Assessment of the reliability of metal structures of lifting and transport machines of the forest complex, taking into account the fatigue strength of the material

Abstract

Currently, in the forest complex, the working conditions of lifting and transport machines (PTM): self-propelled manipulator-type loaders are characterized by intensive technological loads, high speeds of lifting and moving loads, while the required resource characteristics are not always provided. The durability of PTM is mainly determined by the durability of the supporting metal structure. The analysis of various methods for assessing the reliability of PTM metal structures, taking into account the fatigue strength of the material, is given. It is established that one of the ways of designing structures with a minimum mass is to increase the design resistances of materials, however, the margin factor is inconvenient for assessing the readiness of the structure for operation. It is necessary to create a more universal criterion – the probability of failure. The aim of the work is to develop a methodology and algorithm for quantifying the probability of safe operation of a metal structure, taking into account the reduction in load-bearing capacity. To study the fatigue strength indicators of crane beams of forest complex machines and the factors influencing it, a crane of various lifting capacities of 32/5 tons is considered. The calculation of the fatigue strength of the metal structure of the crane was made. The number of loading cycles in the 3K operating mode after the expiration of 5 years is N=3,0∙10^5. With the material used, steel C255 [GOST 27772-88] with a temporary Run=380 MPa and a calculated Rv fatigue resistance taken depending on the temporary resistance of steel Run, therefore, Rv=120 MPa, fatigue strength was from 328.88 MPa to 167.98 MPa for various time intervals of 5-50 years. The calculated dependences of the safety coefficient on the operating time of the crane with a lifting capacity of 32/5 tons, depending on the operating mode of the crane from 7.9 to 2.01, are obtained. The results obtained can be used in the design of PTM metal structures also in construction and agriculture.