Experimental Study On Ultra-high Temperature Tensile Mechanical Properties Of Needle-punched C/C Composites

Needle-punched C/C composites still have strong load-bearing capacity in ultra-high temperature environments,which has been widely used in aviation and aerospace fields,and has become an indispensable material because of its increasing proportion in aircraft materials.The mechanical properties of needle-punched C/C composites at high temperature are very important when they are used in thermo-mechanical coupling components.The test and characterization of mechanical properties at high temperature plays an important role in the reliability design of aircraft.The testing standard of mechanical properties of composites at room temperature is relatively mature at home and abroad,but the lack of experimental data in high temperature environment is relatively serious.The more convincing high temperature testing method in the world is heated by high temperature radiation furnace,it's temperature field distribution is relatively uniform.However,it also has some shortcomings,such as long test period,high test cost,the equipment is difficult to maintain and so on.In view of the above shortcomings,this paper tests the mechanical properties of needle punch C/C high temperature based on the electric heating method and digital image related technology to obtain its mechanical response under high temperature environment.The micro-model of the material was obtained by scanning electron microscope and Micro-CT,and its micro-structure was analyzed.According to the domestic and foreign C/C composite room temperature tensile standards and high temperature mechanical testing machine,needle-punched C/C high temperature tensile samples were designed.And use Abaqus finite element software to conduct heating simulation and thermal coupling calculation on the sample to obtain its temperature field distribution along the sample tensile direction and the vertical sample tensile direction and the stress distribution of the whole sample.Further,the length,width and chamfer of the clamping end of the sample gauge area were optimized to obtain a more reasonable sample with smaller temperature gradient and stress concentration in the gauge length section.And with reference to domestic and foreign standards,the loading mode,loading speed and other parameters of the high temperature test are designed.The theory of electrified heating and the influence of water cooling,thermoelectric effect,contact resistance and material size on the temperature distribution in the process of electrified heating are discussed.according to the relevant theory of electrified heating,the phenomena in the experiment are explained,and the uniformity of temperature field distribution in the high temperature test system of electrified heating is verified.The mechanical properties of needle-punched C/C composites were tested at room temperature,1200 ?,1600 ?,2000 ?,2400 ? and 2800 ?.The strength and modulus of the materials at high temperature were measured,and the stress-strain curves were made.The high-temperature mechanical property data of needle-punched C/C composites were supplemented,the variation law of the material with temperature was explored,and the micro-model of the material was obtained by scanning electron microscope and Micro-CT.The micro-structure of the material was observed.