SU1760432A2 - Method of determining porosity - Google Patents

Abstract

The invention relates to the testing of the physicomechanical properties of materials, in particular, to methods for determining porosity, and can be used in determining the porosity of both plastic and brittle materials. The purpose of the additional invention is to improve the accuracy of porosity determination. This goal is achieved by limiting the range of loads on the indenter with a convex line of the profile of the working surface, the results of the introduction of which determine the porosity and the load of the onset of crack formation. In order to enable the determination of the porosity of brittle, highly rigid materials and the expansion of the load range, the sample is additionally heated. 2 hp ff, 1 ill.

Description

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The invention relates to the field of studies of the physicomechanical properties of materials, namely, methods for determining porosity by introducing an indenter, and can be used to determine the porosity of both ductile and brittle materials.

According to the main author. St. USSR No. 1631250 (application No. 4409959/28. Positive decision of September 28, 1989, second method) is a method for determining porosity, which consists in introducing two indenters (conical or pyramidal) with different angles at the top of the sample under investigation. , for each indenter, an embedding diagram is written in the load-depth of the indenter. the geometrical parameters of the recovered prints are measured (after removal of the load), the depths of the unrestored and recovered prints are determined. restored and unrestored hardness when introducing the first and second indenters. the slopes of the initial sections of the unloading branches of the embedding diagrams, which, taking into account the apex angles and types of indenters (conical or pyramidal), determine the porosity of the material under study.

The method is based on the phenomenon of plastic compaction of a porous material under the indenter imprint and the formation of plastic pile around the imprint. The disadvantages of the method include the low accuracy of determining the porosity in the event of the occurrence of cracks as a result of the insertion of the indenter, as well as the limited range of materials studied.

The aim of the invention is to improve the accuracy of determining the porosity.

The goal is achieved by the fact that in the method of determining the porosity by the author.

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St. USSR 1631250 (Application No. 4409959/28, positive decision of September 28, 1989, second method) according to the invention, indenters are inserted into the sample before cracking.

In order to expand technological capabilities by expanding the class of materials studied and the range of depths of the indenter, as well as to further improve the accuracy of the sample is heated.

In order to increase reliability, acoustic emission signals are recorded to fix the cracking.

The drawing shows the indenter deployment diagram in the coordinates of the load-depth of the indenter, where P is the load on the indenter at the time of the start of unloading;

h is the depth of the unrestored indenter footprint (the depth of the indenter is maximal);

Hb is the depth of the restored indenter footprint (the depth of the footprint after removal of the load);

hy is the displacement of the indenter, defined as the difference between the maximum insertion depth of the indenter (h) and the coordinate point of intersection of the tangent to the initial unloading branch of the indenter with the axis of the insertion depth of the indenter;

O) - (h - ny) - the value of the indentation imprint depth recovery after unloading.

The method is carried out as follows.

Under the loads excluding the formation of cracks, two indenters (conical or pyramidal) with different apexes are inserted into the sample under study. At the same time, for each indenter, an embedding diagram is written in the load-depth coordinates of the indenter. The geometrical parameters of the recovered prints are measured (after removal of the load). The depths of unrestored and restored prints, restored and unrestored hardness when introducing the first and second indenters, the slopes of the initial sections of the branches of the unloading diagrams of the introduction of indenters are determined, which, taking into account the apex angles and types of indenters (conical or pyramidal), judge the material being studied. The porosity is determined by the formulas:

P 3 -eib;

Abjffi o-C + oЈ1b In

i- “m

one

(()

where p is the porosity;

R

H-p- - unrestored hardness (Fh is the area of the unrestored indenter footprint);

p H - restored hardness

(F is the area of the restored indenter footprint);

p is the half angle at the apex of the conical indenter or half the angle of the pyramidal indenter, equivalent

a conical indenter (equivalence is determined by the equality of the areas of the projections of the prints with the same depth of indentation of the indenters);

K 0.78 - for a conical indenter;

K ° 0.63 - for pyramidal indenter;

Indices 1 and 2 are for the first and second indenters, respectively.

If necessary, increase

the accuracy of determining the porosity of a material with large pores or determining the porosity of a brittle material, the sample is heated, thereby increasing its plasticity, and then indenters are introduced at a stabilized temperature.

In order to increase reliability when indenters are introduced, acoustic emission signals are recorded that are judged by the appearance of cracks. Results obtained

in case of formation of cracks, they are excluded from consideration, and during repeated tests they reduce the level of maximum load on the indenter.

Claims (3)

1. Method of determining the porosity of materials by aut. St. Nt 1631250, characterized in that, in order to improve accuracy, indenters are introduced into the sample to cracking. 2. A method according to claim 1, characterized in that, in order to expand the technological capabilities, the sample is heated. 3. The method according to claims 1 and 2. From the band and to the fact that, in order to increase reliability, acoustic emission signals are recorded for fixing the cracking. Load. Depth-Indenter Depth