Abstract: In order to explore the influence of wheel-rail contact spot under different wheelset traverse，and the third medium on the static friction coefficient of wheel-rail, a test bench which can accurately reflect the wheel-rail contact state was built. The wheel-rail contact test with the third medium under different wheelset traverse and starting conditions was carried out by selecting worn wheel and rail test blocks of high-speed trains. And the conclusion was drawn: When the rail is close to the rim, the wheel-rail contact spots are dumbbell shaped and have a large area. In the center position and far away from the rim, the shape of the contact spots are oval and the area are close; Water, oil and leaves can reduce the static friction coefficient between wheel and rail by 49.7%, 54.5% and 75.9%, respectively, compared with dry rail surface; Sand spraying can effectively increase the static friction coefficient between wheel and rail, the maximum can be increased by 81.6% compared with the dry rail surface, the static friction coefficient will remain unchanged after the sand content saturation; The wheel-rail static friction coefficient under the sand-water mixture is significantly increased compared with that under the water medium alone, and the viscosity increase effect is the best when the sand-water mass ratio is about 10:3. The conclusion has reference value for sand quantity and intelligent control of sand.

Key words: rail vehicles, the third medium, wheel-rail contact test, coefficient of static friction