Principle of Local Zones applied to fatigue prone large-scale Designs

On large-size Design (FSD) fatigue damages accumulation (FDA) is marked in some zones. The investigation of stochastic dependence FDA is carried out on samples with numerous concentrators as a model of solid body with embedded flaws. Under the basis that FDA happen dependent, the Hypothesis of Local Zones (HLZ) is proposed. On the basis of double exponential probability distribution of fatigue durability with logarithm scale of loading cycles, the four-parametric mathematical model of Local Zone fatigue strength is developed. This model unites parameters fatigue durability, endurance limits, linear-pieces S-N fatigue curve and a sensitivity threshold on cycles. It is supposed that piecewise and linear description of S-N fatigue curve with various degree m is connected with various mechanisms of FDA, when loading level is changing. HLZ is approved on the Bench Tests and Operation Work of FSD. It is shown that the best method of nondestructive test of critical Local Zones technical health on-line mode is the method of acoustic emission. Then Local Zone is presented as indicator of degradation of total Design. HLZ allow develop design methods by the principle Fail Safe Concept.