Reliability and Life Analysis

Fatigue Life and Load Analysis

​Under realistic service conditions, loads often occur irregularly and cause loads with varying amplitude, in contrast to constant amplitude loads that alternate between fixed levels. Fatigue analysis of variable amplitude loads is performed using statistics together with rainflow count and damage accumulation. Statistical methods are also important tools for characterizing customer loads and operating conditions. RISE can support planning of measurements and carry out analysis of field measurements on operational loads. Testing on materials and components can then be performed at RISE with a corresponding load spectrum where acceleration methods are exploited.

Reliability and Robustness

In fatigue, the variation is large due to the natural scatter in the fatigue strength of the material. RISE employs the reliability method Variation Mode and Effect Analysis (VMEA), which evaluates all possible uncertainties. The sources can be material scatter and uncertainties in load measurements, but also model and parameter uncertainties, which can be difficult to handle in Monte Carlo methods. For service life analysis, the total uncertainty from a VMEA can be used for establishing a fatigue design criterion. Using VMEA for fatigue life analysis and design makes it possible to change from deterministic to statistically based safety factors. The transition to probabilistic methods often allows for products less prone to over-conservative design, which gives the possibility to lower both costs and environmental impact, while keeping the reliability target.