RU2247355C1 - Device for testing long specimens for plastic compression - Google Patents

Abstract

FIELD: testing engineering.

SUBSTANCE: device comprises base, axially aligned loading and bearing clamps for clamping the specimen, and race and sectors mating over the conical surfaces and kinematically coupled with the base and specimen. The cone angle of the conical surfaces of the race and sectors is determined by solving the set of equations proposed.

EFFECT: enhanced precision of testing.

2 dwg

Description

The invention relates to the field of determining the physicomechanical properties of materials and can be used in various sectors of the national economy (mechanical engineering, aircraft manufacturing, shipbuilding, etc.) to study the resistance of metals to plastic deformation.

A device is known [1] for compression tests of long specimens. It contains a base, loading and supporting grips coaxially mounted in it for fixing the sample in them along its ends, mating clips and sectors kinematically connected along cylindrical surfaces with the base and the sample, respectively, to each other along conical surfaces. A deforming force is applied to these grips and thereby compresses the specimen without longitudinal bending due to the presence of the cage and sectors. In this case, the main geometric parameter of the device, which provides compression of the sample under linear stress conditions without longitudinal bending, is the cone angle of the conical surfaces along which the cage and sectors are interconnected.

The disadvantages of this device include the low accuracy of compression of long specimens under linear stress conditions due to the inability to determine the optimal value of the cone angle of the conical surfaces of the cage and sectors.

The invention is aimed at improving the accuracy of compression of long specimens under linear stress conditions by determining the optimal value of the angle of taper of the conical surfaces of the cage and sectors.

This is achieved by the fact that the angle of conicity of the conical surfaces α of the cage and sectors is determined by solving the system of equations

where α is the angle of taper; f ₁ f ₂ are the friction coefficients in kinematic pairs, respectively, the clip is the base and the clip are sectors; l ₀ , r _0, respectively, the initial length and radius of the sample; Q is the total weight of the sectors; L is the length of the sectors; q is the intensity of the distributed load on the sample; And, e ₀ , n - characteristics of the sample material; e 'is the upper limit of integration.

In figure 1. presents a design diagram of a device for determining the angle of taper α; figure 2 shows the design diagram of a compressible sample to determine the intensity of the distributed load q.

The device, the circuit of which is shown in figure 1, includes the following main elements: loading 1 and supporting 2 captures, between which a sample 3; base 4; supporting sectors 5 with coaxial cylindrical and conical surfaces; holder 6 with coaxial conical and cylindrical surfaces.

These elements form the following interconnected kinematic pairs: sectors 5 - holder 6 along a conical surface with an angle α; holder 6 - base 4 along a cylindrical surface of diameter D; sample 3 - sectors 5 along a cylindrical surface of diameter d.

When a compressive force P is applied to the loading grip 1, the sample 3 begins to deform. An increase in its transverse size will cause the distributed load of intensity q (it can be assumed constant over the entire length L of the contact of the sector with the sample) on the sectors 5, as a result of which the latter will move in the radial direction , causing the movement of the cage 6 upward relative to the base 4. The free movement of the cage 6 upward will be prevented by the friction forces T ₁ and T ₂ acting respectively in the kinematic pairs of both yma - base and clip - sectors, as well as the weight of the clip Q (see Fig. 1).

To assess the taper angle α of the mating conical surfaces of the ferrule and sectors at which the device provides uniform compression of the sample without curvature, the equilibrium condition of all the forces acting in the device is considered, as a result of which equation (1) is obtained.

To determine the intensity of the distributed load q, the technique described in [2] is used. Figure 2 shows the calculated compression scheme of the sample. Here 1, 2 - respectively, loading and supporting with the original design length l ₀ and diameter d ₀ captures; 3 - sample; 4 - distributed load of intensity q caused by the action of sectors on the sample and preventing the curvature of the latter.

The criterion of the positive operation of the additional loads dP and dq dz [2], which in this case is written as

Here, δy = f (z) is the curved axis of the sample at the moment of the beginning of its curvature, the equation of which is represented by the relation

where dl is the increment of the sample length; the sign “-” is adopted due to the fact that the distributed load is always directed towards the direction of curvature of the workpiece axis and the loss of its stability. The magnitude of the compressive force can be determined by the formula

Here F is the current cross-sectional area of the sample;

the approximated equation of the flow curve, where A, e ₀ , n are the characteristics of the sample material; e - accumulated deformation.

After substituting (4) - (6) in (3), we obtain relation (2) to determine the intensity of the distributed load q.

Further, by solving the system of equations (1) and (2) for given values of all the parameters included in it, the conic angle α of the conical surfaces is determined, the integration limit e 'can be taken equal to ~ 0.02, corresponding to a relative deformation of ~ 0.02.

Thus, the proposed method for determining the taper angle of the mating conical surfaces of the ferrule and sectors will allow you to assign the optimal values of the geometric dimensions of all the main elements of the device and thereby provide the possibility of deformation of the sample without distortion with sufficient accuracy, as well as design the appropriate die tooling in relation to production conditions.

SOURCES OF INFORMATION

1. USSR Copyright Certificate No. 1810786, G 01 N 3/08, 04/23/1993 Bull. Number 15.

2. Hwan D.V. Resistance to plastic upsetting of a long cylindrical workpiece. Engineering Engineering, 1998, No. 3, pp. 40-41.

Claims (1)

A device for testing plastic compression of long specimens containing a base, loading and support grips coaxially mounted in the base for securing the specimen at its ends, a clip and sectors conjugated to each other on conical surfaces and kinematically connected respectively to the base and the specimen on cylindrical surfaces, characterized the fact that the taper angle α of the conical surfaces of the cage and sectors is determined by solving the system of equations sinα-f ₂ · cosα = 2 · Q / L · q + 2 · f ₁ + f ₂ ;

where f ₁ , f ₂ are the coefficients of friction in kinematic pairs, respectively, the cage base and the cage sectors; l ₀ , r ₀ - respectively, the initial length and radius of the sample; L is the length of the sectors; A, e ₀ , n - characteristics of the material; Q is the total weight of the sectors; q is the intensity of the distributed load; e 'is the upper limit of integration; e - accumulated deformation.

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