These slides were presented at the NAFEMS World Congress 2025, held in Salzburg, Austria from May 19–22, 2025.

Abstract

Historically the plastic bending was analyzed using the integration of the non linear stresses on the critical section. In this method, the stress-strain curve is simplified using the Ramberg Osgood, or the Cossone method, See Reference [1]. Today, due to modeling democratization, a lot of structures are analyzed using the detailed finite element models. This method can have good results in accurately predicting stresses in the linear domain but it can lead to inaccuracies if the wrong material representation or element type is used. Furthermore a special attention should also be given to manufacturing tolerances that also impact the strength of the parts. This paper attempts to address these issues by comparing two cases where DFEM results, the tests, and the analytical methods were compared. First case represents a double shear lug joint. A detailed 3D finite element model was created in order to analyze a force required to close a gap between female and male lugs. These results were compared with a test and an analytical method, based on reference [1]. The detailed finite element model and the analytical method show a good correlation, but the test results vary, due to manufacturing tolerances and the inability to accurately measure preload at the lugs. This case shows a correct modeling technique in respect to element type and material, but it also shows that an analytical method is accurate as well. A further improvement could be made by taking into account the manufacturing tolerances and having a better instrumentation for the preloads. The second case represents a beam with a sideways loading. The beam was initially modeled with 2D elements, but this modeling was too conservative as the capacity predicted by the test was higher. Possible reasons for this discrepancy include inability of the 2D FEM to predict the ultimate capacity of the material especially in the web to flange radius area. 3D modeling showed good test correlation. The result from the test and from 3D modeling were used to develop an analytical method for this analysis that can be applied to similar cases. References [1] E.F. Bruhn 'œAnalysis and design of the flight vehicle structures' 1973 Chapter C3