Fasteners are typically designed to withstand axial or shear loads in a joint assembly. However, in selected scenarios fasteners are subjected to combination of axial, shear and bending loads. The criterion typically used to predict the ultimate failure of a member in combined shear and tension is based on the maximum normal stress and maximum shear stress theories. Test conducted by NASA found that under joint separation condition, the existing combined loading failure criteria over-predicts the strength of the bolts.
This paper develops the methodology of predicting fastener failure using finite element analysis with elasto-plastic material properties under combination of axial load and shear using a strain-based failure criterion. This methodology is validated with NASA test results. Elasto-plastic finite element analysis is shown to be an effective way to simulate test results. In order to define the full range capability values for different combinations of shear and tension loads, several cases were run with different load values. The study further extends to identify new limiting criteria under a combination of axial load and offset shear conditions for a selected stud.
The load capability can be used to calculate margin of safety for flange-joints. Further this approach can be generalized for application to all pins and fasteners subjected to combined shear and tension loads.
