Dynamic Pattern of Safe Operation Indicators for Heavy-Duty Machines

Abstract

This article studies the dynamic pattern of safe (hazardous) operation indicators for heavy-duty machines. A load-carrying structural member of metallurgical overhead crane with a frame manufactured from 09G2S steel and having 50 ton lifting capacity was selected for the study. A generalized limit-state equation for the structural crane element represents hypersurface, which distinguishes the safety zone and the hazard zone. Safety and hazard functions are presented as integral functions of probability distribution density, resulting from various factors that affect the likelihood of occurrence of emergencies, accidents and machine breakdowns. The indicators with the greatest influence on the probability of safe and hazardous states of the structural element or the structure itself can be identified. It is accepted to investigate probabilistic features of stress and deformation fields. The stochastic boundary-value problem of the structural element’s stress–strain behaviour under random load is addressed in this case. The problem can be resolved by obtaining correlation and spectral functions of stress and deformation under given load functions. Considering that heavy-duty machines are operated in steady state, it can be assumed with sufficient assurance that such random processes represent steady Gaussian processes. The probabilistic dynamics of safe operation indicators are studied by using computer-based simulation modelling. The obtained modelled curves of probabilistic machine load allowed one to deduce equations of stress and deformation probability density. Every coefficient of the obtained models is probably significant based on Fisher’s criterion. The obtained relationships allow one to construct graphs of limit and acceptable states when evaluating durability and operating life of heavy-duty machines and the probability density for operating and rupturing loads and stresses.