Russian Federation
Russian Federation
GRNTI 68.85 Механизация и электрификация сельского хозяйства
When repairing agricultural machinery, the pressing of repair bushings for the restoration of worn parts is widely used. In the process of assembling a joint in the external part, cracks are often formed, which can be caused either by defects in its surface or by structural defects. Therefore, increasing the crack growth resistance of the press connection during assembly is an urgent task. The work analyzes the impact of the geometry of the external part on the resistance to fracture. Since it is possible to obtain complete information on defects by nondestructive testing methods only in individual cases, a technique for modeling the defects of the surface crack of a semielliptical shape was used. To evaluate the crack resistance, the force criterion of fracture mechanics is used - the stress intensity factor. As a result, it was found that the relationship between the thickness of the wall of the external part and its outer diameter makes a significant impact on the fracture toughness of the compression joint, which makes it possible to reduce the probability of nucleation and development of cracks by changing these parameters. Such a technique can be used in cases where the mechanical assembly is used for assembling the connection - by means of a press and a thermal one - with heating of the external part, methods of assembly. The greatest strength of the connection is achieved by cooling the internal part during assembly, but in this case the probability of formation and growth of cracks increases. This is due to a decrease in the critical stress intensity factor (fracture toughness), which is a mechanical characteristic of crack resistance when the temperature of the external part is lowered. The effect of this factor can be reduced by using a combined method of assembling the joint by cooling the internal and heating the external part. To evaluate the fracture resistance at low temperatures, it is optimal to carry out full-scale tests, where the cooling and heating temperatures of the press connection parts act as experimental factors.
joint with interference, crack resistance, tensile stresses, stress intensity factor, fracture toughness.
В настоящее время одними из наиболее распространенных неподвижных соединений являются соединения с гарантированным натягом, поэтому исследование влияния конструктивных и технологических факторов на прочность соединения является актуальной задачей.
При ремонте соединений способом вставки ремонтной втулки при сборке зачастую наблюдается появление трещин в охватывающей детали. При уменьшении величины натяга возможен сдвиг деталей и потеря герметичности [1, 2, 3].
Целью исследования является предотвращение трещинообразования в деталях и обеспечение надежности соединений с натягом.
Условия, материалы и методы исследований. Прессовые соединения состоят из двух деталей (рисунок 1а) [3]. Натяг возникает вследствие разности диаметров охватываемой и охватывающей деталей. При сборке в соединении возникают силы трения, препятствующие их взаимному смещению.
Несущую способность соединения обеспечивает контактное давление, которое возникает в стыке деталей после запрессовки. Это давление должно быть таким, чтобы силы трения превышали внешние сдвигающие силы.
При действии внешней осевой силы Pоc величина контактного давления qос вычисляется по формуле:
qoc≥ PоcK/fπdL, (1)
где K – коэффициент запаса сцепления, K = 1,5-2,0, f – коэффициент трения, L – длина стыка.
При нагружении вращающим моментом Mвр:
qвр≥2Mвр K/fπd2L. (2)
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