RU2538419C1 - Method of determination of ultimate tensile strength of dielectric materials during induction heat - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: essence of a method consists in determination of ultimate tensile strength of standard samples at high intensity induction heat of intermediate metal heating element in a heat contact with the tested sample. The method takes into account the specificity of materials use in articles with high heat loads and heating rates. In material operating conditions in such articles a dynamic heating occurs at heating rates 10-100°C/c up to the destruction temperature with total time of heating from several dozens of seconds up to several minutes. As a result the material in operating conditions bears heat loads with smaller duration, than in conditions of mechanical tests of samples using standard methods. Meanwhile the material holding period at high temperature significantly influences its mechanical characteristics. The induction heat allows to perform quick heat of intermediate metal heating element with a possibility of precise heat self-control, that is essential to implement the dynamic heat according to the preselected condition.

EFFECT: decrease of error of determination of mechanical characteristics.

5 dwg

Description

The invention relates to methods for determining the mechanical characteristics of dielectric materials, taking into account the conditions of their use.

A known method for determining the mechanical characteristics of a material when a sample is heated by an electric heater located near the surface of the sample, due to which it is possible to achieve a test temperature of 2500 ° C (Magnitsky I.V., Ponomarev K.A., Mironikhin A.N. Mechanical Testing of Composite Materials at High Temperatures / Materials of the XIX Scientific and Technical Conference of Young Scientists and Specialists. Moscow, Rocket and Space Corporation Energia, November 14-18, 2011). The disadvantage of this method is the use of graphite heaters, which is why tests at temperatures above 650 ° C are carried out in an inert environment, which does not correspond to the operating conditions of the material.

The task of the invention is to increase the accuracy of determining the tensile strength of dielectric materials by approximating the test conditions of the sample to the operational thermal loads of the material in the product. The problem is solved in that the proposed method for determining the tensile strength of dielectric materials, including heating the sample in a given mode, and determining its tensile strength, characterized by a high heating rate due to the use of an intermediate metal heating element having thermal contact with the test sample and heated by induction heater.

The method takes into account the specifics of the use of materials in products with high thermal loads and heating rates. Under the conditions of operation of the material in such products, dynamic heating occurs at heating rates of 10-100 ° C / s to the temperature at which the destruction begins with a total heating time of several tens of seconds to several minutes. As a result of this, the material under operating conditions experiences thermal loads of shorter duration than under mechanical testing of samples by standard methods. Moreover, the exposure time of the material at high temperature has a significant impact on its mechanical characteristics.

The essence of the method is to determine the tensile strength of standard samples during high-intensity induction heating of an intermediate metal heating element having thermal contact with the test sample. Induction heating allows rapid heating of the intermediate metal heating element with the ability to accurately automatically control the heating, which is essential for the implementation of dynamic heating in a given mode.

The invention is illustrated by a specific example of determining the tensile strength of dielectric materials. The tests are carried out on a testing machine, additionally equipped with an induction heater 1 for heating metal plates 2 located on both sides of the sample 3 (figure 1). The temperature of the sample is controlled in the center of the metal plate using a pyrometer or thermoelectric transducer, the working junction of which has reliable contact with the surface of the plate or welded by spot welding.

For testing, samples are used according to the standard GOST 11262-80 in the form of plates of composite material measuring 250 × 25 mm, thickness from 2 to 6 mm. The working area of the samples is 25 mm in the center of the sample. For heating, metal plates with a size of 25 × 25 mm are used. The tensile strength σ, kgf / mm is determined by the formula

, $$\sigma =\frac{P}{S}$$

,

where P is the maximum load during tensile testing, kgf;

S is the cross-sectional area, mm ² .

Figure 2, a shows the calculated finite element model (1/4 part) of the test sample. From the calculations it follows that the recommended heating mode is to reach the test temperature of 1000 ° C in 60 seconds with a subsequent exposure of at least 20 seconds (Fig.2, b). In this mode, the working zone of the sample is heated completely and evenly, and the thermal stresses arising in the sample upon heating do not exceed 3% of the breaking load.

The experiment (figure 3) showed good agreement with the calculation results - the time to reach the test temperature of 1000 ° C is ~ 50 s. Thus, the considered design of the sample and the heating system makes it possible to simulate the temperature regime of the working part of the sample corresponding to the product and correctly test the sample under axial tension.

Figure 4 shows a diagram of the deformation of the sample during the tensile test, and figure 5 shows the sample after the test. The destruction of the sample occurred in the middle of the working area. This nature of the failure was recorded on all samples tested, which indicates good reproducibility of the test conditions. The results are characterized by a low dispersion of strength values - up to 8% at a test temperature of 1000 ° C.

This technical proposal allows us to bring the test conditions of the material closer to the operational thermal loads in the products, thereby reducing the error in determining the mechanical characteristics.

Claims (1)

A method for determining the tensile strength of dielectric materials during induction heating, including heating the sample to a predetermined temperature and determining the tensile strength of the sample, characterized in that the sample is heated to a predetermined temperature at a rate of 10-100 ° C / s and subsequent exposure is at least 20 seconds is carried out by means of intermediate metal elements located in the center on both sides of the sample, heated by an induction heater.

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