PSI - Issue 5

Sebastian Heimbs et al. / Procedia Structural Integrity 5 (2017) 689–696 Sebastian Heimbs, et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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Fig. 3. Method for nonlinear modeling of aluminum material behavior.

4.2. Bolted joints modeling

Fastened joints based on bolts or rivets are mainly loaded in shear or normal tension and exhibit elastic and failure behavior depending on bolt and sheet material and thickness (Heimbs et al. (2013)), which needs to be modelled accurately to capture potential joint failure and detachment. Connector elements are the most suitable and efficient approach in Abaqus to connect different parts at node-independent, discrete locations. Elastic, plastic and damage behavior can be ascribed to the six degrees of freedom in the connector section definition for normal and shear loads. Elastic behavior for tension and compression was defined based on the equations of Schwarmann (2003). The definition of the connector strength, plasticity and damage behavior strictly depends on the failure mode. Therefore, for a general analysis, the prediction of failure mode needs to be performed first based on respective equations for failure loads (Schwarmann (2003)) and the identification of the load case with the lowest failure load. In the current study, bearing failure under shear loads and pull-through failure under normal loads appear as the most relevant failure modes. The calculated failure loads indicate the beginning of plasticity, see point A in Fig. 4. A simplified linear approach for the description of the plastic deformation was used here by defining point B by a value of plastic displacement and force. This point indicates the initiation of damage. The evolution of damage up to point C is represented by a linear softening behavior, characterized by a maximum displacement value when the connector element is removed from the calculation. The values for the description of the plastic and damage behavior (points B and C) were derived from experimental force-displacement curves of joint failure tests of aluminum AA2024 plates, which were e.g. published by Langrand et al. (1999) and Birch et al. (2005).

Fig. 4. Method for nonlinear modeling of connector element behavior.

4.3. Kinematic hinge modeling

Kinematic hinges exist at the attachment positions of the searchlight pod and at the two searchlight rotation axes. The simulation model is not only supposed to represent the degrees of freedom and stiffness for rotation correctly, but also to cover potential failure. This was achieved by using connector elements, again. Failure under bending or shear