Investigation of strength of carbon-carbon composite materials at temperatures from 293 to 3300 K under high-rate heating

Abstract

620.18(035) The paper presents the results of the investigation into the influence of temperatures from 293 to 3300 K on the strength of carbon-carbon composite materials in tension and in compression. The character of specimen fracture is studied in the temperature range from 293 to 3300 K. It is shown that qualitatively similar changes in the material strength are observed both in tension and in compression.Obtaining reliable data on the mechanical properties of carbon-carbon composite materials (CCCM) under conditions as close as possible to the operational ones is one of the determining factors of their efficient use. To carry out the strength tests as applied to those conditions is a complicated problem from the standpoint of the test method. The currently existing procedures for high-temperature tests enable obtaining quantitative experimental results on exposure to temperatures of 2300-2800 K [1, 2].For the purpose of obtaining data on the thermomechanical properties of carbon-carbon composite materials under conditions that are close to the operational ones (temperature of 293-3300 K, heating rate of the order of 1000 deg/s) in accordance with the experimental procedure described earlier [3], short-term strength tests were carried out in tension and in compression in argon. A fully automated test complex designed by the authors for testing CCCM at high temperatures in vacuum, air or inert atmosphere was used for the purpose. The test complex manufactured on the basis of a test setup 1958U10-1 [4] was equipped with present-day experiment control and measurement facilities operated by a PC. In order to increase the reliability of the results for various test types, unique test specimens were proposed [5-7] (Fig. 1).The employed method of heating by running an electric current through the specimen, with an additional heating of the specimen gauge length, made it possible to conduct investigations at heating rates of about 1000 deg/s, with a uniform temperature field maintained along the specimen gauge length. The mode of thermal loading was provided by the operation of three electrically non-connected power supplies (Fig. 2) programmable from a single heating control system. The optimization of the voltage ratio provides for the required heating rate, the compensation of the heat outflow to the grips and thus the minimization of the temperature gradient along the specimen length. Control over the uniformity of the temperature field along the specimen gauge length was exerted by three tungsten-rhenium thermocouples of type VR 5/20 for temperatures up to 2473 K and by an infrared pyrometer INFRATHERM IGA-100 at higher temperatures (2473 to 3273 K).The load was measured using a load cell with the measurement range 0.002-100 kN and allowable relative error ±1%. The elongation of the specimen gauge length was measured with an extensometer. Apart from grip portions 1 (Fig. 3a), a tensile specimen has two pairs of projections 2 from the mutual displacement of which the 0039-2316/05/3701-0099