strain of the material,
Figure BDA0002588034500000133
is a reference strain rate. A is the yield strength, T, of the materialvThe temperature of the shear zone in the ultrasonic vibration assisted machining. B is the hardening modulus of the material, C is the strain rate coefficient of the material, n is the hardening coefficient of the material, m is the thermal softening coefficient of the material, d, e are ultrasonic vibrationsCoefficient of influence of motion on material flow stress.
Under ultrasonic processing conditions, the temperature of the shear band can be expressed approximately as
Figure BDA0002588034500000134
α tool rake angle, φ and shear angle.
Wherein eta is the thermal coefficient for converting strain energy into heat, tau is the shear flow stress of the material in a shear zone, psi is the thermal softening coefficient of the material,
Figure BDA0002588034500000135
is the specific heat capacity of the material.
Heat ratio lambda transferred to the workpiece materialsComprises the following steps:
Figure BDA0002588034500000136
wherein R istIs dimensionless coefficient of heat
Figure BDA0002588034500000137
Where ρ is the density of the material, ctIs the heat transfer coefficient of the material, csThe specific heat coefficient of the material, v and h are the cutting speed and the undeformed chip thickness (corresponding to the cutting depth), respectively.
Ultrasonic vibration energy Density Eu，
Eu＝ρc(v1)2；
Where ρ is the density of the material to be processed, c is the propagation velocity of sound in the material to be processed, v1In order to shear the moving speed of the material, i.e. the shear velocity (the speed of movement of the chip relative to the workpiece) v1。
Figure BDA0002588034500000141
And obtaining the ultrasonic vibration influence coefficient d, e according to the stress state of the boundary BC, CA1 and A1A 2.
With reference to the general equation defining the hot tack elasticity of a material, then
Figure BDA0002588034500000142
εij,
Figure BDA0002588034500000143
Strain, strain rate, temperature at a point in the shear zone
The strain hardening coefficient, strain rate hardening coefficient, and thermal softening coefficient of the material are respectively derived as follows:
Figure BDA0002588034500000144
then the material strain strengthening coefficient, strain rate strengthening coefficient and thermal softening coefficient under ultrasonic processing are respectively as follows:
Figure BDA0002588034500000145
Figure BDA0002588034500000146
Figure BDA0002588034500000147
Figure BDA0002588034500000151
and (4) according to the stress states of the boundaries BC, CA1 and A1A2, simultaneously establishing all equations of the step S5 to obtain the ultrasonic vibration influence coefficients d and e.
In the description of the specification, reference to the description of "one embodiment," "some embodiments," "an illustrative embodiment," "an example," "a specific example" or "some examples" or the like means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
While embodiments of the invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims (7)

1. A method for identifying the influence coefficient of ultrasonic vibration on the stress of a material is characterized by comprising the following steps:
s1, dividing the chips contacted with the cutter rake face into a shearing area and a sliding area according to the contact characteristics of the cutter rake face and the chips, and obtaining the stress of the contact area of the cutter rake face and the chips;
s2, obtaining a boundary A of the shearing area and the sliding area1A2Positive stress σ ofA1A2And shear stress τA1A2；
S3, obtaining a boundary CA of the contact between the shearing area and the front cutter face of the cutter1Normal stress of
Figure FDA0003801581090000011
And shear stress
Figure FDA0003801581090000012
S4, obtaining the positive stress sigma of the boundary BC of the shearing areaBCAnd shear stress τBC；
S5, according to boundary BC, CA1，A1A2Obtaining the influence coefficient of the ultrasonic vibration according to the stress state;
the specific steps of step S5 are as follows:
acquiring normal stress and shear stress on the shear band according to the parameters acquired in the steps S2, S3 and S4;
obtaining a relational expression of the influence coefficients of the normal stress, the shear stress and the material stress according to the correction model of the normal stress and the shear stress;
calculating and obtaining a material stress influence coefficient according to the relational expression;
the correction models of the normal stress and the shear stress are respectively as follows:
Figure FDA0003801581090000013
Figure FDA0003801581090000014
Tm，Tr，Eu，
Figure FDA0003801581090000021
εvrespectively the melting point, room temperature, ultrasonic vibration energy density, strain rate and strain of the material;
Figure FDA0003801581090000022
is a reference strain rate; a is the yield strength, T, of the materialvTemperature of the sheared area in the ultrasonic vibration assisted machining; b is the hardening modulus of the material, C is the strain rate coefficient of the material, n is the hardening coefficient of the material, m is the thermal softening coefficient of the material, and d and e are the influence coefficients of ultrasonic vibration on the flow stress of the material.
2. The method for identifying the coefficient of influence of ultrasonic vibration on the stress of a material according to claim 1, wherein: in step S1, the stress state of the contact region between the tool rake face and the chip is as follows:
under a normal stress of
Figure FDA0003801581090000023
The shear stress is:
Figure FDA0003801581090000024
wherein sigmasIs the positive stress yield strength of the material;
lxthe distance from the target point to the end point of the contact length of the cutter and the chip;
τsis the yield shear stress of the workpiece material, and k is a constant;
l1the contact length of the shearing area and the front tool face of the tool is shown;
l2the contact length of the slippage area and the front tool face of the tool is shown;
μsis the coefficient of friction of the material.
3. The method for identifying the influence coefficient of ultrasonic vibration on the stress of the material as claimed in claim 2, wherein in step S2, the boundary A1A2Positive stress σ ofA1A2And shear stress τA1A2The calculation process of (2) is as follows:
s21, according to the stress state of the contact area between the tool rake face and the cutting chips obtained in the step S1, the compressive stress sigma of the sliding area between the tool and the cutting chips can be obtained4And shear stress τ4，
Figure FDA0003801581090000031
Figure FDA0003801581090000032
S22, by checking the value σ4And τ4Integration to obtain FσAnd FτI.e. by
Figure FDA0003801581090000033
Figure FDA0003801581090000034
S23, obtaining F according to the stress balance of the chip areaτ4And Fσ4；
S24, dividing the boundary A1A2Comparing the normal force with the tangential force and the area of the boundary, σ is obtainedA1A2And τA1A2I.e. by
Figure FDA0003801581090000035
Figure FDA0003801581090000036
Wherein A is1A2Is a boundary A1A2B is the width of the cutter;
Fσand FτRespectively positive force and tangential force of the tool to the chip sliding area;
Fσ4and Fτ4Are respectively boundary A1A2Positive and tangential forces on the chip's slip region.
4. The method for identifying the influence coefficient of the ultrasonic vibration on the stress of the material as claimed in claim 3, wherein the stress balance formula in the x direction and the y direction is obtained according to the stress balance of the shearing region as follows:
stress in the x direction: fx＝0＝Fσcosα+Fτsinα-Fσ4sinφfi-Fτ4cosφfi；
Force is applied in the y direction: fy＝0＝Fσsinα+Fτcosα-Fσ4cosφfi-Fτ4sinφfi；
Obtaining:
Figure FDA0003801581090000041
Figure FDA0003801581090000042
φfialpha is the cutter rake angle, the shear angle of the material flow.
5. The method for identifying the coefficient of influence of ultrasonic vibration on the stress of a material according to claim 3, wherein: length A1A2Can be obtained from the following equation:
Figure FDA0003801581090000043
φinh is the inflow angle of the shearing material, and h is the undeformed chip thickness;
φfialpha is the tool rake angle, which is the shear angle of the material flow.
6. The method for identifying the coefficient of influence of ultrasonic vibration on the stress of a material according to claim 2, wherein: in step S4, the positive stress σ of the boundary BCBCAnd shear stress τBCThe calculation process of (2) is as follows:
according to the stress balance of the shear zone region, there are
0＝Fx＝(Fσ4sinφfi-Fτ4cosφfi)+(Fσ5cosα-Fτ5sinα)+(-Fσ1sinφin+Fτ1cosφin)
0＝Fy＝(Fσ4cosφfi-Fτ4sinφfi)+(Fσ5sinα-Fτ5cosα)+(-Fσ1sinφin+Fτ1sinφin) And positive pressure F of boundary BC can be obtainedσ1With tangential force Fτ1Then applying a positive pressure Fσ1To tangential force Fτ1Dividing by the area of the boundary BC to obtain the positive stress sigma of the boundary BCBCAnd shear stress τBCI.e. by
Figure FDA0003801581090000044
Figure FDA0003801581090000045
h is the undeformed chip thickness, phi is the shearing angle, b is the tool width, phiinIs the shear material inflow angle; fxAnd FyRespectively stressing the shearing area in the x direction and the y direction; alpha is the cutter rake angle and s is the area of the boundary BC; fσ4And Fτ4Are respectively a boundary A1A2Positive and tangential forces to the slip region of the chip; cropped region boundary CA1The positive pressure and the tangential force are respectively Fσ5、Fτ5，φfiThe shear angle of the material flow.
7. The method for identifying the influence coefficient of ultrasonic vibration on the stress of the material according to claim 1, wherein the parameters obtained in steps S2, S3 and S4 are used to obtain the normal stress and the shear stress on the shear band as follows:
Figure FDA0003801581090000051
Figure FDA0003801581090000052
lsto length of the cutting zone, /)x1For point-to-boundary CA on a cropped area1The vertical distance of (a).
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