Numerical analysis of adhesively bonded single lap joints under high speed tensile loading
Adhesively bonded joints pose complex solid mechanics problems through their inherent variations; material properties dependent on fabrication, stress singularities created by geometry of bonded structural assembly, and in a non-uniform state of stress when loaded. When testing adhesives at high strain rates additional variations are observed; particularly in strength. It is hypothesized that a non-uniform field of constitutive relations exists in an adhesive lap joint, owing to the strain rate sensitivity of the adhesive material. This study investigates the non-uniform distribution of strain rate in the overlap region of ASTM D3165 and D5656 single lap joint (SLJ) specimens, and how the strain rate sensitivity of the adhesive affects the stress distribution when the joint is subjected to varying tensile loading speeds. The numerical method of Finite Element Analysis (FEA) has been used to analyze the joint. Commercially available LS-DYNA implicit dynamics solver and one of its standard material formulations, *MAT_19_STRAIN_ RATE_DEPENDENT_PLASTICITY, were implemented to model incremental stiffness as a function of effective strain rate, within the adhesive lap joint. This thesis reports strain rates at various locations in the adhesive overlap for four test speeds, from 25.4 mm/s to 1270 mm/s. Results of stress distributions of the joint are presented comparing the relative effects of using strain rate insensitive and strain rate sensitive material models. Comparative results show that while the force vs. displacement curves show negligible change, strain rate levels and stresses at the bondline edge increase significantly with test speed. As this location is known to be site of failure initiation, these results indicate this may be an underlying mechanism controlling or at least affecting failure strengths of adhesive joints tested at high loading rates.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering