Влияние конструктивных решений на формирование кривой усталости боковых рам тележек грузовых вагонов

Abstract

Fatigue resistance is the main parameter of the quality of cast parts. Fatigue tests allow evaluating performance of designs, feasibility of introducing structural changes, efficiency of used in the manufacture parts of technological solutions. The analysis of the results of fatigue tests of the side frames of different manufacturers is made. The main places of destruction were determined and defects in the centers of origin of the fatigue cracks were systematized. The parameters of fatigue curves (m - exponent equation, ρ - correlation coefficient), as well as limits of endurance and resistance to fatigue safety factor n were calculated in the article. In some cases, the value of the index m greatly exceeds the average level of the entire test volume. Test results of three batches of the side frames with high values of m and n were reviewed. The first batch of the side frames is represented by the base case. Analysis of the fracture of surfaces showed the presence of damage with high operating time of parts without casting defects. Also, there is destruction of parts with low operating time with presence of numerous casting defects. This indicates instability of manufacturing techniques of parts during its development in the enterprise. Side frames in the second batch are reinforced in the zone of internal angle of pedestal jaw opening by introducing additional edge, increasing the height of the vertical walls in 1.2 times and the wall thickness in 1.25 times. Efforts of pedestal opening led to a peak stresses in the lower and diagonal tension members, side frames divided into two groups of parts with different levels of damage. As a result - the formation of the fatigue curve with the magnitude | m | = 17. Side frames of third batch are an option of enhancing inner angle of pedestal opening by increasing the height of the vertical walls in 1.2 times and the thickness of the horizontal zone in 1.3 times. The rigidity of reinforced zone (pedestal opening) has led to an increase in stress in a neighbor zone - diagonal tension member. As a result, obtaining fatigue of the curve with the magnitude | m | = 25. Formation of zones with different levels of stress state distorts results of fatigue tests of the side frames, unreasonably increases the value of index m, and hence index n. When receiving m in absolute value over 10 an analysis of zones of destruction with establishing reasons behind this increase should be made as well.