A Study on Bolted Joint Finite Element Modeling for Vehicle Level Durability Analysis

Bolted joints are widely used connections in automotive vehicle structures. However, it has been a challenge to accurately predict static and fatigue behavior of the sheet metal adjacent to the bearing area of bolted joints when linear analysis approach is used. This paper describes an experiment study on static and fatigue behavior of sheet metal adjacent to bearing area of bolted joints which are typically found on vehicles. These joints cover different bolt sizes (M6 to M14), and nut types (hex nut, hex flange nut, round nut, welded nut etc.). Different sheet metal material grades were selected which were, mild steel, high strength steel, dual phase steel and aluminum. The joints were subjected to coach-peel loading condition, because fastened joints have lowest strengths under this condition. 25 different joint combinations were included in this experimental study. For both static and fatigue tests, three samples were tested for each joint type and loading condition combination. Digital Image Correlation (DIC) technique was used to measure strain distributions at critical locations of the samples. Displacement at the loading point was monitored and the curve of displacement vs number of cycles was used to identify crack initiation. These test results will be used as basis for further CAE methodology development to predict fatigue life of sheet metal adjacent to bolted joints.