RU2451282C1 - Method for determining mechanical characteristics of materials - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: introduction of spherical indenter to tested material is performed at continuously increasing load, recording of indentation diagram with loading and unloading branches is performed and measurement of residual depth of indent after full unloading is carried out. Indentation diagram recording is performed in "load - elastoplastic approximation of indenter and material" coordinates, load, elastic approximation of material and indenter and residual depth of indent is measured, which correspond to the beginning of decrease of derivative of load function from elastoplastic approximation, and elastic material deformation is subtracted from common elastic approximation.

EFFECT: reducing labour intensity, improving accuracy, efficiency and enlarging functional capabilities of the method.

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Description

The invention relates to the field of measurements and, in particular, is intended for use in the study of the mechanical characteristics of materials.

A known method for determining the mechanical characteristics of materials (see US patent No. 5.133.210, IPC G01 N3 / 42, publ. 07/28/1992), according to which, when indenting a spherical indenter, an indentation diagram is continuously recorded in the coordinates "load - depth", which transform into a certain section of the tensile diagram of the sample in the coordinates of "stress - strain".

The disadvantage of this method is the low accuracy of the determination of stresses.

The closest in technical essence to the invention is a method for determining the mechanical characteristics of materials (see USSR author's certificate No. 1145273, CL. G01N 3/42, publ. March 15, 1985), which consists in introducing a spherical indenter continuously under the material increasing load, measure the load and imprint depth under load, then reduce the load to zero at the moment of the beginning of a direct proportional dependence of the load increment on the increment of the imprint depth, and when re-testing at the end of this curvature values, measure the residual imprint depth, taking into account which the temporary resistance is determined in the first test or uniform deformation in the second test.

The disadvantages of this method are: the complexity, low accuracy, performance and information content.

An object of the invention is to reduce the complexity, increasing accuracy, productivity and expanding the functionality of the method.

This technical problem is achieved by the fact that in the known method for determining the mechanical characteristics of materials, including the introduction of a spherical indenter in the test material with a continuously increasing load, recording an indentation diagram with loading and unloading branches and measuring the residual imprint depth after complete unloading, according to the invention, an indentation diagram is recorded in coordinates "load - elastoplastic approach of the indenter and the material", measure the load, the elastic approach of the ma terial and indenter and the residual imprint depth corresponding to the beginning of the reduction of the derivative of the load function from the elastoplastic approach, the elastic deformation of the material is subtracted from the total elastic approach.

The invention is illustrated by drawings, where in Fig.1 shows a General view of the diagram "load P - elastoplastic approximation α", Fig.2 shows a General view of the diagram "dP / dα - P", Fig.3 shows a functional diagram of a device for implementing the proposed way.

In Fig.1-2, the following designations are adopted: P is the indentation load;

P _K is the indentation load corresponding to the end of loading (at point K);

P _B is the indentation load corresponding to the beginning of a decrease in the derivative of the function P = f (α) (at point B);

h _{In the} residual imprint depth corresponding to the load of R _In ;

h _to - residual imprint depth after complete unloading;

α _to - elastoplastic approach, corresponding to the load R _To ;

α _In - elastoplastic approach, corresponding to the load P _In ;

(α _y ) _k - joint elastic rapprochement of the material and indenter at the load R _K ;

(α _y ) _B - joint elastic rapprochement of the material and indenter at a load of R _In

dP / dα is the derivative of the load function from the elastic-plastic approach.

A device for implementing the proposed method for determining the mechanical characteristics of materials contains a loading mechanism 1, which transfers force to the test material, which is pressed against an indenter mounted on a power rod 2, which is connected to a load measurement sensor 3 and an elastic-plastic proximity sensor 4. The sensors are connected to a shape transducer information 5, the output of which is connected directly to a personal computer 6.

A device that implements a method for determining the mechanical characteristics of materials works as follows.

The loading mechanism 1 introduces a spherical indenter into the test material. In this case, the electric signals from the load sensor 3 and the elastic-plastic proximity sensor 4 are continuously fed to the input of the information form transducer 5, which converts the information and transfers it in digital form to a personal computer 6. During the conversion, an indentation diagram is displayed on the computer screen in real time coordinates “P - α” with loading and unloading branches, and differentiation of the loading branch of the diagram is also performed. According to the obtained diagrams, the personal computer determines the load, the elastic approximation of the material and the indenter and the residual imprint depth corresponding to the beginning of the reduction of the derivative of the load function from the elastoplastic approximation, and subtracts the elastic deformation of the material. Then the following mechanical characteristics of the material are determined:

- The modulus of normal elasticity E _m = f (P _B , (α _y ) _B , R, µ _m µ _sh , E _sh ),

where R is the indenter radius; µ _m and µ _W - Poisson's ratios of the test material and indenter material; E _W - the modulus of elasticity of the material of the indenter;

The coefficient taking into account the ratio of the elastic deformation of the indenter and the elastic deformation of the test material, k = E _W / (E _W + E _m );

- The module of the hardening of the material during indentation in the plastic region Q = f (P _in , h _in , R);

- Unrestored Brinell hardness at the level of temporary resistance (HB _t ) _B = f (P _in , h _in , (α _y ) _B , R, k);

- Coefficient taking into account the ratio of the elastic deformation of the indenter and the elastic deformation of the test material, k;

- Temporary tensile strength σ _B = f ((HB _t ) _c );

- The conditional tensile strength σ _0.2 = f (q);

- Relative residual uniform elongation in tension

δ _p = f (h _in , R).

The entire test process with the image of the indentation diagram and the issuance of a table of values of the mechanical characteristics is automated and takes no more than 3 minutes.

The monograph (see VM Matyunin, operational diagnostics of the mechanical properties of structural materials. A manual for scientific and engineering workers. - M.: Publishing House MPEI, 2006, 214 pp.) Describes in detail the methods and technical means for determining the listed mechanical characteristics . In addition, before conducting the test, an indenter of a radius is selected and pressed in such a way that an imprint is formed with a surface area equal to the change in the initial cross-sectional area of the stretched sample when the same relative deformation during indentation and tension is achieved.

The table shows the test results and determine the mechanical characteristics of steel 20X13 and titanium alloy VT-4 by the proposed method of indenter indentation and a known method of sample tension. The tested materials differ greatly in the modulus of normal elasticity and, as a result, have a different coefficient k, taking into account the ratio of the elastic deformation of the test material and the elastic deformation of the indenter. In this experiment, R = 0.5 mm, E _W = 216000 N / mm ² , µ _m = µ _W = 0.28.

From the table it follows that the maximum relative deviation of the values of the mechanical characteristics determined by the proposed method from the values of the same mechanical characteristics determined by the method of stretching the samples does not exceed ± 5%.

The use of the invention provides a reduction in the complexity, increased accuracy, productivity and expansion of the functionality of the method.

Claims (1)

A method for determining the mechanical characteristics of materials, including introducing a spherical indenter into the test material under a continuously increasing load, recording an indentation diagram with loading and unloading branches and measuring the residual imprint depth after complete unloading, characterized in that the indentation diagram is recorded in the coordinates “load - elastoplastic approximation indenter and material ”, measure the load, the elastic approach of the material and indenter and the residual imprint depth, respectively etstvuyuschie top reducing the derivative function of the load elastoplastic approximation is subtracted from the total convergence of the elastic deformation of the elastic material.

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