Simulation And Verification Of C/C Composites' Thermal,Stress Fields During Braking

As a kind of aircraft braking material, C/C composites have excellent tribological properties and ablation resistance, which have been widely used in aerospace. In recent study, the influence of thermal stress becomes more and more important. However, in reality, the thermal stress is difficult to measure. So, in the article, three C/C composites brakes of two aircraft types are studied and the finite element analysis software is applied to calculating the temperature fields and thermal stress fields during braking, and have some research on the tribological behaviour due to its high temperature and thermal stress, too. The main conclusions are as follows:1. Under the conditions of normal landing energy, the foreign sample of aircraft A's new pieces,90% wear, and 100% wear's maximum temperature are 1214℃,1280℃and 1317℃. Due to its poor thermal conductivity properties, and the temperature gradient is very high, too. The temperatures of domestic sample of aircraft A are lower because of its excellent thermal conductivity properties, the maximum temperature are just 733℃,914℃,953℃. However, both brakes have a temperature concentration on the first stator. The domestic sample of aircraft B have a same trend of temperature fields under the conditions of normal and overload landing, just have some numerical differences, and they have temperature concentration on the central stator. The temperature 902.2℃at the overload landing is higher than the normal landing. Compare with the surface temperature from the braking test, the temperatures from simulating are correct which proved the validity of thermal stress fields.2. The thermal stresses of three samples at normal landing condition and the domestic sample of aircraft B at different landing conditions were calculated. At normal landing energy, the thermal stresses of the samples are the highest near the outer circumference and exist obvious gradient in radial and axial direction. The maximal thermal stresses are 34MPa, 13.5MPa,17MPa, and the foreign sample of aircraft A is the highest, the domestic sample of aircraft A is the lowest. The highest thermal stress of sample domestic sample of aircraft B at overload landing condition is 29.4MPa, which is as twice as the thermal stress under normal landing energy.3. Comparing thermal stress curves at the middle radius on three samples'central stator with time. The thermal stress of foreign sample of aircraft A continued to rise, and the domestic sample of aircraft A reached the highest thermal stress in early braking, then the maximum sharply down. The trend of domestic sample of aircraft B's thermal stresses in two conditions are similar, and in the initial stage of braking, there is a peak. With the braking process, thermal stresses decreased rapidly and then gradually increased, became a stability level in the end.4. Comparing the morphology of foreign and domestic samples of aircraft A's friction surface and friction debris. We found that the higher stress during braking makes the sample 1 get stress graphitization, sightly improved its friction and wear properties. The sample 2 generated lower thermal stress on friction surface during braking, and it promoted the formation of sample 2, then formed small debris, increasing the contact area and improved the braking efficiency.