Prediction method for torsional stress of heterogeneous forge piece

Abstract

The invention belongs to heterogeneous material performance testing, and particularly relates to a method for predicting torsional stress of a heterogeneous forge piece. The method for predicting the torsional stress of the heterogeneous forge piece comprises the following steps: substituting the radius of the heterogeneous forge piece, the radius of a core performance uniform area of the heterogeneous forge piece and the gradient change slope of the torsional stress into a formula A to obtain the torsional stress of the heterogeneous forge piece. According to the method, the torsion stress gradient coefficient is introduced, integration and averaging are carried out on the non-uniform region of the heterogeneous forging, and the problems that the torsion performance of the large forging is inconvenient to measure and inaccurate in prediction are solved.

Description

Technical Field

[0001] The present invention belongs to the performance testing of heterogeneous materials, and particularly relates to a method for predicting the torsional stress of heterogeneous forgings. Background Art

[0002] After forging and heat treatment, the structure of the forging shows a non-uniform state from the surface to the interior; after annealing of the forging, due to decarburization and burning loss on the surface, there is a completely decarburized layer or a partially decarburized layer, which is inconsistent with the structure of the core; after quenching of the forging, due to the problem of hardenability of the material, the surface structure is harder and has higher strength, and the core structure is inconsistent with the surface structure because it is not completely quenched. According to the basic assumptions of mechanics of materials, that is, the material is continuous, uniform and isotropic, these components are all treated as having a uniform structure in design. However, the assumption that the structure is uniform does not conform to the actual situation.

[0003] At present, the measurement method of the torsional performance of forgings is to take samples at key parts of the forging, and it is required that the torsional samples are at a certain distance from the surface, and the torsional performance of local samples is detected to characterize the torsional performance of the whole component. This prediction method only detects local performance and does not consider the influence of different tissue parts on the surface and the core on the torsional performance, and cannot accurately characterize the torsional performance of the forging. Similarly, as a forging, the front axle of an automobile is heterogeneous from the inside to the outside due to complex deformation heat treatment during the forging process, so its performance is also heterogeneous, which leads to the existing test methods being unable to accurately test the torsional stress of the front axle of an automobile.

[0004] Therefore, the traditional method has the following problems. 1. Using the test data of several key points to represent the overall performance, the data collection is incomplete and the performance test is inaccurate; 2. The size of the sample is restricted by the overall size of the component. When the overall size of the component is too large or too small, the torsional sample is a non-standard sample, and the performance test fluctuates greatly; 3. When processing parts of different sizes with the same process, the torsional stress needs to be measured separately, and there is no unified and simple prediction method. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for predicting the torsional stress of heterogeneous forgings, and the prediction method provided by the present invention can accurately test the torsional stress of the front axle of an automobile.

[0006] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a method for predicting the torsional stress of heterogeneous forgings, including the following steps:

[0008] Substitute the radius of the heterogeneous forging, the radius of the region with uniform core performance of the heterogeneous forging, the torsional stress, and the slope of the change of the torsional stress gradient into formula A to obtain the torsional stress of the heterogeneous forging;

[0009]

[0010] In formula A, is the torsional stress of the heterogeneous forging; k is the slope of the change in the torsional stress gradient in the heterogeneous region of the heterogeneous forging; r is the radius of the heterogeneous forging, in mm; r0 is the radius of the region with uniform properties at the core of the heterogeneous forging, in mm; τ max0 is the torsional stress in the region with uniform properties at the core of the heterogeneous forging, in MPa.

[0011] Preferably, the shape of the heterogeneous forging is a round bar.

[0012] Preferably, the radius of the heterogeneous forging is 3 mm to 100 mm.

[0013] The present invention provides a method for predicting the torsional stress of a heterogeneous forging. By introducing the torsional stress gradient coefficient of the heterogeneous region and performing integration and averaging calculations on the heterogeneous region, the present invention solves the problems of inconvenient measurement and inaccurate prediction of the torsional properties of large forgings. Moreover, the prediction method provided by the present invention has small fluctuations in the performance test of the torsional stress of the heterogeneous forging, is not affected by the part size, can quantitatively and qualitatively characterize the torsional stress with a unified and accurate theoretical model, has simple steps, a short performance test period, and good consistency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0015] Figure 1 is a schematic diagram of the relationship curve between the performance parameters and the radius of the heterogeneous forging;

[0016] Figure 2 is a schematic diagram of the method for predicting the torsional stress of the heterogeneous forging in Embodiment 1. DETAILED DESCRIPTION

[0017] The present invention provides a method for predicting the torsional stress of a heterogeneous forging, including the following steps:

[0018] Substitute the radius of the heterogeneous forging, the radius of the region with uniform properties at the core of the heterogeneous forging, the torsional stress, and the slope of the change in the torsional stress gradient into formula A to obtain the torsional stress of the heterogeneous forging;

[0019]

[0020] In formula A, is the torsional stress of the heterogeneous forging; k is the slope of the change in the torsional stress gradient in the heterogeneous region of the heterogeneous forging; r is the radius of the heterogeneous forging, in mm; r0 is the radius of the region with uniform properties at the core of the heterogeneous forging, in mm; τ max0 is the torsional stress in the region with uniform properties at the core of the heterogeneous forging, in MPa.

[0021] In the present invention, the shape of the heterogeneous forging is preferably a round bar shape; the heterogeneous forging is divided into a region with uniform properties at the core and a non-uniform region according to homogeneity. The present invention has no special requirements for the preparation method of the heterogeneous forging. In a specific embodiment of the present invention, the preparation method of the heterogeneous forging is preferably: heating the forging and then performing quenching, tempering, and shot peening in sequence; the heating is preferably medium-frequency induction heating; the heating temperature is preferably 1150 °C; the quenching temperature is preferably 850 °C; the tempering temperature is preferably 615 °C.

[0022] In the present invention, the radius of the heterogeneous forging is preferably 3 mm to 100 mm, and specifically can be 5 mm, 10 mm, 20 mm, 40 mm, 60 mm, or 90 mm.

[0023] The computer principle of formula A in the present invention is as follows: First, the present invention calculates the shear strain γ at a distance ρ from the center of the circle on the cross-section of the heterogeneous forging ρ , and the calculation formula is as shown in formula I:

[0024]

[0025] In formula I, ρ is the radius of the heterogeneous forging, in mm; is the angle of twist, in rad; x is the length, in mm.

[0026] Second, the present invention calculates the torsional stress τ at a distance ρ from the center of the circle on the cross-section of the heterogeneous forging ρ , and according to Hooke's law of shear, the calculation formula is as shown in formula II:

[0027] τ ρ = Gγ ρ Formula II;

[0028] In formula II, G is the shear modulus, in MPa.

[0029] Substituting formula I into formula II, the calculation formula is as shown in formula III:

[0030]

[0031] Third, the present invention calculates the torque T on the cross-section of the torque heterogeneous forging, and the calculation formula is:

[0032]

[0033] Using I p to represent the polar moment of inertia of the cross-section about the center of the circle O, then Equation IV is written as:

[0034]

[0035] Fourthly, the present invention calculates the angle of twist per unit length of the heterogeneous forging From Equation IV, we get:

[0036]

[0037] In Equation V, v is the Poisson's ratio, E is the modulus of elasticity, and the unit is MPa.

[0038] During the processing of metal parts, it is very easy to cause non-uniform properties of the modulus of elasticity, Poisson's ratio, and torsional strength from the surface to the interior; decarburization and burning loss result in weak surface properties of metal parts, and after a certain thickness, the properties improve and stabilize at a certain level; after quenching, the metal parts have a hardened structure on the surface, with high surface hardness and poor toughness, and after a certain thickness, the properties tend to be stable. The present invention studies the situation of decarburization and burning loss. Assuming a heterogeneous forging with a radius of r, the performance parameters (modulus of elasticity, Poisson's ratio, torsional strength) within a radius of r0 are P0, and in the region with a radius from r0 to r, the performance parameters change regularly with the radius, approximately expressed as P = P0 + k(x - r0), and the curve shape is as Figure 1 shown.

[0039] Then, the modulus of elasticity E of the heterogeneous forging is:

[0040]

[0041] In Equation VI, k1 is the slope of the gradient change of the modulus of elasticity in the non-uniform region of the heterogeneous forging; E0 is the modulus of elasticity in the region with uniform properties at the core of the heterogeneous forging, and the unit is MPa; x is the radius, and the unit is mm.

[0042] The Poisson's ratio v of the heterogeneous forging is:

[0043]

[0044] In Equation VII, k2 is the slope of the gradient change of the Poisson's ratio in the non-uniform region of the heterogeneous forging; v0 is the Poisson's ratio in the region with uniform properties at the core of the heterogeneous forging; x is the radius, and the unit is mm.

[0045] The torsional stress τ of the heterogeneous forging is:

[0046]

[0047] In Formula VIII, k is the slope of the change in torsional stress gradient; τ max0 is the torsional stress in the uniform region of the properties of the core of the heterogeneous forging, with the unit of MPa.

[0048] Substituting Formula VI and Formula VII into Formula V, we get:

[0049]

[0050] Fifth, the present invention calculates the torque T of the heterogeneous forging, and the calculation formula is as shown in Formula X:

[0051]

[0052] Sixth, the present invention calculates the maximum torsional stress τ max of the heterogeneous forging, which is obtained from Formula I and Formula IV:

[0053]

[0054] On the edge of the circular cross-section of the heterogeneous forging, the maximum value of ρ is r, and it can be known that the maximum torsional stress τ max is:

[0055]

[0056] Seventh, the present invention calculates the average torsional stress of the heterogeneous forging with a radius of r, and the calculation formula is as shown in Formula XIII:

[0057]

[0058] To further illustrate the present invention, the solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0059] Embodiment

[0060] The heterogeneous forging with a radius of 5 mm is stratified from the surface to the non-uniform region of the core, and is stratified at 3 mm, 4 mm, and 5 mm from the inside to the outside, with a single-layer thickness of 1 mm for the stratification. Specimens are prepared, and the torsional stress-strain curves of each layer of specimens are detected. The torsional stress at the same torsional angle is taken, and the results are shown in Table 1:

[0061] Table 1 Test results of the torsional strength of the heterogeneous forgings in Embodiments 1-2

[0062]

[0063]

[0064] Embodiment 1

[0065] According to the test results of the heterogeneous forgings in Table 1, Example 1 obtained the change in torsional strength gradient, specifically as shown in Equation m:

[0066] τ max = 150 - 54(r - 3), Equation m;

[0067] In Equation m, k is -54.

[0068] Substitute r = 5 and r0 = 3 into Equation A, and we get which is 123.3 MPa, only differing from the overall torsional strength result in Table 1 by 4.49%, showing good agreement.

[0069] Example 2

[0070] According to the test results of the heterogeneous forgings in Table 1, Example 2 obtained the change in torsional strength gradient, specifically as shown in Equation n:

[0071] τ max = 213 - 55(r - 3), Equation n;

[0072] In Equation n, k is -55.

[0073] Substitute r = 5 and r0 = 3 into Equation A, and we get which is 201.8 MPa, only differing from the overall torsional strength result in Table 1 by 5.65%, showing good agreement.

[0074] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, not all of them. Other embodiments can be obtained based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for predicting the torsional stress of a heterogeneous forging, characterized in that, Including the following steps: Substitute the radius of the heterogeneous forging, the radius of the uniform property area at the core of the heterogeneous forging, the torsional stress, and the change slope of the torsional stress gradient into formula A to obtain the torsional stress of the heterogeneous forging; In formula A, is the torsional stress of the heterogeneous forging; k is the slope of the change in the torsional stress gradient in the heterogeneous region of the heterogeneous forging; r is the radius of the heterogeneous forging, in mm; r0 is the radius of the region with uniform properties at the core of the heterogeneous forging, in mm; τ max0 is the torsional stress in the region with uniform properties at the core of the heterogeneous forging, in MPa.

2. The prediction method according to claim 1, wherein The shape of the heterogeneous forging is a round bar.

3. The prediction method according to claim 2, wherein The radius of the heterogeneous forging is 3 mm to 100 mm.

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