A numerical study on the triaxiality distribution in a single shear lap fastener joint
Fastened joints are used extensively in the aerospace industry and play an important role in defining the crashworthiness of the structure [1, 2]. As larger finite element models (FEM) are developed, joints are typically simplified as a way to obtain computational time savings. However, these simplification need to be able to account for complex failure criteria, such as triaxiality and Lode parameter dependent failure criteria. In the current study, a single shear lap fastener joint is studied to identify the effects that the coefficient of friction (0 to 1), preload (0 to 2300 N), and fastener fit (interference and clearance) have on the triaxiality distribution of the joint. A series of finite element analysis (FEA) was carried out in LS-DYNA  to quantify the effects of said parameters Higher friction correlated to increases in triaxiality peaks of up to 50% in certain areas of the joint. Variations in preload also affected the triaxiality distribution but only in the low remote stress regime (<250 MPa). Fastener fit also had a major effect on the triaxiality distribution of the joint. Overall, regions of the joint prone to fretting fatigue tended to have high triaxiality peaks at low remote stress. The analysis showed that identifying the operational load range is essential when analyzing joints and determining the appropriate failure criteria to be used in the FEA. Additionally, some simplifications to joints can be made as long as the user is aware of the consequences such simplifications has on parameters such as load transfer, and triaxiality.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering