Measurements and testing during a study of composite materials (CM) and CCCM properties, monitoring of production operations for CM preparation, their carbonization and compaction, and also HTT, were carried out by means of metrologically certified measurement facilities by procedures of the OAO NIIgrafit test center of carbon materials.
The relative change in specimen dimensions and component dimensions in three mutually perpendicular directions were measured by a standard instrument. Density and open porosity were determined by a hydrostatic method. Open porosity from 5 to 35% was certified within these limits by procedure MI00200851-162-2009.
The ultimate strength in bending was determined according to procedure MI 00200851-335-2010 in specimens with a size of 100*15*δ with distance between the supports of 80mm. Specimen thicknessδ did not exceed 6mm and was equal to the thickness of test plate or shell material. Ultimate strength in bending was determined as the quotient of maximum bending moment by the moment of transverse bending resistance. The determination error for the breaking load did not exceed 1%.
Measurement of linear thermal expansion coefficient (LTEC) was carried out by determining specimen elongation directly by procedure MI 00200851.163-2007. Direct measurement of displacement was carried out by means of a horizontal microscope. According to the curve for the dependence of relative elongation on temperature measurements the average LTEC was calculated in prescribed temperature ranges. Test temperature was measured by an optical pyrometer. Measurements were performed in a laboratory electric vacuum furnace in a pure argon atmosphere. In order to reduce the error of optical temperature measurement due incomplete grey body radiation as a result of radiation of the boundaries a special form of specimen edge was developed. The absolute error of the procedure was ～0.1×10-6K-1.
Studies for measuring specimen dimensions during primary heating of carbon-reinforced plastics or carbonized specimens were carried out by a dilatometric method. Temperature was monitored by means of a chromel-alumel thermocouple. Determination error did not exceed 10 K.
The temperature for performing HTT in electric vacuum furnaces with a different working volume was measured by Promin’ optical pyrometer, which during measurements of the processing treatment temperature was used as a standard for the APIRS system. Temperature measured with a Promin’ instrument, according to test data, is lower by 10-20C than the true values, caused by absorption of the atmosphere and sight window. Additional errors, caused by equipment, radiation devices, taking account of the different actual degree of blackness of treatment blank due to shrinkage of a charge, may be in total up to 14C. In turn, the error for the radiation capacity and introduction of corrections for the sight glass compensate each other. As a result of an increase in measurement error due to individual operator sensitivity, absorption of the atmosphere, and glass in the measuring window, incorrect consideration of the degree of body blackness, and some other less significant factors, deviation from the true temperature value is within the limits from -40 to +10C of the nominal value.
Specific electrical resistance was determined by a potentiometric method by direct current using a standard. The drop in voltage at potential contacts of the measuring instrument was from 10 to 20 mV. Specimen dimensions were measured with an accuracy of 0.01mm. On average the level of specimen electrical resistance was ～40 μΩ.m
The average value of thermal conductivity was measured in a steady-state axial heat flux according to procedure Mi00200851.125-2007, based on comparing thermal conductivity of test materials. In order to avoid convection the measuring cell was placed in a thermostat. The maximum calculated experimental error, taking account of measuring instruments and the different heat-resistance of a standard and a test specimens, did not exceed 7%.