Study on high temperature aging characteristics of epoxy materials of electromagnetic coil transmitters
Electromagnetic coil emitter is an important part of the new concept electromagnetic weapon, which has the advantages of large volume and mass range of the launch object, adjustable launch speed, simple energy security, flexible structure, etc., and can be widely used in scientific research, national defense industry and other fields.
Glass fiber/epoxy composite material is an excellent composite insulation material with high dielectric properties, surface leakage resistance and arc resistance, because of its thermosetting and good electrical insulation properties, it can be used for casting electronic facilities.
3240 glass fiber/epoxy is one of the insulation materials for the inner wall of the electromagnetic transmitting coil, guide cylinder, turn-to-turn insulation and other firmware.
Under extreme physical conditions such as high temperature and high pressure, the coil emitter is easily damaged, so it is of great significance to study the aging characteristics of 3240 epoxy/glass fiber for the service life evaluation of the coil emitter.
Research on the effects of thermal aging and analysis of its causes
Under the experimental conditions of 110°C, there was no significant change in the surface of the sample. Under the experimental conditions of 130 °C and 150 °C, with the increase of aging time, the color of the surface of the specimen changes significantly, and under the same aging time, the higher the aging temperature, the deeper the color change of the surface of the specimen; Under the experimental conditions of 150°C, by the end of the experiment, the surface color of the specimen has completely appeared as carbon black and no longer changes.
Under the three aging temperatures of 110, 130 and 150°C, the mass loss rate of samples showed an upward trend with the increase of aging time. At the same aging time, the higher the aging temperature, the greater the mass loss rate of the specimen. This is because in the early stage of aging, high temperature causes water in the epoxy plate sample and some substances with poor thermal stability to decompose and escape. In the middle and late stages of the experiment, the stop loss change rate of the sample tends to be stable and the linearity is better, because in the middle and late stages of the experiment, the macromolecular substances of the sample are broken by chemical bonds, and small molecular substances with volatile properties are generated at the same time, resulting in the mass loss rate of epoxy plate samples continuing to increase, but the change of mass loss rate is relatively stable. Therefore, the residual service life can be calculated by fitting and analyzing the loss data of the epoxy plate specimen after 72h to obtain the function expression of the mass loss of the specimen.
Due to the insufficient aging time and low aging temperature in the actual experiment, the volatilization of water molecules and other volatile substances in the early stage of aging is slower, resulting in a smaller mass loss rate of the sample than that of the high temperature test, so that in the middle and late aging process, the mass loss rate of the sample is affected by the double influence of water molecule volatilization and macromolecular chemical bond breakage, resulting in poor fitting effect.
Because the higher aging temperature makes volatile substances such as water molecules in the sample quickly volatilize in the early stage of aging, only the change of mass loss caused by the breaking of the chemical bond of the macromolecule needs to be considered in the middle and later stages of the experiment. This is because 3240 glass fiber/epoxy contains a certain glass fiber, and glass fiber has high thermal stability and will not react to produce volatile substances, at this time, only the epoxy resin part of the entire glass fiber/epoxy sample is partially oxidized and decomposed to produce volatile substances. Therefore, in the later stage of the experiment, the change in the mass loss rate of glass fiber/epoxy specimens will have a more obvious slowdown trend than that of epoxy resin.
Before the aging test, the impact strength of the sample was 104.85kJ/m2, and when the experiment was carried out to 216h, the impact strength of the sample was 88.15kJ/m2 (110°C), 89.03kJ/m2 (130°C), 87.11kJ/m2 (150°C), at which time the impact strength of the specimen decreased to 84.07% (110°C), 84.91% (130°C), 83.08% (150°C) of the impact strength of the specimen before aging, respectively); In the later stage of the experiment, the impact strength of the sample began to slow down, and when the experiment reached 648h, the impact strength of the sample was 84.20kJ/m2 (110°C), 82.50kJ/m2 (130°C), 80.32kJ/m2 (150°C), and the impact strength of the specimen dropped to 80.31% (110°C), 78.68% (130°C), and 76.60% (150°C) of the impact strength of the specimen before aging, respectively.
It can be seen that under the same aging time, the higher the experimental temperature, the faster the impact strength of the specimen decreases. This is because the experimental conditions of hot oxygen accelerate the oxidation reaction of the epoxy resin matrix, so that the ether bond connecting the carbon skeleton is broken, the matrix resin and glass fiber are debonded, and the originally tight molecular network structure in the epoxy plate becomes loose, resulting in a decrease in the activity capacity of the cross-network chain, destroying the interface bonding ability of resin and glass fiber, which is not conducive to stress dispersion, and reducing the impact strength of the sample.
Before the aging test, the elastic modulus of the sample was 26.30GPa, and when the experiment was carried out to 216h, the elastic modulus of the sample was 25.21GPa (110°C), 24.42GPa (130°C), 23.94GPa (150°C), at which time the elastic modulus of the specimen decreased to 95.86% (110°C), 92.85% (130°C) and 91.03% (150°C) of the elastic modulus of the specimen before aging, respectively. At the end of the experiment, the elastic modulus of the sample began to slow down, and when the experiment reached 648h, the elastic modulus of the sample was 24.80GPa (110°C), 23.74GPa (130°C), 23.06GPa (150°C), respectively, and the elastic modulus of the specimen dropped to 94.30% (110°C), 90.27% (130°C), and 87.68% (150°C) of the specimen before aging. It can be seen that under the same aging time, the higher the experimental temperature, the faster the elastic modulus of the specimen decreases.
This is because the aging process, as an irreversible chemical reaction, is accompanied by changes in appearance, structure and properties.
