| Carbon fiber reinforced plastic(CFRP)with many excellent properties are widely used in various engineering fields,but the real environment,among which temperature influence is most common,will often cause damage to their properties.Understanding the influence law and mechanism of temperature effects on CFRP mechanical properties is beneficial to effectively evaluate the stability and long-term applicability of the materials during service.Therefore,the mechanical properties of CFRP before and after treatment with different temperature were studied in this paper.First,CFRP composites were prepared by using CFRP as a reinforcement material and epoxy-e51 resin(EP)as a matrix material.Then,ultra-low temperature(-196?),high temperature(100?,200?)and temperature cycling were processed to explore the changes of mechanical properties of the material.And the changes of chemical structure,thermal properties and microstructure were studied.The main contents and conclusions were as follows:1.The change rule and mechanism of material mechanical properties under the ultra-low temperature(-196?)treatment of liquid nitrogen were studied.CFRP samples were completely immersed in liquid nitrogen,and the effects of different soaking times(0 days,7 days,14 days,21 days)on material properties were compared.It was found that the tensile strength of the material did not change significantly after the ultra-low temperature treatment,but the flexural strength increased by 12.65% after the liquid nitrogen immersion for 21 days.It was also found that the ultra-low temperature environment did not affect the chemical structure of the material,but can make the fiber bundles bind more tightly.2.The changing rules and mechanisms of mechanical properties of materials under different high temperature(100?,200?)treatment were studied.(1)with the increase of high temperature treatment time of 100?(0h,5h,20 h,50h,100h),the mechanical properties of CFRP are improved.After 100 h,the tensile strength was increased by about 14.6%,and the flexural strength was increased by 17.5%.FTIR test showed that the epoxy matrix was cured after treatment at 100?,and more resin was bonded on the surface of CFRP after high temperature treatment.(2)with the increase of 200? high-temperature treatment time(0h,5h,20 h,50h,100h),the mechanical properties of CFRP increased first and then decreased.After 100 h high-temperature treatment,the flexural strength of the material was decreased by 5.08%,and the tensile strength was decreased by 35.2%.The test results of FTIR,TG and DMA showed that the chemical bond absorption strength,TG and thermal stability decreased slightly,indicating that CFRP treated at 200? would degrade the matrix.At 200?,the volatilization of small molecular substances inside the material made the material form holes.Through the analysis of the micro-morphology of the section,it was also found that the high temperature is conducive to the bonding of resin and carbon fiber.3.The change rule and mechanism of mechanical properties of materials under the treatment of sudden temperature cycle change(-196?~200?)are studied.The CFRP sample was thermal cycled for different times(0 times,50 times,100 times,150 times,200 times)within the temperature range of-196?~200?.After 50 cycles,the tensile and flexural strength were increased by 10.7% and 8.2% respectively.After 200 cycles,the tensile strength was decreased by 9.7% compared with the initial value,while the flexural strength was decreased by 6.4%.Both the decrease of FTIR absorption peak strength and the decrease of TG thermal stability indicate that the matrix degrades during the cycle.After several cycles,the carbon fiber layer and resin layer of the sample were layered.The mechanical properties of CFRP were mainly influenced by the aging of epoxy matrix and the decrease of the interlayer strength of CFRP.In this paper,the influence law and mechanism of different temperature environment on the mechanical properties of CFRP were studied,which provided effective data support and theoretical basis for the safety evaluation in the practical application of materials. |
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