Experimental and numerical study on the pin-load distribution of multiple-bolted joints

Test and finite element analysis were carried out to characterize the pin-load distribution of multiple-bolted metal-to-composite fastener joints. The specimens are the single-lap and double-lap joints with an array of three bolts and subjected to tension loading. The surface strains at certain cross-sections of the metallic plates were measured using the strain gage technique. The pin-load fractions of the multiple bolts were then estimated indirectly using the measured strains. Two-and-three dimensional finite element models were also constructed to calculate those strains and the pin-loads. The calculated strains agree well with the measurement, whereas significant difference is observed between the pin-load fraction results of both methods. The investigation reveals that the way to determine the pin-load distributions ratios according to the plate surface strains is not able to account for the built-in effects of additional bending moment concurrently with the tension loading. The authors believe that the numerical calculation to estimate the pin-load fractions, based on finite element modeling which has been validated by the surface strain measurement, is a technically feasible approach. The two-dimensional models formed by beam and shell elements are of satisfied accuracy to determine the pin-load distributions.