Estimating the reliability of forestry machine elements with possibility theory application

Abstract

The working conditions of forestry machines differ from those of agricultural machines. The presence of obstacles during the clearing of forest areas increases loading of machine components and assemblies and, consequently, leads to their failures. This paper deals with an improvement of probabilistic methods of forestry machine design by applying fracture mechanics and possibility theory. The main fracture mechanics expressions linking stress intensity factor with crack-like defect length are presented in the introduction. Fracture toughness and crack-like defect length are viewed as Gaussian random values, maximum applied stress is presented as a fuzzy variable with unknown distribution law in the second part of the paper. Analytical equations for reliability evaluation are obtained by estimation of upper and lower bounds of reliability function. The real value of reliability function is located within this interval. The proposed approach may be applied to give recommendations for engineering of forestry machine and equipment elements in the case of limited statistical information.