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Determination of minimum doubler length for tapered sandwich structures

Altun, Aslıhan
Sandwich structures are widely used in aerospace industry due to their structural efficiency. In order to connect the sandwich structures to the adjacent parts, monolithic region is necessary. Because of the design requirements and strength necessities, this monolithic region must be strengthened. This reinforcement is provided by doublers [26]. In order to retain the weight advantage of sandwich structures, doubler span length must be minimum that keeps the core flatwise tension stress below the core allowable. In this thesis sandwich structures with different materials and different geometries under bending load are analyzed and the geometry of the doubler is designated such that minimum weight of the sandwich structure is obtained. ABAQUS Standard solver is used for the analyses. In the first part of the study after the determination of the mesh size, the effects of the friction coefficient between the parts in contact and the value of tightening torque of the bolts that connects the sandwich structure to adjacent parts are investigated. The effects of geometric and material nonlinearity are also examined in this part. Second part of the thesis covers the finite element model verification done by using tests and analytical approaches. At the final phase of the thesis, failure types of the sandwich structures are investigated and minimum failure load among these failure criteria is determined. The effect of doubler geometry on the failure mechanism is studied for several sandwich structures with specified geometry and materials. Doubler geometry is specified by doing a parametric study. This parametric study is performed by running Python scripts in ABAQUS Standard.