Combined Numerical/Experimental Approach for Rivet Strength Assessment

The failure mechanism of common aeronautical structures is influenced by the crash behaviour of the riveted joints. Therefore, crashworthiness analyses of aeronautical structures require accurate models of the joints under crash conditions for a correct prediction of the crash behaviour of the structure. In this work, a method to create reliable FE models able to reproduce the behaviour of rivets under crash conditions is introduced. Using explicit FE codes, it is common practice to model rivets and bolts with rigid links or beams, and adopt as a failure criterion the allowable forces envelope obtained for a single rivet after tests [1]. It is shown here that numerical simulations of tests carried out on a single rivet under different loading conditions can be used to characterise the crash behaviour of riveted joints in place of expensive and time-consuming test campaigns. A specific test device was built in order to apply multi-axial loads to a single rivet and perform tests to evaluate the behaviour of a rivet under different loading conditions: from pure shear to pure tension. Numerical simulations of the single rivet test were then carried out using LS-Dyna [1] to reproduce experimental test and to validate the numerical model of the rivet. The rivet was discretised with solid eight-node elements and the piecewise linear plasticity material model was initially used. However, different constitutive laws were then used to characterise areas with either compressive or tensile loads. The whole loading process, from bucking to failure was simulated. Numerical results and test data were compared and it was observed that the numerical models are able to correctly represent the behaviour of a rivet after a tuning of the material parameters and therefore can be used to characterise a riveted joint. At this stage of the research, only quasi-static loading conditions were considered. This assumption allowed reducing the number of parameters that affects the calculations thus simplifying the model set-up. Future works will investigate the effect of strain rate to reproduce crash conditions.

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