Estimation of forest machine ROPS reliability in terms of fracture mechanics

This paper deals with the estimation of reliability measures in terms of fracture mechanics. The main fracture mechanics expressions linking stress intensity factor with the length of the crack like defect are presented in the introduction. Analytical equations evaluating the reliability function are obtained. The fracture toughness and the stress intensity factor are viewed as Gaussian random values in the second part of the paper. The statistical linearization method is used to determine distribution parameters (mean value, dispersion). The tracked skidder ROPS (roll-over protective structure) is used as an example of reliability function evaluation and is described in the last part of the paper. The stress intensity was estimated by the finite element method. Calculations are done for different types of cracks: through wall, edge and semi elliptic. It is shown that the presence of crack like defects, even of small length, reduces the level of reliability.