A study of thickness effect on fatigue in thin welded high strength steel joints

It is well known that the fatigue strength of welded joints decreases when plate thickness increases. This decrease in fatigue strength is known as the thickness effect. In many standards for fatigue design the thickness effect is taken into account for joints with plate thickness typically greater than 25 mm. Previous work has mainly been focused on joints with plate thickness between 12-200 mm. Less attention has been paid to thinner joints. Published investigations on joints with sheet thickness 2-12 mm show an increase of fatigue strength with decreasing sheet thickness. In the present study results from constant amplitude fatigue testing of non-load carrying welded joints in high strength steel of thickness 3-12 mm are presented. The results show an increase in fatigue strength with decreasing sheet thickness down to 3 mm. Fracture mechanics calculations confirm the test results.