SU1747957A1 - Method of detecting tensile stresses - Google Patents

Abstract

The invention relates to load measuring technique and can be used in metallurgy to detect internal tensile stresses in continuous casting of aluminum alloys. The purpose of the invention is to expand the functionality due to the possibility of detecting internal stresses and their intensity. Liquid metal is applied to the surface of the sample by a strip along a line passing through its center, maintained for a period of time that varies during the incubation period, mechanical destruction of the sample is carried out along the line of deposition. the presence and intensity of internal tensile stresses in the plane of destruction are determined by the liquid metal and the length and depth of the trace of the penetrating metal. 1 or 1 tab. ate with

Description

The invention relates to methods for measuring forces / mechanical stresses and can be used in metallurgy, in part, to detect internal dissolving thermal stresses in continuous cast ingots of aluminum alloys.

An optical method of measuring stresses is known, based on the photoelasticity of other materials that are carried out under normal incidence of rays using field risk handlers with circular polarization and a rotating analyzer or a linearly polarized analyzer at two positions, then measured at oblique incidence of rays in one direction in any inclined plane.

The disadvantage of this method is the need to make a photoelastic model and special risk fields, which limits the use of the method under production conditions. Using the method; and it is almost impossible to detect residual internal thermal stresses:

There is also known a method for measuring the stresses of 1 uT | and lhhhhhhhl tires by breaking the specimens.

The disadvantage of this method of measuring stresses is the impossibility of obtaining a picture of internal stresses in a sample over its cross section, therefore this method cannot also be used to determine internal residual thermal stresses.

The most effective approach to the proposed technical essence is the method of detecting surface radial and concentric tensile stresses.

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by applying liquid metals, in particular mercury, to the surface of the article.

However, the known method makes it possible to estimate the direction of the active tensile stresses only on the surface of the product. In the direction of the development of cracks on the product surface, the locations of tensile stresses and their nature can be detected, but this makes it impossible to determine the magnitudes of internal stresses, and even more so the relationships between tensile and compressive stresses over the cross section of the product. The method eliminates the possibility of determining the depth of propagation of internal stresses in the product. In addition, when using a known method, the stress pattern is distorted when 4 surface cracks are found, since the stresses are redistributed and the initial stress distribution pattern changes.

The purpose of the invention is to expand the functionality by detecting internal stresses and their intensity.

The discovery of internal tensile stresses by the proposed method provides the possibility of adjusting the speeds casting directly at the production site.

 The proposed method, in comparison with the known method, makes it possible to detect internal stresses that arise as a result of rapid cooling during continuous casting of ingots of aluminum alloys, which gives fairly accurate results at production levels x.

The need to hold the liquid metal on the surface of the product for some time is explained by the rate of penetration of the liquid metal into the product. Gallium, mercury or alloys of these metals are used as the liquid metal at a temperature not lower than their melting point. This holding time is called the incubation period. When the exposure time of a product with a liquid metal deposited on it is less than the incubation period, the metal does not have time to penetrate into the product and its boundaries do not penetrate into the fracture. If the exposure time corresponds to the incubation period, the liquid metal penetrates deep into the product and is clearly visible in the fracture with the naked eye. Exposure time exceeding the incubation period is impractical, since practically the liquid metal during the incubation period

is inserted into the product and the process stops.

Determine the presence and intensity of internal tensile stresses.

can only be kinked, for which the product is destroyed. A complete picture of the penetration of the metal is obtained under the condition of destruction) in the course of applying the liquid metal, therefore it is necessary to apply

liquid metal strip, the width of which is greater than the thickness of the destructive tool copra or press.

Inspection of the fracture gives1 a clear picture of the penetration of the liquid metal in place

action tensile stresses. The presence of the penetration sites of the liquid metal at the fracture corresponds to the sites of the occurrence of tensile stresses. Thus, a boundary is established between tensile and compressive stresses.

Measuring the depth of penetration of a liquid metal makes it possible to reveal the intensity of tensile stresses.

Based on the measurements, a plot of the action of tensile stresses is constructed (see drawing), at which a greater depth of penetration of the liquid metal corresponds to a higher stress,

The drawing shows the distribution of the internal tensile stresses and the transverse fracture of the round template obtained during the experiment.

The proposed method is carried out in the following sequence:. production of templates from ingots;

applying a liquid metal, such as gallium, on the end surface of the templet, while the ambient temperature should not be higher than the melting point of gallium:

holding at this temperature, the time of which is determined by the incubation period {the incubation period is determined experimentally);

mechanical destruction of the templet, for example on a press, along the line of a liquid metal deposited on the surface; 0 fracture inspection, photographing (if necessary);

measuring the penetration depth of the liquid metal a:

plotting and determining the location of 5 the occurrence and intensity of tensile stresses;

adjustment of the modes of speeds to pour ingots.

Example Of round ingots 165-300 mm of alloys D16. D1.AK6 and AMGZ, cast

in a semi-continuous manner, templates with a height of 40 mm were cut

Gallium strips were applied to the end surface of each template in the form of a 3–5 mm wide line passing through the center of the template. After the templates were kept at room temperature (more than 30 ° C) for 0.1–3 h, they were destroyed on a 0.6 tf press in gallium strips. The resulting kinks on the templates were examined and photographed to reveal the location and depth of penetration of gallium. The points of onset of the action of tensile stresses were determined from the place of penetration of gallium, and the intensity of their action was determined from the depth.

As a result of the experiments, it was established that the location of the points of onset of tensile stresses depends on the casting speed and the diameters of the ingots. The maximum intensity of stresses was observed in the center and, according to a parabolic law, decreased to the edge of the templet. The experiment performed is fully consistent with the theoretical concepts of the nature of the action of tensile stresses.

The results of the experiment to determine the exposure time of liquid gallium

surface templates are given in the table.

From the obtained results it follows that the incubation period for different alloys is different, therefore, the exposure time is a criterion for determining the depth of penetration of the liquid metal, and, consequently, analyzing the places of origin and intensity of tensile stresses.

Claims (1)

Claims of Invention A method for detecting tensile stresses in metals, comprising applying a liquid metal to the sample surface, by changing the surface layer of which stresses are detected, characterized in that, in order to extend the functionality due to the possibility of detecting internal stresses and their intensity, the liquid metal is applied by a strip along the line passing through the center of the sample, is kept for a time equal to the incubation period, then mechanical destruction is performed The sample and the intensity and intensity of internal tensile stresses in the plane of fracture are determined according to the line of deposition of the liquid metal, the length and depth of the trace of the metal penetrating into the sample. Determination of the holding time of liquid gallium on the surface of the templates before destruction on the press  fiffiS-300 Q rassufemia © -;: v  / 7j 0 # e / # ti / Pt u: zff / wut