| Popis: |
The paper presents studies carried out in order to determine the causes of destruction, by cracking, of a crankshaft from the composition of a tractor used to process soil.Experiments were carried out in two directions, namely a step by step study on the degraded area and a investigation into the operating conditions of the machine, on that specific work cycle.The degraded shaft was investigated visually at a magnification of 10x and by hardness tests on the areas with embrittlement cracking.Hardness test enfolded large variations (in hardness), of up to 40%, leading to a high sensitivity to cracking by mechanical fatigue, induced by the structural tension concentrators. However, hardness examination did not reveal areas of shaft degradation due to fatigue, which determined us to study the operating conditions. The shaft cracking occurred during soil processing, using a multilayered plow and in difficult exploitation conditions.Variations of mechanical characteristics of soils in the area of operation of the machine, is relatively large, fact which corroborated with the lack of safety elements when overloaded, of the endowment of the tractor-plow system, led to the overcoming of the permissible load, which on a background of high hardness material, determined the embrittlement cracking of the crankshaft. Research performed highlighted, for the area in which the machine activates, the necessity of introducing in the power-generating system of safety and protection elements to prevent the destruction of components. |
