SU1649245A1 - Method for determining stress epure in parts worked by cold-work hardening - Google Patents

Abstract

The invention relates to the control of stresses in machine parts. The purpose of the invention is to improve the accuracy of stress diagram determination by meeting the same conditions when machining the surfaces of the part and the control plate. Control plates made of the material of the part are bent and fixed to the gesture - up to the mandrels up to the curvature of the maximum allowable elastic bending, and after the surface plastic deformation processing, the plot of residual stresses is determined, for example, by by layer etching, in the control plate with the smallest positive difference between the pre-bending created and the surface hardening remaining after the treatment, and the curvature 4 of the yoke, s

Description

This invention relates to the control of stresses in machine parts.

The purpose of the invention is to improve the accuracy of determining the stress profile due to the observance of the same conditions when machining the surfaces of the part and the control plate.

Fig. 01 is a diagram of the fixing of the control plate; FIG. 02 is the graphs of the maximum allowable radius of curvature of the elastic bending of the plate as a function of its thickness; FIG. 3 is a plot of normal stresses in a plane along the section of the plate; Fig. 4 shows diagrams of normal stresses in a plane along the thickness of the ppastically deformed layer of the plate and part.

The method is carried out as follows

Control plates 1 (Fig, 1) of different thickness (for example, I, 2., 4, 6 mm) are bent on a rigid mandrel 2 having a radius of curvature R, and fixed in this position with screws 3. Then the free (convex; side of each the plates are processed by a specified method of IND on the surface treatment modes of the part. After the work hardening, the plates are fastened and removed from the mandrel. The plate having the smallest positive difference between the curvature created by the pre-bend and the remaining after the processing of the IND and detaching is examined General stresses

But the plot of residual stresses in the control plate is judged on the stresses applied by surface hardening to the reinforced surfaces of the part “

The maximum curvature of the elastic curvature is determined by the formula ЭЬц $ г 1 / Кизг, where Кцзг The radius of curvature of the bend, on which the control plate 1 is previously bent and according to which the mandrel 2 is made (Fig.).

From the hypothesis of flat sections and the condition of equality of the deformation on the most jiee loaded fibers to the elastic limit of the material follows

 - L - -

 R 11;

(SOUTH ll

where the deformation of the elastic limit of the material; H is the thickness of the plate. The magnitude of Sg in the linear-power approximation of the material hardening curve is determined as follows:

e, A

U)

e EhJ K

I

n shows the reinforcement modules on the linear and nonlinear sections of the dependence of stresses on the strain:

a measure of the degree of control of material in a non-linear region of dependence. With a cylindrical bending plate

. °

En s

where E, K is the elastic modulus and the hardening modulus of the uniaxial tension dependence; 45 fU - Punch coefficient Pre-bend on the maximum possible curvature of the elastic bend is caused by the following: the greater the curvature, the tighter the plate is pressed to the mandrel. However, when the curvature exceeds the elastic, the error in determining the residual stresses in the plate is influenced by the zone of plastic deformations squeeze on. the concave side of the plate. Therefore, the preliminary bending should be the greatest, but within the elastic deformations 0

five

Yu

15

0

five

jo

five

°

5 g

From equation (I), it follows that the greatest curvature of the elastic bending ta depends on the plate thickness. As an example, in Fig. 02, the f (H) plots are plotted for materials D16T, V95T, ZOHGSNAo

Thus, for each of the thicknesses of a specific material, a mandrel should be formed that is shaped to the corresponding radius of curvature. Kieg. The set of thickness of the control plates and mandrels is explained by the fact that the S1D processes can be both low-intensity and large for SH-processes with low intensity. or in soft modes, thin plates are more sensitive, and thicker control plates are needed for high intensity P11D processes.

The pitch of the control plate to the mandrel provides the necessary elasticity of impact on its surface by the machining bodies. Moreover, this elasticity remains until the gap between the control plate and the mandrel is formed. When fixing the plate, this gap is almost impossible to fix. If the plate is unbendable after unfastening, then there was a tight fit during processing, and if it is bent (the curvature increases), then there is no tight fit. However, too much unbending is undesirable, as it reduces the sensitivity of the proposed method. The most favorable case is when , but very little. Practically for any method of operation in any modes of its implementation, two, a maximum of three sets of mandrels and plates are enough. After processing, comrade, wherein razgib smallest plate, and further analysis is performed "

In addition to increasing the impact elasticity, pre-bending increases and the compliance of the stress pattern of the stress condition applied by the work hinge with the residual stress profile in the control plate. This is explained as follows.

During bending, a stress pattern appears over the cross section of the plate (Fig. 3a), which is balanced by the moment in

5164

touched her ends. Processing the PDD of an unloaded plate with the same absorbed impact energy as the parts gives a non-equilibrium in strength and moment diagram that occurs only in plastically deformed layers, 0 0 at a depth h PA from the surface (Fig. 36). In the proposed method this diagram is the desired, In the control plate, fixed, curved and processed through convex fibers, the appearing plot (Fig. 3a) is a combination of the first two. Numerous experiments have confirmed (I), with plastic deformation of the surface layers, the stresses formed by the work hardening are almost independent of the initial, after

Consequently, the thickness of part of the diagram (Fig36, c) should be practically the same. At the same time, the internal forces change significantly, which leads to a reduction in the moment of plate sealing. Subsequent detachment by this moment loads surface-glued layers with the formation of the final residual stress diagram (figs) 0 This diagram will subsequently be determined by the experimental Additional load of plastically deformed cold layers. the nonlinear dependence law (j 6 according to which even significant deformations give a very small increase in stresses; therefore, the residual stress diagram in the plastically deformed layers of the control plate, it will differ little from that created by the surface work hardening of relatively rigid (practically deformable when machining) parts (fig. 03b). Thus, the degree of correspondence of the residual stresses to the riveted control plate subjected to preliminary bending, with the stresses formed in the surface layers of relatively rigid parts, is much higher than with the processing of a plate fixed on a flat plate (mandrel) with However, obstacle still is, which is taken into account as follows obrazomo

20

25

thirty

the thickness of the plastically deformed layer, which is determined by the plot of residual stresses (at the point of transition of compressive residual stresses to tensile stresses) о From equations (4) we find

& Veer

4 Е -, Н 3. Н ,, ..

 - f (-) .. (b)

| C

pl

Equation (5) is the control for the residual stress plot in the plate under study. Equivalent (P / b) EXP residual stress plot (JOCT (Z)

35 eGGCT Z dZ 6, should be equal to the value (P / b) oc g If their values are different, then the coefficient C (P / L) OCT is determined

4Q / (P / b) gKtn, correcting the experimentally constructed residual stress diagram

Equation (b) determines the resultant of internal forces in the plasticity of the deformed layers, found from the final plate shape. Let us establish this resultant in the active loading components of the control plate.

50 when processing LEEDs are formed by stresses applied and reduced by working hardening. In this case, the stresses taken are stresses created by preliminary bending, the Uniform internal forces introduced by (P / L). Remaining with after releasing the PLA and the LRA

Since the host curvature is associated with the deflection boom of the control plate f based on the measurement and the moment of internal surface hardening, the moments (M / b) ppd and UM / b are defined by the following relations:

these forces are Moog and a single internal force (P / b) oc.f as follows:

2 |

aC ° sg

- 2 M0Јt

 l (nn „: y

 Bridge. En i

(four)

five

0

five

Where

IT 1V

one

LH 12

Uh

- reduced modulus of elasticity of the plate, deformed by surface hardening}

IL

the moment of inertia of the section (L - width; H - thickness);

the thickness of the plastically deformed layer, which is determined by the plot of residual stresses (at the point of transition of compressive residual stresses to tensile stresses) о From equations (4) we find

& Veer

4 Е -, Н 3. Н ,, ..

 - f (-) .. (b)

| C

pl

Equation (5) is the control for the residual stress plot in the plate under study. Equivalent (P / b) EXP residual stress plot (JOCT (Z)

The factor JGeCT Z dZ 6 must be equal to the value (P / b) oc g. If their values are different, then the coefficient C (P / L) OCT is determined.

/ (P / b) gKtn, correcting experimentally plotted residual stress diagram

Equation (b) determines the resultant of internal forces in plastically deformed layers, found from the final plate shape. Let us establish this resultant by the components of the active loading of the test plate.

during processing, LIDs are formed by stresses applied and reduced by hardening. In this case, the stresses taken are the stresses created by the internal forces introduced by (P / L) and the LR / LRA.

surface hardening, give moments (M / b) ppp and UM / b defined by the following relations:

№ ,, 1-1 S-isi 4m

VnrsD Vntro 2 b

- J E

(

Considering that

mosg Mnrw

p X, w (f

+ Dm,

from the joint solution (4), (5), (7), (8) after integrating the second of the JQ equations (7), we find

D} E And

VnnD (1-рО (Н-би

t a-) g ah

(9)

-G

) B

 -%. (H-2hn,),

Calculated by the equation (Y), the ena-1iin (P / b,) ,,,,, is compared with the corrected resultant residual voltage (P / b), the coefficient K is found to be 1p sho1 / h. P / b) P ,. / O / b. 3) Taking into account which experiment the opyur (Z) (the first graph of fig 4) is rearranged into the plot

about

n. (Z) (second graph in FIG. 04),

ppp

Claims (1)

Coefficient k is like. the scale would be the scale of these graphs, and: - the formula of the invention The method for determining the stress-jr plot in parts treated with a workpiece surface hinge, including one side of a test pad made of part material, on the part surface treatment modes, and the determination of stresses in the part by deflection boom after processing and residual stresses in the control plate, is different from the fact that, in order to test the accuracy of the stress plots, by observing the same conditions when machining the surfaces of the part and the control plate, Q S 0 five 0 5 5 use a set of control plates of various thickness, before processing they are bent and fixed on rigid mandrels up to the curvature of the maximum allowable elastic bend, processing i is subjected to the convex side of the control plate, after which the control plate with the smallest linear difference between the created pre-bend and the remaining processing and breaking the curvature, experimentally determine the plot of the residual stresses in the plate and the resultant of this plot (P / b) Etsp, the resultant these forces (R / b) of the PDP surface hardening is determined by the formula (P / b) - gy-l2 (P / b) PPD - (l-jKMH-h) j, 3f V hfujaeujr / m 9b -l 2 (1 + (U) ( where (P / b) P (1 resultant internal forces, BiiocHNibix; into the plate by surface hardening, kg / mm; E is the modulus of elasticity of the material of the plate, KP / MM J H is the thickness of the control plates, mm; U - Punch coefficient; h PD - the thickness of the plastically deformed layer, MMJ f - the deflection of the control plate, mm; ai - base of arrow measurement deflection of the control plate, mm; nv pre-bend curvature of the control plate, 1 / mm, and the stress plot in the part is determined based on the ratio (P / b). / Wbm, Fia1 D "G zotA V95T 1 2 3 4 5 d Nmm FIG. 2 5 8 in