Speaker
Description
Fatigue estimation is an essential aspect of robust machine design. To prevent potential problems with fatigue in operating machines, typical designs are conservative in excluding fatigue damage under predicted working conditions. However, such an approach results in heavy, bulky, energy-inefficient designs with restricted payload and operation speed. We need a robust and online fatigue assessment system (virtual sensor) to enable lightweight designs with modern materials, like high-strength steel and composites. Virtual sensing of fatigue assists an operator, guides the control system, and monitors machine damage.
We propose a framework based on recovering stresses from flexible real-time multibody simulations and rainflow cycle counting of the nominal stresses of a structure to provide an online fatigue assessment system.
The traditional approach to estimating fatigue in complex systems uses very detailed finite element models to obtain stresses. Typically, that implies that only a small fragment of the structure is considered in the finite element analysis with the boundary conditions obtained from significantly simplified simulations of the entire system. While this approach proved to provide accurate enough results in numerous scenarios, its application is limited by two inherent properties of the method. The first relates to the computational cost of detailed finite element analysis, which makes it not feasible to perform such simulations in real-time. The second is the accuracy limitation resulting from the boundary conditions coming from simplified dynamic simulations.
In the suggested approach, we aim to relax the limitation mentioned above related to the computational speed while keeping the accuracy of stress calculations at a sufficient level.
We study techniques for recovering stresses directly from dynamic simulations with reduced-order models and investigate the feasibility of obtaining a stress history suitable for fatigue estimation in this manner. A model of the PATU crane available at LUT for research purposes was used to test the proposed approach. The technique of storing stress modes to generate a reduced order model and using them to calculate stress fields in the entire structure was computationally effective for the stated purposes. Conclusions about requirements for the finite element mesh used for generating reduced order models and the parameters of the reduction method for achieving the desired accuracy of dynamic stress fields in the regions of interest are drawn.
