The stress state analysis of the links of the technological machine basic mechanism

The stress state of the links of the basic crank-rocker mechanism, due to the loads acting during the movement has been studied. The initial data for the analysis are the loads found earlier as a result of the mechanism dynamic analysis by uniform crank rotation. The finite element solution of the problem of finding stresses in the mechanism links is carried out using a 10-node tetrahedral element. The reliability of the numerical results is substantiated by comparing the solutions for meshes with initial and increased density. Calculations of the moving mechanism was performed for three variants of external loads: 1) taking into account only inertia forces; 2) taking into account the inertia and gravity forces; 3) taking into account the forces of inertia, gravity, as well as friction in kinematic pairs. The distributions of equivalent stresses in each of the mechanism links were obtained. The nature of the stresses change in the links during the cycle of the mechanism movement was studied, while the highest stress state level was noted near the bottom dead center (BDC) position i.e. 0.5 turn of the crank from the starting position. It has been found, that with simultaneous consideration of the inertia and gravity forces, the gravity forces exert the predominant influence on the links stress state for a given speed of the crank rotation. It has been shown, that taking into account friction in kinematic pairs does not fundamentally change the results of stress calculation, excluding the local region of the mechanism positions near the BDC. Quantitative data of the links stress state are the basis for their strength estimating. The obtained dependences of stresses on the position of the mechanism indicate their cyclic nature. The obtained dependences of stresses on the mechanism position indicate their cyclic nature. This circumstance means the need to exclude stress concentrators in the links structure in order to reduce the danger of fatigue failure.

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