The paper deals with the safety criteria of design for an infinite fatigue life of machinery parts. Uniaxial and multiaxial zero mean stress states are considered. In the latter case, constant-amplitude in-phase stress components, as well as random-amplitude synchronous stress components, are taken into account. Dimensionless and relative safety margins for these stress states are defined. The presented criteria refer to ductile materials showing true fatigue limits. Transformation rules in the plane are given for fatigue limits referenced to coordinate system different than the components of the plane stress.

The development of a novel design for the toothed segment of drive transmission in longwall shearer is expected to significantly reduce

the cost of individual components of the feed system and the related work of repair and renovations, increasing at the same time the safety

of mine repair teams.

The conducted experimental and numerical analysis of the state of stress and strain in the innovative design of the toothed segment has

enabled estimating the maximum effort of the developed structure. Based on the results of fundamental mechanical studies of the cast

L20HGSNM steel and fatigue tests combined with the numerical stress/strain analysis, the fatigue life curve was plotted for the examined

casting of the rack.