Assessment of Fatigue Lifetime of a Forestry Crane Based on Flexible Dynamic Simulation

Reducing structural weight while ensuring sufficient durability and fatigue lifetime are key challenges in the design of non-road mobile machinery (NRMM). This research introduces a purely simulation-based approach for developing lightweight NRMM with fatigue life considerations, positioned in the early product development phase where no prototype or measured load data are available. The approach is demonstrated through a forestry crane case study utilizing methods of flexible multibody dynamics. The goal is to enhance the performance of crane by leveraging the advantages of ultrahigh-strength steels (UHSS), which enable lighter structures and increased load capacity. The research involves simulating the forestry crane in two scenarios: one with the original lift boom based on conventional structural steel S355 and the other optimized design using S960-grade UHSS. Simulations are conducted using commercial Siemens NX software with real operator input generated in Mevea multibody dynamics software to replicate realistic work trajectories. The analysis focuses on identifying high-stress weld areas and evaluating fatigue lifetime based on retractive phase of the work cycle. Results show that UHSS can reduce the weight of load-bearing structures by approximately 35%. After applying high-frequency mechanical impact (HFMI) treatment, the fatigue lifetime nearly doubles. The study underscores the importance of advanced steels and purely simulation-driven design processes in developing more efficient and environmentally friendly solutions.