Utmattningshållfasthet hos kallformade höghållfasta stål.

This master’s thesis investigates the comparative longitudinal fatiguestrength of welded and cold-formed rectangular hollow section beamsmade of high-strength steel subjected to cyclic loading. Using a four-pointbending test setup, the study evaluates the performance of conventionallywelded beams against press-braked cold-formed beams with identicalnominal dimensions. Experimental tests were performed at load ratio R = 0.1 with a stressrange ∆σ ≈ 300-370 MPa. Results indicated that cold-formed beamsoutperformed welded beams, demonstrating at least a 6.4-foldimprovement in fatigue life under comparable loading conditions.However, the fatigue failures in cold-formed specimens initiated outsidethe region of pure bending, limiting definitive conclusions regardinglongitudinal fatigue performance. Key challenges included managing controlling welding imperfections suchas heat-induced distortions and geometric inconsistencies. Future workshould focus on refining test setups, expanding specimen variability, andexploring additional design parameters such as varying thicknesses andbend radii to further elucidate fatigue phenomena in cold-formed structuralelements loaded longitudinally.