RU2240358C1 - Metal strengthening method - Google Patents

Abstract

FIELD: plastic working of metals, possibly in aircraft- and ship-making machine engineering.

SUBSTANCE: method comprises steps of tensioning shaft blanks before twisting them until accumulated deformation "e"; according to preset yield limit for shearing τ_0.3 (at allowance for plastic shearing 0.3%) determining accumulated deformation by deciding equation

where ς(e) = Aeⁿ - material yielding curve, β(e) = β₀ + (1 -β₀)exp(c e) - parameter characterizing Bauschinguer effect; A, n, β₀, c -material characteristics.

EFFECT: possibility for enhancing constructional strength of shafts of metals non subjected to heat treatment, improved reliability of machines and mechanisms with such shafts.

1 dwg

Description

The invention relates to the field of metal forming in relation to increasing the strength of thermally not hardened metals and can be used in aircraft, shipbuilding and mechanical engineering.

A known method of hardening metals for which the Bausinger effect is realized, including plastic stretching of the workpiece to cumulative deformation e ₁ and subsequent compression in the direction opposite to stretching to cumulative deformation e ₂ . In this calculation, these deformations are established that provide isotropic hardening of the metal.

The disadvantage of this method is the impossibility of its application to increase the strength of the shafts working under alternating torsion.

The invention is aimed at increasing the strength of shafts made of thermally not hardened metals working in alternating torsion.

This is achieved by the fact that the shaft blanks are stretched to accumulate deformation e. In this case, according to a given conditional yield strength for shear τ _0.3 (with a plastic shear tolerance of 0.3%), the accumulated deformation is determined by solving the equation

при сжатии предварительно растянутого образца до накопленной деформации е к напряжению растяжения σ_р(е) при этой деформации; σ(е) - кривая течения металла.Here β (e) is a parameter characterizing the Bausinger effect and is equal to the ratio of the conditional yield strength

when compressing a pre-stretched sample to accumulated deformation e to tensile stress σ _p (e) under this deformation; σ (e) is the metal flow curve.

For convenience of calculation, the flow curve and the function β (e) in this ratio are approximated in the form

where A is the characteristic of the material, determined by statistical processing of the experimental material flow curve σ = σ (e) and having the dimension MPa;

n <1 is a dimensionless exponent that determines the nonlinearity of the function σ = σ (e) and is established in the same way as A; β ₀ - asymptotic value of the parameter β, determined by statistical processing of the experimental values β = β (e); c is a constant set in the same way as β.

The graph depicted in the drawing shows the dependence of the tangential stresses τ on the accumulated strain e.

It was established [2, 3] that the initial isotropic material during its plastic deformation becomes anisotropic due to the Bausinger effect. To assess the increased value of the yield strength for shear τ _0.3 , the theory of anisotropic hardening by G. Buckhaus [3] is used, according to which relation (1) is obtained.

The proposed method of hardening shafts is confirmed by the following example.

For testing, cylindrical specimens with a diameter of 17 mm and a working length of 110 mm were made of austenitic steel (thermally unreinforced) 1X18H9T. The characteristics of the specified steel: A = 1450 MPa; n is 0.3; β ₀ = 0.38; c = -100; σ _T = 385 MPa.

Before twisting, in order to assess the yield strength for shear τ _0.3, samples (3 pieces each) were stretched to a strain e = 0.040; 0.084; 0.126.

The graph shown in the drawing shows: 1 - shear diagram τ (e), constructed according to the theory of plasticity of Mises [2]

2 - dependence (1); 3 - yield strength of the material for shear under reverse torsion, determined according to formula (2) for estimating the parameter, characterizing the Bausinger torsion effect taking into account relation (5)

points are the experimental values of the yield stress on shear during torsion of plastically stretched samples.

From the analysis of the data presented, it follows that with an increase in the preliminary deformation (е≥0.03), a monotonic increase in the yield strength τ _0.3 with respect to the initial value τ _T is observed and the calculation data with a deviation of ~ 10% are confirmed by experiment. For example, with a strain of e = 0.2, an increase in the yield stress on shear relative to τ _T is ~ 54%. The yield strength, taking into account the Bausinger effect (5) at strains e ≤ 0.2, turns out to be lower than the initial yield strength τ _T = 220 MPa.

Thus, the proposed method of hardening metals is quite accurately confirmed by experiment, and in this regard, its use in industry will increase the structural strength of shafts made for one reason or another from thermally non-hardened metals.

Sources of information

1. A.S. RF №1756368, C 21 D 7/00 (prototype).

2. Del G. D. Technological mechanics. - M.: Mechanical Engineering, 1978, p.23-36.

3. Backhouse G. Anisotropy of hardening. Theory versus experiment. Izv. USSR Academy of Sciences, MTT, 1976, No. 6, pp. 120-129.

Claims (1)

A method of increasing the strength of metals with the property of the manifestation of the Bausinger effect, including plastic tension and determination of accumulated deformation, characterized in that according to a given yield strength τ _0.3 , for working with alternating torsion of the shafts, the accumulated deformation e is determined by solving the equation

where σ (е) = Ае ⁿ is the metal flow curve; β (e) = β ₀ + (1-β ₀ ) exp (s · e) - parameter characterizing the Bausinger effect; And, n, β ₀ , C - characteristics of the material.